replacing what I thought was a simple fixture

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Old 08-09-04, 12:31 PM
JohninVA
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replacing what I thought was a simple fixture

I recently moved into a Sears bungalow and started replacing many of the cheap light fixtures with more appropriate pieces. In one room my switch plate box and and the fixture box each had only one set of wires running into them. I ignored this figuring there must be a hidden box in the attic.

I disconnected the switch and started to wire the fixture only to get zapped. Figured the neutral was wired to the switch and turned off the power and wired my light. turned on the power only to find my light stayed on regardless if the switch was on or off. I reversed the wiring on my fixture (not sure why) only to find out my light now worked and turned on and off properly. Just curious what is going on? Is this dangerous?
 
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Old 08-09-04, 12:51 PM
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Never ever count on turning a switch off to eliminate power from a box. Even if the switch properly disconnects the hot wire, there still may be power in a box.

What you did could have killed you. Don;t make that mistake again.

You need to figure out the wiring. Start with the switch. Determine what wires come into the switch. Then go to the light. Determine what wires are present at the junction box for the light.

If what you say is true and a single cable enters each box, then there is another box involved somewhere. Perhaps it is a recepticle outlet, or some other light.
 
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Old 08-09-04, 01:07 PM
JohninVA
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thanks, Believe me I won't make that mistake again

However, I'm still confused why the light stays on when wired one way and I switch the 2 fixture wires and the switch works fine.
 
  #4  
Old 08-09-04, 01:23 PM
rlrct
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You might want to pickup one of the little inductive voltage sensors. They're only about $10 and can save your life. They are about the size of a fat pen. You hold the tip near a single conductor that has voltage in it, the sensor flashes and beeps. Mine has saved my keister when I thought I had killed the correct circuit but hadn't (crazy wiring in our house).

The correct usage procedure is:
  1. Use the sensor to check a known live circuit (verify it beeps/flashes).
  2. Check your suspect circuit.
  3. Check the known circuit again to verify the sensor is still working properly.
 
  #5  
Old 08-09-04, 03:14 PM
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There is only 2 wires on the fixture? When you reverse the connections to those wires the fixture stays on? There has to be something wrong with the fixture.
 
  #6  
Old 08-10-04, 08:32 AM
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Remember that the fixture only needs two wires: a hot wire and a neutral to get back to ground. If there is no neutral then the light has no way to turn on unless it is grounded to the box its screwed to, and the box is grounded somehow.

The switch only needs the hot wire since it shouldn't be interrupting neutral. Typically when you separate the fixture from the switch like this there generally is a junction box somewhere providing power to the switch. Then the switch provides power to the fixture. To do this the power coming to the switch connects to the black side of the switch. The white comming from the switch is used as the return power to the light. Typically an electrician should paint the wire black on the ends, or use some electrical tape to avoid confusion - especially back up at the junction box. Then that new white-turned-into-a-black is wired to the black side of the wire going to the fixture, or the brass screw on the fixture itself (or wired to the short black wire coming out of the fixture if you're just wiring straight to the switch). The white comming out of the fixture (or the white wire, or the silver screw) has to tie to the white that came with the black wire originally supplying power to the switch.

Clear as mud?

If you interrupt the neutral using the switch then that means power is given to the fixture first, and the neutral from the fixture goes to the switch. I never wire switches this way because it's horribly misleading to whoever has to come along and change the circuit - plus there is no way to get power from that switch to use somewhere else if needed.

How are you grounding the fixture and the switch? Do you have metal boxes? Your switch may be interrupting neutral, which would turn off the switch if the fixture isn't grounded locally, but if it is grounded locally it would explain why the light stays on, but this should be the case regardless. I'd be confused why the light turns off using the switch when you reverse the wires unless you're accidentally using the ground wire in one case...

Find out where your grounds are. That's what I'd do first. Make sure one of these wires isn't goign to ground, and if it is WHERE is it going to ground. The panel box like it should, or locally to the box the fixture is in.
 
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