light fixture wiring
 

I am at my wit's end, so I thought the collective intelligence of the OT board could help me.

I moved into an apartment and there was a light switch by the door. I flipped it and sparks shot out of the ceiling where there was a cover plate, and the circuit breaker flipped. So I inspected it, and sure enough someone had removed the existing fixture and just left bare wires. So I was going to complain to management and then it dawned on me that I could use this opportunity to install a really sweet light instead of the junky ones.

Long story short, I bought a sweet light and the installation has failed, but in strange ways. I actually installed another one and it works great, so I can't be too far off.

The light came with 3 wires- white, black, and green. The junction box in the ceiling only has white and black. So I connected black to black, white to white, and green I sandwiched in where one of the 2 screws attaching the backplate to the junction box is. I turned the light on, and it worked. Yay! But then the 3rd time I turned it on, the fuse built into the light blew. The light came with a fuse on the black wire. In case you're wondering, its 250v, 3.15A. I bought a box of 4 fuses. So now, if the light turns on, it stays on with no problem. Unfortunately, about 30% of the time when switching the light on the fuse blows. It is as if when turning the switch on, there is a brief surge of extra current draw. The circuit breaked hasn't tripped once. One experiment I tried was leaving the light switch on and turning the light on and off with the circuit breaker. Same results, about 30% of the time I'm blowing the built-in fuse.

My area of prime concern might be the green wire, which had no corresponding wire to connect to.

What are your thoughts? Is it possible that the fixture itself is defunct? Also, my multimeter won't be here until the 4th...

The green wire would tie into the bare ground wire in a modern home, but it sounds like you only have a two wire source. The light should work fine without it though, I wonder if you have other issues. It's just another ground, try tying it in with the white wire and see what happens.

Is it an incandescent light?
If so, the initial current inrush will be far greater than 3.15A. More like 20-30A. However, this is only until the filament warms up, a split second.
You need a slo-blow fuse. I've never seen a light like that with a fuse in it. Around here, they just expect that the circuit breakers in the house work, which IMO is just fine.

If it is flourescent or something else, then the problem might be elsewhere. More information is needed.

The green wire should be tied to the ground wire if present, or to the bonding screw at the back of the box. If it's only a 2-wire source, just tie it to the box. It's not worth trying to re-wire to add a ground just for that one light.

FWIW I'm an electrician.

I had some crappy switches in my old house that would blow bulbs pretty often. Once replaced it happened a lot less.

...FWIW I'm so far away from being an electrician its not even funny...

DON"T Tie the ground TO THE WHITE! Depending on how the switch is wired, the frame of the fixture could then be live!

??? How would that work? Unless whoever wired it was really stupid, the white should be the ground, that's the standard. I agree that wiring the green ground to the white one is pointless, but I've never heard of a light with a fuse in the wire either.

The additional information requested:

The fixture is halogen, with ten 20 watt bulbs.

The replacement fuses I bought from radio shack (which were blowing) were slow-blow (although just by chance, I didn't know any better).

I think I have effectively made the green wire contact the box by sandwiching it between the screw head and the box, although I could be wrong...

So I had one idea for getting around this current inrush- I could install one of those one-touch electronic dimmers that gradually brings the light on. Would this set things straight perhaps?

I found out my building was erected in 1922, so that might explain the 2-wire fixture job.

The fuse thing is weird, but I just bought this thing from Home Depot, so its not an alien contraption (hopefully).

Thanks as always for the help. I love this board.

Couple things.
1) I would guess there was a problem in that circuit to begin with and thatis why the fxiture was removed and abandoned.
2) The fixture you installed is effectively drawing 200 amps which is a lot for an apartment light. You don't have any idea what else is on that circuit so it's very possible you are overloading the circuit.
3) I would go buy a $1 porcelain keyless socket, like the ones in your closet, and connect it with a $.50 light bulb. Use it for a few days and find out if the circuit is functioning properly. Then you can upgrade the fixture if things seem ok.

Ummm....
How do you get 200 amps?
You will NOT pull 20 to 30 amps 'starting' an incandescent light.
White wire is neutral.
Black is hot.
Green is ground.
In the US.

250v residential lighting is not common in the US.

If the existing wiring is going through a metal box, then check for worn or cut insulation where it enters the box.

Call an electrician!
:D

Better yet, since the problem was there when you moved in, ask the super to get an electrician for you.

If the black is hot to the fixture, the bulb is in the socket (acting as a resister), and the white wire disconected or open in the circuit, you will measure 110volts at the white wire. Now connect the ground to that white wire, and the metal frame of the fixture will be hot.

Don't always assume a white is neutral either. It is pretty common that if power is supplied to the light fixture, a two wire is brought down the wall to the switch box, in which case the white wire is switched hot. As is demonstrated here: http://www.electrical-online.com/howtoarticles/lights.htm

Note in the case above, the white & black are connected to the switch, and the white & black tied together in the light box.(making the white wire hot)

White is not ground. In some cases it is neutral, others it can be live.

I'm no electrician Alan, but in the case where your white is switched hot, wouldn't you normally wrap it with black to signify that it is hot? I used the wrong terminology too, white is neutral, green is ground. I'll shut up now.......

Maybe there's a reason the fixture was removed and the box covered.