Tenant called describing a problem. She turns on living room light. I works for a while then cuts out. When it cuts out, two other fixtures also cut out. I assume these are downstream. I'm guessing there's a poor connection that fails when it gets warm. My question is: Where is the connection likely to be? Are the downstream fixtures more likely to draw their hot feed from the switch box or the fixture box? I'm thinking the switch box and speculating that one of those push in connectors in the switch is cutting out.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

My father always told me to find an old walkman or handheld AM radio - tune it as far down as it will go, hold it close to the switchplate and listen to the volume of the AC hum that you hear - it'll get louder near any fixtures where there might be a loose connection.
The idea being that 'more 60hz will leak out' if there is a loose wire or flakey connection.

I thought that the theory on this was kinda flakey (radios have RF bandpass filters...) but it worked on my house - I found a screw on a light switch that was making good contact but was loose.

More to your point- screws and wire nuts will work loose first - if there are multiple light fixtures in line, there is probably a wire nut somewhere that connects everything. I'd start at the flakey fixture - I've seen more variance in light fixtures/connections than light switches.

-John

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Husband, Father, sometimes friend =)

...........the switch box.

I'm a licensed master electrician and electrical contractor.

If the fixtures downstream are operated by the switch as well, then they would likely be wired in series after the fixture nearest the switch. But not always.

If the fixtures are not operated by that switch but fail coincidentally, then they may be fed from the same circuit breaker and that might be the source of failure, or they may be fed from the same switch box, where you might find the source of failure.

Or they might, in fact, be fed from the same fixture box and the one fixture that is switched is done so by means of a switched leg.

Or you may find some other scenario which is causing the failure, including, perhaps, a failing hot leg from the utility providing power to the building.


And these are just some of the more reasonable failures I've seen. You'd shudder at some of the home handi-man and shadetree fixit-guy stuff I've seen out there in the field (like live junction boxes intentionally covered up with sheetrock mud and paint. Or a ground lug in a non-grounded home with a hot wire attached, thus energizing every metal box, fixture, coverplate, etc in the whole domicile. 120v AC to ground [you] is no damn joke.)

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1998 E300 +310,000K
1996 E300 +460,000K

Neither of the failing (downstream?) fixtures are switched. One is in the hall and one is outside on the porch. They are both hot all the time. (if memory serves me correctly, there's a former switch box with a solid cover in the hallway. I assume the switches were removed when the house was converted to apartments so the hallway was always lit.) I don't think it's the circuit breaker because other lights on the circuit continue to function. I also doubt that it the hot leg from the utility because there are a lot of circuits in the building and this is the only one exhibiting symptoms to my knowledge.
So, I guess I'll look in the switch box first, then the fixture box, and go from there.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

That's where I'd start. Your added info points more closely to that area. Or the fixture box.

Older two-wire and knob-and-tube homes used to be wired in a "skeleton" fashion, whereby the branch circuit feeder would be run to the ceiling box in the center of the room and then the few receptacles would branch out and down from that box. The switch would be fed by a loop without a neutral -- simply a loop from the hot bundle of wires going to the switch and then carrying back to the hot side of the fixture -- if that makes sense.

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1998 E300 +310,000K
1996 E300 +460,000K

Here's a decent drawing of a switch leg:

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1998 E300 +310,000K
1996 E300 +460,000K

That radio trick sounds cool! Anyway, I would suspect any of those switches/receptacles that have the wires that just push in little holes in the back. Those can't handle high current. I think they only allow those for 14GA anymore.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Thanks. The house was built in the 1890's. Electrical was upgraded in approx 1970's. I don't know the extent to which the part of the house with the problem is still original wiring or whether it was upgraded.
I'll start with the switch box and move from there if I can't find the bad connection.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Oh good, so that'll make diagnosis a breeze.



Good luck with it. Post here or PM me if you need any help.

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1998 E300 +310,000K
1996 E300 +460,000K

I've seen two types of switches in my day, well, 2 in a particular category, which is: power comes to the switch box, or power comes to the fixture. In the latter case, only a two line romex or more primitive is going to the switch, where it interrupts the hot line. If the connection is loose where the hot connects back in up at the fixture or rather where it originates from, the downstream fixtures might draw their current from the same hot line, the same bundle of wire nuts and therefore act in concert.

Could be the extra draw of the light that is switched on is the straw on the camel's back that makes the connection fail temporarily.

I do know electrical gremlins can be a MF but you already knew that.

I'd take everything apart and introduce separate power from an extension cord and see what works and what doesn't.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

That's pretty genious dude. I'll definately remember this one.

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1989 300E 144K

You've gotten some good advice, but I just wanted to add one item.

Given the date of the rehab, you may also have some aluminum wiring, which was particularly susceptible to heat expansion issues. Almost all problems with aluminum wiring result from using it with switches, plugs and connectors designed for copper wiring. So be very watchful for that and if you have Al wiring, be sure to use approved Al items.

That radio trick basically allows you to hear the "arcing" of the bad switch/connection, similiar to having the radio on during a lightning storm. Lightning and "arcing" are somewhat similiar enough, in that both contain a VERY WIDE range of frequencies mixed with all sorts of harmonics...therefore, you're able to hear the "music" of the arcing in the radio...which will get louder as you get closer to the source of the "music" - the "arcing" itself.

Old homes/apartments are traps waiting to bite you when it comes to electrical wiring. As Lux mentioned, you never know where the Hot, Neutral and/or Ground are run from, to or connected/spliced/terminated.

I'd invest in a decent voltage-tracer and label every socket/switch I could possibly reach.

And when the stuff starts making no sense whatsoever, I'd PM Lux and stand back.

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M. G. Burg
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OK, went and took a look. Light is controlled by a dimmer switch. Tenant says problem began about 3 weeks ago and occurs only after light has been on for at least half an hour. Opened up switch box. Two wire romex to the dimmer switch and nothing else in the box. I think this means other lights are not fed from the switchbox. Dropped light fixture. Only two wires immediately evident at light fixture and connections seemed secure. I expected to find more. Light fixture box sticks out of ceiling a bit. Looks like it might be an extension on a deeper box perhaps with more wires. I didn't dig deeper since I wanted to give it more thought. I opened up the covered switch box in the hallway. 4 older wires, joined together in pairs with wire nuts. I assume these were the original switch wires for the hallway and porch light. Any more insight out there. Was someone suggesting that the dimmer switch itself might be the problem?
I haven't run across any aluminum wiring yet.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13