Light fixture overloading circuit

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  #1  
Old 01-16-12, 10:46 PM
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Light fixture overloading circuit

In the summer I replaced a light fixture with a ceiling fan with a 60w candlabra light. Everything worked great (or at least I thought). I recently changed out a surge protector on the same circuit with one that lights up an indicator if the circuit is overloaded.

with everything is plugged into the surge protector, the overload light is off. It stays off until I turn the light on. Running the fan with the light off doesn't cause the overload light to trip. (the fan has a remote control allowing the light and fan to operate independently despite using a common power source.)

Since the light fixture should only draw .5 of an amp, I am guessing there is a short somewhere. The lightbulb that just burnt out in the fixture only lasted for about 4 months of light usage even though the package indicates it should last for 1.5 years bolstering my theory that something is wrong.

The voltage from an outlet on the same circuit is 118v.

I used my multimeter to check for continuity as suggested by googling. Using the resistance setting on my multimeter, if the test probes aren't touching the LCD reads a 1. If the probes touch it displays a 0.

Placing one probe on the inner contact point of the fixture and the other probe at the outer jacket keeps the meter at a 1. Touching the outer jacket and a screw on the fixture shows a 0. Touching the inner contact point and the same screw yields something besides a 0 or 1 which seems to be where I should start looking for a fault. Is that correct?

Any help is appreciated. Thank you!
 
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Old 01-17-12, 12:50 AM
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What type of surge protector is it? (What manufacturer & model?)

I'm used to seeing overload LEDs on battery backup units, and I'm used to those indicating when the battery is having more drawn from it than it is supposed to or can provide. Usually indicates that the devices connected are drawing more wattage than the unit is designed for, or that something's wrong with the backup unit or battery.

I'm definitely not a pro, but I'm not sure how a surge protector could know when a circuit was being overloaded. (As long as it's a traditional surge protector, like a plugbar or battery backup, not an entire circuit surge protector at the panel.) Current being drawn on the circuit for devices not plugged into the surge protector (like the light) won't go through the surge protector, so it won't be able to see it. Everything else on the circuit not on the surge protector is being ran in parallel (again assuming that it's not an entire circuit surge protector at the panel.) It wouldn't know what sized circuit it was on anyway to determine when it was overloaded, either.

This doesn't mean nothing's wrong, just my initial thoughts...
 
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Old 01-17-12, 06:52 AM
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I don't see how a device could see the usage upstream from it.

A short should have tripped the breaker, unless you have ungrounded wiring.
 
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Old 01-18-12, 10:07 AM
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I don't see how a device could see the usage upstream from it.

A short should have tripped the breaker, unless you have ungrounded wiring.
Good point - It is an APC SurgeArrest Model P11VNT3. It is not a UPS, just a surge protector. The comment in the manual is, "OVERLOAD Detection Indicator - illuminates (yellow) when the unit is loaded above 12 amps."

I am inclined to believe there is an issue as I tried to fire up the XBOX 360 and with the light on it would not boot (red ring) but with the offending light off, it worked without an issue.

As noted earlier, I would assume that when checking resistance between the threaded part of the light socket and a screw that is part of the fixture, the resistance should be zero. I would also assume (from testing other fixtures) that the resistance from the centre of the socket to the same screw on the fixture should be infinite (i.e., no continuity). As I received a resistance figure when testing from the centre of the socket to the same screw grounded to the fixture, can I assume there is an incorrect short to ground?
 
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Old 01-19-12, 09:32 AM
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From the silver screw to the shell should show continuity.

You should show an open between the tab and screw shell.
 
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