Hot Tub GFCI troubleshooting

[bmbouter]

I am the homeowner of a hot tub that's been working for well for 6 years. One day the water began to provide a shocking sensation which would prevent you from putting your finger fully into the water. I determined the shock was coming from a 12V light mounted in the tub whose water seal had broken. The light has not worked for a long time, but it was still powered from the hot tub's circuit board. A multimeter in the water and the other lead in the earth confirmed the voltage amount. I have disconnected the light (there was only 1) from the board, and the shocking stopped.

Why did my GFCI on the external breaker disconnect not prevent this from happening?

The most likely root cause is that the hot tub or its circuitry are not properly grounded, or that the GFCI is broken or not wired correctly. Here's the mystery though: upon inspection and continuity testing, everything does seem properly grounded and a GFCI breaker properly installed...

Let's start with the circuit panel which uses a 50A non-GFCI split phase circuit. The split phase circuit's ground is connected firmly to the ground of the circuit panel. I verified both with a visual inspection and a multimeter continuity test. For good measure, I ensured the screw holding it was tight, and it already was. I also verified the neutral and two hot lines similarly. Pics below.

The hot tub has an external service disconnect, and that's where the 50A GFCI breaker is installed. I verified similarly that the ground, neutral, and two hot lines are correctly wired to the GFCI. Same visual inspection; same continuity tests passing, and same loose screws check with none being loose. Pics below.

Then the wiring from the outdoor GFCI circuit to the tub was inspected at the tub itself. I visually inspected the neutral, two hot lines, and ground wires are wired to the board correctly and every looks right. I also ran continuity tests with a multimeter for the neutral and two hot lines, all checked out fine. For good measure I checked various metal points on the hot tubs metal internals (various pumps, circuit board box, etc) for continuity against the incoming ground wire and it also showed connectivity. All screws are tight. Pics below.

Both breakers provide power as expected in the ON position and disconnect power as expected in the OFF position. While both breakers are on the hot tub powers on. When I press the "test" button on the GFCI it trips the breaker and a manual reset is needed to power the GFCI breaker on again. This can be repeated over and over and it trips as expected with its self-test each time and powers on as expected each time after reset.

Question 1: So how could this happen? Here are my theories, and I'd like to hear other possible causes too.

a) my inspection reached an incorrect conclusion, something is miswired here and I did not find it. If so, what can I check to investigate if this is the case.

b) The GFCI self-test is working, but somehow the GFCI is actually broken. I don't have a proper GFCI tester, but I've read such things exist.

c) The 12V signal is too weak to trip the 50A GFCI. My multimeter showed 12V, but I didn't see if it was DC or VAC. I could safely measure this again if this is helpful.

d) Somehow the hot tub circuit board was to blame? Extra info: a spa company tested this board 4 months prior to this event due to a motor issue being investigated. Their statement was "it tested correctly on their test equiment". It's still a possibility though? How would a board be able to do something the GFCI wouldn't detect though?

e) your suggested root cause.


Question 2: Is possible a bad hot tub board could create an unsafe situation in a way the GFCI could not protect against?

Question 3: Is installing an additional 50A GFCI Square D breaker in the main breaker panel to provide a 2-layer GFCI protection sound useful or ridiculous?

Question 4: What would you do if you were me and your family went in this hot tub?

 

[DPG]

I would get a grommet or gland fitted where those cables go through the metal box. Not good that. Although it wont be causing your problem.

 

[pc1966]

The two most likely reasons to me are:

1. The shock was below the GFCI trip limit, either because it was low (even if it felt bad) or because the trip limit is too high.
2. The shock was coming from an independent 12V supply used for safety reasons. In this case the GFCI would not see anything wrong as the power to the isolation transformer would not be leaking, it would be from the secondary side.

I don't know what is used in the USA but for something like a hot tub I would assume it should be a 10mA limit from a dedicated device, where as the common size in the UK is 30mA at the board as protection for general use (not high risk areas). A proper tester would allow the actual trip current to be verified.

This is a bit of a worry, and you really ought to get in a professional electrician who has such test equipment to be sure it is working as intended. In the UK a "multi function tester" that has that capability typically costs in the £500-£1k region so it would be much cheaper to get someone in!
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Example of a MFT:

Multifunction Testers | Fluke 1662 Multifunction Tester

The 1662, one of our multifunction testers, tests to all local regulations & provides test results for complete documentation. Learn more today!

www.fluke.com

 

[westward10]

That looks like a GE GFCI and from a bit of searching is probably Class A which is 5ma. I am wondering whether the 12v lighting supply is actually suitably isolated from the mains supply.

https://www.homedepot.com/p/GE-50-Amp-Double-Pole-Ground-Fault-Breaker-with-Self-Test-THQL2150GFTP/206602330

 

[pc1966]

That GFCI looks quite fancy with periodic self-test, so I guess if it is seen to trip on test (as reported) then most likely it is working to specification.

So that kind of points to the 12V light supply as the cause of it. I'm a bit surprised you would get a lot of sensation from that (outside of a salt bath!) but maybe there are other leakage issues as westward10 suggests?

 

[Megawatt]

That GFCI looks quite fancy with periodic self-test, so I guess if it is seen to trip on test (as reported) then most likely it is working to specification.

So that kind of points to the 12V light supply as the cause of it. I'm a bit surprised you would get a lot of sensation from that (outside of a salt bath!) but maybe there are other leakage issues as westward10 suggests?

It appeared that the GFCI Breaker is wired wrong. The squiggly wire on the GFCI breaker should terminate on the neutral bar and the neutral feeding the hot tub should terminate on the GFCI breaker, in that pic it’s hard to tell
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It appeared that the GFCI Breaker is wired wrong. The squiggly wire on the GFCI breaker should terminate on the neutral bar and the neutral feeding the hot tub should terminate on the GFCI breaker, in that pic it’s hard to tell

I also agree with DPG you need to a install connector where the wire enters the panel which could very easily cut the wire

 

[bmbouter]

I would get a grommet or gland fitted where those cables go through the metal box. Not good that. Although it wont be causing your problem.

Thank you for pointing this out. I agree. I will ensure this is resolved.

 

[Megawatt]

Thank you for pointing this out. I agree. I will ensure this is resolved.

Good luck my friend and make that hot tub safe

 

[bmbouter]

That looks like a GE GFCI and from a bit of searching is probably Class A which is 5ma. I am wondering whether the 12v lighting supply is actually suitably isolated from the mains supply.

https://www.homedepot.com/p/GE-50-Amp-Double-Pole-Ground-Fault-Breaker-with-Self-Test-THQL2150GFTP/206602330

Thanks for the reply. If the 12v lighting supply was not suitably isolated from the mains, would that be an issue with the hot tub's control board design? Or is that something that would happen on a single tub's installation? Could you describe this a bit more if possible? Thanks!

 

[Lucien Nunes]

The GFCI only protects, and only needs to protect, the AC line circuit and components connected to it that operate at 120/240V. The 12V lighting circuit is derived from a transformer or power supply unit; even if that obtains its power via the GFCI, its 12V secondary side should be independent and the current used at 12V does not pass through the GFCI, therefore, if an imbalance or leakage occurs, the GFCI will not detect it. A GFCI on this circuit is not considered necessary because at 12V, the maximum current that can pass through the water is very limited and not hazardous, although you can often feel it if you are in very good contact.

There is one other possible source of leakage and that is from the AC line, through a fault or moisture in the power supply unit across its isolation barrier to the 12V secondary side and then through the faulty 12v light into the water. A small amount of leakage, usually less than a milliamp, can and does occur normally across the isolation barrier. However, since its source is the AC line and it is merely passing through the 12V circuit, the GFCI would detect it and trip if it became excessive.

The insulation resistance and the leakage of the power supply or transformer can be tested. There may be limitatations imposed by the manufacturer on the kind of tests they advise are carried out, to avoid damaging the electronics. In the UK we would conduct an insulation test at 250V DC to measure the resistance, and a differential leakage test at normal line voltage to measure the leakage in mA. The leakage test can detect both leakage from the AC line to ground, and also to the 12V secondary side. However we have a habit of testing and measuring anything and everything - even a new light socket will be given a bunch of tests before it's considered ready to use.

 

[Megawatt]

Thanks for the reply. If the 12v lighting supply was not suitably isolated from the mains, would that be an issue with the hot tub's control board design? Or is that something that would happen on a single tub's installation? Could you describe this a bit more if possible? Thanks!

All I can tell you is if that breaker was wired correctly it would have tripped the GFCI breaker. The hot tub internal wiring is correct but with the cover broke you done the right thing by taking those particular wires loose
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All I can tell you is if that breaker was wired correctly it would have tripped the GFCI breaker. The hot tub internal wiring is correct but with the cover broke you done the right thing by taking those particular wires loose

Just because you can push the test button and it trips don’t mean it’s wired correctly

 

[bmbouter]

All I can tell you is if that breaker was wired correctly it would have tripped the GFCI breaker.

I also suspect the wiring of the GFCI is incorrect, but here is some info if you can tell me what you think. The pictures don't make it very clear, but here's what I just confirmed (along with another not-so-great picture). The neutral from the hot-tub is not connected to the neutral breaker bar; it is connected to the GFCI at the terminal with the white dot. The GFCI pigtail is connected to the neutral breaker bar, along with the incoming neutral from the main breaker box. The hot-tub's two load lines are also connected to the GFCI directly also. The ground bar does connect the hot tub ground line and the main breaker circuit ground and nothing else. Based on my reading, this seems correct, but what do you all think?

 

[Megawatt]

I also suspect the wiring of the GFCI is incorrect, but here is some info if you can tell me what you think. The pictures don't make it very clear, but here's what I just confirmed (along with another not-so-great picture). The neutral from the hot-tub is not connected to the neutral breaker bar; it is connected to the GFCI at the terminal with the white dot. The GFCI pigtail is connected to the neutral breaker bar, along with the incoming neutral from the main breaker box. The hot-tub's two load lines are also connected to the GFCI directly also. The ground bar does connect the hot tub ground line and the main breaker circuit ground and nothing else. Based on my reading, this seems correct, but what do you all think?

In your pictures the neutral for the hot clearly hooks to the ground bar not the breaker. The squiggly wire should terminate on the neutral bar and the neutral for the hot tub hooks to the terminal on the breaker. It looks like that both the wires are attached to the bar in the extra panel with the GFCI which puts them both together and then your neutral goes to another panel and terminates on the neutral bar. They have to be separated. I see a spare double pole breaker in your main panel that is labeled spare, that should have been taken out and your GFCI breaker installed in its place

 

[westward10]

Surely the neutral is connected correctly at the GFCI or it would constantly trip but I agree the neutrals appear to be at the ground bar.

 

[Lucien Nunes]

It looks OK to me. The ground bar is bottom left, I see two wires. The neutral bar is top right. Cables coming in from the back go to the neutral bar and the top terminals of the GFCI. The cable going out at the bottom connects to the bottom terminals on the GFCI. And yes, if the neutral were going through in the wrong direction, any neutral current (i.e. any 120V loads) would immediately trip it.

 

[bmbouter]

Yes the photos do make it seem as if the hot tub side neutral is wired to be neutral breaker bar, but in examining it up close, it is not the case. Sorry to not have a better photo to demonstrate this with. I appreciate all the time and concern folks have put into helping confirm the wiring is correct.

 

[bmbouter]

The GFCI only protects, and only needs to protect, the AC line circuit and components connected to it that operate at 120/240V. The 12V lighting circuit is derived from a transformer or power supply unit; even if that obtains its power via the GFCI, its 12V secondary side should be independent and the current used at 12V does not pass through the GFCI, therefore, if an imbalance or leakage occurs, the GFCI will not detect it. A GFCI on this circuit is not considered necessary because at 12V, the maximum current that can pass through the water is very limited and not hazardous, although you can often feel it if you are in very good contact.

What you're saying makes sense, but I still want to learn more. In this case the GFCI circuit is the only power to the hot-tub control box, so the 12V lighting circuit's transformer does power it. How can AC current flowing into the light's transformer transfer power to it's secondary side without loosing any current? Feel free to refer me to something I should read also.

I'm still very concerned... I've been reading some about stray voltages here Mike Holt Enterprises - the leader in electrical training. - https://www.mikeholt.com/technical-stray-voltage-newsletter-menu.php and also here Stray Voltage - No You are not Crazy - https://www.mikeholt.com/mojonewsarchive/SV-HTML/HTML/StrayVoltageNotCrazy~20031020.htm The shock I felt was not small, I think if I had been in the tub when the light failed I would have died.

I don't know what to do because how can I be sure it's not caused by something like what is described in these articles. I'm concerned that even a good electrician could not solve such a strange problem. After verifying (as we have) that the wiring is good, and if the GFCI tests good what could they do to assure me that this is safe?

 

[marconi]

This is so important please could you post a better picture so those 'in the know' can confirm the wiring is actually correct for you.

 

[Megawatt]

What you're saying makes sense, but I still want to learn more. In this case the GFCI circuit is the only power to the hot-tub control box, so the 12V lighting circuit's transformer does power it. How can AC current flowing into the light's transformer transfer power to it's secondary side without loosing any current? Feel free to refer me to something I should read also.

I'm still very concerned... I've been reading some about stray voltages here Mike Holt Enterprises - the leader in electrical training. - https://www.mikeholt.com/technical-stray-voltage-newsletter-menu.php and also here Stray Voltage - No You are not Crazy - https://www.mikeholt.com/mojonewsarchive/SV-HTML/HTML/StrayVoltageNotCrazy~20031020.htm The shock I felt was not small, I think if I had been in the tub when the light failed I would have died.

I don't know what to do because how can I be sure it's not caused by something like what is described in these articles. I'm concerned that even a good electrician could not solve such a strange problem. After verifying (as we have) that the wiring is good, and if the GFCI tests good what could they do to assure me that this is safe?

bmbouter you would have piece of mind if you would call an electrician to rewire that breaker. I’ve seen enough pictures to know it’s wired wrong, and if it was me I would take that spare double pole breaker out and put that GFCI breaker in the main panel where it belongs. Then it would have tripped when the lens on the light broke. Good luck

 

[Lucien Nunes]

How can AC current flowing into the light's transformer transfer power to it's secondary side without loosing any current

In a conventional wirewound transformer, the 120V / 240V primary circuit energises a coil that creates a magnetic flux in the iron core. That magnetism then induces a current in a totally separate coil on the 12V secondary side. Because there is no electrical connection between primary and secondary, a faulty circuit or device connected to one side of the transformer can only create leakage on that side. The quality and strength of insulation between primary and secondary depends on application; a transformer made for safety isolation (e.g. between AC line and hot tub) will have insulation made to a recognised standard.

In an electronic power supply unit there is still a transformer, but by converting the incoming AC power electronically to a much higher frequency the transformer can be made smaller, lighter and more efficient. This frequency conversion can cause a small amount of leakage to pass across the transformer capacitively, from primary to secondary, but under normal conditions it is too small to cause harm and too small to trip a GFCI.