Whirlpool Tub and Ground / Neutral Bonded in Subpanel

[pianomannick]

A friend of mine was putting a whirlpool tub in a house with a 125 amp subpanel that only had a 3 wire (2 hot, 1 neutral) supplying it. The tub will be GFCI protected on a 15 amp dedicated breaker in the MAIN panel. It will also be bonded to the copper tub supply pipes from the pump motor.

He was just paranoid because someone told him that he may be electricuted in the tub because of stray current from the neutral and ground being bonded in the subpanel. He was saying that if for some reason the ground wire carried current from the subpanel, it would electrify the ground wires in the main panel, up to the tub and through the supply pipes to ground. This sounded absurd to me because to go all the way up to the tub is probably the longest path of resistance.

My question is, if a subpanel with a bonded neutral and ground carries current to the main panel, exactly what would be electrified along the way?

 

[Dennis Alwon]

I believe the OP has a hydromassage tub not a spa. So you are asking if he can get hurt by using the tub that is wired to a 3 wire subpanel where the neutral is bonded to the can. Is that correct???

 

[pianomannick]

Yes it is a hydromassage tub. It is wired to the main panel, NOT to the subpanel. But, yes I am asking if there is any way to get hurt if the ground wires in the main panel become hot from the subpanel.

 

[Dennis Alwon]

Yes it is a hydromassage tub. It is wired to the main panel, NOT to the subpanel. But, yes I am asking if there is any way to get hurt if the ground wires in the main panel become hot from the subpanel.

I don't see how that would be possible. The main panel has the neutral and ground bonded together and as long as the tub is wired to that panel your friend should be fine.

 

[hillbilly1]

The sub panel would not be a problem unless.........for some reason the neutral feeding it became disconnected, this would cause everything grounded to THAT neutral to become live to the hydro massage tub because it is properly bonded. That is the reasoning behind separating the neutral and grounds past the main disconnecting means. With the four wire feed, if the neutral becomes disconnected or loose for some reason, you may have equipment damage, but not a shock hazard.

 

[kwired]

The sub panel would not be a problem unless.........for some reason the neutral feeding it became disconnected, this would cause everything grounded to THAT neutral to become live to the hydro massage tub because it is properly bonded. That is the reasoning behind separating the neutral and grounds past the main disconnecting means. With the four wire feed, if the neutral becomes disconnected or loose for some reason, you may have equipment damage, but not a shock hazard.

Agreed.

It is not the fact that it increases the risk of shock at the whirlpool - it is the fact that the risk increases everywhere the EGC from this imporperly grounded subpanel exists. If that EGC becomes elevated voltage it will have potential to anything grounded.

 

[K8MHZ]

Yes it is a hydromassage tub. It is wired to the main panel, NOT to the subpanel. But, yes I am asking if there is any way to get hurt if the ground wires in the main panel become hot from the subpanel.

I'm confused.....what does the sub-panel have to do with it if the tub is wired to the main panel???

in a house with a 125 amp subpanel that only had a 3 wire (2 hot, 1 neutral) supplying it.

That being said, if the unit is 240 volt three wire, the third wire should be the EGC, NOT the neutral. I just looked at a diagram for one and that is how it was wired. There was nothing 120 volt in it so no neutral was required.

 

[pianomannick]

Thanks... That confirms what I had already thought. A subpanel without separate ground and neutral would only negatively affect the things grounded to that panel. If the tub was grounded to the main panel, it wouldn't be affected in any way by the improperly wired subpanel.