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A million questions, sub-panels, old romex, multiwires, and more...
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A million questions, sub-panels, old romex, multiwires, and more...
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Thread: A million questions, sub-panels, old romex, multiwires, and more...

  1. #1

    Question A million questions, sub-panels, old romex, multiwires, and more...

    I knocked out the wall between my office and the kitchen upstairs so that the combined space will be all kitchen with room for two freezers so there will be no more running to he garage for meat n' bread. The downstairs kitchen then becomes a bar / art studio functionally. I'm installing a subpanel upstairs, in the middle of the house, and then another subpanel in the garage.

    I read at

    http://www.diychatroom.com/f18/circu...menets-135770/

    If there are permanent provisions for food prep and cooking appliances AND a sink, then it's still considered a kitchen.

    Q1: Would I be able to argue that the gas stove in the lower kitchen will remain for candlemaking/commercial purposes ? Does a lack of food make it no longer a cooking appliance ? If I were to move the stove to the garage and have a sink in the garage, does my garage then become a kitchen ?

    I should mention that the house has some older cloth-covered romex type NM that is green, which has a reduced ground size. I have read that a full-sized ground has been required since ~1972, although, I am used to seeing a reduced ground on all wiring of larger scale, so I'm skeptical about that requirement.

    Q2: True ? If so, does it only apply to "small conductors" ?

    Q3: What is the rating of this NM cable and what are the conductors rated for seperately ? Many of these wires run through the attic. Do I use the 60 degree column of 310.16 and apply the correction factor from the 60 degree column as well or do I get to use a higher column for applying correction factors ?

    Q4: I understand that modifying or extending a circuit requires upgrading to code. If I were to take the home-run for a circuit out of the main panel and run it to the nearer and newer subpanel, would this still be considered a modification ? I know extending under 6 ft is not a problem but is cutting back the home run ?

    At a later time, I plan on adding additional lighting to every room in the house. The builders thought one overhead light in the middle of a room was adequate, hence, I find I am always working in my shadow, especially at the lower kitchen counters since there is no under cab lighting.

    Q5: The refridgeration circuit I have planned has three appliances: 3A, 6A, and 7.8A , for a total of 16.8 Amps. Times that by a 1.75 for heat pump / compressor motor loading, that comes to 29.4A. I would put it all on one circuit but the plugs on the appliances are for normal 15-20A receptacles. I was thinking of putting them [(3A + 6A) and (7.8A)]on a multiwire circuit since I have some 12/3-w/grd cable. Or seperately. I would have to derate the wire for ambient temp in the attic which I figure is ~125-130 degree F . What do you think would be the cheapest or best way of wiring for this?

    Q 6-7-8: I will be putting in 12 volt tape light all over in the kitchen and the tape light itself is fairly cheap but the little transformers are going to kill me at about $40 a pop. Instead of buying 10 of these, I have an old battery charger that's mid-size, probably 20 or 30 Amp. Haven't quite figured out yet, but it's heavy. I would like to cut the clamps off of the leads and put plugs on them, feed power to the charger from a Rx, break the tab on the Rx, and feed power backing into the rest of the switched and dimmed circuit and effectively power the rest of the Rx's that will power the individual tape lights. The kitchen tape lighting would only take ~5A and I would like to use the extra capacity to power tape lights in closets throughout the house. Effectively, I'd be making my own 12 volt lighting circuit. I would stash the charger in a kitchen cabinet so it might have to be derated for being in an enclosed space as well. A couple of other questions arise out of this idea. What are battery chargers or transformer's rated for with continous usage ? The normal 80% ? Also, would I need to have a special receptacle and plugs so that no one ever tries to plug a 120 volt appliance into the 12 volt circuit or would labeling suffice ?

    Q9-10: I'm installing two garbage disposals under two single 25x22 side-by-side undermount sinks. They are 6A and 8A and I figure that multiplied by 1.75 for motor loads is 10.5A and 14A. Should I put two motors on a multi-wired receptacle ? I hear people say that multiwire's are bad practice because if the neutral is broken, the circuit is still live. I could see that, with higher voltage at some of the appliances or devices on the side that is less loaded and lower voltage on side that is more loaded. I wouldn't want to fry appliances or bulbs later on from a loose neutral. I say that if the loads are perfectly balanced it won't, but what will happen if the neutral is broken and there is an amp or two difference between the loads ?

    My father-in-law is a industrial electrician and we went over my calculations about the cable I need for the sub-panels and we disagree on wire sizes. I need someone to tell me whether I'm right or whether I have my head cross-threaded on my neck.

    I'm inclined to buy from Menards and they sell only two sizes of SER cable, 2-2-2-4 AL and 4/0-4/0-4/0-2/0 AL. SE-R is basically like Romex and there are new rules that allow me to use the 310.16 table for branch circuits since the subpanels do not supply the whole load of a family dwelling.

    My calculation goes like this: The old NEC Table 310.16 shows an ampacity of 100 in the 90 degree column for the 2-2-2-4 AL SE-R cable. I use the 90 degree column because the subpanel feeder goes through the attic for most of the run and attic temp around here can go as high as 125-130 degrees in summer, so I apply a correction factor of 76%. So, 100 x .76 = 76 Amps . The feeder is also going to run from the main in the basement, up through an outside wall that has thermal insulation, so I'm required not to exceed the 60 degree ampacity after correction factors are applied. The 60 degree ampacity is 75 Amps, so very close to the 76 after corrections using the 90 degree ampacity. Being that these subpanels will have two hot legs, to me, that means each leg can carry 75 Amps for a combined 150 Amps of power. I'm plenty happy with that, since the worst case demand would be 144 Amps with all the future additions and a full house of kids that leave all the lights on like my brother did growing up... Is this calculation right, or should I get the 4/0 like my father-in-law says because... Table 310.16 actually refers to the ampacity of two conductors ?

    My main requires a QO-C style 4 space breaker for a 150-200A branch. Personally, I would want a 4 space for anything 100A or more. If there was a 6 space 150A breaker I'd buy it. The main sticker states that a 2 space breaker is okay for 125A. Yeah right. Personally, I think big breakers are okay for motor start-ups, but I don't trust those blades to carry continuous power. Am I just paranoid or a little OCD ? Anyone know of a big box store that carries 4 space QO-C breakers ? I've got an electrical supply place picked out otherwise.

    I have inherited a box of spare breakers that I intended to use in the new subpanels of the same style. With the new Arc fault requirements on everything 20A and under, many of the breakers I have now are going to be useless except I read that commercial electric is exempt from the arch-fault requirement. Being that I will be starting a business in my garage, would I be able to use up some of these plain breakers in conjunction with GFCI receptacles to wire up the new circuits ?

    I believe the difference between calculations stems from my belief that Table 310.16 refers to the ampacity of a single conductor, and not two as my father-in-law believes. I say that the ampacity listed is for the conductance of voltage to the neutral point, where the neutral wire is not a 2nd conductor, but merely an extension of the first conductor to the neutral point back at the neutral bus bar. Each leg of a two leg subpanel conducts to the neutral point at it's neutral bus bar and the neutral grounded conductor only carries the minor imbalance between the bus bars. True ?

    In an imperfect world, with a sub-panel imperfectly balanced due to difference in breaker numbers, I'm bound to have a load that is 5, 10, 15, worst case 20 Amps out of balance between the two legs. I could figure on having the legs at max 20 amps out of balance, so I could safely expect one leg to carry 75 and the other 55, for a combined 130 Amps total load. So then I should only put a 125 breaker in the main feeding a 125 Amp subpanel instead of a 150A breaker and subpanel ?

    I know that sounds like a lot of power and I probably could run the whole house off of that. One of the items in my load calculation that I think is off is for the electric range. It has a 50A plug on it. I know it will never draw that. I assume that the name-plate rating is for all four burners on and the oven on high. Typical use would be one or two burners being turned on at a time with the oven. I know I can apply an 80% demand factor on an electric range, but that seems to get canceled out by the 125% loading factor typical of 240V heating units. I feel that 50A is really at least 10A overboard, and I don't really believe I would need 144A of peak power. But on the otherhand, I'd feel like an idiot for putting a 125A panel on a feeder that is actually rated for 150A cable that I paid good money for.

    Extra credit, why is the neutral tied to the wider blade of a plug ? It has to be one way or the other. Is it because if an applaince receives current from outside of it's supply current, it will be able to handle the load and the short ? Or is it because if there is a short from the supply side, we would prefer the smaller blade to burn out first ?
    Not really important, just thought I'd throw it out there while I'm asking a million questions...

  2. #2
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    Kent, WA
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    Quote Originally Posted by Ephemeral_Glow View Post
    If there are permanent provisions for food prep and cooking appliances AND a sink, then it's still considered a kitchen.
    That's the NEC definition of kitchen.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q1: Would I be able to argue that the gas stove in the lower kitchen will remain for candlemaking/commercial purposes ? Does a lack of food make it no longer a cooking appliance ? If I were to move the stove to the garage and have a sink in the garage, does my garage then become a kitchen ?
    I think if the room looks like a kitchen, the inspector will want it wired as such. You don't know what a future buyer will do with the space. I bought a house where the previous owner wired up a separate kitchen in the downstairs, but the idiot fed the entire kitchen and lights and wall outlets in the surrounding room with a single 15A circuit. They may let you skate on putting it in the garage, especially if the sink and stove are not near each other and there doesn't appear to be food prep counters.

    Quote Originally Posted by Ephemeral_Glow View Post
    I should mention that the house has some older cloth-covered romex type NM that is green, which has a reduced ground size. I have read that a full-sized ground has been required since ~1972, although, I am used to seeing a reduced ground on all wiring of larger scale, so I'm skeptical about that requirement.
    Q2: True ? If so, does it only apply to "small conductors" ?
    I think you can continue to use the reduced ground wire. If you can easily remove some sections of old cable I would, but they'll usually consider a wire stapled in place to be grandfathered, but any new extension to it would need a full sized ground.

    Small conductors is a different rule. However, larger conductors usually have a reduced size grounding wire. The size ground you need depends on the circuit breaker protecting the circuit. Up through 30A, the ground matches the conductors size. From 40A to 60A, you only need a #10 copper ground wire. From 70A to 100A, you need a #8 grounding wire.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q3: What is the rating of this NM cable and what are the conductors rated for seperately ? Many of these wires run through the attic. Do I use the 60 degree column of 310.16 and apply the correction factor from the 60 degree column as well or do I get to use a higher column for applying correction factors ?
    You can use the 90C ampacity of NM cable for thermal derating (e.g. run in a hot attic) and for reductions due to bundling. This is ampacity A. You can't load it more than its 60C rating, call this ampacity B. And 240.4(D) limits most 15A circuits to #14 wire, 20A circuits to #12, and 30A circuits to #10. Call this ampacity C. Any circuit load and breaker is limited to the lowest of A, B, and C.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q4: I understand that modifying or extending a circuit requires upgrading to code. If I were to take the home-run for a circuit out of the main panel and run it to the nearer and newer subpanel, would this still be considered a modification ? I know extending under 6 ft is not a problem but is cutting back the home run ?

    At a later time, I plan on adding additional lighting to every room in the house. The builders thought one overhead light in the middle of a room was adequate, hence, I find I am always working in my shadow, especially at the lower kitchen counters since there is no under cab lighting.
    How this is handled is usually specific to your jurisdiction. Usually, only what you add must follow current rules unless what was there was never legal. But, if AFCI protection is required on the new circuit, that most likely means you'll need an AFCI breaker for that circuit which will also protect the older wiring. They may want an AFCI used if you just move the circuit to a different panel and only added an extension but no outlets.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q5: The refridgeration circuit I have planned has three appliances: 3A, 6A, and 7.8A , for a total of 16.8 Amps. Times that by a 1.75 for heat pump / compressor motor loading, that comes to 29.4A. I would put it all on one circuit but the plugs on the appliances are for normal 15-20A receptacles. I was thinking of putting them [(3A + 6A) and (7.8A)]on a multiwire circuit since I have some 12/3-w/grd cable. Or seperately. I would have to derate the wire for ambient temp in the attic which I figure is ~125-130 degree F . What do you think would be the cheapest or best way of wiring for this?
    You don't multiply refrigeration by 1.75. If it is a plug in appliance, any factor you need will most likely be included in the nameplate. I'd run a 20A circuit. If you have high ambient temperatures and bundle with other cables, you may need to go to 10-2. But your breaker may not be larger than 20A if using normal 15 or 20 amp receptacles.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q 6-7-8: I will be putting in 12 volt tape light all over in the kitchen and the tape light itself is fairly cheap but the little transformers are going to kill me at about $40 a pop. Instead of buying 10 of these, I have an old battery charger that's mid-size, probably 20 or 30 Amp. Haven't quite figured out yet, but it's heavy. I would like to cut the clamps off of the leads and put plugs on them, feed power to the charger from a Rx, break the tab on the Rx, and feed power backing into the rest of the switched and dimmed circuit and effectively power the rest of the Rx's that will power the individual tape lights. The kitchen tape lighting would only take ~5A and I would like to use the extra capacity to power tape lights in closets throughout the house. Effectively, I'd be making my own 12 volt lighting circuit. I would stash the charger in a kitchen cabinet so it might have to be derated for being in an enclosed space as well. A couple of other questions arise out of this idea. What are battery chargers or transformer's rated for with continous usage ? The normal 80% ? Also, would I need to have a special receptacle and plugs so that no one ever tries to plug a 120 volt appliance into the 12 volt circuit or would labeling suffice ?
    Don't even think about this if it is going to be inspected. Most jurisdictions and the code itself frowns on cobbling things together anymore. You'll need a listed Class 2 or Class 3 power source if that is what the lights were designed to be powered from. I think you could use a proper larger power supply and feed either heavy CL2 cable to create this lighting circuit, or even run 12-2 or 14-2 in the walls that is 12VDC to feed these tape lights in different locations. You can have that cable stub coming out of the wall and connect to the transformer. I'd also want to use a cable that is visually different so someone doesn't try to tap it in the future for some 120V thing, or even worse connect it to a 120V source. Also think about how the light switching is done -- is it switching the 120V to the transformers, or do the lights have 12 VDC switches?

    I don't think you can ever have wiring that needs an energized plug, even if that plug is 12V. Although 12V won't shock you in most cases, if you have enough current available it can make large sparks. So I think that 12V plug idea is still a fire hazard.

    Quote Originally Posted by Ephemeral_Glow View Post
    Q9-10: I'm installing two garbage disposals under two single 25x22 side-by-side undermount sinks. They are 6A and 8A and I figure that multiplied by 1.75 for motor loads is 10.5A and 14A. Should I put two motors on a multi-wired receptacle ? I hear people say that multiwire's are bad practice because if the neutral is broken, the circuit is still live. I could see that, with higher voltage at some of the appliances or devices on the side that is less loaded and lower voltage on side that is more loaded. I wouldn't want to fry appliances or bulbs later on from a loose neutral. I say that if the loads are perfectly balanced it won't, but what will happen if the neutral is broken and there is an amp or two difference between the loads ?
    The factor for motors is 125%, not 175%, and you only apply it to the largest one if you have multiple on the same circuit. SO a 20A circuit will work to power both of these. Multiwire branch circuits aren't a bad practice, but they do have a bad fault condition that can burn stuff up (voltage will raise or lower based on the connected resistance on each leg of the circuit). If both sides of the circuit each have a 100W light bulb, it will work normally. Have two 100's on one and a single 100 on the other and you'll get 160V applied to one bulb and 80V applied to the two. A much better reason to avoid them is the residential AFCI requirements. Few breakers are available in 2-pole AFCI (and they usually aren't available in twins either). So get a panel with enough space without using twin breakers, and avoid multiwire branch circuits because just about everything needs to be AFCI'd anymore.

    Reply too long, continued in a second response....
    Mark
    Kent, WA

  3. #3
    Join Date
    Feb 2012
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    Kent, WA
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    Quote Originally Posted by Ephemeral_Glow View Post
    My father-in-law is a industrial electrician and we went over my calculations about the cable I need for the sub-panels and we disagree on wire sizes. I need someone to tell me whether I'm right or whether I have my head cross-threaded on my neck.

    I'm inclined to buy from Menards and they sell only two sizes of SER cable, 2-2-2-4 AL and 4/0-4/0-4/0-2/0 AL. SE-R is basically like Romex and there are new rules that allow me to use the 310.16 table for branch circuits since the subpanels do not supply the whole load of a family dwelling.

    My calculation goes like this: The old NEC Table 310.16 shows an ampacity of 100 in the 90 degree column for the 2-2-2-4 AL SE-R cable. I use the 90 degree column because the subpanel feeder goes through the attic for most of the run and attic temp around here can go as high as 125-130 degrees in summer, so I apply a correction factor of 76%. So, 100 x .76 = 76 Amps . The feeder is also going to run from the main in the basement, up through an outside wall that has thermal insulation, so I'm required not to exceed the 60 degree ampacity after correction factors are applied. The 60 degree ampacity is 75 Amps, so very close to the 76 after corrections using the 90 degree ampacity. Being that these subpanels will have two hot legs, to me, that means each leg can carry 75 Amps for a combined 150 Amps of power. I'm plenty happy with that, since the worst case demand would be 144 Amps with all the future additions and a full house of kids that leave all the lights on like my brother did growing up... Is this calculation right, or should I get the 4/0 like my father-in-law says because... Table 310.16 actually refers to the ampacity of two conductors ?
    In the 2014 code book, the correction factor for 130F on a 90C conductor is .84 which is 84 amps since it has a 100A ampacity. But as you said, you can't use this above 60C in many cases, so your final ampacity is 75A. Don't run any other conductors along with this one in the attic (maintain spacing so adjacent cables don't heat it even more). Each conductor will have an ampacity of 75A and you'll have two, so you'll have 150A at 120V or 75A at 240V available.

    Quote Originally Posted by Ephemeral_Glow View Post
    My main requires a QO-C style 4 space breaker for a 150-200A branch. Personally, I would want a 4 space for anything 100A or more. If there was a 6 space 150A breaker I'd buy it. The main sticker states that a 2 space breaker is okay for 125A. Yeah right. Personally, I think big breakers are okay for motor start-ups, but I don't trust those blades to carry continuous power. Am I just paranoid or a little OCD ? Anyone know of a big box store that carries 4 space QO-C breakers ? I've got an electrical supply place picked out otherwise.
    Here's what I think you're going astray. Each of your wires is limited to 75A, so that cable should not be on a breaker larger than 75A (actually 80A, since they don't make 75A breakers). This should be a normal DOUBLE POLE 80A breaker, each of the hots landing in its own 80A breaker whose handles are internally tied together. Most residential panels can't take branch circuits larger than 125A because there is insufficient bending space from the breaker to the panel wall. Usually, you're limited to a #2 conductor or maybe a 1/0. To maximize amp availability, you'd need to use copper wire rather than aluminum.

    Quote Originally Posted by Ephemeral_Glow View Post
    I have inherited a box of spare breakers that I intended to use in the new subpanels of the same style. With the new Arc fault requirements on everything 20A and under, many of the breakers I have now are going to be useless except I read that commercial electric is exempt from the arch-fault requirement. Being that I will be starting a business in my garage, would I be able to use up some of these plain breakers in conjunction with GFCI receptacles to wire up the new circuits ?
    No. The building is most likely classified as a dwelling, so you can't skate on the AFCI requirements. If you had an outbuilding used solely for business, you may be able to get around AFCI for that. There are still some places where AFCI's are not required such as garages, the outside receptacles, bathrooms, and unfinished basements. Remember that all it takes is one outlet (and outlet means receptacle or light fixture or any hard wired appliance -- any box where power gets used) in a room to require the AFCI protection for the whole circuit. So keep the circuit contained only to the room that doesn't need an AFCI if you want to use a regular breaker. In Washington, a bathroom that is entered solely through a bedroom (e.g. typical master bathroom) is considered part of the bedroom, so it needs AFCI protection.

    Quote Originally Posted by Ephemeral_Glow View Post
    I believe the difference between calculations stems from my belief that Table 310.16 refers to the ampacity of a single conductor, and not two as my father-in-law believes. I say that the ampacity listed is for the conductance of voltage to the neutral point, where the neutral wire is not a 2nd conductor, but merely an extension of the first conductor to the neutral point back at the neutral bus bar. Each leg of a two leg subpanel conducts to the neutral point at it's neutral bus bar and the neutral grounded conductor only carries the minor imbalance between the bus bars. True ?
    The ampacity is for each wire, but how did you do your load calculation? Usually, you divide the load by 240V, so if the load calc says 50A, that is 50A on each of the two conductors. If your load calc was 18 KVA or less, that is 75 amps per leg of your feeder and you're OK with #2 SER. If your load calc was 36 KVA, you need 150A per conductor. If you divided by 120V instead of 240V, that will confuse most electricians doing a feeder calc and would make an amp value twice as high as required. Do you want to post your load calculation (I think you should after reading this)?

    Quote Originally Posted by Ephemeral_Glow View Post
    In an imperfect world, with a sub-panel imperfectly balanced due to difference in breaker numbers, I'm bound to have a load that is 5, 10, 15, worst case 20 Amps out of balance between the two legs. I could figure on having the legs at max 20 amps out of balance, so I could safely expect one leg to carry 75 and the other 55, for a combined 130 Amps total load. So then I should only put a 125 breaker in the main feeding a 125 Amp subpanel instead of a 150A breaker and subpanel ?

    I know that sounds like a lot of power and I probably could run the whole house off of that. One of the items in my load calculation that I think is off is for the electric range. It has a 50A plug on it. I know it will never draw that. I assume that the name-plate rating is for all four burners on and the oven on high. Typical use would be one or two burners being turned on at a time with the oven. I know I can apply an 80% demand factor on an electric range, but that seems to get canceled out by the 125% loading factor typical of 240V heating units. I feel that 50A is really at least 10A overboard, and I don't really believe I would need 144A of peak power.
    If your feeder calc says 75A, you assume that is what the load will be per leg. Don't combine the two numbers, as each leg is breakered separately. There is usually enough margin in the load calc that imbalance isn't going to get you especially if you've spread the breakers out evenly between both power legs. The range is a 240V device, and it balances out well. Which calculation are you doing -- the Standard or Optional? Ranges are handled differently in each, and in neither one would you apply an 80%factor or a 125% factor. For ranges under 16KW, a 40A circuit is fine because of the way ranges work (even on full power the burners still cycle).

    Quote Originally Posted by Ephemeral_Glow View Post
    Extra credit, why is the neutral tied to the wider blade of a plug ? It has to be one way or the other. Is it because if an applaince receives current from outside of it's supply current, it will be able to handle the load and the short ? Or is it because if there is a short from the supply side, we would prefer the smaller blade to burn out first ?
    Not really important, just thought I'd throw it out there while I'm asking a million questions...
    It is for things where you possibly have exposed parts and no ground in the power cord (without a ground to orient it, the cord could be inserted either way). The most typical example is a table lamp. The screw shell where the lamp goes is somewhat exposed, especially when screwing in the lamp (the lamp screw shell will be in contact with the base screw before being seated all the way). So if you touch lamp base while screwing it in, you'd want that screw shell to be the neutral since it won't shock you. So a device that cares about which parts are 120V and which parts are neutral will have a "polarized plug". These have the neutral wider than the 120V prong, so they will only fit one way in the receptacle.
    Last edited by suemarkp; 03-17-2014 at 11:26 PM.
    Mark
    Kent, WA

  4. #4

    Default

    I had a thought about the subject of reusing the older 15 and 20 amp QO breakers. Does the newer requirements for arc-fault protection on 15 and 20 A circuits in dwellings apply to 120V only ? I was just thinking that if it only applies to 120V circuits, then maybe I could find a use for two old breakers in a 240V circuit. My new air compressor trips the 15A 120V circuit it is now on when it cold starts and I have to leave the cage on around the belt pulley, otherwise I would crank it by hand briefly before throwing the switch like I used to with my old compressor. I'm thinking of rewiring the motors on the air compressor and the table saw for 240V, and then maybe putting one or both on a 15 or 20A 240V circuit.

  5. #5

    Default A thought on old wire and new lighting

    I was thinking about the reduced ground size issue I will be having. Do I have a 16awg ground with 14awg conductors and 14 ground with 12awg conductors, or does the 12awg have a 16awg ground as well ? I thought, what if I were to derate the wire to the guage of the ground ? If I have a 14awg ground with 12awg conductors, then I should be able to use that wire for the ampacity of a normal 14awg circuit and change the breaker. This would prove useful for older lighting circuits that are getting the new LED bulbs, since their amperage is a little over 1/10th of the incandescent amperage that it was originally intended for.

    I'm kind of a resourceful guy and was feeling a bit guilty about scrapping all my old wire, besides using it for pigtails, or just giving it away to my relatives that are living rural still.

    I couldn't help but notice the free 310.16 table I printed out from southwire's website, doesn't list the ampacity for 16 or 18 awg cable. Most other references did not list them as well. I noticed that there were no 10Amp breakers at the big box store's website for sale either. Is there no such thing or is it merely not common enough to carry ? I'm implying that a 10A breaker would be good for a 16 awg wired circuit.
    Last edited by Ephemeral_Glow; 03-22-2014 at 04:46 PM. Reason: I left out one thing

  6. #6
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    Arc faults are only required on 120V 15 amp and 20 amp circuits. So if you have some 240V tool, they would not need to be arc faulted. But where are these tools located? Workshops and garages are not a required location for arc faults (at least not yet). Rec Rooms would be the closest thing is you had a finished room that was dual purpose.

    Yes, the old cable dropped the ground by one size -- a #16 in 14 gauge cable, and a #14 in 12 gauge cable. The required size of equipment ground is based on circuit breaker. So if you put a 15A breaker on the 12 gauge circuits you'd think that would work as a 15A breaker required a #14 equipment ground. However, when wires have been upsized from "normal", you need to upsize the equipment ground as well. I think a big problem with the old grounds is durability. The 16 gauge ones are easy to break. As long as the cable segment is short (less than 50 to 100 feet), the smaller ground should be fine if it is well made up.

    The minimum size wiring for premises wire is #14. That's why you can't find #16 or #18. A few people make 10A breaker, but there is no need for them as the "floor" for wiring has been established at #14 and 15 amps.
    Mark
    Kent, WA

  7. #7

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    Okay, that makes my eyes cross a little bit, but I think I can understand that.

    So, what I should be hearing is that with a 10A load on a 240V circuit, the circuit experiences 10A on the black and 10A on the red, just as a 120V circuit's would experience 10A on the neutral and 10A on the hot, where they are not experiencing 10A separately, but are both experiencing the same 10A together, and not 20A together. I shouldn't be splitting the load between two conductors, because "they are one", as Spock would say. I just need to visualize the red and black as one when dealing with 240V, as the ungrounded and grounded conductors are one when dealing with 120V.

    I am so glad to have that straight in my mind finally. Haven't had that kind of trouble since logarithms. It took seven years for me to re-invent them before I understood. Just goes to show that I'm not as open-minded as I thought I was.

    As far as, the nameplate including the loading factor goes, I suppose that if the nameplate was a real nameplate, it would have a power factor or service factor on the nameplate, and if not there, is already included. I suppose the manufacturers dial the appliance up all-the-way and that load becomes the nameplate rating, just to cover their bases. I'm just going to have to trust the manufactures and you on that issue. The only thing that I would have to account for would be whether it is continuous or non-continuous, which nothing seems to be except for lighting.

    I think the optional method for load calculation is out, from what I read here:

    http://www.iaei.org/blogpost/928475/...lectrical-Code

    " The optional method is much simpler than the standard calculation, but is restricted in 220.82 to "... a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.” Most one-family dwelling units meet this requirement, so the optional method is used frequently. "

    From that, I gathered that this method applies to the load calc of the main feeder cables only and does not apply to subpanel feeders. My father-in-law also said that I don't apply demand factors when wiring for a sub-panel.

    I've only become recently familiar with what a standard or optional load calculation looks like. I'm thinking I will give the nameplates and continuous ratings for the lighting and group together the loads that I expect to be coincidental while the top floor is occupied and we can go from there.

    I don't care much for the VA allowances that are given on a "per square footage" basis . I don't think that's a very good way for me to figure out lighting loads considering that I require about twice the lighting other people do and I think 3VA per square foot is way too high with the LED bulbs that I now insist on using. It just doesn't seem relative. I have each bulb and fixture planned out for the future additions so I'd rather just go by those numbers since they will be exactly relative.

    All of my old bulbs can go on a garage sale. It just doesn't pay to heat your house up in the summer with lights and then cool it with the A/C again. That's paying for energy twice. They're way cheaper in the long run.

    The following list will resemble the standard method for load calculation. I'd like to compare what a standard load calc would yield, and compare that with what I think the load the sub-panel would bear with a full house with a holiday or party. I'm using the following data entry format:

    # on list
    appliance, plug style

    nameplate,

    feeder load after ( calculation ), where required

    branch circuit load after ( calculation ), where required

    wire size

    breaker size, type

    Poles / spaces occupied

    List A:
    Grouping 1: Coincidental loads for occupation of 2nd level


    1.
    Stove, 50A plug, 4 pin '14-50P', cord with 6awg

    8.8 KW @ 120V / 240V, does not say how much of each voltage... so is it impossible to compute the Amps then ?

    Assuming the controls run off 120V and most of load is at 240V,
    The sub-panel load is: 33.34`A : ( 8 KW / 240V = 33.34`A ), required by 220.55, ~8KW for appliances over 8.75KW. Reference: http://www.charlesrmiller.com/index....F_October_2008

    The branch circuit load is: 36.66`A --> 40 A : ( 8.8 KW / 240V = 36.66`A ) , required by "[210.19(A)(3)]. Note that the minimum branch circuit for ranges rated 8? kW and more shall be 40 amperes "

    Logically, if the appliance cord is wired for 50 A, I would think I should follow suit. However, someone may have over-wired the appliance. Due to the indetermination of Amps from the appliance being dual rated for 120 / 240V, it's hard to say what is required and I must refer to the nec requirements on a KW basis. I could skate by with the minimum 8awg wire, only good for 40A max through the attic. It's a case of max wire ampacity meets min nec requirement. And what if someone puts in a 12KW stove someday? By the time this stove is replaced, all the electrics will probably be induction-based and those draw more or less energy ? I'm leaning towards 6awg wire for 50A.

    40A or 50A breaker, will probably cost the same anyways.

    2pole / 2sp


    2.
    Microwave w/fan and lights, 15-20A 120 plug

    1.58 KW @ 120V

    9.87A : ( 1580W / 120V = 13.16A, x.75 = 9.87A ), required as part of Standard method, 75% for fastened in place appliances.
    I could see there being continuous use of lights, but I would only use the fan for getting rid of smoke and would have it on low otherwise.

    13.16A

    14awg wire, good for 15A of non-continuous.

    15A, AFCI

    1 pole / 1sp


    3.
    Refrigerator, stand-up freezer, and chest freezer. 15-20A 120 plugs

    7.8A, 6A, 3A.

    12.6A : ( 16.8A, x.75 = 12.6A )

    16.8A

    12awg wire, good for 20A

    20A breaker, AFCI

    1pole / 1 space

    4.
    Dishwasher, 15-20A 120 plug

    7.5A : ( 10 A, x.75 = 7.5A )

    10 A

    14awg, good for 15A

    15A breaker, AFCI + GFCI combo

    1pole / 1 space

    5.
    2 Garbage Disposals, 120V, generally non-coincidental, but would like to put on one circuit.

    6A and 8A

    6A : ( 8A x .75 = 6A )

    14A : ( 6A + 8A )

    14awg, good for 15A

    15A breaker, AFCI + GFCI combo

    1pole, 1space

    6.
    Kitchen cab + overhead + dining area lighting

    11.75A : ( 9.4A x1.25 = 11.75A )

    11.75A : ( 9.4A x1.25 = 11.75A )

    14awg, good for 12A continuous

    15A breaker, AFCI + GFCI combo, GFCI because some under-counter Rx's and over-counter switches will be within 6 ft of the sinks .

    1pole, 1space

    7.
    Hallway + living room area lighting

    11.75A : ( 9.4A x1.25 = 11.75A )

    11.75A : ( 9.4A x1.25 = 11.75A )

    14awg, good for 12A continuous

    15A breaker, AFCI + GFCI combo

    1pole, 1space

    8.
    Entertainment Center + Media Center via old computer, in Living Room

    7.5A : ( 10 x .75 = 7.5A )

    10A

    14awg wire, good for 15A

    15A, AFCI

    1 pole / 1sp


    If I leave out the disposals, and fully figure in the lights for a full occupation of the 2nd level, I come up with about 94 A with the 75% reductions for appliances. 33.34A of that will be 240V, so that leaves 60.66A of 120V to split, so I have 63.67 final (( 33.34 + ( (94 - 33.34 ) / 2 )) = 63.67A ). And then I have about 106 A without the 75% reductions if I look at it my way from a holiday point of view. So that would be (( 33.34 + ( (106 - 33.34 ) / 2 )) = 69.67A ).

    I just so happen to have a 2 space 240V 70A breaker in my possession.

    And for the garage sub-panel, I have a 4 space 100 A QO breaker that I snagged on a garage sale for about $5. I still have to test it to be sure it works. It has a 60 degree rating and my panel is 60/75 rated, so I don't see a problem using it otherwise. I read that welders can have a 200% service factor. I think they were referring to a stick welder. I have a beast of the stick-welder with a nameplate of 90A. I only plan on using half the dial, so I figure 45A will be typical usage. I'd like to teach junior how to some day and I can just see him stabbing and having to twist his rod off. It occurred to me, that rather than have a 100 A breaker supplying the sub-panel in the garage, and an additional 90 or 100 breaker for the stick welder, perhaps I can double tap off of the top of the sub-panel and wire the receptacles directly off the top. Any problems with that ? I would probably have to put a bigger cord on the welder to match, but I have about 45 feet of 1/0 AL good for 100A at 60degree that I can chop up and run in conduit ? Is it possible to use the spiral flexible metallic conduit for extension cord ? I could see it getting crushed so I'd say no.

  8. #8
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    215

    Default

    Keeping the load as watts (or KVA) prevents confusion as to what is a 120V load, a 240V load, and a 3 phase load. It is assumed that the installer will attempt to balance the circuits so things pretty much work out. So yes, a 240V 10A load has 10A on each pole of the breaker, so it is a 10A circuit. But it is 2400W. A 120V 10A load would be 1200W. This would come out of a load calc as 5A, but as long as you have another 120V load that will help balance things out on the other leg while adding about another 5A to the load calc. The only time imbalance is going to be an issue is if the feeder is small, like 15A or 20A, and things ended up 20/10 instead of 15/15. In a small feeder, I add some margin to take care of this. If the feeder breaker is 30A or larger, you shouldn't need to fudge anything.

    Nameplate values are usually a worst case load. Branch circuits are typically sized for worst case and some items even get hit with a 125% continuous factor even though they may not really be continuous. However, they don't have you apply this 125% factor to the feeder or service. An electric heater is a good example. The BRANCH CIRCUIT must be treated as continuous, but the feeder or service calc takes the heater at 100% or even less of nameplate (depends on the calc and the nameplate...).

    You can use the optional method as long as you install a 100A feeder and things come to 100A or less. If you don't want that large of feeder, then you must use the standard calc. Either calc can be used for subpanels. A subpanel is no different than a service as far as the rules go. The difference is you only include the loads and square footage served by the subpanel in the calc. Demand factors can still be used (10KVA threshold for optional, 3KVA threshold for general and appliance loads in standard). Your FIL may not think you apply the demand factors to a subpanel because in industrial installs, there isn't much that could be applied. The Optional calc is dwellings only. Industrial panels usually have general outlets and lighting segregated from heavy stuff, but demand factors can be applied to general lighting if you want to. You don't have to, but I would because dwelling calcs always come in higher than they need to (hence the puny wire to your house from the power company versus what you have to run up the power mast under NEC rules).

    The VA/square foot rules cover more than lighting. In the old days, lighting may have been a cord connected lamp and not much else. They haven't really updated the term, but it covers all the GENERAL USE RECEPTACLE and light fixtures. So your stereo and TV in the family room, the computer in the office, and the tools and fridge in the garage all get covered by this square footage value. Since the garage is excluded from the square footage, the rest of the house area needs to make up for that and they determined that 3VA/sq ft seems to work. There's a whole table in the code book with different factors for different types of establishments.

    Also, lighting for dwellings is not considered continuous. The definition of continuous is things you expect, in normal operation, to be on at full power for 3 hours or more. Dwelling lights usually are not, especially when there are multiple rooms on a given circuit. If you have kids who never turn lights off, well you could say continuous. But as you mentioned, new LED lights draw so little power that you should have plenty of margin for lighting. A business that opens at 8:00 and closes at 6:00 will most likely have its worker area lights on during then entire hours of operation. So industrial/commercial lighting is usually considered continuous. It is really the breaker that's the issue for continuous -vs- non-continuous. The wire table in the code assumes a continuous loading of the wire. But a breaker needs to be derated to 80% for continuous loads unless the breaker is "100% rated".

    Your stove goes in as 8KW in the standard calc, and 8.8KW in the Optional. The branch circuit must be 40A minimum. The plugs for 40A and 50A are the same, so you can use either breaker on it. However, if you run 8/3 cable, the max breaker is 40A (and that's what I would run for this). If you use a 50A breaker, you must use 6-3 cable which is harder to work and fit in the box. The 120/240 on the nameplate tells you that a 3-wire circuit is required (hot-hot-neutral) and you also need a 4th grounding wire which is implicit. The most the unit will draw is 36.6 amps. It could be all on one leg, all on the other, or both. IF it has a light bulb in the oven, that will be 120V. The burners are 240V, except some do switch to 120V to help adjust the heat level. Really, you don't care, as all you need to worry about is the total VA and assume it is balanced. A 40A range circuit is actually usable for a range up to 16KW based on the factors in 220.55 column C and note 1 . So put in a 40A circuit and don't worry, as that will cover just about any range a person could buy in the future.

    Microwave goes in a 1.58 KVA and it is not continuous. You can only apply the .75 factor if you have 4 or more fastened-in-place appliances (see below).

    If your fridge/freezers are on your kitchen small appliance circuits, then you don't need to add them. Do you have the mandatory two 1.5 KVA circuits for kitchen counters in your calculation? If you've added an additional kitchen appliance circuit to cover those fridges/freezers, then use 1.5 KVA to cover that circuit (that's the code value for a kitchen small appliance circuit). These are not fastened-in-place, so you can't apply the .75% factor. If you want a dedicated circuit for them, you can put it in your calc at the sum of the nameplate loads (converting to KVA). In the optional calc, you'd need to cover those if there is a specific circuit for them. In the Standard, the 3VA/sq ft covers them if they aren't in a kitchen, or the two mandatory small appliance circuits could cover them, or if you add a third small appliance circuit then those are specifically called out at 1500 VA each.

    Dishwasher is 1.2 KVA and the .75 factor may be applied if you have enough fastened-in-place items to use it.

    Garbage disposals are typically treated as motors in the code book. It is kind of silly in that it makes the circuit a bit large and they are a rarely used item. A 15A circuit would work, but you should make it 20A. The motor calc for this is the sum of the motor amps plus 25% of the largest motor. So you'll have 8 + 6 +2 = 16A. This requires a 20A branch circuit since it is over 15A. A hard a$$ inspector would make you treat those as motors and get the amp values from the horsepower tables in the code book (which are larger than what is on the nameplate). That will be a even larger number so lets hope they don't go there. In your feeder calc, you can treat these as two separate fastened-in-place appliances, so you get:
    (8+2) * .75 = 7.5A = 0.9 KVA
    6 * .75 = 4.5A = 540 KVA

    Switches within 6' of a sink don't kick in a GFCI requirement. But any 120V 15A or 20A receptacles will. Branch circuits for kitchen lighting is fine, but only use the 3 VA/sq ft rule to cover this circuit for the feeder calc. Only when you go to implement the lighting circuit do you need to pay attention to possible load (which limits the number of fixtures you can put on it). You have to treat the load as the max size allowed in the fixture. So if you use a normal recessed can that can take a 100W flood light, you use .8A per fixture, even if you have a 13W compact fluorescent in it or a 7W LED. If a circuit has a mix of lights and receptacles, the lights can only use 50% of the circuit rating (again, using the largest rated light the fixture will accept and not what you plan on installing).

    Media center is not fastened-in-place. Again, use the 3VA/sq ft rule in the feeder to cover this. But you can have as many 15/20A branch circuits as you want to make sure you don't overload a specific circuit. You could make every receptacle in the house on its own circuit and the service or feeder calculation would not change because it is based on area and not outlet count.

    Will this panel feed a bathroom? If so, you need a 20A circuit for its receptacle. The load value is zero in the feeder calc, as it again is covered in the 3 VA/sq ft rule.

    Welders have their own special section in the code. The term isn't demand factor for them, it is duty cycle. The welder nameplate should have its duty cycle value. You use that, in conjunction with the primary amp (input amp) value to determine its load. If the duty cycle is in the 20% to 30% range, can get to cut the wire requirement about in half. However, the breaker tends to remain large even though the wires are small. If you are using a 50A receptacle for the welder, you need to label it "welder use only" if you've got #10 wire and an 60A breaker on the welder circuit using a range receptacle.

    If the 100A breaker is labeled as 60C only, then you are limited to using the 60A column when choosing the size of wire to connect to it. You'd need #2 copper wire if the calculated load is 95A or less, or #1 copper if it is 96 to 100 amps. Your panel may not have bending space for wire larger than #2 (2.5" required from breaker lug to panel wall). A #1 wire requires 3" from breaker lug to panel wall. This is assuming the wire bends coming out of the breaker and does not leave the panel on that wall next to the breaker terminal. If it leaves the panelboard out the wall that is directly in line with the breaker lugs, you need even more space.

    I can do a "normal" load calc for you if you indicate how many square feet will be served by this subpanel. Also assuming there is no HVAC or laundry equipment on this subpanel.
    Last edited by suemarkp; 03-27-2014 at 04:53 PM.
    Mark
    Kent, WA

  9. #9

    Default

    When I read that I needed two dedicated 20A circuits for a kitchen, I thought that meant dedicated to the counter-tops and everything else that is not listed as requiring a dedicated circuit. The problem with that, is that I don't have the owner's manuals for the fridges or freezers or even the microwave. It would make a heck of lot more sense to me to put them on the 20A circuits cause I don't see using the rest of the circuit otherwise except for vacuuming the floor, which will be flat, so not a lot of draw there, so it shouldn't trip with the 12A vaccuum and 6+3A of freezers on one side. Thank you for mentioning that, you saved me a circuit.

    As far as having 4 or more appliances goes, I count the fridge-1, stand-up freezer-2, chest freezer-3, dishwasher-4, microwave-5.

    I think I'm in the same frame of mind when it comes to accounting for the disposals. They are like vacuums, used for a minute every other day. With each disposal on separate sink, on side-by-side under-mounts, I figured they would be non-coincidental, ran one at-a-time, so I thought 15A would be enough. But that did get me thinking, when we have open house, the wife will run both of them, just for show, and pop the breaker. I can see it. It's not a long run so only a couple of bucks difference. Why not.

    People have told me to put the microwave on a 20A also, cause they have a high start-up, but I think there are capacitors to take care of that and I'm not aware of whether a magnetron has a rotor, that it could have anything close to 'rotor-lock'. There's a fan but that's it. I always wanted to tear one apart for the magnets, but I think they are built like a brick dog-house.

    I left out allowances for receptacle circuits I know are mostly gonna sit unused and will probably only serve for vacuuming or a floor lamp cause I will still have a few from when my house didn't have lights in it. If the inspector is gonna want to see a load calc, then I guess you don't have to twist my arm to add extra power. I was going to wire the sub-panels for a little extra "what if" , like what if we get a hot tub... but now I have a legitimate excuse.

    Let's see, and there's about three more rooms that will need separate receptacle circuits because I will be maxing out the lighting circuits, so 3 x 1500VA = 4500. And I forgot to mention an outdoor perimeter lighting circuit for motion sensor lights that will be maxing out the circuit until the old bulbs burn out, so plus another 1920VA or 16A's there. So then / 240 is another 26.75A on top of the previous 64 or 70 so Amps I had earlier, that comes to ~90 or ~96 final. Seems like overkill to me, but it would be convenient to pick up the same 100A cable for both subpanels.

  10. #10
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    215

    Default

    The two mandatory kitchen circuits are for the kitchen counter receptacles, and the wall receptacles ONLY in the dining room and eating area. The fridge is also allowed to be on this circuit, but not the built ins like dish washer or garbage disposal or gas range. The microwave can be if it is a counter plug in unit. If built in, it needs its own circuit. Lighting cannot be on this circuit either.

    The 75% rule for appliances only applies to fastened-in-place appliances. Fridge/freezers are not fastened in place. Things that are, are the dishwasher, disposals, built-in-microwave, range hood, water heaters, well pumps, etc.

    Circuit breakers will accommodate starting surges in just about anything you have (microwave will be fine on a 15A circuit if that is most of what is on it). I think even both disposals would work on a 15A circuit. But what works and what is code compliant are not always the same. Huge motors (e.g. a whole house air conditioner) will have a breaker one or two sizes larger than its amp rating. Most breakers will allow a 10% overload for quite a while -- at least 10 minutes and could be an hour or more.

    Outdoor lighting is not usually included in a feeder calculation (again, the 3VA / square foot covers that along with vacuum cleaners). Having separate circuits for those is fine. There are many circuits in a panel whose calculated load is 0 because it is covered elsewhere (e.g. garage, outside receptacles, outdoor lighting, bathroom receptacles).
    Mark
    Kent, WA

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