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Thread: Well pump and outdoor outlet wiring

  1. #1
    Join Date
    Nov 2014
    Posts
    4

    Default Well pump and outdoor outlet wiring

    I'm planning to install wiring to a well pump that is down in a vault that is about 6 foot deep below ground level. (The previous owner of my place had installed wiring that was not even close to being code-compliant).

    My plan is to power the pump from the main house panel, which is about 120 feet away from the pump vault. I want to size the wire for a 2 HP pump, although I currently have a 1 HP pump. The pump (1HP or future 2HP) will be 240V. For a 1HP, single-phase motors, it looks like the "full load current" table shows 8 amps @ 240V, so I expect that I would be using a 15-amp breaker in the house panel -- maybe a 20-amp breaker in the future if I switched to a 2HP pump. 10-gauge copper should do it for the conductors at this distance, even for the 2 HP pump. The vault is (as might be guessed) rather damp inside, and the electrical box that the previous owner installed is very rusty. I'm hoping that I can get away with a lock on the breaker in the house panel to serve as the disconnect, and nothing more than a plastic box in the well vault for making connections.

    While I'm at it, I also plan to install an outlet either in the vault or above-ground next to the vault. Preferably, this would be a 20-amp outlet... but voltage drop is a challenge at this distance. I plan to run a separate circuit from the house panel with a 20-amp GFCI breaker in the panel. Looks like this needs to be 8-gauge copper to keep to 3% voltage drop at 20 amps.

    Questions:
    1) Any gotcha's with what I described above?

    2) I think I will run conduit from the panel to the well vault, as I think it will save me some $ as compared to two separate direct-bury cables for the two circuits. Given this, can the two circuits share a ground wire in the conduit? If so, what size does the grounding conductor need to be if it is allowed to be shared?

    Thanks!

    Jeff

  2. #2
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    245

    Default

    One general question. What are these circuits going to -- a post, a small shack, an underground vault? A detached structure require a local power disconnect and cannot be fed with 2 circuits unless that are different characteristics. If the outlet isn't in the vault (e.g. on a post near it) then you'd have one circuit to the vault and one to a separate post which is fine. If both go to the vault, you could argue that the two circuits are different because of voltage (one 240V, one 120V), but that argument is easier when they are completely different sources (e.g. 120/240 -vs- 277/480).

    So because the vault is a structure, the vault may require a disconnect for the pump. A 20A AC Only double pole wall switch (or better a 30A one) would work, as would an air conditioning disconnect box. A post for a receptacle generally doesn't require a disconnect, but a small shack would.

    Why the 20A outlet? Do you have anything with a 20A cord? Are you wanting 20A because you may run 2 things that together add up to 20 amps? Code has no mandates for voltage drop, so you can use whatever drop you want. If you're running a large motor from that outlet (e.g. a chop saw), then I'd watch the voltage drop. Most things aren't going to care. So I'd consider also using #10 for that circuit and put it on a 15A or 20A breaker.

    Yes, you only need 1 ground wire in the conduit if you have multiple circuits. It is sized based on the largest single circuit ground you'd need (most likely #10 for what you're describing unless you upsize that 120V outlet to #8 wire then the ground also has to be upsized because of voltage drop).
    Mark
    Kent, WA

  3. #3
    Join Date
    Nov 2014
    Posts
    4

    Default

    It's an underground vault. About 4 feet by 5 feet, and 6 feet deep. The well goes down another ~15 feet below the floor of the vault (there is a cover over the well with only the pipe coming through.) . The pump is a "shallow well jet pump" that is in the vault, but above the well.

    I think your idea to keep the outlet separate is a good one. I'd occasionally like to run a small power tool, but probably could make due with < 15 amps.

    Thanks,

    Jeff

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