Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 09-26-2009, 03:46 PM   #1
Newbie
 
Join Date: Sep 2009
Posts: 3
Share |
Default

Voltage not 120 through fixture?


So, I've read about phantom voltage, and floating grounds, and I'm still confused at what I'm seeing. I have a wire coming directly from the panel and a wire going to a ceiling light fixture. I connect the blacks then measure the voltage across the white wires and i was expecting 120v, but I see 80 or so volts varying +-5. Shouldn't I see 120 volts? Thanks.

ps, I get 120volts across the black and white wire coming from the panel.

dunnlow is offline   Reply With Quote
Old 09-26-2009, 04:36 PM   #2
My License Ain't 4 Sale..
 
Join Date: Feb 2008
Location: Atlanta, Ga/Hamilton, Al
Posts: 1,813
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by dunnlow View Post
So, I've read about phantom voltage, and floating grounds, and I'm still confused at what I'm seeing. I have a wire coming directly from the panel and a wire going to a ceiling light fixture. I connect the blacks then measure the voltage across the white wires and i was expecting 120v, but I see 80 or so volts varying +-5. Shouldn't I see 120 volts? Thanks.

ps, I get 120volts across the black and white wire coming from the panel.
If it is an incandescent light, you should see 120 V, but if it is a fluorescent light, it can be different.

InPhase277 is offline   Reply With Quote
Old 09-26-2009, 04:46 PM   #3
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,542
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by dunnlow View Post
So, I've read about phantom voltage, and floating grounds, and I'm still confused at what I'm seeing. I have a wire coming directly from the panel and a wire going to a ceiling light fixture. I connect the blacks then measure the voltage across the white wires and i was expecting 120v, but I see 80 or so volts varying +-5. Shouldn't I see 120 volts? Thanks.

ps, I get 120volts across the black and white wire coming from the panel.
I can't tell exactly what you're measuring from the description, but it sounds like you're inserting the meter in series with the fixture? That should show 120V, assuming there are lamps in the fixture. If the lamps are CFL that might cause some of the problem, but still doesn't really explain it. Maybe if you describe your setup better it would make more sense.
mpoulton is online now   Reply With Quote
Old 09-26-2009, 07:56 PM   #4
Newbie
 
Join Date: Sep 2009
Posts: 3
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by mpoulton View Post
I can't tell exactly what you're measuring from the description, but it sounds like you're inserting the meter in series with the fixture? That should show 120V, assuming there are lamps in the fixture. If the lamps are CFL that might cause some of the problem, but still doesn't really explain it. Maybe if you describe your setup better it would make more sense.

Yes, I suppose in series. Cable comes from panel, I connect the black to the black going to the light. Then I put one lead from my voltmeter on the white wire from the light and put the other lead on the white going to the panel. If I connect the two white (neutral) wires, the light turns on. BTW, the ground wires are connected.

The light fixture is a plain jane incandescent light fixture mounted in the ceiling and poking through a drop ceiling. (there has been a compact fluorescent bulb in the fixture since we moved in a few months ago)

It seems like from what I seeing so far, it is agreed that I SHOULD be seeing 120 between the two neutral wires. Does this mean the fixture needs to be replaced?

Thank you again.
dunnlow is offline   Reply With Quote
Old 09-27-2009, 12:53 AM   #5
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,542
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by dunnlow View Post
Yes, I suppose in series. Cable comes from panel, I connect the black to the black going to the light. Then I put one lead from my voltmeter on the white wire from the light and put the other lead on the white going to the panel. If I connect the two white (neutral) wires, the light turns on. BTW, the ground wires are connected.

The light fixture is a plain jane incandescent light fixture mounted in the ceiling and poking through a drop ceiling. (there has been a compact fluorescent bulb in the fixture since we moved in a few months ago)

It seems like from what I seeing so far, it is agreed that I SHOULD be seeing 120 between the two neutral wires. Does this mean the fixture needs to be replaced?

Thank you again.
You definitely should be seeing 120V. Do you see 120V between hot and neutral in that box, with the light connected and operating? If so, then don't worry about it.
mpoulton is online now   Reply With Quote
Old 09-27-2009, 06:24 AM   #6
Newbie
 
Join Date: Sep 2009
Posts: 3
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by mpoulton View Post
You definitely should be seeing 120V. Do you see 120V between hot and neutral in that box, with the light connected and operating? If so, then don't worry about it.
Sorry, I'm not sure what you mean. If I connect the white wires in the configuration i described above, the light turns on. Where would I measure to see the voltable "between hot and neutral in the box?"

Also, would you please explain (or point me to an explanation of) why I shouldn't worry about that case if it measures 120 with the light on.

Thanks again very much.
dunnlow is offline   Reply With Quote
Old 09-27-2009, 11:33 AM   #7
Member
 
Join Date: Jun 2007
Posts: 3,503
Default

Voltage not 120 through fixture?


Quote:
Originally Posted by dunnlow View Post
Yes, I suppose in series. Cable comes from panel, I connect the black to the black going to the light. Then I put one lead from my voltmeter on the white wire from the light and put the other lead on the white going to the panel. If I connect the two white (neutral) wires, the light turns on. BTW, the ground wires are connected.
Take the bulb out and you will read zero volts.

You cannot measure voltage in series PERIOD. You must read voltage in parallel. Connect the lights white to the source white. Connect the lights black to the source black. Measure from black to white you read 120 volts. PERIOD. The way you are measuring this is wrong. The way you are connecting your meter leads is the problem. You have one lead on the source black and one lead on the light white. Now do you see? You have now put a resistor in a series circuit in a sense. I am not going to give you a class on series and parallel circuits. Just measure VOLTAGE in parallel with everything in your house and you will be correct each time.

Try this:
Install a bulb thats double the wattage of the one you have. Test like you where doing before. You will read 1/2 the voltage you were reading before.

J. V. is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
3-way illuminated switch - voltage present ktulu05 Electrical 18 11-29-2009 04:01 PM
Installing One Light Fixture Causes Another Not To Work pythagras Electrical 2 07-02-2009 08:15 PM
Low voltage box question WShawn Electrical 7 08-19-2008 06:22 AM
double-ended halogen fixture bulbs stop working watt-ever-ny Electrical 6 11-20-2007 05:25 PM
Old house, new light fixture, too many wires Persephonee Electrical 3 01-15-2007 08:58 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.