Installing One Light Fixture Causes Another Not To Work
 

Hello all,

I recently replaced a 2 40 watt flourescent (with the tube bulbs) light fixture with light fixture containing space for 3 60 Watt bulbs. I installed the light fixture using the same wiring that was used for the flourescent fixture.

Once installed, the new fixture worked great. However, a nearby flourescent tube fixture in a utility room suddenly stopped working. I've replaced the bulbs with brand new bulbs (just in case a surge from flipping on the surge protectors did something) and no dice.

The strange thing I noticed about the box with the new fixture is that there are 4 wires going into the box. I surmised maybe these were connected in series? However I'm pretty certain all these wires are connected as they were before.

How could installing the new fixture cause the old fixture to fail?

Also, is there anyway to test the seemingly disabled fixture to see if its still working? Testing the voltage between the terminals and ground seems to give me the same voltage as a wall socket.

Most likely, there is a wire that has become loose, or broken in a wire-nut when you disturbed the connections. That wire is the feed to the adjacent room.

If you had 4 cables in the junction box, one would be the power coming in, two would be power going out to other boxes, and one would be the switch loop.

That would mean you might have 4 wires together in one wire-nut, 3 wires in another, and a single lead hanging (not counting any ground wires present) in the ceiling box. If one of those other wires broke off, or came loose, whatever it fed downstream would cease to operate.:huh:

Check your connections again to ensure all conductors are still connected and in one piece.:whistling2:

4 wires, the problem isn't there.

4 cables (eight wires), that's the place to start.

Test voltage at the fixture between the black and white. If it reads 120v, turn off the switch and check all the connections including the wires stabbed into the back of the tombstones (lampholders).

In a fl fixture, all you have is the voltage, the connections, the lamps and the ballast.