GFCI Not Fully Tripping under small load

Question

Our kitchen is supplied by a multi-wire branch circuit to provide 2x 20-amp circuits. One circuit has the fridge and a single GFCI receptacle on it (the fridge is not protected by the GFCI receptacle). The second circuit has a GFCI receptacle followed by 2 additional receptacles on other walls. The neutrals for the GFCIs are not protected by the other GFCIs (I think this is called pigtailed). This circuit was last modified about 2 years ago and has been stable that entire time. The second circuit has a microwave and toaster oven on it, sometimes running at the same time which is definitely overloading the circuit as both have an audible change in sound when this happens (we do try to avoid this situation...). The microwave was also on a surge protector (which was rated high enough, but I have since read that the rating may apply to the entire strip and not each outlet).

In the last two weeks, the circuit has gone "weird". It appears as though sometimes the GFCI receptacle is almost but not quite tripping when placed under a small load (even just ~200W). The indicator light on it flickers green, sometimes flickering between green and red, but not tripping. During this flickering, the devices on the circuit lose power for an instant. However, there have been times when we have been able to still have the circuit under load without any flickering (like running the toaster oven, although at this point the microwave has been completely removed from the circuit).

So my questions are:

• Why isn't the GFCI actually tripping? Or why is it almost tripping without an apparent ground fault? (I have checked the wires in the receptacles and they all look)
• What needs to be fixed? Does just the GFCI receptacle need to be replaced?
• Did overloading the circuit cause the damage (to the GFCI receptacle or whatever else)? [we always planned to add an additional circuit, just haven't gotten to it yet]
• Is it possible the other branch of the circuit with the fridge has any damage to it (currently no symptoms though)

Answer 1

That sounds like series arcing, probably caused by a bad connection. Take everything apart and look for signs of overheating/burning/melting. When reassembling, be sure to only use screw terminals on devices - never the push-in-only “backstab” connections as they are a notorious cause of this sort of failure.

The lights on your GFCI devices are going out just because they’re losing power. Regardless, GFCIs don’t detect series arcing because that’s not a fault to ground. There’s also a chance the fault is upstream of the GFCIs and they can’t detect upstream faults even if they are to ground.

This is a serious problem and could cause a house fire. This is why AFCI (arc fault) protection is required on most circuits in the 2020 NEC.

Answer 2

First the GFCI has more than just 1 function, as most breakers it will fail on current overload, it will also fail on a residual current path down to ground, (neutral crossed with ground), for these reasons there is more than one reason for a GFCI to create problems, I believe the GFCI is the problem here.

Bullet point 1: The GFCI will not trip without over current or sensing a neutral path to ground, if the GFCI is faulty, (not good), this may cause the device to fail.

Bullet point 2: The GFCI is showing problems, this needs to be replaced ASAP.

Bullet point 3: Overloading would cause the device to trip, but putting the device close to overloading over a period of time, in my experience can create problems, an electrician would determine if an additional circuit is required or if the present circuit cable if sufficient for a higher rated GFCI, but it will be one or the other.

Bullet point 4: If in relation to this circuit, absolutely not, there is no correlation between the two.