GFCI devices work by measuring the current flowing on the ungrounded (hot), and grounded (neutral) conductors. They do this by running both the conductors through a current transformer (CT), which produces a current on the secondary winding whenever there's a difference in current between the two primary conductors. So as long as both the ungrounded and grounded conductors are carrying the same current, there will be no current on the secondary of the CT. If there was a ground-fault, the current on the conductors would be different and a current would be induced on the secondary of the CT.
If there's no current flowing on the circuit conductors, then there's no way to induce a current on the secondary of the CT. Therefore, there's no way to trip the GFCI. So if you've removed the fixture, the GFCI should not trip.
If this diagram is accurate...
The only way the GFCI could trip, is if current was being introduced somewhere. Like if one of the conductors was shorted with a conductor from another circuit, or a different part of this circuit.
There has to be more to this situation, than the information you've provided. Simple explanations might include:
- If the switch is in a box with other switches, and the grounded (neutral) from the GFCI was interconnected with the other grounded (neutral) conductors in the box.
- A couple cables are stapled together, and the staple has shorted some of the conductors together.
Since you say that removing the white (grounded (neutral)) conductor from the LOAD terminal fixes the problem, I'd guess that the problem lies with that conductor.
If you have a really accurate ammeter, you could clamp it on the white wire and see if there's any current on it. To do this, you'll have to connect the wire to the line terminal (as you described in a comment). You'll only do this temperately, while you're taking the reading.
Alternatively, you could trace the wire and look for damage, or interconnection with other wires.
The GFCI device only protects part of the circuit, that's why there's a difference between the breaker tripping and the GFCI device tripping. When the GFCI is tripped, only the protected items lose power. When the breaker trips, the entire circuit; including the GFCI and protected devices, loses power.
It sounds like you may have a serious problem, that you might want to have a professional investigate.
Best Answer
Never do random things in electrical. You will stumble upon combinations that will work but will kill you.
Pause to learn what exactly it is you are doing. Only then proceed.
OK, so you had a GFCI that was previously installed and worked before, and now suddenly is tripping.
The most important point is that GFCI devices are capable of protecting downline loads. Those are the ones that are now dead.
First, unplug all the appliances that are downline from the GFCI device, and plugged into it if it's a receptacle. That will clear up 99% of your problems in a "didn't trip before, now does" situation. Once it clears, start plugging stuff in again When you plug a certain appliance in, it will trip. Try that in a different GFCI and see if it still trips there. Off to the appliance repair it goes.
Second, unwire the GFCI device and disconnect and cap off the
LOAD
wires only. Now, see if the GFCI device clears. If it does, the problem is in either a hardwired device (lamp, fan etc.) or is in the wiring itself.Then, you reconnect LOAD and start removing hardwired devices. You need to remove both hot and neutral to have an effective test. Obviously when you remove a device and it stops tripping, you found the problem.
If you have removed all hardwired devices and it still trips, then you must do a bug-hunt for any crossed neutrals - anywhere a device uses one cable's hot yet another cable's neutral. Also check for this in the GFCI itself. If you get stuck or confused, take photos and post them here.
Third, if the GFCI device still won't clear with nothing on LOAD, and (if it's a GFCI receptacle) nothing plugged into it, then you definitely have a bad GFCI. Otherwise, you do not.