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Old 05-23-2010, 04:35 PM   #1
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Question about wiring and voltage with switches and lights


I have a laundry room with a ceiling fan and florescent light on two separate switches. These share a breaker with the room next to it. The laundry room also has a GFI outlet that is on a separate breaker (no problems with this, works fine). The washing machine and dryer are on separate breakers and are working fine.

Here is the problem. A few days ago, the lights went out in the laundry room. The fan has also stopped working. Below is a diagram as best as I can tell on the wiring. I have indicated Hot1 and Hot2 for the two black wires I have, but differentiated on the diagram for readability. I do not know which one is the hot wire and which is the return, this is my best guess.

I have a multimeter that is working properly and I have tested the voltage at the switches between 1a-1b as well as between 2a-2b. I get a 0 reading. However, if I attempt to read from 1a-ground or 2a-ground, I get a reading of around 120V. I do not get a reading from 1b-ground nor 2b-ground. I have checked the spliced wire nut connections in the switch box and they seem fine.

The Fan is small and plugs into an outlet in the enclosure. For that outlet, I do not get a reading if I check the plug, but if I go from either one of the plugs to the metal frame around the Fan (grounded), I get a reading of 120V.

All of my tests of the switches are with the wires directly and switches removed. I have attempted to replace the switches and this did not resolve the problem.

Any thoughts as to why I would have a problem with just these switches? All of the outlets and switches in the bedroom on the same breaker as the laundry room work fine. Thank you in advance for any help!


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Old 05-23-2010, 05:40 PM   #2
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Question about wiring and voltage with switches and lights


If you wired according to your posted schematic you should be popping breakers and the fluorescent should never come on.

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Old 05-23-2010, 06:15 PM   #3
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Question about wiring and voltage with switches and lights


Like mentioned before your picture is far from correct and you would be popping breakers if it was wired like this.

You must have one hot comeing in and then going from the switches you would have a feed to the light and the fan.

So if the hots are connected to 1b and 2b and the feed to the light and fan is connected to 1a and 2a this is what you should get for voltage readings.

When switch is in off position
1b to 1a-120V
2b to 2a-120V
1b to ground-120V
2b to ground-120V
2a to ground-0V
1a to ground-0V

When switch is in on position
1b to 1a-0V
2b to 2a-0V
1b to ground-120V
2b to ground-120V
1a to ground-120V
2a to ground-120V
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Old 05-23-2010, 06:17 PM   #4
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Question about wiring and voltage with switches and lights


For basic electrical measurements, measuring voltage across the two screws on an ordinary switch, for example 2a to 2b, does not give useful results. (The results may be useful for some advanced topics in electricity.)

When the switch is "on", the voltage across the two screws is always zero. When the switch is "off" the voltage is usually 120 volts.

There should be a (white) neutral in the circuit. Light fixtures usually have one white lead and one black lead which must be matched to the incoming power cable, black for hot and white for neutral. The neutral may or may not go into the switch boxes depending on the exact wiring layout but should not be attached to any switch terminal. If a white wire is attached to a switch terminal, then it is a hot wire.
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Last edited by AllanJ; 05-23-2010 at 06:25 PM.
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Old 05-23-2010, 06:22 PM   #5
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Question about wiring and voltage with switches and lights


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Originally Posted by AllanJ View Post
For basic electrical measurements, measuring voltage across the two screws on an ordinary switch, for example 2a to 2b, does not give useful results. (The results may be useful for some advanced topics in electricity.)
I'm sure Yoizit could fill us in on the advanced topics of electricity and how these measurments can be useful:lau ghing:
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Old 05-23-2010, 07:30 PM   #6
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Question about wiring and voltage with switches and lights


Thank you for the quick replies. I took a guess as to how Hot1 is wired, since the room is finished and wired and I am not an electrician, I could only speculate.

I used the voltmeter only to check if there was voltage and completing the circuit. I have a setting on my multimeter that gives an audible alert if there is a connection. Is this the same thing? It would seem so since I have the same effect with checking other outlets.

All of the measurements that I took were with the switches removed, and with two black wires on each switch, with the 1b-2b wires both connected via wire nut to another black wire.

Any other thoughts as to why the light or fan do not operate? Or other troubleshooting that I can attempt?

I have updated the drawing, let me know if this is correct. The dotted line representing White (Neutral) and the black is the black in the fixtures.


Last edited by rswurth; 05-23-2010 at 07:34 PM. Reason: added diagram
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Old 05-24-2010, 06:58 AM   #7
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Question about wiring and voltage with switches and lights


When you say 'with the swithces removed'.....removed from the "box" or removed from the circuit? Are you SURE you have 110 volts feed to the two gang switch box in your diagram? If you disconnect the switches and twist 2a with 2b you should be able to put your meter probes on the black and white wires of the fan box and have 110 volts. The same with eliminating the switch and shorting the two leads of 1a and 1b together, you should have 110 volts at the light box with your meter across the white and black wires. If you don't, then you are missing the "hot" feed or you are missing your "neutral" coming from your other room. If you trouble shoot this way, you are eliminating the 2 switches, your fan and your light from the picture. Hope this helps. RB
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Old 05-24-2010, 07:26 AM   #8
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Question about wiring and voltage with switches and lights


The new diagram is correct (what it should be).

Measuring voltage across the two loose wires after the switch is removed completely generally gives 120 volts in a correctly wired circuit but certain incorrectly wired circuits can also give 120 volts here.
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Last edited by AllanJ; 05-24-2010 at 07:36 AM.
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Old 05-24-2010, 08:21 AM   #9
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Question about wiring and voltage with switches and lights


The lights and fan were working correctly as per the OP statment, one could assume that it was correctly wired.
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Old 05-24-2010, 01:52 PM   #10
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Question about wiring and voltage with switches and lights


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Originally Posted by rburke65 View Post
The lights and fan were working correctly as per the OP statment, one could assume that it was correctly wired.
Just to reiterate, this is the existing wiring, switches, and lighting that were working for 10+ years since the home was built. Nothing has changed in this configuration: no installs of lights, switches, fans or anything. Last week, the lights went out, and now both the lights and the fan do not work.

These are florescent lights. Would the starter box for those lights cause any problem, for both the lights and the fan? What troubles me is why both would go out.

Additionally, with the switches removed, I do not get any voltage reading across the wires at 1a-1b, nor 2a-2b. I do get a reading of ~120V if I go from 1a-ground and 2a-ground.
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Old 05-24-2010, 04:05 PM   #11
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Question about wiring and voltage with switches and lights


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Originally Posted by rswurth View Post
this is the existing wiring, switches, and lighting that were working for 10+ years since the home was built.
Then your posted diagram cannot be correct. That leaves a component failure or a change in your house wiring.
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Old 05-24-2010, 04:36 PM   #12
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Question about wiring and voltage with switches and lights


If you have voltage to ground at the light and fan but not to the neutral, then you must not have a neutral! Trace your neutral back! Does it come from the switch box (is there a neutral splice there) if so test it there to the hot.

(DO NOT take splice apart while breaker is on, stick your tester lead up inside the wirenut), if you still don't get a reading, turn the circuit/s off and check the splice to see if all the wires are tight in the wirenut.

If they are all tight find the conduit or cable that has the hot circuit coming in and continue to trace that back to the last working device or fixture.

I think you said this room and the next one over share a circuit...right? Did you do any work in that room? If you did, that would be the first place I'd look! If you didn't trace the circuit as described above until you find where the neutral splice went bad.

WARNING: Taking a neutral splice apart while the circuit is energized on a multi wire branch circuit (MWBC) can cause damage to anything connected to either of the circuits that share the neutral! It can also KILL you if you get in between the the open neutrals.
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Old 05-24-2010, 06:11 PM   #13
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Question about wiring and voltage with switches and lights


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Originally Posted by Yoyizit View Post
Then your posted diagram cannot be correct. That leaves a component failure or a change in your house wiring.
I have not changed any of the wiring inside nor outside the house. My second posted diagram is the best I can do without taking out dry wall to see where the wires go. I have 1 black and 1 white at each fixture, 2 black at each switch, 4 total in the switch panel for the 2 switches.

The breaker seems fine since the outlets and lights in the bedroom on the same breaker are all fine. There is a GFI outlet in the laundry room on a separate breaker, working fine.

What kind of component would fail and cause both the fan and the light to go out?
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Old 05-24-2010, 06:38 PM   #14
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Question about wiring and voltage with switches and lights


Using a long single conductor wire (#14 or #16 that can be stretched across the floor from one outlet box to another, together with a voltmeter, an electrician can do several tests and figure out what wire goes where in the wall and where loose connections might be in other outlet boxes along the daisy chain which your circuit is.

Also they make electronic testers that inject an audio signal into a wire and using an electronic "stethoscope" the wires can be traced.
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Old 05-25-2010, 06:33 AM   #15
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Question about wiring and voltage with switches and lights


Forget wiring diagrams and audio injected stethoscopes! You need troubleshooting skills! What you are describing IS a neutral loss.

Did you not say the 2-rooms are side by side and share the SAME circuit and the bedroom lights and receptacles work but laundry room does not...correct?

Does the feed to the laundry room come into the light or fan first or into the switch first?

If it comes to the light or fan first I would check the connections in the bedroom light outlet.

If it comes to the switch first I would check in the switch in the bedroom.

But either way the bedroom is on the same circuit and you probably have 4-receptacles, a light switch and a light outlet and from one of those the laundry is probably fed so if you have to, check the connections in all those outlets.

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