Q&A for How to Wire GFCI

There could be a ground fault, or the GFCI was wired improperly or is faulty.

You can use a GFCI breaker in the panel to protect the entire branch circuit.

Yes, it's possible, but probably pointless and potentially trouble-causing when both trip and you have to remember to reset both, or when one becomes more sensitive than the other.

Yes, a GFCI can be powered from another outlet, a "regular outlet" if you're referring to a receptacle outlet and not a lighting outlet.

A GFCI without a grounding wire will not provide "ground," but the mechanism to trigger upon a "ground fault" will work because it does not involve the ground wire - it only measures the current to and from the hot and neutral wires to make sure they are identical.

As with any breaker, the terminals are designed for one conductor, although some may be designed, tested and UL listed with instructions for attachment of more than one. This is in addition to the "neutral" wire that is usually integral to the GFCI breaker for attachment to the neutral bar.

A GFCI breaker is meant to protect against electric shock. In the event the ground fault current is exceeded, a GFCI will open the breaker within nanoseconds. If your main breaker trips because of your GFCI outlet, it could mean that the GFCI in your main breaker has a lower rating, or it could mean that you are exceeding the current rating for your breaker with a potential short circuit.