GFI disconnect for hot tub.

[J.P.]

I ran power for a hot tube yesterday. Edit: it was a hot tub not a hot tube..........

The unit itself required 2 hots and a grnd.
The disconnect was a CH 50A 2pole GFI Nema 3R

Ran 2 hots a neutral and a grnd to the disconnect.

Ran 2 hots and a grnd to the unit.

Separate neutral (isolated) and ground ( to chassis) bars in the disconnect. Treated them as you would a sub panel ( kept them separate )

The GFI disconnect kept tripping sometimes within a few seconds and sometimes after a minute or so. Then it held and only tripped when I hit the test button.
Had the hot tub on maximum settings the whole time. ( full of cold water, so it was heating )
Current draw was 41A peak for just long enough to read it and then dropped to 19A with everything on.

Don't really know what to make of it. I almost made the 1/2 hr drive to town to exchange the GFI breaker for another. Bad breakers aren't unheard of, but aren't all that common either.

What would cause it to trip like that? %99.99999 sure it was not a overload trip.

 

[JFletcher]

Did you check the nameplate on the tub/mfg directions? We did one today, had to go back to the supply house to get a 2p 60A main breaker and GFCI breaker. Mfg specs. Had to wire it in #6. Also, this one was listed at drawing 48.0A full song (everything running). When the pump motors kick on, you could be well over 50 or 60A for a few moments. and the heater will be running continuously until that cold ground water is up to around 100*F.

Some hot tubs have enough smart controls that they will test everything out on their own on install/first power-up. Wouldnt surpise me in the least if some also have an auto-test for the GFCI breaker, creating a false ground fault to check its operation.

eta: you positive it doesnt require a neutral from disco to tub? What make/model of tub?

 

[Dennis Alwon]

The gfci neutral from the breaker still needs to be connected to the neutral bar in the disco

 

[mopowr steve]

Could there have been possibly a little water laying on the water heater connections causing a ground fault until the water evaporated?
Just throwing some thoughts out there, I have come across leaking heating element connections which caused gfci to trip.

 

[kwired]

The gfci neutral from the breaker still needs to be connected to the neutral bar in the disco

And it likely was or else it wouldn't have tripped - except for standard thermal magnetic overloads.


mopowr sort of beat me to the other thing I had to say, there may have been a ground fault and it cleared itself when the breaker finally started holding.

 

[J.P.]

Didn't get a call from the customers today so I'm assuming everything is fine. I did tell them to let me know asap if they had any problems.
It's warm now, but you sure don't want it tripping and freezing something in de vinter.

 

[J.P.]

Could there have been possibly a little water laying on the water heater connections causing a ground fault until the water evaporated?
Just throwing some thoughts out there, I have come across leaking heating element connections which caused gfci to trip.

This maybe. The drain line was over the electrical box with the cap crossthreaded when I first started it up. Things got damp, but not too bad.



How would a gfi disconnect even work on something that only spec'ed 2hots and a ground? The neutral only ran from the panel to the disconnect and nowhere else.

 

[GoldDigger]

The GFI detects any imbalance between the current in the two hot lines. Presumably this will be the result of fault current to ground/EGC since the neutral is not involved.
The GFCI breaker may require a neutral connection for its internal power, but that does not need to extend to the load.

 

[ActionDave]

How would a gfi disconnect even work on something that only spec'ed 2hots and a ground? The neutral only ran from the panel to the disconnect and nowhere else.

Correct.

 

[iwire]

How would a gfi disconnect even work on something that only spec'ed 2hots and a ground? The neutral only ran from the panel to the disconnect and nowhere else.

Basically the GFCI measures the current going out on one hot and the current coming back on the other hot. If the two currents don't match that means the current is going another direction so the GFCI trips.

That is an oversimplification but pretty much how it goes.

 

[kwired]

The GFCI must have the supply neutral as it is one of the supply leads to the electronic control board that drives the logic of the thing.

The load does not need to utilize the neutral conductor. All three circuit conductors (both hots and the neutral) pass through a CT within the unit, any current going out on one conductor must return on one or both other conductors to cancel effects on the measurement by the CT. If any current from any of the three measured conductors returns via any other path - the imbalance there is measured in the CT - for class A GFCI protection once this current is over the 4-6 mA range it is in the trip zone.

 

[J.P.]

Thanks, the GFI explanation makes sense. I'm one step closer to knowing everything!

 

[goldstar]

I usually run a neutral to both the disconnect and the tub irrespective of whether it's required or not. You never can know that maybe somewhere down the line if the control unit goes bad that the maker now only has replacements that require a neutral. I terminate the neutral in the disconnect and safe it off in the control.

Anyway, when I have a GF problem at start-up I usually open the control section and disconnect all the EGC's to the motors, etc. I then connect one at a time back onto the ground bar to find which component is causing the GF problem. As others have mentioned there could be leakage to ground in any of these components.