So here’s my weird electrical problem:
The light over my front door suddenly stopped working. It’s got two light sockets, and it’s under an overhead roof so it’s not terribly exposed to the weather. Both lights stopped working at essentially the same time (as far as we can tell).
I took the bulbs out and they work when I put them in a different lamp, so that’s not the problem. Then I checked whether there was voltage on the light sockets. Both read 118 volts when the switch is flipped, and sub-one volt when the switch is off.
There’s no apparent damage to the socket contacts. No water, bugs, moss (it’s Seattle, after all) or anything else in the sockets. When they first went out, I stuck a single new bulb in the socket and it turned on but with an orange cast to the light and a slight flicker (not quite an on-off type of flicker but more like a rheostat getting cranked up and down). The test bulb here is a 25 watt incandescent, but normally we used flourescents.
Any clues as to what’s going on here? BTW, it’s an old (1928)house with some knob and tube, and some more modern wiring. This is one of the old original circuits.
Help
Matt
Replies
I'm guessing that there is in fact a bad contact or corrosion. Bet your test meter is digital... they will often read phantom voltages, or show a higher voltage then can really be "drawn" when a normal load (like your test bulb) is applied. I'd start looking in the box where the fixtures connect, since they're outdoor, that's a good place to look for corrosion or a bad connection... Hope this helps!
PaulB
Edited 1/21/2006 8:22 pm ET by PaulBinCT
Agreed- almost certainly a poor connection. What happens is when you have a poor connection anywhere in the circuit, your voltmeter, which draws almost no current at all, will read full line voltage with the switch on. As soon as you install a bulb, which draws some current, the voltage drops to zero, because the voltage is now all dropped across the high resistance of the flakey connection. To illustrate this, measure the full voltage at the empty socket, then put a bulb in the socket, and measure the socket voltage "under load". It will now read near zero. Treat electricity with the greatest respect, be careful!
In addition to what you say, which is entirely possible, such situations are prone to other common errors.
Depending on how you checked it and with what it is entirely possible that the switch is set up on the neutral and it is going bad. Connections to switch would also be possible. Similar effect.
K&T is notorious for being hooked up backwards, with the neutral instead of the hot switched. The wires, once aged a bit and worked in a dark area, look much the same.
Also such systems, type and age, are usually not grounded so there is no really easy and totally reliable way of referencing against ground. A known good long-line ground reference is the gold standard. Hooked into the ground at the panel is best.
A non-contact voltage detector might work but even a single weak neutral connection, not exactly an unknown situation in such old wiring, can have the neutral triggering it along with or, in the case of a defective hot line, instead of the hot. An then, sometimes, it just gets weird.
Bad connection somewhere. The switch is the first place to check, and then the connections behind the fixture. It's also possible that the switch itself is failing.
happy?
Sometimes a bulb socket, for what ever reason, does not make full contack with the working end of a light bulb. What I have done in the past, is to look at the screw end part of the light bulb, and pry up a little bit of the copper, so it stands proud, and screw the bulb back in. If that does the trick, I know that the problem is with the socket. If I leave it in, I generally check my fire insurance, and make sure its up to date! LOL.............Pop
My dad (industrial journeyman electrician) always used a solenoid tester (wiggy), or a rubber socket with a rough service bulb for testing rather than a meter. Way less confusion, and who really cares what the exact voltage is when something electrical does not work at all.
My guess is the problem is at the ficture, pull it down and test there first.
Lots of good advice , you have an easy way to make sure it is not just your digital or otherwise sensitive meter giving you a phantom voltage. Put a bulb in one and measure the voltage at the other socket. If you did not have a two bulb fixture you could use one of the cheater socket devices that have polarized plug ins and socket for bulb.
With power off at the fuse or breaker, pull the switch out and make sure the screws are tight holding the wires. Check any splices in the box while you're at it. (If it's a backstab switch, toss it and put in a new one). If you kept the old switch, with the incandescent bulb in, put the power on and read the voltage across the switch. If it's not zero, power off again and replace the switch.
With the switch known to be good, if you still have a problem, check the fixture and its splices.
-- J.S.