Current on GEC

[Doc13067]

Testing out my handy new Fluke T-6 and I found 4 amps on my GEC! I confirmed it with 2 other meters. I shut off my main and it went to 0. Then I started throwing branch circuits one by one and found the furnace circuit was the one that when turned off the amperage left the GEC. I followed the GEC to the water pipe and put my ammeter around the pipe and continued the exercise and found the same condition. There are 2-4 amps running up my cold water pipe and into my panel. Any ideas on how this is happening?

 

[infinity]

Do you have a metallic city water system?

 

[Doc13067]

Yes. But the current goes away when my furnace breaker is turned off.

 

[jim dungar]

Yes. But the current goes away when my furnace breaker is turned off.

Is there a good EGC to the furnace?

 

[retirede]

What kind of furnace? (Gas, heat pump, etc.)
Does the furnace have to be running or simply energized?

 

[TwoBlocked]

Yes. But the current goes away when my furnace breaker is turned off.

Looks like a partial ground. See what the resistance is on the hot leg(s) to ground with the power off, to start with.

 

[Doc13067]

Is there a good EGC to the furnace?

Yes I believe so. Theres continuity all the way back to the panel but I can’t say for sure that every component in the furnace has a good connection to the EGC because it’s simply terminated at a junction box in the beginning and after that there’s nothing but the bolts of the enclosure that ensure connectivity to the EGC

 

[Doc13067]

What kind of furnace? (Gas, heat pump, etc.)
Does the furnace have to be running or simply energized?

Gas forced hot air

 

[Doc13067]

Looks like a partial ground. See what the resistance is on the hot leg(s) to ground with the power off, to start with.

Ok thank you

 

[ptonsparky]

Use a a mega ohm meter.

 

[Eddie702]

Could be a bad neutral to the furnace. Current coming back on the EG

 

[Dsg319]

Could be a bad neutral to the furnace. Current coming back on the EG

There would have to be a N-G bond somewhere at the furnace than right.

 

[Doc13067]

There’s no current on the EGC.

 

[Doc13067]

Current is on the water pipe and then traveling up the GEC back to the main neutral. Remove the GEC from the panel and the current stops.

 

[GoldDigger]

Use a a mega ohm meter.

If you use a megohmmeter (megger) for power off hot to neutral or hot to ground measurement, be sure to disconnect all loads that may be damaged by the high applied voltage.

 

[Dennis Alwon]

Can you trace the wire to the furnace?

 

[Eddie702]

If the current goes away when you shut off the furnace breaker the next thing is to find if it is coming back to the panel on the neutral or EG or if wired in AC cable or another metallic wiring method that could be touching a water pipe somewhere

 

[jaggedben]

How much current is on the neutral? The same or more?

I mean, with a metallic city water system this could be essential normal.

 

[GoldDigger]

How much current is on the neutral? The same or more?

I mean, with a metallic city water system this could be essential normal.

Probably not going to be specific to the furnace circuit unless there is something special going on there. Gas furnace may not even be a specially high single phase load. I am assuming that gas furnace will use 120 though, unlike dryer. But toaster, dishwasher, etc. could cause the same problem.
Important question: Is the current there only when furnace is actually running?

 

[jaggedben]

Probably not going to be specific to the furnace circuit unless there is something special going on there. ...

Agreed but I'm skeptical that the current on the GEC is actually zero when the furnace is not on. With a metal city water network I wouldn't ever expect it to be truly zero.

I suppose we should ask to confirm that the GEC is well terminated to the neutral.