Need help - Troubleshooting question for any good electrician.

On Thu, 24 Jun 2004 11:46:29 -0400, Bumbledor put forth the notion that...

Does the light dim when another appliance kicks in... like a refrigerator or a coffee maker for instance? If so, your circuit may be loaded up to the max. It's not a big deal, just a minor annoyance. You could also have a bad neutral connection where two 120 volt circuits are sharing a common neutral. This is a big deal, because you essentially end up with everything on two 120 volt circuits being in series across

240 volts. Open neutrals are a bit tricky to trace out for the average person. If you're able to rule out the first possibility, I'd recommend calling an electrician to check it out. I doubt that there's anything wrong with the mercury switch... they're pretty reliable.

I'm not an electrician.

There is a loose connection somewhere -- it can be on either the hot or the neutral wire, and it may be on the previous device on the circuit that feeds the light or the switch.

Mercury switches don't ever wear out (that's part of their charm), but there may be a bad connection where the wires connect to it.

I'd vote for a back-wired switch or outlet somewhere that has the spring-loaded terminals that you just poke a wire in. Replace with a screw-terminal device, or (if the wires are cut too short) a heavy-duty backwired device that clamps the wires in the back when you tighten the side screws. Also check the wirenuts or whatever where the light fixture wires are tied to the house wiring.

Bob

Can you further explain "...have a bad neutral connection where two

120 volt circuits are sharing a common neutral. This is a big deal, because you essentially end up with everything on two 120 volt circuits being in series across 240 volts." Can you possibly draw this bad circuit diagram with dashes and lines and such? How can it be avoided by a DIY installer, and how can you test for this problem? Thanks!

| Can you further explain "...have a bad neutral connection where two | 120 volt circuits are sharing a common neutral. This is a big deal, | because you essentially end up with everything on two 120 volt | circuits being in series across 240 volts." | Can you possibly draw this bad circuit diagram with dashes and lines | and such? How can it be avoided by a DIY installer, and how can you | test for this problem? | Thanks!

Normal circuit:

\/\/\/\/\/\/\/\/\/ =================== transformer /\/\/\/\ /\/\/\/\ * * * | | | | | | | | | [breaker] | [breaker] | | | | | | | | | *-light--*--light-* | | | *-light--*--light-* | | | *-light--*--light-*

Broken circuit:

\/\/\/\/\/\/\/\/\/ =================== transformer /\/\/\/\ /\/\/\/\ * * * | | | | | | | [breaker] [breaker] | | | | | | | *-light--*--light-* | | | *-light--*--light-* | | | *-light--*--light-*

Now one group of lights combined is in series with the other group at twice the voltage. If the two groups are equal wattage, they will each get half that voltage, ending up with the usual amount.

But, change the lights so that one side has more, such as by turning more of them on:

\/\/\/\/\/\/\/\/\/ =================== transformer /\/\/\/\ /\/\/\/\ * * * | | | | | | | [breaker] [breaker] | | | | | | | *-light--*--light-* | | | *-light--*--light-* | | | *-light--*--light-* | | *-light--* | | *-light--* | | *-light--*

Now one side (more lights) has lower resistance, and the other side has more. The voltage will not divide evenly. The side with more lights gets less voltage and the side with fewer lights gets more voltage. For example the lights on the right might be getting 160 volts while the lights on the left are getting 80 volts.

The sum current flowing through the left group is equal to the sum current flowing through the right group. That means the left group divides its current over 6 lights while the right group divides its same current over only 3 lights (so they get more current and burn brighter).

A broken neutral (what this is) is hard to detect because everything seems to be working. The steps needed to trace it, if done slightly wrong, can result in extreme voltages applied. For example if 2 of the lights on the right side are turned off, then you get a case where the one remaining light ends up with all the current (though it will now be slightly less) on its side, and thus has most of the

240 volts. Turning things OFF one by one can cause problems. The only safe way to turn this off is to shut off the main breaker.

Then you can turn off all the individual breakers except one and see if that one works after turning the main back on. If not, then you almost certainly have a broken neutral.

On 25 Jun 2004 01:19:58 GMT, snipped-for-privacy@ipal.net put forth the notion that...

An excellent explanation, and thank you for drawing the ASSCI diagram... I hate doing those.

An easy way for the non-electrician to see if he has two circuits sharing a common neutral, is to turn of the breaker affecting the suspect circuit. Then take the deadfront (cover) off the breaker panel, and follow the colored wire attached to that breaker to where it exits the panel. If it's in a conduit or a jacket containing two different colored wires (usually black and red) and a white wire, you have a three wire circuit... two 120 volt circuits with a common neutral. What you can do at that point, is follow the other colored wire back up to its circuit breaker, and shut that one off too. Normally, the two breakers will be side by side, but not always. With both circuits off, you can make a diagram showing everything in the house that is controlled by those two circuits. Now, with the power off, you can visually inspect the white wires in every one of those boxes for a bad connection. Don't forget to check the neutral wire in the breaker panel as well, where it connects to the neutral bus bar. If you have aluminum wiring, call a licensed electrician immediately, and have him install copper pigtails throughout the entire house using an antioxidant compound such as NoAlox.

After all this high-tech mumbo-jumbo, just check the center tab in the light fixture screwshell. The screwshell has probably arced and burnt the socket. P.S. Don't stick your finger in the socket with the switch on! Lol!

Hire a good electrician, you cheap bastard!