[Texas Tom]

Mysterious Low Voltage Problem

My daughter & her husband called me about an electrical problem they were having. I got my tools & multimeter and went to their house (11 years old).

They had just finished redecorating their master bath. They had removed the wallpaper, and applied texture and paint. They had taken down two light fixtures on adjacent walls, and were going to replace the light fixtures. The old fixtures had been removed for several weeks.

When the first light fixture was hooked up, the lights glowed very dimly. I removed the fixture and probed with my multimeter. The voltage was 20VAC. I probed the wires at the other fixture and also measured 20VAC. I probed a wall socket and measured 122VAC. Both lights were controlled by a single ON/OFF switch. I pulled out the switch and moved the out wire to the in position, effectively bypassing the switch. However, the voltage was still 20VAC. The two light fixtures are the only items on this circuit.

Next I went to the main circuit breaker panel. I checked the output voltage at the circuit breaker for the bath circuit and it measured 122VAC. This indicated that the breaker was not the problem. I didn't have time to explore the attic to see if anything was amiss. The circuit breaker box is about 30 feet from the bath light fixtures.

Even if there was a loose connection somewhere, the voltage (with no load) in the bath should still read 122VAC. If there was some type of load in the circuit, the voltage might drop a volt or so, but not 100 V. If there was some large load, the breaker would trip.

A real mystery. Anyone got a suggestion?

[ballengerb1]

What was the voltage on "in" wire at the switch box? Here is another mystery, why would a new house have a separate circuit for two light fixtures? Builders save money whenever they can and this is not how they normally wire a house. Are they/you 110% sure there is no second switch somewhere? Hallway lights are frequently controlled by a 3 way switch at each end of the hall.

[labman]

Shut the breaker off, and recheck the voltage. If you still have 20 volts, likely you have a bad connection somewhere in the hot wire, and picking up the voltage from a shared neutral. Go back to the breaker box, and see if the breaker and one next to it are feeding the red and black wires of a 3 wire cable. Track down the other circuit. Somewhere the 3 wire cable splits into separate 2 wire circuits. Check all the connections.

Yes builders try to save money and shared neutrals is one way I don't like.

[Texas Tom]

Thanks to both of you for responding.

The master bath entrance is from the master bedroom, so no hallway is involved.

With the breaker Off, there was no voltage on the wires at the light fixture.

The one thing that I forgot to measure was to see if there was voltage between the hot wire & the safety ground wire. If I had measured any voltage, this would be a clue. I live about 30 miles from my daughter's house, so it will be later in the week before I can go back.

[tkrussell]

Having only two lights on one circuit is odd. Were the switches or outlets in the bath pulled out, replaced, etc.

Follow Labmans suggestions to determine if there is a shared neutral for this circuit.

When you shut off the breaker does any outlets or lights in the master bedroom go off also?

Yes a loose connection can show a low voltage, and not necessarily 120 volts.

Need to find the hot feed into the switch box and trace it back to the panel to see if any other outlet , switch, light, or junction box is involved.

Need to insure that both hot and neutral wires are connected tight in the panel.

Is there any chance the two lights were wired in series at the light outlet boxes somehow? At the first light there should be two 2 wire cables with two blacks together, and two whites together. At the second light there should be only a black and a white.

Of course each box should have the bare grounds, assuming this is all done in Romex cable.

The black from the fixture should connect to the black in the outlet same for the white.

Testing between a hot black and ground should measure 120 volts +/-. As should between the black and white. If the hot shows 120 volts to ground, then this will show that the neutral is defective somehow.

With these suggestions, and some time troubleshooting you should find the problem.

[NorthernHeat]

What are the voltage rating on the old fixture bulbs? I know this seems silly but there are allot of low voltage light fixtures out there. Is there possibly a ballast or step down transformer somewhere?

[Texas Tom]

I made a quick trip to my daughter's house to look at the problem again. This is what I found.

1. There are 3 more fixtures, in addition to the 2 wall fixtures, connected to the circuit breakered line - a ceiling light in the toilet room, a ceiling exhaust fan in the toilet room, and a ceiling fixture in the shower stall.

2. Using the multimeter on the wires at the wall fixtures, I measured the following:
Wht to Blk - 19V,
Wht to Gnd - 122V,
Gnd to Blk - 4V
This shows that there is a miswiring.

3. I dropped the light fixture in the toilet room. Using the multimeter on the wires, I measured the following:
Wht to Blk - 122V,
Wht to Gnd - 0V,
Gnd to Blk - 122V
This shows that wiring is correct.

4. I didn't have time to go up into the attic to determine the location of the miswiring.

My son-in-law doesn't remember how the wires were connected when he removed the fixtures to do the painting. But I'm about convinced that when the house was being finished, the light fixture installers couldn't get the lights on when connected to the Blk & Wht wires. So they connected to the Wht & Gnd wires rather than fix the problem. Thinking that no one would know.

[ballengerb1]

That was a real disservice to the owners. Did you really mean they used white and grd or did you mean possibly blk and ground? There should not be any voltage between what and grd. My next guess is that someone switched colors where the wires leave the toilet room and head towrd the wall fixtures. The toilet room readings llok fine. How about the light fixture in the shower stall? Bet it is OK too.

[tkrussell]

At the one wall fixture, there is two whites, as per your statement:

2. Using the multimeter on the wires at the wall fixtures, I measured the following:
Wht to Blk - 19V,
Wht to Gnd - 122V,
Gnd to Blk - 4V

What are these whites connected to? Is one to one fixture white, and the other to another fixture white? If so, then the neutrals are in series with the light bulbs.

I think you need to look for something like this, where one cable or wire is in series with a fixture(s). These all worked fine before the reno. So something must have been taken apart and put back together wrong. I know that is obvious, just trying to get you to look closer.

[Texas Tom]

Did you really mean they used white and grd or did you mean possibly blk and ground? There should not be any voltage between wht and grd. My next guess is that someone switched colors where the wires leave the toilet room and head towrd the wall fixtures. The toilet room readings llok fine. How about the light fixture in the shower stall? Bet it is OK too.

They used Wht & Gnd to get the 122V. A BIG No No!!!!!

I didn't check the shower stall, but when the circuit breaker is On, The light in the shower & toilet work OK, and the fan runs OK, when their respective switches are turned On.

[Texas Tom]

At the one wall fixture, there is two whites, as per your statement:

2. Using the multimeter on the wires at the wall fixtures, I measured the following:
Wht to Blk - 19V,
Wht to Gnd - 122V,
Gnd to Blk - 4V

What are these whites connected to? Is one to one fixture white, and the other to another fixture white? If so, then the neutrals are in series with the light bulbs.

I think you need to look for something like this, where one cable or wire is in series with a fixture(s). These all worked fine before the reno. So something must have been taken apart and put back together wrong. I know that is obvious, just trying to get you to look closer.

There are 3 wire colors at each wall fixture. At one fixture there are 2 white wires twisted together, 2 black wires twisted together, and 2 bare ground wires twisted together. The second set of wires go to the second fixture on the adjacent wall where there is only one set of colored wires. Currently the wires are not connected to anything because the light fixtures have been removed. The voltage measurements I made were between the individual colors of wires listed.

My son-in-law did nothing to the wires. He only removed the fixtures & put the wire nuts back on the bare ends for protection. Based on my observations of the voltages, the wiring to the 2 fixtures is wrong and has been since the house was new.

[tkrussell]

OK good, just trying to imagine what may have been done and what to look for. Then with the voltages you have across the wires, there is clearly a miswire, as you have already mentioned.

What do you have for test results at the switch in the bathroom that controls these lights? If the results are the same feeding the switch, your only recourse is to begin tracing this feed back to the panel, looking for the miswire. This may even be caused by nail or screw driven into a cable.


If the feed to the switch is fine, then this narrows down the troubleshooting to the cable from the switch to the fixtures.

Once you find the problem please let u know what you found.

[Texas Tom]

Once you find the problem please let u know what you found.

I just noticed that I had not posted back the resolution of the mis-wire. I did not have time to go to my daughter's house to troubleshoot the problem, so my daughter got an electrician to come. The bath had two wall switches controlling the lights. There was a mis-wire in one of the switches.