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This is my first time posting here. I hope someone can give me some help.

The issue I have is new construction wiring for a driveway light and outdoor outlets at the head of the driveway. The contractor wired a sub-panel and buried the wire (8 awg 3 + gnd). I would like to have two 20 amp GFCI circuits, one for the lamps and one for two outlets. The contractor had left a single pole 20 amp GFCI breaker in the sub-panel for me to use.

I initially wired this up to the two GCFI outlets (overkill) and everything was OK. So since I have another 8 awg wire buried I thought I would just replace the single pole GFCI with a 2 pole (expensive) and have two circuits. The problem is the 2 pole GFCI breaker trips with no load. The single pole GFCI breaker worked fine when wired to just the outlets.

I did see that the 2 pole breaker stated that wire lengths should be less than 250' and I am at 350'. Could this be my problem? If so what can I do? Do I need to use GFCI breakers? Attached is a crude drawing of how it is currently wired.

Thanks in advance![enter image description here]1

  • You have both GFCI breakers and GFCI outlets? This can cause problems, from what I've read. I'd remove the outlets and replace with standard. – isherwood Sep 14 '16 at 16:05
  • Does it hold if the lamps are not wired up? Did you install the breaker as per the instructions? – Tester101 Sep 14 '16 at 17:04
  • Yes, both outlets and breaker is GFCI. I realize that the outlets don't need to be. They were already wired and works fine with the single pole GFCI. The problem showed up when switching to the 2 pole GFCI breaker. – Gklop Sep 14 '16 at 17:04
  • The lamps are not wired up yet. I have double checked that the breaker is wired correctly. The neutral from the j-box to the sub-panel is wired to the GFCI breaker and the pigtail from the breaker is attached to the neutral bar in the sub-panel. – Gklop Sep 14 '16 at 17:05
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    Disconnect all remote devices (including GFCIs) and see if trips. Add one thing at a time; repeat. – Carl Witthoft Sep 14 '16 at 19:23
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This is probably a leakage problem

GFCIs are differential trips -- if too much current (more than 4-6mA) is going out but never getting back to the GFCI (remember that current flows in loops!), they trip on the assumption that current is going somewhere bad (like through you). As thus, a variety of leakage sources can trip them:

  • Cable leakage due to water in non-wet-rated cables, degraded insulation, or physical damage
  • Faulty or intentionally leaky appliances or fixtures
  • Capacitive leakage on long lines
  • Water in splices and boxes causing leakage currents to flow
  • Miswiring that routes current around the GFCI

In your case, even with 350' of cable, you should be fine -- you'd need a cable running at 200-300pF/foot of capacitance to get into trip territory from capacitive leakage alone. (I can't find any figures for UF, and only a passing mention online of 20-30pF/foot for NM, nor do I have a capacitance meter and cable samples otherwise I'd test it myself.)

So, once you rule out a miswire, I'd have your nearest friendly electrician megger the cable hot-ground and neutral-ground to make sure the insulation is good -- make sure to disconnect the cable at both ends when doing so though! If the buried cable passes the insulation test with flying colors, then I'd check the devices at the load end for water infiltration or insulation damage.

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You have "leakage" to ground. GFCI compare the amps going out with the amps coming back on the proper normal conductors, if any(6 milliamps) escape the expected path, say down the safety ground wire, then they trip. Occasionally old motors can trip them due to inductive electrical noise. A single GFCI receptacle if wired properly can optionally protect all downstream outlets and devices much like a GFCI breaker, you only really need one on a branch circuit unless you have a special reason that requires an unprotected segment. Though the breaker would also protect the conductors that feed that first receptacle.

It's possible the nano leakage through the insulation and surface moisture over 350 feet of 3 wires encased in earth is enough to trip it while two wires was not quite enough but I doubt this with modern bits and complete fresh install.

The first thing to check is how the breaker is wired. If the circuit neutral is wired to the normal panel neutral rather than the breaker, the breaker will see it as leakage to ground. All hots and all neutrals for a circuit must be wired to the GFCI device, the only conductor that does not connect to the GFCI device is the bare/green safety ground. Next check for properly made connections in all junction boxes.

It could also be a capacitive or inductive phase shift issue making the GFCI think falsely think that there is leakage.(the current goes out gets stored for a fraction of a cycle then released, the storage viewed at a single instant is seen as leakage. This is the issue with motor loads) As a test put a small load on the circuit, like 50watts say an incandescent light bulb. This should be enough to counter most of the phase shift caused by minor conductor coupling.

  • Need not be. Could easily be just the 350' of wires acting as capacitors. Some GFCI are very sensitive to this! – yo' Jun 16 '17 at 23:07

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