There is a line for a hot tub that I am trying to reconnect. Hot tub side has black, red, white and green wires. Power supply side has three black and one green wires.

The green was previously connected to green. Three black wires were disconnected after being exposed to water for a long time (see my previous question here).

I am now trying to figure out how to connect the three black wires on supply side to black/red/white on hot tub side. How would I do that?

Hot tub wires: hot tub wires

Power supply wires: power supply wires

  • Is your hot tub running on 3 phase circuit ? check the circuit breaker. Are there 3 of them ?
    – Traveler
    Commented Jun 5, 2022 at 8:17
  • 1
    Measure the voltage between the blacks
    – Traveler
    Commented Jun 5, 2022 at 8:21
  • 1
    Green to green. But where's neutral? Is one of the wires not actually black? Should be white or gray. Commented Jun 5, 2022 at 9:33
  • Can you provide a picture of the inside of the spa panel?
    – JACK
    Commented Jun 5, 2022 at 15:17
  • Could you either change everything to do with hot tubs to "something" or ask a qualified electrician directly? Commented Jun 5, 2022 at 21:05

1 Answer 1


To find neutral if this is the common North American house system, 120/240 volt split phase.

Being very careful, with the breaker off, separate all the wires from each other so the bare ends cannot touch.

Turn on breaker, after making sure everyone knows what you are doing. You do not need kids or a guy with a beer, daring each other to touch live wires with their tongues.

Take voltage reading for each black wire to the green wire. Both hots to green should read about 120 volts.

Neutral to ground should read around zero, but some meters might read phantom voltage of some volts.

The two hots should read 240 volts together, each hot to neutral should read 120 volts.

It does not matter which hot is connected to the red or black of the hot tub.

Having a black neutral(even if marked by white tape) is probably against code and a good chance of not passing inspection, depends on gauge, but think that gauge is not large enough.

One good thing is that it is in conduit, so replacing with a white wire should not be too difficult.

Remember the test will be done with live power, so be careful and keep anybody else well away.

  • 1
    Why do you say the neutral isn't heavy enough? There's no way the neutral can be called upon to carry any more power than either of the hot wires. Suppose this is a 20A circuit--if both hots are drawing 20A the neutral has 0A, not 40A. And your safety list should include no pets. If this is outside I would have a sane adult standing guard while I energized it. Commented Jun 5, 2022 at 22:20
  • 6
    @LorenPechtel After a certain gauge number(I do not know the exact gauge), you can mark a non-white wire as neutral(like for large size feeders). Below that gauge number, you must use a white or grey wire for neutral, you cannot use white tape/paint on a black wire to say it is a neutral. This is only about saying a black wire can be neutral, has nothing to do about current capacity.
    – crip659
    Commented Jun 5, 2022 at 22:38
  • 1
    @crip659 #4 or larger is the threshold for remarking wires (as up until very recently, you could get #4 or larger wire in whatever color you wished, as long as it was black, and even now, the other colors are special-order in most places) Commented Jun 7, 2022 at 11:46

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