Homeline 50 Amp 2-Pole GFCI Circuit Breaker Tripping with tiny load

marcoguidi · May 29, 2023

Hello,
I had an electrician install a 100Amp subpanel which feeds a mini split. I addition I added a Homeline 50A GFCI breaker to power a shed. I ran 80feet of 6/3 direct burial cable into a breaker panel in the shed. Here I tied the Neutral and Ground on the same bar. Neutral and ground are not tied in the subpanel. In the shed I have a breaker for outlets and a breaker for light. I measured resistance and voltages with no loads and all is great as soon as I introduce a load, no matter how small the 50A GFCI trips. I tried plugging in a LED work light or a smart switch, the 50A GFCI trips. The only load it tolerates is the voltmeter and the outlet tester which impedance approximates infinite or an open.

What am I missing?

Thank you!
MMG

westward10 · May 29, 2023

Probably one for @Megawatt but the fact you have tied the ground and neutral together is the reason it is tripping.

pc1966 · May 29, 2023

As above, @Megawatt is most likely to know what the NEC says, but from other discussions the neutral and ground should only be linked together at your main/incoming panel.

marcoguidi · May 29, 2023

westward10 said:
Probably one for @Megawatt but the fact you have tied the ground and neutral together is the reason it is tripping.

Well that is easy to test! Thank you!

marcoguidi · May 29, 2023

pc1966 said:
As above, @Megawatt is most likely to know what the NEC says, but from other discussions the neutral and ground should only be linked together at your main/incoming panel.

Well that is easy to test! Thank you!

marcoguidi · May 29, 2023

I purchased and added a ground bar but the GCFI breaker still trips. I read somewhere that the line fed by the CB should not exceed 100ft. I am really close to 100. And the first device, outlet or light switch is probably in the vicinity of 95ft. That may be the issuse. But I'd love to see if there are any GFCI that can protect the whole shed. Or it's a bad idea alltogether because there will beinductive loads such as table saw, mitre saw and probably an AC.

pc1966 · May 29, 2023

marcoguidi said:
I purchased and added a ground bar but the GCFI breaker still trips.

What do you mean by "added a ground bar" here? Have you now separated neutral and ground?

marcoguidi said:
I read somewhere that the line fed by the CB should not exceed 100ft. I am really close to 100. And the first device, outlet or light switch is probably in the vicinity of 95ft. That may be the issuse. But I'd love to see if there are any GFCI that can protect the whole shed. Or it's a bad idea alltogether because there will beinductive loads such as table saw, mitre saw and probably an AC.

The normal limit for cable length here is due to voltage drop, and the resulting lower fault current and so longer disconnection times. Which raises the risk of fire and shock (if not GFCI).

You can protect a number of devices from one GFCI as common in the UK & EU, but I think the USA specification has a much lower trip current so more likely to spurious trips. However if you can't run even a normal light then you have a fault!

Again, really one for @Megawatt as the USA NEC is very different to the UK regs and practices.

Lucien Nunes · May 30, 2023

Is the neutral of the cable to the shed definitely running through the GFCI in the 100A sub-panel? If only the phases go through (without the neutral) it will incorrectly sense any 120V load as a ground fault.

Since fitting the separate neutral and ground bars in the shed panel, have you double-checked that there is no connection at all between them and that all neutrals and grounds are attached to the right bars?

That 100ft maximum cable length is just a ballpark suggestion; nothing magical happens at 100ft that will cause a GFCI to trip. Every foot of cable adds to the total capacitive ground leakage and if there's too much coming from the cable itself, the total permissible leakage from connected equipment will be unreasonably reduced. What is the trip threshold of the GFCI?

marcoguidi · May 30, 2023

pc1966 said:
separated

Lucien Nunes said:
Is the neutral of the cable to the shed definitely running through the GFCI in the 100A sub-panel? If only the phases go through (without the neutral) it will incorrectly sense any 120V load as a ground fault.

Since fitting the separate neutral and ground bars in the shed panel, have you double-checked that there is no connection at all between them and that all neutrals and grounds are attached to the right bars?

That 100ft maximum cable length is just a ballpark suggestion; nothing magical happens at 100ft that will cause a GFCI to trip. Every foot of cable adds to the total capacitive ground leakage and if there's too much coming from the cable itself, the total permissible leakage from connected equipment will be unreasonably reduced. What is the trip threshold of the GFCI?

Yes I installed a ground bar and separated neutral and ground. I took a lot resistance and voltage measurements but I cannot find anything wrong. I replaced the GFCI breaker with a regular one and it all works. I will ensure the neutral is indeed goung through the breaker

marcoguidi · May 30, 2023

pc1966 said:
What do you mean by "added a ground bar" here? Have you now separated neutral and ground?

The normal limit for cable length here is due to voltage drop, and the resulting lower fault current and so longer disconnection times. Which raises the risk of fire and shock (if not GFCI).

You can protect a number of devices from one GFCI as common in the UK & EU, but I think the USA specification has a much lower trip current so more likely to spurious trips. However if you can't run even a normal light then you have a fault!

Again, really one for @Megawatt as the USA NEC is very different to the UK regs and practices.

Thank you!