GFCI Home Wiring Questions


Everyone has home wiring questions from time to time. Here we answer some of your most pressing questions.

Q. My whirlpool tub is plugged into its own circuit, which is wired into the basement panel on a GFI. Whenever I try to energize the pump, I blow the circuit and trip the GFI in the basement. When I ran a short extension cord and plugged it into the vanity outlet as a test, it worked fine. We haven't used it because we're nervous since there's no GFI protection if we operate it in this manner. What's happening to trip the GFI and how do we fix it? In addition, is it safe to use on the vanity outlet?

A. Have you tried temporarily plugging this into a GFCI receptacle? Your bathroom vanity should be on a GFCI circuit, but it may not be if it is older. If everything works fine using a known good GFCI receptacle, then I would suspect either the GFCI breaker or the wiring. Another test you can make would be to use the GFCI breaker for a regular circuit. Temporarily swap the wires. You will need to do this carefully, and remember to swap the neutrals as well. If you have problems on the "new" circuit on the breaker, then that is another reason to suspect the breaker.

Q. I read in several threads that a good solution for replacing two-prong receptacles with needed three-prong receptacles is to add a GFCI to protect each circuit. The post said that the GFCI should be located at the first receptacle in the circuit, but how do I determine which is the first receptacle in each circuit?

A. Trial and error.

1. Shut off the breaker.

2. Make a list of everything that is now dead (i.e., everything on the circuit).

3. Remove one receptacle, carefully recording all the connections and then disconnecting all the wires. To minimize the iterations, start with the one closest to the panel. For any receptacle with only one pair of wires, don't bother.

4. Turn the breaker back on and test all the remaining receptacles on the circuit. If they are all now dead, then you have found the first receptacle. If not, select one of the receptacles still live and try again.

Note that in some older houses, there may be more than one "first" receptacle on a circuit, since the receptacles may not be wired in a daisy chain. The worst case is that all the receptacles are "first".

Q. I'm adding a room in an unfinished area of the basement. The 20-amp circuit currently has only one receptacle. I'm going to tap off of that receptacle to go to the new room. Would it be ok to put a 15 amp GFCI in that receptacle?

A. It is okay to put a 15-amp GFCI on a 20-amp circuit. It is definitely not okay to put any 14-gauge wire on a circuit protected by a 20-amp breaker. You must use 12-gauge wire.

Having answered your direct question, there are dozens of ways that this might violate code anyway. Specifically, I'd like to know everything that the existing 20-amp circuit currently serves. Often it is serving bathroom receptacles upstairs. If so, it would make it a code violation to add your bedroom receptacles to it.

There are other possible problems, too. If that existing receptacle is a 20-amp type (the larger slot will have a side slot forming a sideways "T"), then you will need to downgrade it to a 15-amp type to go with the 15-amp breaker. Although not specifically prohibited by the NEC, some inspectors don't like to see you mix #14 and #12 on the same circuit, especially if there is #12 at the panel. So if you want to maximize your chances of passing on the first try, replace your #14 with #12. Besides, putting a 15-amp breaker on this circuit is like putting training wheels on your muscle car.

Q. I know that a separate circuit is required for a bathroom. Can the same circuit serve more than one bathroom if they are on separate GFCI's?

A. You have two options:

1. You can put a bathroom receptacle and zero or more other things in that same bathroom on the same 20-amp circuit, as long as nothing outside that one bathroom is on the circuit.

2. You can put one or more bathroom receptacles in one or more bathrooms on the same 20-amp circuit, as long as nothing except bathroom receptacles are on that circuit (e.g., no lighting, no fans, nothing outside a bathroom). If your family members are big hairdryer users, you do not want more than one bathroom receptacle on a 20-amp circuit.

Q. My receptacle tester (yellow with three prongs) indicates open ground on my GFCI outlet. The reset button on the GFCI works. Please tell me if open ground means the GFCI is not working. In addition, part of the house has been updated with new wiring and circuit breakers, but the older wiring doesn't have a ground wire. At least one of the GFCI's with the open ground does have a ground wire to the receptacle. Maybe it is not connected at the breaker or fuse box?

A. GFCI receptacle will work just fine without a ground wire, so having an open ground on the receptacle will not reduce the shock protection. Be leery of using computers or other electronics on this ungrounded circuit, however. GFCI will protect people from shock, but will not protect equipment from lightning/spike damage even with a surge protector.

It's quite possible that the ground wire is not connected at the panel box if your original wiring was not grounded. The inspector may want you to replace the GFCI receptacles because newer GFCI's have better technology that makes them more reliable. I doubt he can enforce this unless there is a code article giving him that right, however.

With an ungrounded GFCI, it's okay if pushing the "TEST" button on the face of the GFCI causes the receptacle to lose power, then the GFCI is working properly. No other test is reliable, especially the GFCI test button on any external tester. It is amazing to me how many inspectors don't realize that just because their external tester won't trip an ungrounded GFCI, it does not mean that the GFCI is not working properly.

Q. I have one 120v GFCI outlet on my garage wall and two 120v regular outlets in the ceiling (for my garage openers). I am looking to put in two 220v outlets in my garage for power tools. Do they have to be GFCI?

A. The code states that a 125V 15A or 20A receptacle is required to be installed in a garage and requires GFCI protection. 220V does not need GFCI. GFCI only applies to 120V Nominal receipts that are located in the garage. You do not need to worry about it with the equipment you are referring to.