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Old 02-26-2009, 08:24 PM   #1
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GFCI feeing subpanel question


I have a 50 amp gfci in main panel which leads to a fused 50 amp disconnect outside of house and then goes to my garage where I installed a newer subpanel. I tried wiring the neutrals to the neutral bar and grounds to ground bar like everyone says and this method keeps tripping my main gfci breaker as soon as i flip it. The 2 breakers in the sub panel are on the "on" position when I flip the main 50 amp gfci. If I wire all the grounds with the neutrals on the neutral bar it works fine with no tripping. So what exactly is the proper wiring method when my sub panel is being fed by a 50 amp 2 pole gfci breaker and not a standard 2 pole breaker? Double checked all the wiring to a circuits and see no neutrals or any other wires grounded out that could cause a problem.

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Old 02-26-2009, 08:31 PM   #2
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GFCI feeing subpanel question


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Originally Posted by scott2332 View Post
I have a 50 amp gfci in main panel which leads to a fused 50 amp disconnect outside of house and then goes to my garage where I installed a newer subpanel. I tried wiring the neutrals to the neutral bar and grounds to ground bar like everyone says and this method keeps tripping my main gfci breaker as soon as i flip it. The 2 breakers in the sub panel are on the "on" position when I flip the main 50 amp gfci. If I wire all the grounds with the neutrals on the neutral bar it works fine with no tripping. So what exactly is the proper wiring method when my sub panel is being fed by a 50 amp 2 pole gfci breaker and not a standard 2 pole breaker? Double checked all the wiring to a circuits and see no neutrals or any other wires grounded out that could cause a problem.

Why are you feeding with a gfci?

I suspect You have return current on a ground wire, if so you need to find the source of the problem and fix it.

How long is the run to the garage?
Jamie

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Old 02-26-2009, 08:39 PM   #3
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GFCI feeing subpanel question


The gfci was already in the main panel when i moved here and the wiring out to the garage may not have been buried deep enough and the previous homeowner decided to install the gfci in case anyone should run a shovel into the wiring i guess. The garage is about 150 ft away from house. Would a standard breaker been enough protection if someone should accidentally cut the wiring below the ground? If the grounds and neutrals are all attached to the same block in the main and the pigtail off my gfci is attached to that same block then how would isolating the grounds and neutrals in the sub panel change things? Very confusing to me
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Old 02-26-2009, 09:36 PM   #4
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GFCI feeing subpanel question


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The gfci was already in the main panel when i moved here and the wiring out to the garage may not have been buried deep enough and the previous homeowner decided to install the gfci in case anyone should run a shovel into the wiring i guess. The garage is about 150 ft away from house. Would a standard breaker been enough protection if someone should accidentally cut the wiring below the ground? If the grounds and neutrals are all attached to the same block in the main and the pigtail off my gfci is attached to that same block then how would isolating the grounds and neutrals in the sub panel change things? Very confusing to me
The GFCI affords a little bit of protection against a fatal shock if the conduit is breached, but is no substitue for the conduit being burried at a legal depth. If the proper depth is not obtainable, then you can back fill to make it deeper or use Ridgid metalic conduit to compensate since it does not need to be burried as deep.

What kind of conduit is this run in?

I had a thought that the breaker could be tripping due to capicitive coupling, but I don't think it is a long enough run. If Micromind is around he will know the answer to this.

More likely as I mentioned before there is return current on a ground from an improper connection.

The easiest explaination to a complicated electrical question is to tell you to think of the connections at the main panel like one way valves. Most of the return current will see the lowest resistance return path, so even though the wires are physically connected at the SE -service equiptment (main panel), nothing should be flowing back out on your connections. AC current needs a to complete a path back to the transformer, the neutral wire on the drop from the power company is the (should be) best return path to the transformer. Since that current needs a return path in order for the circuit to function, it is going to flow out on that neutral not back onto your wires.

Using a 4 wire setup is considered safer, as it keeps the grounds free and clear of return current. When a GFCI breaker sees return current to ground (any path other than neutral) it opens.

Depending on a couple factors you may be allowed to combine the neutrals and grounds on that sub panel, but it's a bad idea imo, even if it is allowed. The gfci tripping suggests a problem that should be found.

Have you checked over all your outlets and light fixtures to make sure they connections are good and that the neutrals are all connected to neutral connections and none are connected to ground wires?

Jamie
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Old 02-26-2009, 09:37 PM   #5
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GFCI feeing subpanel question


How many wires feed the subpanel from the GFCI? It has to be 4 (H,H,N,G) and the two hots and the neutral must terminate on the appropriate terminals of the GFCI breaker. At the subpanel, the neutral must be isolated from the panel enclosure. The ground should go to a separate grounding bus and it should be bonded to the enclosure.
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Old 02-26-2009, 09:38 PM   #6
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GFCI feeing subpanel question


Detailed close up & wide photos of both panels would be very useful at this point in trouble shooting.

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Old 02-26-2009, 10:07 PM   #7
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GFCI feeing subpanel question


i have checked over half of the connections and so far everything is where it should be grounds to grounds and so forth. It is 6/3 wire (total of 4 wires) fed to the sub panel. The wire is not in any conduit, it is direct buried. Should i isolate all the 4 wires from the main panel and the sub panel and do a ressitance or continuity check with my multimeter to see if maybe a root or something has caused the neutral to short to the ground? If the hots were shorted then i would have been an immediate trip originally before adding the sub panel however it would trip maybe 2-3 times per week. On the gfci, u say "When a GFCI breaker sees return current to ground (any path other than neutral) it opens." Now how does this happen when the gfci has no ground wire connected to it? Just the 2 hots and neutral. Are you saying that amps are flowing through the white wire into the gfci and out the pigtail to the block in the main box? And they shouldn't be? I'm trying to understand...lol. The gfci is properly wired in the main also.
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Old 02-26-2009, 11:13 PM   #8
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GFCI feeing subpanel question


Ok, i am more clear about gfci's now that i did some more reading on them. Tell me if I'm right, there is voltage flowing to my subpanel though the 2 hots and returning on the neutral which should be 100% equal as far as whats being sent down the line and reurned down the line in amps. And with no loads on at the sub panel there is basically 220volts potential sitting there but 0 amps are being used given my circuit was working properly. So 0 amps are flowing to the sub and 0 amps are returning from the sub. But in my case X amount of amps are being used say on the hot side but maybe 0 amps are returning from it back to the gfci? As this difference is causing the circuit to trip? There is just 2 circuits in the sub panel. I know that the 15 amp lighting circuit is wired in the "middle of the run" method and the 20 amp receptical circuit is just standard wiring from the breaker to the 1st receptacle with the black wire connected to a pigtail off the bronze screw, wirecapped with black feeder wire to next receptacle, and the neutrals done in the same method but secured to the silver screw by a pigtail and wirecapped in 1st box going to 2nd and the grounds grounded to receptacles.
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Old 02-26-2009, 11:19 PM   #9
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GFCI feeing subpanel question


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Originally Posted by scott2332 View Post
i have checked over half of the connections and so far everything is where it should be grounds to grounds and so forth. It is 6/3 wire (total of 4 wires) fed to the sub panel. The wire is not in any conduit, it is direct buried. Should i isolate all the 4 wires from the main panel and the sub panel and do a ressitance or continuity check with my multimeter to see if maybe a root or something has caused the neutral to short to the ground? If the hots were shorted then i would have been an immediate trip originally before adding the sub panel however it would trip maybe 2-3 times per week. On the gfci, u say "When a GFCI breaker sees return current to ground (any path other than neutral) it opens." Now how does this happen when the gfci has no ground wire connected to it? Just the 2 hots and neutral. Are you saying that amps are flowing through the white wire into the gfci and out the pigtail to the block in the main box? And they shouldn't be? I'm trying to understand...lol. The gfci is properly wired in the main also.
The GFCI works by sensing the current on the hots and neutral. There can be be no less current on the neutral than the difference of the currents on the two hots. If there is, then the current must be returning on a path that is unattended, and thus the GFCI automatically disconnects the faulty circuit.
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Old 02-27-2009, 12:49 AM   #10
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GFCI feeing subpanel question


Quote:
Originally Posted by scott2332 View Post
i have checked over half of the connections and so far everything is where it should be grounds to grounds and so forth. It is 6/3 wire (total of 4 wires) fed to the sub panel. The wire is not in any conduit, it is direct buried. Should i isolate all the 4 wires from the main panel and the sub panel and do a ressitance or continuity check with my multimeter to see if maybe a root or something has caused the neutral to short to the ground? If the hots were shorted then i would have been an immediate trip originally before adding the sub panel however it would trip maybe 2-3 times per week. On the gfci, u say "When a GFCI breaker sees return current to ground (any path other than neutral) it opens." Now how does this happen when the gfci has no ground wire connected to it? Just the 2 hots and neutral. Are you saying that amps are flowing through the white wire into the gfci and out the pigtail to the block in the main box? And they shouldn't be? I'm trying to understand...lol. The gfci is properly wired in the main also.
I'd unplug everything in the garage, and disconnect the wires from the main panel (i'd turn the breaker off and disconnect the ground wire, just be sure it is off.) Then I would check for continuity in the garage between the ground and the other conductors, both at the panel and at the outlets. If the wires were damaged, I am inclined to think it would short and the breaker would stay open.

It is possible an appliance you have plugged in is causing the fault as well. What is plugged in in the garage? -- Have you tried turning on the main breaker with the breakers off in the sub panel in the garage? What about with the disconnect pulled?

Jamie
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Old 02-27-2009, 07:54 AM   #11
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GFCI feeing subpanel question


there is nothing at all plugged in to any outlet in the garage and the light switch for the 2 lights in in the off position. If i turn the main gfci breaker on with the 2 breakers in the sub panel the gfci won't trip until i flip either one of the breakers and then it trips. If I were to pull the fused disconnect out then there would be no power running to the garage right? If the disconnect was wired with the neutrals to the grounds (which is in between the main and the sub) would that cause this problem? I haven't looked in that box yet though. I'll be back this afternoon to follow up. Thanks.
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Old 02-27-2009, 09:54 AM   #12
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GFCI feeing subpanel question


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Originally Posted by scott2332 View Post
I have a 50 amp gfci in main panel which leads to a fused 50 amp disconnect outside of house and then goes to my garage where I installed a newer subpanel. I tried wiring the neutrals to the neutral bar and grounds to ground bar like everyone says and this method keeps tripping my main gfci breaker as soon as i flip it. The 2 breakers in the sub panel are on the "on" position when I flip the main 50 amp gfci. If I wire all the grounds with the neutrals on the neutral bar it works fine with no tripping. So what exactly is the proper wiring method when my sub panel is being fed by a 50 amp 2 pole gfci breaker and not a standard 2 pole breaker? Double checked all the wiring to a circuits and see no neutrals or any other wires grounded out that could cause a problem.
Scott

Lets go back to post one (above) and reorganize so you can find your problem and get some sleep....

1.) Start at the service panel with the 50 amp gfci. The pigtail of the gfci should be connected to the neutral. The neutral of the feeder going to the disconnect and then to the new sub-panel should be connected to the gfci load lug. Then of course the hots to the gfci. In this panel it is correct to have neutral and ground connected but only in the service panel.

2.) Go to the fused disconnect, make sure that neutral and ground are not connected in any way. Remember any connection between the neutral and the metal of the panel will bond the neutral to ground. So make sure the are not bonded.

3.) At your new sub-panel. You should have a ground bar and a neutral bar. All grounds, including the feeder ground, go to the ground bar. All neutrals go to the neutral bar. Make sure that there is no connection of the neutral bar to the metal of the panel. Manufacturers sometimes have a green screw that goes through the neutral bar into the metal of the panel. You do not want that screw installed. It will bond your neutral to ground and trip your gfci at the service panel. Look the panel over carefully one bar should be connected or mounted to the metal of the panel...this is your ground bar. The terminal bar that you connected the feeder neutral to should not be connected to the ground bar or the metal of the panel. So make sure there is not a green screw thru the neutral bar into the metal of the panel or any other connection method between the neutral and panel metal. Please post the maker of the sub-panel you installed so we can find out the bonding method they use for that panel to make sure you don't have it installed. You can also check continuity between the two at the sub. There should not be continuity. Get all the neutrals on the neutral bar and all the grounds on the ground bar.

4.) If neutral and ground are separate turn off all the breakers in the sub. When you turn on the gfci at the service panel it should hold if there is no problem with the wires between the service panel and the sub-panel.

5.) If the gfci holds and all the breakers in the sub are turned off. Find a circuit breaker that has garage lights on its branch circuit. Turn all the lights off and make sure any receptacles on that branch circuit do not have anything plugged into them that is 'on'. Turn on the circuit breaker...if the gfci trips you have a overcurrent ground fault to a hot wire. If it holds turn on a light...see if it trips the gfci. If the gfci trips you have a fault in that branch circuit neutral to ground because the gfci did not trip until you turned a load on.

6.) If the gfci does not trip then turn the breaker back off and move to another one and repeat the test.

It would be unlikely to have faults on all the branch circuits unless somehow you are sharing the same neutral between branch circuits and have a common connection between neutral and ground.

Tell us what you find doing these tests.

None of this is going to work unless you are positive the sub, and disconnect do not have bonded neutral and ground. Focus on the sub that is new to the installation and your problem with the gfci instantly tripping started after you installed that sub panel.
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Old 02-27-2009, 10:08 AM   #13
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GFCI feeing subpanel question


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Originally Posted by scott2332 View Post
there is nothing at all plugged in to any outlet in the garage and the light switch for the 2 lights in in the off position. If i turn the main gfci breaker on with the 2 breakers in the sub panel the gfci won't trip until i flip either one of the breakers and then it trips. If I were to pull the fused disconnect out then there would be no power running to the garage right? If the disconnect was wired with the neutrals to the grounds (which is in between the main and the sub) would that cause this problem? I haven't looked in that box yet though. I'll be back this afternoon to follow up. Thanks.
Stubbie did a great job of explaining the testing procedure. Yes double check the wiring in that disconnect. It sounds like it is the wiring in the garage causing the fault.

How much wiring is in the garage (estimated feet)? Is this a very large building?

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Old 02-27-2009, 10:10 AM   #14
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GFCI feeing subpanel question


Quote:
If i turn the main gfci breaker on with the 2 breakers in the sub panel the gfci won't trip until i flip either one of the breakers and then it trips.
Scott

If this means that with all the loads off on the branch circuits at the garage and as soon as you turn a breaker on the gfci trips instantly and this happens with any breaker in the sub panel you have a serious miss wire somewhere causing an overcurrnet fault and not a current leakage that would trip a gfci. Your gfci breaker is tripping on overcurrent.
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Old 02-27-2009, 10:16 AM   #15
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Scott

If this means that with all the loads off on the branch circuits at the garage and as soon as you turn a breaker on the gfci trips instantly and this happens with any breaker in the sub panel you have a serious miss wire somewhere causing an overcurrnet fault and not a current leakage that would trip a gfci. Your gfci breaker is tripping on overcurrent.
How could an overcurrent condition trip the 50 A feeder breaker before it trips the closer 20 A branch breaker? It seems to me that closing the branch breakers is completing a ground fault. Someone probably used a ground for the neutral and landed it on the ground bar. When the circuit is closed, instant ground fault.

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