I live in a house built in 1970-72 with a 200 amp SQ-D main panel (A) and a 100 amp subfeed panel. As per early 1970’s set ups the gound and neutral bars are not separated in either.
A second 200 amp main panel (B)was added in 1972 to accomodate the final construction sequences which included Intertherm Liquid filled electric baseboard heat. This 200 amp box is wired back to the pole where it is kernied to the other 200A main and the service drop.
In panel B there is a GFI breaker to the patio/water pond/swimming pool.
In panel A there is a kitchen receptacle circuit that has a switched set of undercabinet puck lights…installed in a 1998 remodel. When the puck lights are switched “ON” the GFI breaker in Panel B kicks off. Weird, but the puck lights are rarely used and we tolerated the inconvenience.
But last week when we used the microwave, about 15 seconds into the heating cycle the GFI breaker in Panel B “pops”. The microwave has a dedicated circuit in Panel A. Now at this point the popping GFI is an inconvenient PITA!
All circuits test good as per tester……So, What Could Cause This???? Back EMF?
…………………Iron Helix
Replies
To get this straight, the original 200amp panel (A) is the home's service entrance panel and can we call the 100amp subfed panel (C)? Panel (B) was added next to panel (A) and is in parallel with (A)?
Based on those assumptions, panel (C) has to have a 4 wire feed to it even way back in the early 70's. (2 hots, 1 neutral, and 1 ground with the neutral bar electrically isolated)
What size are the service entrance conductors? How is the service entrance grounded? (Ground rods, water system, etc)
As per your first paragraph...yes you may. Panel A has a subfeed panel C. Panel B is wired parrallel to A, both from the Utility Service Pole.
I took the cover off Panel C...there are only three conductors (#6 SEU ??)...two hots and a neutral.....no separated ground/neutral bars and no ground as a fourth service wire.
Panel A & B each are overhead 4/0 aluminum triplex. Panel A has a #4 stranded wire via conduit to an 8ft copper ground rod. Panel B appears to have no ground rod or ground attchment anywhere. Looks as if this needs a retrofit.
The whole house is piped in genova plastic...and the water service line is polycoil,so no ground to water line. The locals would ground to the black iron gas pipe in the basement.... ;o).
..................Iron Helix
PS...Panel A is in the Kitchen Pantry, Panel B and C are in the stairwell to the basement 25 feet from Panel A.
Edited 6/3/2003 8:59:28 PM ET by Iron Helix
Edited 6/4/2003 6:39:36 AM ET by Iron Helix
Sounds more like a shared nuetral problem, than a grounding issue. Find the nuetral for the GFCI circuite check the amps on it when the puck lights or microwave sre turned on. There shouldn't be any if the neutrals are all seperate. If there is current on the neutral when the GFCI circuite is non use, you have a shared ground or it is crossed with one of the other circuite grounds in a device or j-box somewhere.
nuetral problems do weird things huh? I see it a lot.
Panel A contains the circuits that pop the GFI in Panel B. The only common wires between panel A & B are the entrance wires at the service pole.
Pulled the cover on Panel B where the GFI is found. All breakers except the GFI are 12-2wg-wire 20A-220 breakers or larger combinations. It looks strange to see only bare wires lugged into the neutral/ground bar....the only white wire is from the GFI.
What puzzles me is how can the GFI which appears to be remote from the two offending circuits can be affected to throw. The flow difference would have to feed from panel A back through the entrance cable to the service pole and then along the service cable to Panel B and then trip the GFI.
Still pondering how to make a fix..................................Iron Helix
No. You are lookingin the wrong place.
There is nothing done in either pannel that can cause this if the GFCI is wired correctly.
You have the not and neutral connect to the GFCI breaker and then a neutral pigtail from the breaker to the neutral bus.
The GFCI works by measuring the difference in current between the neutral and hot legs and trip if the difference is more than 6 ma.
You have either the hot or neutral (most likely the neutral) from the GFCI cross connected a neutral or ground from another circuit.
Disconnect the hot and neutral from the GFCI and measure the voltage on each one, with and without the offending load on.
And do you have a sensitive amp meter (like 2 amps full scale) with FUSE to protect it?
If all is correctly wired in the panel then the problem is down stream in a device box somewhere. Easy enough to get wires confused in a box with two to four romex wires stuck in it. Tieing neutrals down on a lighting circuit is the most common place nuetrals form two circuites get crossed. Doesn't cause problems most of the time because they both end up at the ground bus in the panel. Throw a GFCI circuite into the mix and that shared or crossed neutral becomes a problem. Nuetrals are current carrying conductors and your explanation of how a GFCI works eplains why it trips. The GFCI breaker with no load on the hot wire is seeing a load on the nuetral greater than the 6 ma limit and trips the breaker. The current/voltage on the neutral must be coming from one of the other two circuites involved.
Dave
Dave.........looks as your suggestion will send me into the assorted boxes on the lighting circuit. The microwave circuit should be a breeze...it's a dedicated circuit.
So considering the hook-up configuration on the two main panels A & B, is the ma differential backfeeding out of Panel A through the main to the pole and then back down Panel B's main and popping the GFI in panel B? The only 110v circuit in B is the GFI...all others are 220v.
Still perplexed, but will chase the wires.....stay tuned............Iron Helix
That makes me more sure that the is a cross conected neutral or one bundled with the GFCI nuetral in a box somewhere downstream of both distribution panels. Neutrals can be a bear to trouble shoot. A good meter or a bell set tester will make it easier, but mostly it is just searching.
Good luck, and let us know what you find.
Dave
It was a bad day in the Iron Helix Kitchen..................
I first chased the dedicated microwave circuit....only about 12 ft of wire, a breaker, and one 471 recpt box. Checked out to a "T", although I removed the ground wire from the bar with another and placed same by itself. Tested microwave with a glass of water...1.5 minutes on high and no GFI pop on the other main panel.
Chased the circuit with the puck lights through 4 boxes, three can lights, and the lo volt pucks. Nothing tested bad, nothing looked bad. I removed the existing lo-volt transformer and inserted a pigtailed work light......upon switching the pigtail light on/off for several cycles the GFI was not popped. Maybe a bad transformer...so I picked up a replacement and installed....BOOOOOM went the GFI!!!????
On the opposite wall is another set of puck lights on a different breaker in panel A, same panel as pucks above. Never has popped a breaker or the GFI in Panel B.
Ended up chasing a third circuit due to a bad tester reading and found that the ground had been dropped after the first receptacle.....the three following receptacles were wired with 12-2 only romex. No fix except conduit on the walls or GFI receptacles w/o ground present. More to do!!!
In the meantime the Microsoft update that was loaded on Friday pm continued to throw an error message.....so I called Gateway about my problem. Microsoft had sent a partial update and had omitted a key file that is required to open microsoft Word which holds all my business records and correspondence. Tech says harddrive will have to be "fdisced" and then reloaded with Windows XP.
All files in Works that were not B/U will be lost!! My last B/U was on Wednesday and I've been busy typing since then......but had NOT done a B/U. Lost it all!!!! DA!!
Then supper was left-overs and the first plate into the microwave with the smoked turkey leg......POPPED the GFI.
All the effort....but NO gain.....still have that Weird GFI in the opposing panel.
Sometime this week I will run a true ground to panel B.
Still perplexed........three fingers of bourbon, three ice cubes, three drops of cola,
..............................three minutes till bed. Tomorrow has to be better day!
The Saga continues...................Iron Helix
PS.....What is a bell set tester?????
IH,
Just saw your thread,find the problem yet?If not,find the cable that attachs to the suspect GFCI breaker,and remove and isolate those connections from the panel.Test for voltage, and then use an ohmmeter to test one wire at a time to see if they are connected downstream to anything else.If nothing is plugged in (no loads)on that circuit you should read an open,or infinite ohms, between the neutral and ground.If it is connected another circuit you'll read 0 ohms between neutral and ground(via the other panel and loads).Then with the same wires disconnected test all other circuits to see if everything else still works.The advice you're getting about a cross connection sounds right.The chances of it being a problem going back up the feeder and into the other panel are almost nil.
I did not think it could have a backfeed to the pole and back either. BUT...I'm not a professional electrician.
I purchased the ground rod and wire to do the retro on panel B for it's ground. It will be a while till completed since we have 5 days of rain forecast...but that will help the letting-in of the rod.
I will follow your suggestion on the GFI circuit and report back.....I sure do appreciate everyone helping with this perplexing problem.
......................Iron Helix
To IBEW
Twenty days later and I finally try your explanation of finding a solution....Still no change. Although the main panel B now has a proper ground rod & wire set-up.
As you prescribed...no voltage present on any of the lines attached to the breaker, ohmeter registered .oo1 on all lines to ground bar. With all lines disconnected to gfci everything still workson other circuits. Still seems a back EMF is sneaking from panel A to panel B via the service drop.
After adding the new ground, still have the same sequence as in message #1.
If I drop the transformer in the puck light circuit and add an incandescent bulb, then the GFCI does not blow when the circuit is turned on. All recepatcles on all circuits involved check "good" with 3-light/gfci tester.
Could the transformer that powers the microwave generator have become defective? How else could this circuit have only lately become part of the problem? Dedicated circuit to MW still tests "okay".
Still perplexed after three hours of frustration.....................Iron Helix
Edited 7/1/2003 7:17:53 AM ET by Iron Helix
Here's an observation from a dumb carpenter. A bath exhaust fan downstream when turned on (most times) would trip the gfi (switch only type). They replaced the gfi sw. and I believe that solved the problem. It was explained to me by the ho that the motor start up was just enough to trip it. Could that be? I thought too that a non portable appliance like a mounted micro with the outlet in the cab didn't need gfi if a dedicated outlet. Could it be street legal to eliminate it.Remodeling Contractor just outside the Glass City.
Quittin' Time
I finally got my electrician friend to drop by and bump heads over this problem last week.
He pulled the covers, looked about, pulled some readings, and scratched his head. He had never seen a GFCI breaker trip by backfeed to the powerpole and then return down the second main where the GFCI was installed.....But even 40 years experience brings something new each day.
Didn't make sense to him either, but had two suggestions.......
1. Move the GFCI breaker to the other 110v leg in main panel B...he assumed the two offending circuits would then be on the oppposit leg in main panel A.
2. If #1 failed to correct, then replace the GFCI.
Well suggestion #1 worked....
.....and I owe him a bottle of Single malt Scotch
..........and the pleasure of our company at his house.
Good friends and Good working relationships are priceless.
Thanks to all at Breaktime for being friends and partners....Salute!
..................Iron Helix
Bill......I don't have an amp meter....but I know where I can borrow one.
Opened Panel B again and checked to confirm that the SQ-D pigtail is correctly attached to the neutral.grnd bar. and the circuit neutral is to the GFI breaker.
Thanks..........Iron Helix
You might find the neutral has been tapped into after the gfi causing an inbalance in the live and neutral, so the gfi trips.