Reduced Voltage Supply to Outdoor Light

mark2741

Moved into this home a couple of months ago. Love it, but the electrical has been goofy (main problem was that most of the receptacles were reverse polarity - fortunately it was just that they were each wired backwards, so reversing them solved that). I have just one more problem:

There is an outdoor 'motion sensor' light fixture. It is connected directly to an older 'fuse' based (the twist in fuses) subpanel that is approximately 10 feet below it (on the other side of the wall, inside the house of course). The subpanel is in a utility closet (so I guess it would not be a code violation), but I do plan on having it relocated soon to be near the main panel in the basement. At that time I'll replace it with a new circuit-breaker type subpanel.

When I moved in I noticed the motion light didn't work, so I changed the bulbs. No luck. I then waved my voltage tester over front of it and it was getting voltage, so I figured it just needed replacing, so I did that. No luck.

I then pulled the new motion light back off, disconnected it from the hot/neutral, and measured the voltage feed. It's measuring 32.8v (AC of course).

It *appears* to be a straight run through the wall, right down to the subpanel directly beneath it on the opposite side of the wall. So I cut power, attached a tone generator to the wires, and then used the tone probe and it picked up the signal through the wall and was crystal clear/loud when put near the opening where the fuse would go. So that tells me the wiring is not 'open' anywhere in the run.

I'm 99% sure that this motion light is the only thing on that circuit. I've been through and mapped out that entire subpanel (it is for an extension that was added to the house a number of years ago). No receptacles or switches are on that circuit.

What could be causing this? It couldn't be a bad fuse, right? They are either open or closed.

Any suggestions are greatly appreciated. I have the equipment (multimeter, tone/probe, voltage tester) and enough knowledge to not get myself hurt/killed : )

TimPa

i have in the past found poor fuses connections causing lower then normal voltage readings. go to the fuse panel and read all the voltages at fuse outputs, looking for the similar low voltage value you found. if necessary, remove power to sub-panel, clean all connections under fuses.,

AllanJ

If you measured just 32 volts, either there is a loose connection somewhere or a miswiring somewhere.

Is this the only light fixture that is not working?

Unscrew each fuse and screw it back in, not with tremendous strength. This helps clean the contacts. (Don't use tremendous strenth on anything electric.)

__________________
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a7ecorsair

Panels are OK in a utility room (closet); they can't be in a clothes closet.

Why didn't you keep troubleshooting? If you measured 32 volts at the fixture, the next step would be to measure the power at the fuse terminal and neutral bus in the panel and then the incoming power connection at the sub panel. Is this really a sub panel or just a fused disconnect? A sub panel would have a 240v feed, a neutral and a ground bus.

mark2741

Thanks everyone for your help.

I had to stop troubleshooting as I had some appointments yesterday to go to. So I reconnected the motion light (was worried it might rain) and had to leave for a while.

When I came back, I then removed the fuse from the subpanel** and measured the voltage by putting one probe on the inside side (i.e., the metal part inside the fuse 'hole' but to the side...I assume this is neutral?), and the other probe on the nub/contactor in the back of the fuse 'hole'. I measured ~70vac. I expected 120vac, but now as I type this I realize I should have disconnected the motion light again before measuring the voltage across the fuse, so that it wouldn't be under load, correct?

** The 'subpanel' is a wierd situation. House was built in 1950's. There is a 'newer' (~1995) 200a service panel in the basement. In 1999 there was an extension added to the house, and that extension includes a family room on lower level and master bedroom/master bath on upper. I bought this house 2 months ago. Before we bought it, when we had it inspected, neither the inspector nor I noticed the fuse subpanel as it was in a 'game' closet (i.e., small closet in corner of family room, with shelving, where the prior owners keep kid toys and games), in the side wall and covered up by the game boxes. What is odd to me is that it is still there, in that closet (and not in the basement with the main panel), and they reused the old 'fuse' screw-in style panel. The subpanel just takes a 120v feed off of one of the circuit breakers in the main service panel. So I can just switch off that circuit breaker in the main panel and it kills power to that subpanel. The subpanel ONLY powers this outdoor motion light, and the large family room. It doesn't power the upstairs of the extension (the main panel has circuit breakers for that).

My brother is very knowledgeable on electrical work and has replaced service panels, etc (he's a commercial electrician for a utility company). He checked it out and said we can replace it if I want but it's fine as is. I'm thinking I will replace it and relocate it to be next to the main panel in the basement.

a7ecorsair

You can't check the voltage that way. Leave the fuse in the box and measure from where the wire connects to the fuse terminal and to the ground bar inside the panel. It doesn't sound like you have a sub panel. How many fuses are in this "panel?" Is there some type of disconnecting switch or lever with this box?
If you have 120V at the terminal screw and the ground bar, measure at the connection point were the wire from the main panel connects to this panel.

mark2741

Thanks A7. I'll see about checking that voltage first thing tomorrow when I get some time. I'm not sure how to get to the back of the panel to measure it. I'll cut power to the panel and have a look.

The 'subpanel' is basically just a panel that is fed by a circuit breaker on the main panel. It has 6 old-school fuses (the round screw-in kind). Each are 15amp fuses. There is no cutoff/main fuse on this 'subpanel' - to cut power to all of the fuses/circuits fed from this 'subpanel' I would just shut off the circuit breaker in the main panel that feeds it.