Shed outlet is powered from a GFCI breaker in the main panel. I want to add a switched light in the shed using power from the outlet. The outlet is a standard 20a grounded outlet, not a GFCI. No issues with doing the wiring, except I am unsure whether using an ungrounded pull-chain type light fixture will cause a ground fault when switched on. Can I use an ordinary ungrounded pull-chain type light or do I need a light that is grounded to avoid a GFCI trip?
Electrical – Will an ungrounded light fixture on a GFCI circuit cause the GFCI to trip
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Related Solutions
Since it's a Ground Fault Circuit Interrupter (GFCI) breaker, it's very likely that you have a ground fault.
GFCIs work by detecting an imbalance in current between the ungrounded (hot), and grounded (neutral) conductors. This is why you only see the trip when the circuit is under load. If there is 0 current flow, the current is balanced.
I'd start by inspecting the receptacle. Turn off the breaker, then open up the box where the receptacle is installed. Look for damage to the receptacle itself, or water/moisture in the box.
For outdoor installations you should always have a weatherproof box, and a cover that is weatherproof even when the receptacle is in use.
Check for a neutral to ground short somewhere on the load side of the GFCI and downstream outlets. Also, make sure there isn't a shared neutral with any other circuit and that you don't have a connection from the neutral load directly to the line side of the GFCI (in other words, the whites cannot all be pigtailed together, the line and load neutrals must be separated by the GFCI).
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Best Answer
This is a common misconception when using Ground Fault Circuit Interruption (GFCI) devices. GFCI devices do not require an equipment ground to function, they detect unbalanced loads within the circuit using the "hot" (ungrounded conductor) and the "neutral" (grounded conductor).
In a properly functioning circuit, the current on the ungrounded conductor and grounded conductor should be equal.
You can test this yourself, using a clamp on ammeter. If you clamp the meter around both the hot and neutral wires, you should read 0 Amps (If you read anything other than 0, you have current leakage). This works because the current flowing through the wires creates an electromagnetic field, and since the current is flowing in opposite directions the fields cancel each other out.
A GFCI device takes advantage of these principles, and is able to detect current leakage by comparing the current on the ungrounded and grounded conductors.