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Mike, Master Electrician
Category: Electrical
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50 volts across a light switch that should show 120v and 2

Customer Question

50 volts across a light switch that should show 120v and 2 other lights and switches on the circuit with no power at all.
JA: Sometimes electrical issues that that you think will be really complicated end up being easy to fix. The Electrician I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so we can help you best.
Customer: i have a circuit with 4 lights and 4 switches on it. 2 lights work, 2 lights do not. One of the switches only has 50 volts going across the poles of the switch when it is off, the other has 120 volts. i have replaced the switch that measured 50 volts across the poles and it still is at only 50 volts. this is old wiring in an even older house (150 years).
JA: Is there anything else the Electrician should be aware of?
Customer: not that i am aware of
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Electrician about your situation and then connect you two.
Submitted: 11 months ago.
Category: Electrical
Expert:  Steven Parent replied 11 months ago.

Hello, my name is***** me try and assist you with your issue. Are all your switches in the same box or are they in different locations? Are there any receptacles on the circuit that are out? Or are these lights the only thing on the circuit?

Customer: replied 11 months ago.
there are 4 switches in 4 different rooms. the switches in the 2 rooms that are working have only lights on them. the 2 rooms with no power to the switches have combo light fan units.
Customer: replied 11 months ago.
the switch with 50 volts over the poles is in 1 of the 2 rooms where the light is working
Expert:  Steven Parent replied 11 months ago.

Just standard single pole 2 screw side wired switches?

Customer: replied 11 months ago.
correct, all switches 2 poles, no 3 ways
Customer: replied 11 months ago.
wiring probably from the 30's
Expert:  Steven Parent replied 11 months ago.

OK, so in a room that isn't working, at the switch box is there just the 2 wires going to the switch? Or is there other wiring in the box?

Customer: replied 11 months ago.
in all the rooms, working or not, their are the 2 wires connected to the switch but there are also wires at the back of the boxes. the wiring was put in probably 50-60 years after the house was built.
Expert:  Steven Parent replied 11 months ago.

OK, would you be able to upload a photo of the wiring inside one of the boxes?

Customer: replied 11 months ago.
as near as i can tell the wiring comes up from the basement into room #1 to an outlet then to a switch next to it in the box. that switch reads 120 v across the poles with light off. i believe the wiring moves onto the next room #2 where the light also works bit this switch only measures 50 v across the poles with light off. all of the lighting has been working for several years without incident until the other day when the lights in 2 rooms just went out as if the switches had been turned off.
Customer: replied 11 months ago.
let me try a pic
Customer: replied 11 months ago.
pic does not work, just a mess of black. there are 2 wires coming into the box. the hot from one wire goes to one pole, the hot wire to the other pole is spliced with a wire from the other line. the 2 remaining wires (neutrals) are wired together.
Expert:  Steven Parent replied 11 months ago.

OK great

Expert:  Steven Parent replied 11 months ago.

So where you want to measure your voltage is from a hot wire and a neutral. Across the switch wont tell you what you need to know.

Customer: replied 11 months ago.
ok
Expert:  Steven Parent replied 11 months ago.

so if you test between the blacks that are spliced together and the whites, that will tell you if you have 120v live in the box

Customer: replied 11 months ago.
correct, just did that and there is 120v in the box
Customer: replied 11 months ago.
i have no clue why the lights in the other rooms lost power, frustrating
Expert:  Steven Parent replied 11 months ago.

Have you tested voltage in the switch boxes in the rooms that don't work?

Customer: replied 11 months ago.
only across the switch poles, will go test hot to neutral now
Expert:  Steven Parent replied 11 months ago.

Yea, just test from one screw to neutral, see if there is 120v, then turn the switch on and check from the other screw and neutral to check if the switch is working

Customer: replied 11 months ago.
no power in the box of room i think is #3. trying other room now. switch in room #2 is new, changed it just before contacting you. power on the new switch is fine across each of poles to neutral when switch is on.
Customer: replied 11 months ago.
room #4 has only 1 wire coming into it. no power.
Expert:  Steven Parent replied 11 months ago.

OK, so room #1 and #2 work ? 3 and 4 have don't have power?

Customer: replied 11 months ago.
yep #1 & #2 have 120v in the box & lights work, no power across hot and neutral in rm #3 & no power in #4 with just 1 wire in the box.
Expert:  Steven Parent replied 11 months ago.

in rooms 3 and 4, do you have power in the receptacles?

Customer: replied 11 months ago.
someone was in box #3. hot is spliced with a wire nut. going to go check to see if splice is loose. yes both rooms have outlets but they are wired into a different circuit, working fine thank goodness.
Expert:  Steven Parent replied 11 months ago.

well it sounds like you loose power between room 2 & 3 then somewhere then. Have you confirmed 100% that all the plugs work and are for sure feed from a different circuit?

Customer: replied 11 months ago.
all outlets definately working and on different circuit. took apart splice in #3 box, the spliced wires appear to have been soldered. when i took the old tape off it crumbled in my hands whereas all the other old tape unwound as you would expect. there is no power coming into the box, it seems there is some kind of break between #2 & #3. Rooms 1 & 2 only have 1 or 2 bulbs per light - no fans - each fan/light in room #3 & #4 has 5 bulbs plus the fan, too much draw?
Expert:  Steven Parent replied 11 months ago.

how many watts are each bulb?

Customer: replied 11 months ago.
will have to check, where does the wire coming out of box #2 go to first, box #3 or the light fixture in room 3 then onto the box from there?
Expert:  Steven Parent replied 11 months ago.

in box #2 there are 3 separate 2 wire cables correct?

Customer: replied 11 months ago.
no, should have spotted it earlier. there are 2 wires into box #2 & 3, a 2 line wire & a 3 line wire. there are 2 neutrals and 3 hot wires in box 2 & 3
Expert:  Steven Parent replied 11 months ago.

so is the hot from the 3-wire spliced with the hot from the 2-wire and a pigtail to the switch. Then the other hot from the 3-wire to the other screw of the switch?

Customer: replied 11 months ago.
that is exactly it
Expert:  Steven Parent replied 11 months ago.

OK, so then the power must come from the light box then, and then that 2 wire is taking power somewhere else.

Customer: replied 11 months ago.
the power runs from box 2 on a 2 wire to the light in room 3. at the light box room 3 the 2 wire connects into a 3 wire and also leaves light weight pig tails for the light to connect to. the 3 wire from the light box in room 3 goes to the switch box in room 3. at the switch box the 3 line neutral connects to the outbound 2 wire neutral, one of the hot wires splices to the 2 wire hot with a pigtail to one pole on the switch, the other 3 wire hot goes to the other pole on the switch. the 2 wire from the switch box in room 3 goes to the light in room 4... is that it? if so, then the power break could be at the light box in room 3, between switch box in room 2 and light box in room 3 or between light box in room 3 and switch box in room 3. so now i need to open up light box in room 3... right?
Expert:  Steven Parent replied 11 months ago.

Well maybe. Since there is power and switched power in the 3-wire that comes from the light it might run from light to light to light to light, and then from each light down to the switch. For sure that is the case in room #4 as you said there is only 1, 2-wire cable in the box and both go to the switch.

Customer: replied 11 months ago.
light box 3 wiring is a disaster, all the insulation on the 3 wire and 2 wire in the box are gone. still working on sorting out which way the wiring runs.
Customer: replied 11 months ago.
why didn't the bare wires trip the circuit breaker? i have pulled the light box separated the wires and tested for power but not getting any on the incoming 2 wire. any thoughts?
Expert:  Steven Parent replied 11 months ago.

well it is possible there is a break in the wire before it gets inside the box #3, or perhaps wherever the connection is before that box has gone bad, maybe in light box #2?

Customer: replied 11 months ago.
just pulled up a few floor boards in the attic, we have a bigger job than is going to get done tonight. it is Sunday and V-day so time to clean up and we will rewire another section of the house, but not tonight. thanks much for your help, would not have had the nerve to get this far so quickly without it. take care and hope you enjoy the rest of your evening. best, jim
Expert:  Steven Parent replied 11 months ago.

You're welcome. At least you are on the right track, just have to run a few new lines. Happy to help. Thanks, ***** ***** a good night as well.

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