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Old 05-30-2007, 10:23 AM   #1
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Perplexing electrical problem

I have an outdoor lamp post that used to work, but won't light anymore. Ive taken the lamp part off the post and hooked up the leads going into it to an electrical outlet and verified that everything is OK there - the two bulbs light.

Out at the post, three wires are protruding from the top. One is black, one white and one bare metal. A voltmeter indicates 115 volts between the white and black wires and 110 volts between the bare wire and the black wire. But when I hook the lamp back up to the wires coming from the post I get no light. What could be the problem?

By the way I've completely disconnected the electric eye element (that's supposed to shut off the lamp during daylight hours) from the system so it can't be what's keeping the light from lighting.

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Old 05-30-2007, 10:33 AM   #2
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Perplexing electrical problem

You could have a corroded or partially broken connection between the switch in the house (or where ever the light is feed from) and the pole.

Due to the meter you are using having almost no load of its own, it can sometimes read correct system voltage through a connection that is not good enough to carry a load.

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Old 05-30-2007, 10:57 AM   #3
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Perplexing electrical problem

try another light out at the pole maybe? Is the bulb you were using high wattage? Incandescent or other? Like JWhite said maybe there is a weak connection somewhere (I would check the switch first) that is good enough to provide voltage but not strong enough to light up a powerful bulb.... If they used to "quickwire" ports on the back of the switch (where you just stick the wire in instead of wrapping it around the screws) that could be the problem. I've heard electricians say that they do a lot of service calls for those.

P.S. I'm no electrician, just a self taught DIY'er.
"Good judgment comes from experience. Experience comes from bad judgment."
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Old 05-30-2007, 11:21 AM   #4
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Perplexing electrical problem

Dumb question but is the bulb good? if you have proper voltage at the wires then you either have a bad bulb or a bad bulb socket or something between the wires you tested and the bulb.
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Old 05-30-2007, 02:20 PM   #5
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Perplexing electrical problem

Thanks for the replies. I think the suggestion of a weak connection may be the answer. When I hooked up a table lamp to the wires coming out of the post and turned on both the switch to the table lamp and the lamp post, the table lamp did not light and the voltage between the black and white wires was ZERO. When I turned off the switch to the table lamp but left the switch to the lamp post on, the voltage between the two wires was 115 and of course the light bulb did not light.
Next I went to a junction box in the basement just before the Romex cable goes into the basement wall (and subsequently underground to the lamp post). When I hooked up the table lamp to the wires coming into the junction box and turned both switches on, the lamp lit.
So ...... I'm guessing that there is a short in the underground line going to the lamp post that somehow still allows the voltage at the lamp post to read 115 volts with no load on the line, but 0 volts when a lamp is in the circuit?
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