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Old 11-13-2019, 09:30 AM   #1
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GFCI in bathroom trips when furnace comes on

My search skills have failed me, so....


There is a GFCI outlet in the bathroom that is tied to a bunch of seemingly random outlets in the fiver. Nice electrical work. It seems to work flawlessly until it's time to use the gas furnace.


When the furnace kicks on, 9/10 times the GFCI outlet will trip. Most times, it will reset even while the furnace is running. It always resets and works fine post furnace run.



I'm a little confused here - I was under the impression that the furnace was a 12 VDC appliance, so why the effect on the 120 VAC outlet?


Any suggestions as to the cause? Is this one of those "replace the outlet and hope it goes away" situations?
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Old 11-13-2019, 10:54 AM   #2
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First off the GFCI outlet in the bathroom is wired to all of the 120V outlets in the trailer (at least on my 2016 CC). I believe that the electrical code requires that one outlet in the circuit first in line needs to be a ground fault outlet in the circuit. Every thing after that is wired to this GFCI needs to add up to 15AMPS when used! So, they wire all of the 120V outlets to that GFCI outlet after the 15A GFCI, meeting the code!

The only 120V outlet not wired to the GFCI is my residential fridge that the invert powers when traveling.

I replaced my 15A outlet to a 20A outlet on my trailer, since it was tripping every time I plugged something into any outlet. The 15A outlet was defective, they do fail once in awhile.

The reason I went to a 20A outlet is there is a little LED bulb that is lit when the outlet is working correctly. If it is out the outlet has tripped.

One possible issue is that you may have a higher total usage, current draw that adds up to using more amps. Such as coffee pot, toaster, electrical frying pan, TV on and some other electrical appliance on, all at the same time. These are all drawing AMPS and they may add up to more than 15 AMPS so, when the furnace comes on this too may draw some AC electrical amps from the converted. Thus tripping the GFCI.

Even though the furnace is 12V DC, if the battery is not up to capacity (fully charge) than the convert is required to turn AC current into 12V DC current to operate the furnace. So, this all may add up to 15AMPS or more when working causing this to be near the tripping point of the 15AMP GFCI!

Also if the 15A GFCI is old the GFCI maybe near the end of it's useful life, requiring the GFCI to be replaced.

Just a thought
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Old 11-13-2019, 11:34 AM   #3
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Originally Posted by Jim34RL View Post
First off the GFCI outlet in the bathroom is wired to all of the 120V outlets in the trailer (at least on my 2016 CC). I believe that the electrical code requires that one outlet in the circuit first in line needs to be a ground fault outlet in the circuit. Every thing after that is wired to this GFCI needs to add up to 15AMPS when used! So, they wire all of the 120V outlets to that GFCI outlet after the 15A GFCI, meeting the code!

The only 120V outlet not wired to the GFCI is my residential fridge that the invert powers when traveling.

I replaced my 15A outlet to a 20A outlet on my trailer, since it was tripping every time I plugged something into any outlet. The 15A outlet was defective, they do fail once in awhile.

The reason I went to a 20A outlet is there is a little LED bulb that is lit when the outlet is working correctly. If it is out the outlet has tripped.

One possible issue is that you may have a higher total usage, current draw that adds up to using more amps. Such as coffee pot, toaster, electrical frying pan, TV on and some other electrical appliance on, all at the same time. These are all drawing AMPS and they may add up to more than 15 AMPS so, when the furnace comes on this too may draw some AC electrical amps from the converted. Thus tripping the GFCI.

Even though the furnace is 12V DC, if the battery is not up to capacity (fully charge) than the convert is required to turn AC current into 12V DC current to operate the furnace. So, this all may add up to 15AMPS or more when working causing this to be near the tripping point of the 15AMP GFCI!

Also if the 15A GFCI is old the GFCI maybe near the end of it's useful life, requiring the GFCI to be replaced.

Just a thought



I've got three circuits for outlets - they make no sense where they go, as the bathroom gfci is connected to the rear of the trailer. The other GFCI is in the kitchen, above the counter. There are a few outlets that are not on gfci, so it sounds like out trailers are wired a bit differently. The actual breaker never trips, just the GFCI. Batteries are nearly new, fully charged, and I have been plugged in for a month to 50 Amp service.


I think I'll grab a new GFCI and throw it in next time I'm at the hardware store.
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Old 11-13-2019, 11:48 AM   #4
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I think I'll grab a new GFCI and throw it in next time I'm at the hardware store.
While you are at it check and tighten all the AC connections at the power center on both ground and neutral buses. A loose connection can cause the same fault the GFCI is designed to trip on.
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Old 11-13-2019, 12:43 PM   #5
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Remember the GFCI is just one component in that leg of power from the AC distribution panel. If you upgrade the GFCI from 15 to 20 amps, the actual breaker at the AC panel is still 15 amps (and should not be changed to a 20 amp breaker - it is matched to the wire gauge to protect the wire).

I suspect the tripping GFCI may just be faulty. But replacing a 15 amp GFCI gains you nothing in extra capacity (and likely violates all sorts of electrical codes). If you have eliminated all other possibilities, you probably have a flaky GFCI and can replace it.
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Old 11-13-2019, 01:02 PM   #6
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I'm really confused by this. The furnace is 12v and should have nothing to do with the 120v GFCI.

I'd replace it (with a 15amp outlet), but it doesn't make sense as to why it's an issue and corresponds to the furnace running.
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Old 11-13-2019, 01:10 PM   #7
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I'm really confused by this. The furnace is 12v and should have nothing to do with the 120v GFCI.

I'd replace it (with a 15amp outlet), but it doesn't make sense as to why it's an issue and corresponds to the furnace running.

Yeah, this is what gets me - I get both 12v and 120v for the most part, but they should be separate. But this stupid thing - the second the furnace blower kicks on, the outlet trips. Gonna replace it with the proper rating and see what happens.
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Old 11-13-2019, 01:11 PM   #8
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I'm really confused by this. The furnace is 12v and should have nothing to do with the 120v GFCI.
Normally that would be the case but since 12 v and 120 v supplies do meet each other in the Converter it might happen. Depending on furnace size and current draw the increase in load on the converter might cause the GFCI to trip if there is a loose connection in their common wiring (neutral and ground) at their respective buses.

That's the only place wiring from either "circuit" comes in contact with the other If not that then it's merely coincidence.

As for merely replacing a GFCI outlet with a standard outlet, I wouldn't do that myself. That would eliminate the protection that and other outlets on the string and the results could be "shocking". The GFCI is there for more than just "code" purposes.
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Old 11-13-2019, 01:13 PM   #9
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While you are at it check and tighten all the AC connections at the power center on both ground and neutral buses. A loose connection can cause the same fault the GFCI is designed to trip on.

I wonder if the vibration from the blower is causing something in the power center to move or arc. They are right next to each other, so I'll have to check it out. Outlet first, then power center if the problem doesn't go away cause that's the easy fix.
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Old 11-13-2019, 01:15 PM   #10
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I'm really confused by this. The furnace is 12v and should have nothing to do with the 120v GFCI.

I'd replace it (with a 15amp outlet), but it doesn't make sense as to why it's an issue and corresponds to the furnace running.
X2 My thoughts exactly. There should be no physical connection between the two. Really odd.
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Old 11-13-2019, 01:17 PM   #11
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Normally that would be the case but since 12 v and 120 v supplies do meet each other in the Converter it might happen. Depending on furnace size and current draw the increase in load on the converter might cause the GFCI to trip if there is a loose connection in their common wiring (neutral and ground) at their respective buses.

That's the only place wiring from either "circuit" comes in contact with the other If not that then it's merely coincidence.

As for merely replacing a GFCI outlet with a standard outlet, I wouldn't do that myself. That would eliminate the protection that and other outlets on the string and the results could be "shocking". The GFCI is there for more than just "code" purposes.
I didn't mean to imply otherwise- I'd replace GFCI for GFCI (and keep the 15amp for 15amp).

Good call on the distribution center. I think I'd start there.

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I wonder if the vibration from the blower is causing something in the power center to move or arc. They are right next to each other, so I'll have to check it out. Outlet first, then power center if the problem doesn't go away cause that's the easy fix.
I think Mike makes a good point. I might be tempted to just hit the power distribution sensor with a screwdriver and see if there's anything loose. It's quick easy and free.
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Old 11-13-2019, 01:41 PM   #12
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Normally that would be the case but since 12 v and 120 v supplies do meet each other in the Converter it might happen. Depending on furnace size and current draw the increase in load on the converter might cause the GFCI to trip if there is a loose connection in their common wiring (neutral and ground) at their respective buses.

That's the only place wiring from either "circuit" comes in contact with the other If not that then it's merely coincidence.

As for merely replacing a GFCI outlet with a standard outlet, I wouldn't do that myself. That would eliminate the protection that and other outlets on the string and the results could be "shocking". The GFCI is there for more than just "code" purposes.
This was my thought as well. I'd suggest checking all the connections even at the receptacle, and the ones between the pedestal and RV. You could also have a converter going bad, and could be putting trash back on the neutral line

Replacing the GFCI with a 20 amp rated unit isn't a problem as long as you don't replace the breaker feeding it with a larger breaker (unless of course the wiring and downstream devices can handle it).
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Old 11-13-2019, 01:46 PM   #13
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I think Mike makes a good point. I might be tempted to just hit the power distribution sensor with a screwdriver and see if there's anything loose. It's quick easy and free.

Over the years I've become a firm believer in Occam's Razor when it comes to diagnosing problems.

The old saying "when you hear hoof-beats think horses, not zebras" holds a lot of weight when chasing electrical issues.

Start with the power sources and make sure they are "steady" before tackling the troublesome item. It may merely be showing the symptoms while the problem is elsewhere.


RE: GFCI removal, wasn't directed to you but merely put out there as a caution should anyone decide to make that change without understanding it's importance.
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Old 11-13-2019, 01:49 PM   #14
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I agree with the vibration logic. I suspect there is a wire touching somewhere on the 120 volt side. It must be touching when the blower starts, or one of the semi metallic flex ducts is rubbing the back side of an outlet? You could pull the GFCI out and disconnect the load side (all down stream outlets) and test it again. If it doesn't fail, pull every downstream outlet from the wall and investigate. Of course, be safe and call an electrician if this is out of the comfort zone.
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Old 11-13-2019, 01:59 PM   #15
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It does sound like there is some point the 120v is being affected by the 12v turning the furnace on. Could be a screw or staple that nicked a 120v wire and the vibration is enough to cause leakage on that line to ground. That is what GFCI's are made to trip on, a slight leakage to ground (not a dead short) before it becomes deadly.

I know it's going to trip the GFCI fairly quickly, but could you not check to see if there was 120v or any AC of lower voltage leaking to the frame when the blower first starts? A non-contact AC sensor at the frame might show leakage just before the GFCI trips. That would help confirm it is likely a fastener that nicked a AC wire. I'm talking about a sensor like these, they usually will chirp and light up with as low as 12v AC (depends on brand/model). A good unit is $20 or less. It will likely chirp for a second or less before the GFCI trips, but you may see the indication of AC on the frame (or even the furnace metal housing)

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Old 11-13-2019, 02:04 PM   #16
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Will have to do some trouble shooting - banging away at the power distribution, wall, and wall around the outlet didn't trip it.
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Old 11-13-2019, 02:20 PM   #17
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The converter is not going to be run through the GFCI.

Have you tried unplugging all appliances and seeing if it still happens? I cannot imagine a condition where this would help but it will eliminate one item.

The other possibility mentioned of vibration is possible. You should be able to duplicate that by thumping things and seeing if the GFCI trips. If you thump the GFCI itself, does it trip? Use the handle of a screwdriver for the thumping.

A tech clued me on to that trick. When he has a circuit breaker randomly tripping he thumps it and if it trios he replaces it. That happened on one of our air conditioners. After he replaced that breaker the problem vanished.

Is that GFCI anywhere near the furnace physically?

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Old 11-13-2019, 02:29 PM   #18
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Will have to do some trouble shooting - banging away at the power distribution, wall, and wall around the outlet didn't trip it.
Try banging around the furnace since it seems to be the vibration from the furnace that is most likely related to the event.
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Old 11-13-2019, 06:01 PM   #19
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On the home front, I have had GFCI outlets trip from surges and sudden/exceptional power draw. Thinking outside the "box," is it possible something that comes on at the same time as the furnace could be causing that power delta? Something like a heat pump? If not, I'll cast my "vote" with those who suggest checking for loose wires or 120 volt leakage.
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Old 11-13-2019, 08:53 PM   #20
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Another off the wall idea. I wonder if the 12 volt wires for the furnace are running very close to the 120 volt wire going to one of the outlets on the circuit with the GFCI. Could the 12 volt wire be creating some kind of radio frequency that the GFCI is interpreting as grounds for tripping?

BTW, this is WAY out of my realm of expertise...
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