Baffling light fixture problem


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Old 05-14-12, 01:54 AM
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Baffling light fixture problem

Hi guys,

Our front porch light has stopped working. I changed the bulb, obviously, but no luck. (Both bulbs test fine in another fixture.)

I removed the fixture and used my power tester (not a meter, but a simple on/off tester) and it shows power there. Though the fixture has only positive and negative leads, I've also tested the box's positive and ground, and there's power.

I've tested the fixture several times by plugging it into outlets (via an extension cord with no female end), and it always goes on immediately and stays on. But when I reconnect it to the box—being sure the leads are visibly connected—it doesn't work.

Is there a point in buying a voltmeter to test the box? That is, is it possible there's not enough power? (Shows you how much I know...) Or is there a simpler possibility I'm overlooking?

Thanks for your help! – Ander
 
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Old 05-14-12, 03:20 AM
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Ander, it appears you have a lifted or broken neutral. BTW, in alternating current there arent' positive and negative. I would remove the power to the light at the breaker, remove the switch and see if there is possibly a break in the neutrals in the switch box, which should be stuffed back in the box and wire nutted. If not there, find out where it is being fed (most likely a nearby receptacle), and check for a stab back neutral that has come loose.
 
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Old 05-14-12, 07:25 AM
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Even if you don't find an obviously loose back stab move all back stabbs to the screws. Pigtail if necessary.
 
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Old 05-14-12, 10:28 AM
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Even a poor connection can register as hot, but not be secure enough under a load to complete the circuit.
 
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Old 05-15-12, 04:23 PM
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Hi guys,

Thanks for your replies.

chandler > I would remove the power to the light at the breaker, remove the switch and see if there is possibly a break in the neutrals in the switch box, which should be stuffed back in the box and wire nutted.

Everything in the switch box looks okay.

chandler > If not there, find out where it is being fed (most likely a nearby receptacle), and check for a stab back neutral that has come loose.

ray2047 > Even if you don't find an obviously loose back stab move all back stabbs to the screws. Pigtail if necessary...

Thanks, but I've replaced most of our switches and outlets with AL-compatibles, and everything's on terminals.

pcboss > Even a poor connection can register as hot, but not be secure enough under a load to complete the circuit.

That seems like the logical explanation. I'm just wondering what's changed, as it's always worked before.

I should also mention the switch is in a a three-switch box. I've also replaced the other two (for internal fixtures), and one of them is a switch + CFL-compatible dimmer. Could that have anything to do with it? I'll try substituting a rocker and see if there's a difference.
 
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Old 05-15-12, 04:30 PM
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Thanks, but I've replaced most of our switches and outlets with AL-compatibles, and everything's on terminals.
Are you saying you have aluminum branch circuit wiring in your house?
 
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Old 05-15-12, 05:45 PM
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A connection may have come loose while working in the box. Check the connections.
 
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Old 05-15-12, 08:48 PM
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Now that I've tested again, I can see there's less power at the fixture box than the switch box (my tester glows visibly dimmer). What an odd thing—I always thought you either had power or you didn't.
 
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Old 05-16-12, 03:35 AM
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casualjoe > Are you saying you have aluminum branch circuit wiring in your house?

I don't know if it's "branch" wiring, but it's aluminum. Most of the houses in our neighbourhood have it. It wouldn't have been my choice either, but the home inspector we hired said it'd be okay as long as we were careful to use compatible components. This is the only time in several years that anything hasn't worked.

pcboss > A connection may have come loose while working in the box. Check the connections.

Ah, there are a couple of other connections in the fixture box. They looked snug back there, but one never knows... I'll check that today.
 
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Old 05-16-12, 06:27 AM
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Ah, there are a couple of other connections in the fixture box. They looked snug back there, but one never knows...
Yes, they must be taken apart and examined. Regular wire nuts aren't usually rated for aluminum. Are you using anti oxidation grease when making up connections? Also aluminum wires are brittle and break easily.

From: Are Wire Nuts Necessary? | DoItYourself.com

Wire Nut Restrictions

Wire nuts are designed to be used generally for connecting copper wires. They are not recommended to be use on aluminum wire. Why? One reason is that aluminum wire expands and contracts when subjected to thermal loading, loosening certain types of connections such as those made with wire nuts. In addition, connections made by twisting the wire create a torque that can damage the wire if the torque is too high. In addition, aluminum wire twisted together can overheat. Neither is aluminum-to-copper connections advised for use with wire nut connectors.
You wrote:
but the home inspector we hired said it'd be okay as long as we were careful to use compatible components.
Most don't have the training to give that advice. Best to hire a master electrician experienced in dealing with aluminum wiring.
 

Last edited by ray2047; 05-16-12 at 07:43 AM.
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Old 05-16-12, 05:06 PM
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casualjoe > Are you saying you have aluminum branch circuit wiring in your house?

I don't know if it's "branch" wiring, but it's aluminum. Most of the houses in our neighbourhood have it. It wouldn't have been my choice either, but the home inspector we hired said it'd be okay as long as we were careful to use compatible components. This is the only time in several years that anything hasn't worked.
FYI.....There is NO wire nut that is safe to use on aluminum wiring. If you Google "Dr. Jesse Aronstein" you'll find literally tons and tons of documentation supporting this. Ideal does make a purple #65 Twister wire nut that has been U.L. Listed for aluminum to copper connections (not aluminum to aluminum), however, there are also documented cases of numerous failures of this product. The SECOND BEST thing you can do at your devices and light fixtures is to pigtail the wires with copper wire pigtails using the AlumiConn connector. The BEST thing to do is replace the aluminum wire with copper wire. There is so much material and information available on this subject that I cannot possibly provide it to you, you'll have to do the research yourself.

Most don't have the training to give that advice. Best to hire a master electrician experienced in dealing with aluminum wiring.
Ray is correct, most home inspectors know little if anything about aluminum wiring. A master electrician is your best bet, but many of them know little more than the inspectors. You need to educate yourself if you must continue to live with aluminum wiring.

Here is a condensed version of what you need to know.

http://www.cpsc.gov/cpscpub/pubs/516.pdf
 
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Old 05-16-12, 08:53 PM
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Ideal does make a purple #65 Twister wire nut that has been U.L. Listed for aluminum to copper connections (not aluminum to aluminum).
Here's a picture what's left of an Ideal Purple twister and what appears to be the aluminum to copper connection it was protecting. I'm back to your original statement:
There is NO wire nut that is safe to use on aluminum wiring.
Ander, the suggestion that you that you pigtail the wires - everywhere -
with copper wire pigtails using the AlumiConn connector
is a valid one. There is also a technique used by some specially-trained electrical contractors to change the ends of aluminum conductors to copper. It's called the COPALUM system.

If we haven't already scared you enough about this, consider that According to the Consumer Product Safety Commission, homes wired with old technology aluminum wire "are 55 times more likely to have one or more connections reach Fire Hazard Conditions' than is a home wired with copper."
 
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Old 05-18-12, 07:21 PM
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Hi guys,

Thanks for your concern and advice. We're not in a position to have all of our house's wiring replaced, but I do understand the drawbacks of aluminum wiring and why it was discontinued. Soon after we moved in 16 years ago, I upgraded all connections with AL-compatible switches and outlets, nuts, and thermal grease (which, amazingly, wasn't done in the first place), and we're always very careful with our loads. This is the only problem we've had so far, and it occurred just after I changed something—so I'm assuming it's related to some action of mine, not necessarily the system's integrity.

Anyway, an electrician is stopping by tomorrow. I'll let you know what he says, as I'm sure you're all lying awake at night wondering what the devil could be going on here. :?)
 
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Old 05-18-12, 07:52 PM
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Just remember the so-called compatible wire nuts probably are not as good as claimed. Please let us know the outcome. Take good notes. There will be a test afterward.
 

Last edited by ray2047; 05-19-12 at 08:09 AM.
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Old 05-19-12, 07:26 AM
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I upgraded all connections with AL-compatible switches and outlets, nuts, and...
Ain't no such critters. CasualJoe's suggestion
to pigtail the wires with copper wire pigtails using the AlumiConn connector
is a good idea for something you can do yourself at very low cost to make your wiring safer and more reliable.
 
 

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