So I inherited a bit of a nightmare for wiring in my bathroom. I'll be calling in an electrician, but wanted to have an understanding of the problem first, as not to be ripped off, lead astray, etc.. So here is the setup/symptoms. The entire bathroom is run off one 20amp line (both outlets and lights). It is a pretty small bathroom, but has a bit of a complex circuit. The line comes in from the breaker box, and splits in a 1-gang junction- one side of the split goes through a GFCI, the other is passed through non-protected. Both halves go into a 3-gang junction box. In this three gang junction, the GFCI protected branch goes into an outlet, then off to a switched light above the toilet (the switch is reachable from the toilet, which is why I think they GFCI protected it). The non-protected branch goes off to the main lights over the sink, a fan, and a recessed shower light over the shower.

The symptoms- when this circuit is on, the whole house lights flicker occasionally. Turn the circuit off, and the flickering goes away (it seems that when the shower light is on the flickering increases). Also, occasionally the GFCI trips when the fan is turned on. Now the fan is on the branch that is not protected by the GFCI, which worries me a bit. So my questions are:

1) Why would the GFCI trip when the fan is turned on sometimes?

2) How bad is this wiring setup (see schematic)? Was the electrician a moron? How might it be cleaned up?

3) What would cause the whole house lights to flicker? I was thinking there may be some arcing going on somewhere in this mess. Where can I look on my own, or suggest to the electrician?

4) Should the recessed shower light be GFCI protected? Does the toilet light need to be? It seems that those two branches should be swapped.

Wiring Schematic

  • I'd call a couple of electricians to get more than one quote. Ask them to break down the work too - that way you can see what they'll be charging you for.
    – ChrisF
    Commented Sep 9, 2010 at 16:01
  • Does the GFCI trip when the fan is turned on all the time? If not when it does is there anything plugged in to it when it trips?
    – Tester101
    Commented Sep 9, 2010 at 16:28
  • When you say "When this circuit is on" do you mean when the breaker in the panel is on, or when the lights in the bathroom are on?
    – Tester101
    Commented Sep 9, 2010 at 16:29
  • @ChrisF- thanks for the tips. I'll definitely be getting a few opinions on this one.
    – MarkD
    Commented Sep 9, 2010 at 16:45
  • 1
    Your schematic is really clear. Could you put what program you used as an answer in diy.stackexchange.com/questions/1794/… Commented Sep 14, 2010 at 15:01

3 Answers 3


Sure sounds like you may have a couple of unrelated problems. Usually, a nuisance tripping GFI is a sign of a worn or aged GFI device. This is assuming there are no down line devices or lights that are leaking small amounts of current to earth ground. This would be uncommon for a light or simple switch, more likely with a motor load on start up or shut down. The more important and potentially dangerous problem is the whole house lighting flickering when the fan and shower light is on. If you have an accurate digital VOM, you can look at the voltage drop at the breaker that controls the bathroom. If you see variations of much more than 5 to 10 volts then isolate which device is causing the fluctuation. (fan or bath lite) by turning them on individually and test again. A older fan is a common source of your problem as moisture and humidity may have invaded the motor and causing larger than average voltage drop to ground. If this fan is in fact the culprit, the fan may be heating up more than normal as well and could become a hazard. If you do not have a VOM or know how to test voltages inside your circuit breaker panel, I'd advise you to seek a licensed electrician soon to correct the situation.

  • Thanks shirlock. I am actually quite comfortable within a breaker box, and with a volt meter, and have access to a very good digital VOM. I may probe around, and see what I can find- after doing some reading (thanks Tester101 and Google) it looks like it might be a loose neutral connection, or a loose connection somewhere in the bathroom. The VOM should be able to isolate it, and save me some time with the electrician. It looks like the recessed lights, fan, and even the switches and GFCI are fairly new (the model fan only started being sold 18-months ago).
    – MarkD
    Commented Sep 10, 2010 at 14:29
  • I'm actually starting to think this may be a problem outside of the house. Today was my first day here all day on a week day. All day, there was no flickering of the lights at all, when suddenly, at around 4:30pm, when neighbors start arriving home from work, the lights start flickering. Humm.....
    – MarkD
    Commented Sep 10, 2010 at 21:59
  • I'm marking this one as the correct answer, as I am pretty sure shirlock hit the nail on the head with the two unrelated problems. After some investigating, our detached garage, which is on a forked line from the meter, has a 20-amp line that is only showing 60-volts- i.e.- there is some major issue out there. I turned off the main service breaker in the garage panel, and since then, I have only seen a very slight dimming when our well pump/pressure tank kicks in (which is a relatively large draw).
    – MarkD
    Commented Sep 11, 2010 at 17:57

Do any of your light fixtures have CFLs or other fluorescent bulbs installed? I've read that fluorescent starting ballasts can cause these types of problems with GFCI outlets, even if they're upstream of the GFCI and not on the branch it's protecting. It's also possible that your GFCI outlet is bad -- does it trip when you press its test button?

Anyway, as long as the 20A circuit going into this bathroom is not shared by anything else in the house, this diagram looks fine. Light fixtures aren't required to be GFCI protected, only outlets are, but there's nothing that says they can't be.

  • Unfortunately, all of the fixtures have incandescent lights on them. One other thing I should have noted- the switch on the tub light is a lutron digital dimmer (it is rated for loads of 40watts up to 600 watts, and is only switching a 45 watt bulb over the shower). As for the GCFI working properly, the test button/reset works fine.
    – MarkD
    Commented Sep 9, 2010 at 16:49

Just change the second outlet to a gfi and line side everything on the first and second outlet. Now light is no longer on load of gfi but both outlets are still protected.

  • welcome to Home Improvement. Would you please edit provide some additional information about how this will fix the problem? Especially in light of the checked answer and comments from 10 years ago.
    – FreeMan
    Commented Apr 14, 2021 at 10:52

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