Generator tripping GFCI

[BillP]

I have a large (9200 watt) sine-wave Champion generator, which charges a 1500 VA Smart-UPS, which in turn keeps satellite internet running when the generator is turned off.  The Smart-UPS trips the GFCI on the generator, generally after 30 to 90 minutes of operation.  The satellite internet device draws around 30 watts and the generator has a 30 amp (3300 watt) GFCI.  If I take the Smart-UPS out of the circuit, the GFCI on the generator never blows.  Occasionally the generator will fully charge the battery but usually it blows the GFCI before that happens. 

Advice?  I've grounded the generator with a copper rod in the ground.  Should I also ground the UPS?

[BillP]

Mostly I am pinging this, hoping to get a reply.  A specific question is whether using a 3 to 2 prong adapter might reduce the GFCI tripping, by circumventing the neutral/ground discrepancy that is causing the tripping in the first place.  Alternatively, will grounding the APC likely stop the tripping of the GFCI?

[BillP]

Hi Randolph - 

I apologize for not responding sooner. You have a couple factors working against you here - a GFCI and a small portable generator. Both of these tend to have issues with Smart-UPS. You could try replacing the GFCI outlet on the generator or possibly using a non GFCI outlet if one is available. Definitely do not add additional grounding direct to the Smart-UPS. You may still find that even if you overcome the GFCI hurdle that the UPS doesn't like to operate online with the generator power. In that situation you could reduce the power quality setting on the UPS to "Poor" and see if that does the trick. 

Thanks

Liam

[BillP]

Thanks.  I think I can avoid the GFCI by converting a 30A 120/240 twist-lock plug to a 3-prong 120v, and using that.   Since it generally takes quite a long time for the APC to trip the GFCI, it isn't the power draw, but the discrepancy between neutral and ground.  Hopefully avoiding the GFCI will fix it.

9200W is quite a large generator and it produces a decent sine wave, with claimed specs similar to the power grid. 

Why do you suggest not grounding the APC?  I would have thought grounding was always a good idea, at worst harmless.

I think my use case -- I want to power a small appliance (30W) or LED lights after I turn off the generator, my only source of power, would be pretty common among lake cottages and cabins.

[BillP]

Your twist lock plug is likely an L14-30, which can easily be converted to a standard 120v Hot/Neutral/Ground with an adapter.

I suppose "Small" and "Large" when it comes to generators is very much relative. Our primary market for Smart-UPS is data centers and computer rooms. They would typically have something like a whole building diesel or natural gas hard wired generator, which I would put in the "Large" category. These types of gensets have very clean output that is very tightly regulated. Any of the small portable gas units that you might find at a big-box store are going to have more issues with frequency drift and THD. Generally as long as the generator is 3-5 times larger than the total load attached, you can get a Smart-UPS to play nice, but it is very much a matter of "your mileage may vary". 

[BillP]

Yes, I've ordered an adapter for the L14-30 twist-lock.  Hopefully it is just a GFCI issue; UPS's often have trouble with GFCIs (at least according to several websites including Schneider's) and this is one way to avoid GFCI.

You are right that 9200W is large for a gas powered generator, tiny for diesel-powered data center generators.

[Terry_Kennedy_apc]

Just another user here, but 2 comments:

In the US, any electrical system is required to have a single grounded conductor, generally attached to the main electrical panel where it is bonded with the neutral from the electric utility. Note that that the grounded conductor may be provided by a grounding system such as a ground rod and a water pipe (if metal) coming from the street to the house. Between the main panel and subpanels, or between panels and receptacles, there is a grounding conductor. But that works its way back to the main panel, where the grounded conductor is bonded to the neutral. Multiple grounds (other than as described above) are a no-no. Adding a generator to a system that has utility power has its own complications, such as a transfer switch. But I believe you are running a standalone system, not supplied by any utility power. You should still follow the code I have described above. Note the distinction between grounded and grounding.

2) You might have better results with a battery system (not necessarily a UPS) designed for solar power applications, as they should be more tolerant of input power variations. The difficulty would be in finding one that operates at line (120/240) voltage and not from the DC bus that the solar cells are powering.

[BillP]

Thanks, that was helpful!  You surmised correctly that we have a standalone system, with a couple of lights, some phones recharging, the satellite internet and the occasional power tool.  Everything works perfectly if I don't use the UPS, but when the UPS is plugged in, it trips the GFCI.  We don't have an electrical panel, just a six plug power strip.

I've bought the adapter for the twist-lock to 120v 3 prong plug.  I hope that will fix the GFCI problem for me, but I can't test it until I return to the cabin. 

I intend in the future to put solar in, but not until two to three years from now (after some construction), so would like to make this work in the meantime.

[Terry_Kennedy_apc]

I don't think the 3-prong will help, but give it a try.

I have an oddball theory you might want to test - load up the output of the UPS closer to its rated capacity and see if the GFCI trips still happen. This is based on what I know about much older APC models and may not hold true on more recent units.

You don't need to go for the full solar system, just the part that works when there isn't enough sunlight. I don't think it will be economical, but you may want to check.

[BillP · Accepted solution]

Thanks, I can try that, although my use case is really a bit different -- I just want to be able to run the internet some of the time without the generator.  So having a higher power draw (and hence less time) somewhat defeats the purpose of the APC.

My theory is that it is the GFCI and that the regular fuses won't trip, because GFCIs measure a cumulative power deviation, where the regular fuses only measure the instantaneous power draw (and at a much higher level than I am drawing).  So by converting the twist-lock output (which doesn't have a GFCI) to 3 prong, I am essentially creating a non-GFCI power source.