GFI trips when light switched on

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Old 12-11-05, 10:21 AM
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GFI trips when light switched on

Hello:
A while back, in one of my rental properties, I noticed that the home was wired with a 2 wire system, rather than the current 3-wire system. All of the receptacles were 2 prong, rather than 3-prong. In an effort to update the home, and since I could not feasibly run a ground wire to each box, I decided to use GFI receptacles in each of the rooms. This plan worked fine in the living room, dining room, and master bedroom. I did this is both of the smaller bedrooms, and the tester showed an "open ground", as it should, and I thought I was done the job.

Leaving the room, I turned on the hall light (3 way switched), and both of the GFI's in the two smaller bedrooms tripped every time I flipped the switch. I tried to figure out what I had done wrong, but, to this day, I have not figured it out. As a result, I switched the receptacles back to 2 prong. I would still love an answer to this question. Is the current drawn by the light the reason the GFI tripped? This is hard to imagine, since I would guess that I have plenty of circuits with lights on the same circuit as the receptacle.

Any ideas? Is this normal, or should I do some testing?

Thanks in advance.
 
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Old 12-11-05, 11:34 AM
Bob Haller
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Short answer, you cant use GFCIs without a ground. You should of run a ground wire back to the service panel. if that was impossible converting back to 2 prong was your only option.

Do you have knob and tube wiring?
 
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Old 12-11-05, 12:02 PM
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Originally Posted by Bob Haller
Short answer, you cant use GFCIs without a ground.
This is not true. In fact, the ONLY code compliant way to install a three prong receptical on a non-grounded circuit without rewiring is to provide GFI protection and to label the receptical(s) as having "no equipment ground".
 
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Old 12-11-05, 12:08 PM
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OK, you replaced EACH receptical with a GFCI receptical, correct?

When you installed the GFCI recepticals, do you connect the wires to the LINE side only, or did you also connect wires to the LOAD side?
 
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Old 12-11-05, 12:30 PM
Bob Haller
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I had a book somewhere around here who said always use a grounded system.
I went to lOTS of work to add grounding everwhere. My home and my old rental were all 2 prong. now all 3 prong with solid grounds

Those 2 to 3 prong adapters are a joke, since so few connect the ground lug, and even if they do the outlet case may not be a good ground.

I fix office machines for a living and found about 20% of outlets in schools had bad grounds. the machines I service, laminators carry high current and tend to have wires burn off inside the case. with no grounds or plug ground pins cut or pulled off its a significant shock hazard, the wires contact the machines frame
 
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Old 12-11-05, 12:34 PM
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I suspect one of two things.

One possibility is that someone incorrectly wired a three way switch using the ground as a current carrying conductor.

The other possibility is that this is what is commonly called a Chicago three way circuit. This unsafe wiring method allows a light to be controlled by swiutches at two different locations by swithing the polarity of a wire. A wire is actually switched from being a hot to being a neutral.

If you look at the wiring of the light and the two switches you will be able to determine what the problem is and how to make the corrections.

I do suggest that you investigate this, as either of the above two possibilities are very unsafe and should not be allowed to continue.
 
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Old 12-11-05, 01:06 PM
dcohalla
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GFCI trips when light switched on

Originally Posted by racraft
The other possibility is that this is what is commonly called a Chicago three way circuit. This unsafe wiring method allows a light to be controlled by swiutches at two different locations by swithing the polarity of a wire. A wire is actually switched from being a hot to being a neutral.
Racraft,
Could you please describe more fully or provide a sketch of how this is done? I don't want to do it, rather my interest is peaked and would like further explanation. I'm visually oriented and am having a hard time coming up with the mental picture of how this would work. (or not work, given it's an unsafe wiring practice.)

Thank you,
Drew
 
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Old 12-12-05, 06:26 AM
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Originally Posted by chirkware
OK, you replaced EACH receptical with a GFCI receptical, correct?

When you installed the GFCI recepticals, do you connect the wires to the LINE side only, or did you also connect wires to the LOAD side?
Chirkware:
I replaced each of the duplex receptacles in each room (3 each) with GFI's. Since only one duplex in each room was on the same circuit as the 3 way switch in the hall, they were the only two that tripped when I switched on the light. Therefore, I replaced those two GFI's with 2 prong receptacles.

I have wired many GFI's in my business of rehabbing properties for rentals, so I am absolutely sure that I wired them correctly (ie line on line side and load on load side if there was a downstream load).

Does that give you any ideas on what was (and possibly still is) wrong?

Thanks.
 
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Old 12-12-05, 06:35 AM
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Originally Posted by racraft
I suspect one of two things.

One possibility is that someone incorrectly wired a three way switch using the ground as a current carrying conductor.

The other possibility is that this is what is commonly called a Chicago three way circuit. This unsafe wiring method allows a light to be controlled by swiutches at two different locations by swithing the polarity of a wire. A wire is actually switched from being a hot to being a neutral.

If you look at the wiring of the light and the two switches you will be able to determine what the problem is and how to make the corrections.

I do suggest that you investigate this, as either of the above two possibilities are very unsafe and should not be allowed to continue.
raccraft:
I replaced both of the 3-way switches, since I replace all switches and duplexes in my properties. I am familiar with how to wire a 3-way, and I believe I wired them both correctly. However, knowing myself, I probably believed the old switch was wired correctly, and simply followed the wiring of the old switch (ie. what was the common on the old switch became the common on the new, etc). I know FOR SURE, that I did NOT use a ground as a current carrying conductor. However, I do not know what a Chicage three way circuit would look like, so I am not sure if that is what I have. Could you please direct me to a diagram of such a circuit?

Thanks.
 
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Old 12-12-05, 06:50 AM
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JMattero,

If you open up the switch boxes and explain to use the wiring at each switch box we can probably sort out the problem.


Drew,

I tried to find a digram on the Internet, but could not find a decent one. One of the more common Chicago 3 way applications was to get power to a detached building, say a garage, using a three wire cable. The Chicago three way allowed the light to be controlled from either location (house or garage), while allowing power to always be on at the garage.

Please do not try this at home.

The wiring would be as follows: At the house run power into a switch box.Connect both the hot wire and the neutral into the traveler connections on a 3 way switch. Connect the common to the red wire of a three conductor cable, and the original hot and neutral to the black and white wires of the 3 conductor cable. Run the three conductor cable to the garage.

At the garage run this 3 conductor cable into a junction box. Connect the black and white into three way switch traveler connections. Take the common of that three way switch and the red wire from the 3 conductor cable and use those to connect to a normal two conductor cable to power a light. You can run normal unswitched power from the black and white that you connected to the travelers of the 3 way switch.

It will help to understand why this works if you draw it on paper. The two wires going to the light are one of the four combinations: hot-hot, hot-neutral, neutral-hot, neutral-neutral. The light works when there is a hot and a neutral, but not when there are two of the same.

The reasons this circuit is bad are multiple. First, at least one wire ends up switching between a neutral and a hot. This wire (or these wires) cannot be properly identified by cable color. Second, you end up switching the inputs to the light. In two of the four switch combinations you end up with the hot wire on what is supposed to be neutral wire of the fixture.
 
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Old 12-12-05, 07:11 AM
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JMattero,

It is unlikely that you have a Chicago 3-way or other imaginative wiring scheme, especially if the house is fairly new.

Another likely suspect is a neutral ground short somewhere. What you will have to do is to divide and conquer. Disconnect half the circuit and see if the problem remains. if it does it is int eh first half of the circuit. If it doesn't, it is in the second half of the circuit. Then do the same thing on the part of the circuit where the problem is. Continue until you find it.
 
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Old 12-12-05, 07:30 AM
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Originally Posted by racraft
JMattero,

It is unlikely that you have a Chicago 3-way or other imaginative wiring scheme, especially if the house is fairly new.

Another likely suspect is a neutral ground short somewhere. What you will have to do is to divide and conquer. Disconnect half the circuit and see if the problem remains. if it does it is int eh first half of the circuit. If it doesn't, it is in the second half of the circuit. Then do the same thing on the part of the circuit where the problem is. Continue until you find it.
racraft:
This is a row home that was built in the 50's, outside of Philadelphia, PA. Anyway, I am going to the home later today to see what I can figure out. I should have explianed that there is NO POSSIBILITY of a ground connection, since this entire home is wired without a ground conductor (ie. a two wire system).

As far as checking half of the circuit at a time... If I remember correctly, the power source goes into the ceiling box (where the light is), and then to each of the 3-ways, and to the problem receptacles in each of the bedrooms. I am guessing that you are saying I should disconnect the branch that goes to BR#1 and see if the problem still occurs in BR#2. If so, the problem is in BR#2. If not the problem is in BR#1. However, since I don't think there are any other branches on this circuit (since no other GFI duplexes tripped when the light switch was flipped on, and all other lights did not effect the problem GFI's), then the problem must be in one of the connections in the ceiling box (assuming that I connected the GFI's correctly, which I AM sure of). Am I thinking correctly?

Thanks.
 
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Old 12-12-05, 07:55 AM
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Your thinking is correct. What you want to do is to eliminate pieces of the circuit until the problem goes away, or conversely start with none of the circuit and add pieces until the problem appears.
 
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Old 12-12-05, 08:24 AM
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Originally Posted by JMattero
Chirkware:
I replaced each of the duplex receptacles in each room (3 each) with GFI's. Since only one duplex in each room was on the same circuit as the 3 way switch in the hall, they were the only two that tripped when I switched on the light. Therefore, I replaced those two GFI's with 2 prong receptacles.

I have wired many GFI's in my business of rehabbing properties for rentals, so I am absolutely sure that I wired them correctly (ie line on line side and load on load side if there was a downstream load).

Does that give you any ideas on what was (and possibly still is) wrong?

Thanks.

If you are using GFCI recepticals at each receptical location, you should be using ONLY the line side of the receptical. Connect BOTH incoming AND outgoing to the line side . If you use line/load connections this way, you are taking power that already has GFCI protection into the line side of the next GFCI.

Not sure whether that has anything to do with your problem.
 
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Old 12-12-05, 08:31 AM
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Another possibility:

The neutral the the light controlled by the three-way switches may be connected to the neutral of a different circuit.
 
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Old 12-12-05, 10:12 AM
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Originally Posted by chirkware
If you are using GFCI recepticals at each receptical location, you should be using ONLY the line side of the receptical. Connect BOTH incoming AND outgoing to the line side . If you use line/load connections this way, you are taking power that already has GFCI protection into the line side of the next GFCI.

Not sure whether that has anything to do with your problem.
chickware:
Let me make sure I understand you correctly... If the GFI duplex I installed was NOT the end of the circuit, you are saying that I should hook the wire going downstream to the LINE side of the GFI, and NOT the LOAD side? I realize that I need no downstream protection, since all of the receptacles are GFI's, but I though what you suggest was illegal. Please clarify, and thanks.
 
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Old 12-12-05, 10:16 AM
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Originally Posted by mikewu99
Another possibility:

The neutral the the light controlled by the three-way switches may be connected to the neutral of a different circuit.
Mike:
I hadn't thought about that, and I know that anything is possible, but why would two different circuits come into one box? The only thing I can think of is if there are two switches (each on a different circuit), or a switch and receptacle (each on a diffferent circuit) in one box. While that is the case downstairs in the kitchen (switch and duplex), each of the 3-way switches are in a single switch box. However, if the other explanations don't solve the problem, I will check what you suggest. Thanks.
 
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Old 12-12-05, 12:13 PM
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Originally Posted by JMattero
chickware:
Let me make sure I understand you correctly... If the GFI duplex I installed was NOT the end of the circuit, you are saying that I should hook the wire going downstream to the LINE side of the GFI, and NOT the LOAD side? I realize that I need no downstream protection, since all of the receptacles are GFI's, but I though what you suggest was illegal. Please clarify, and thanks.

What I suggest is perfectly legal, and is the correct way to provide GFCI protection to a single receptical location. By using the LINE side only, you are providing GFCI protection to that receptical only, not to anything downstream. You then have to provide GFCI protection to the next receptical by installing a GFCI receptical there as well.
 
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Old 12-12-05, 12:16 PM
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Originally Posted by JMattero
I hadn't thought about that, and I know that anything is possible, but why would two different circuits come into one box?
I changed a ceiling fan in my mother-in-law's house a few years back and discovered not only were there two circuits in the ceiling box, someone had actually connected the two circuits together (both hots and neutrals)! Took me a while to figure out why I couldn't kill the power to the circuit...
 
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Old 12-12-05, 12:28 PM
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It is perfectly legal to have two different circuits in the same junction box. To make matters worse, the ground wires must be connected together. However, the neutral and hot wires must remain separated.
 
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Old 12-12-05, 08:10 PM
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Originally Posted by mikewu99
Another possibility:

The neutral the the light controlled by the three-way switches may be connected to the neutral of a different circuit.
I'd bet on this one. May be a case of tying all the neutrals in a box together when it isn't appropriate.
 
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Old 12-13-05, 04:48 AM
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If the two GFCI's are on two different circuits, and these two circuits go into the same junction box after being connected to the load side of the two GFCI's, and their neutrals are crossed, then the GFCI's will each sense an unbalanced load and trip.

Sounds like the GFCI's are doing their job, and discovering a wiring error made in the past.
 
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Old 12-13-05, 07:13 AM
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multiple gfi's & shared neutrals

Another possibility is that there is now multiple gfi's on seperate circuits w/a shared neutral. I know it's a no-no now, but shared neutrals was a common thing to do back then. So you might not only have two neutrals from different circuits improperly tied together (which I'm betting is the case) they may have instead shared a neutral (via a pig tail or tie in off one of the old receptacles) Wiring multiple GFCI's w a shared neutral can be done (NOT preferred!!), but it's a very tricky wiring job. Unless done absolutely correctly, the gfi's will trip constantly. Regrettably, I don't remember the correct way to wire it.

We had a similar situation in a kitchen of a 1981 built apartment building. They had originally separated the kitchen receptacles into two circuits, but they shared the neutral from one circuit to the other. It wasn't discovered until the kitchens were "modernized" w/GFCI protection in an attempt to bring them up to current code.

Sharing neutrals creates LOTS of hazards, like even if the 1st circuit is off the neutral can still zap you unless you turn the second circuit off.

An old electrician once told me, "Even if you have flipped the breaker, removed the fuse, or flipped the switch, treat em ALL as if they're still hot!! Then there are no ooops or accidents." Plus you don't have to THINK about how to handle the circuit... in your mind it's ALWAYS hot, so only one method/behaviour to remember. Can't tell you how many times I have worked on a circuit that was supposedly off, but wasn't, but I didn't know until afterwards because I treated it as if it was still hot. (ESPECIALLY important in older wiring where one might not be certain just exactly whats there....)

All this to further the point that it is very important to know how EVERYTHING is wired, if possible, before you start a modernization or upgrade. The older wiring can be VERY tricky sometimes since the rules were different then and frequently they're not run as we would think or would do now. (and the kicker is assuming that code was followed THEN... which you will frequently find it was not)

Some of the other folks here will correct me if I'm wrong on the amount, but it only takes 5 milliamps to kill you if grabbed wrong... electricity has very little margin for error and is unforgiving.

(okay, stepping off soap box now. Sorry. This from someone who used to be terrified of electricity. Go Figure. Now I'm not terrified, rather it now has my utmost RESPECT!)

Drew
 
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Old 12-13-05, 11:27 AM
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The bottom of this page has a link to the illegal 3-way switching arrangement that racraft was describing.

There are many pejorative names for it; this is why it is hard to locate using google...I learned to call it a 'French Three Way'.

The way it works is that you have two standard 3 way switches, but _both_ switches are separately connected to supply conductors. The _traveller_ terminals are connected to the hot and neutral, and the _common_ terminals get connected to the load, by a _single_ wire from each switch to the load.

Depending upon the switch position, either both terminals of the lamp are 'hot' or 'neutral', and thus the lamp is off because there is no voltage difference...or one terminal is 'hot' and the other is 'neutral'.

This circuit is unsafe for a number of reasons, and you shouldn't use it.

-Jon
 
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Old 12-13-05, 04:20 PM
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Is the light a flouresent light???

I have had trouble with flourescent lights on GFI protection. They nuisance trip GFIs
 
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Old 12-13-05, 04:24 PM
dcohalla
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link?

quote: "The bottom of this page has a link to the illegal 3-way switching arrangement that racraft was describing."

I don't see the link. Am I missing something?

Drew
 
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Old 12-13-05, 04:27 PM
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Sorry, managed to leave the link off.

Take a look at http://www.act-solutions.com/kingery08.htm and scroll down to figure 7.

-Jon
 
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Old 12-13-05, 04:43 PM
dcohalla
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French/Chicago Three Way

Jon,
Thanks. Seeing the diagram cements it in my noggin.

I can see why that would be the source for MANY problems.

Can you say OUCH!!

Suppose w/ knob & tube that was pretty common... but thank goodness it's illegal now.

So the light would stay off when pwr was applied from both lines because there would be no differential, i.e. no flow of electrons or EMF. Right? Bet that bulb gets might hot though, among other things.

Thanks again for the link. I could "understand" it by description, but the diagram cements it for me.

Drew
 
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