Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

Dual switch and two leads: 30V of power 'bleeds' from one wire into the other

Dual switch and two leads: 30V of power 'bleeds' from one wire into the other

Reply

  #1  
Old 03-21-16, 12:54 PM
Member
Thread Starter
Join Date: Mar 2016
Location: United States
Posts: 2
Dual switch and two leads: 30V of power 'bleeds' from one wire into the other

Hi, thanks in advance for any information or next troubleshooting steps you can provide. Sorry for the long post, I'm trying to include any pertinent information.

I have a strange situation (at least strange to me) where it seems power is 'bleeding' from one wire to another.

I have a dual wall switch that controls two hot wires: red, and black, going to a ceiling fan with a light. So one switch should control the fan and one should control the light. Both switches receive power from the same hot lead.

The black wire (currently goes to the light) does not work to turn the light on.
The red wire (currently goes to the fan) does work to turn the fan on.

If I turn on the switch for the black wire, the light does not turn on, I get 120V in the black wire at the switch, and 0 V on the red wire.

If it turn on the red wire, the fan turns on, I get 120V in the red wire at the switch, and I see 30V on the black wire. As tested with an analog meter.

This happens even if the fan and light are disconnected. I tested the dual switch with the wires disconnected and it works normally with the wires off.

Could damage to one or both of the wires cause these conditions?

If so is there a way to test to see if one of the wires is safe to use?

If needed I could just wire both the fan and light to one switch and use the pull cords on the fixture to control it.

I'd guess the black wire is damaged. This is in a double wide mobile home and the house was split in half and moved, and the fan/light is in the middle of the ceiling, so maybe the wiring was damaged at that time.

I have asked this question elsewhere and I'll reply to this thread if I get an answer that helps.
 
Sponsored Links
  #2  
Old 03-21-16, 01:24 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,296
The 30V reading is an artifact called phantom voltage detected by digital meters. It is caused by magnetic induction from nearby energized wires, and is not a meaningful reading. You will get a more reliable reading using an analog meter or a simple solenoid or neon bulb tester. My guess is that the black wire is open, perhaps a bad connection somewhere, bad bulb, bad fixture, etc.
 
  #3  
Old 03-21-16, 01:43 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,374
From paragraph six: opjp-ojinbu9g90o

As tested with an analog meter.
 
  #4  
Old 03-21-16, 02:03 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
Do you mean a duplex switch, two switches in one yolk?

Remove the black power in and black power out from the switch. Connect with a wire nut. Does the light now work? If so the switch is bad.
 
  #5  
Old 03-21-16, 02:55 PM
Member
Thread Starter
Join Date: Mar 2016
Location: United States
Posts: 2
Yes a duplex switch. I tested the switch previously and it worked as normal when there were no wires attached to the "out" side of it.

Thanks for the hint of phantom voltage.

Upon further testing I determined the black wire is likely damaged / cut.

If I applied power to the black wire I got 0V at the electrical outlet box in the ceiling, but I did get 30V induced/phantom voltage in the red wire. Without the fan/light attached to the wires either wire will induce a phantom voltage in the other wire. But if the red wire is connected to the fan it has a complete circuit and does not get phantom voltage induced.

I believe the cable containing the 4 wires (black, red, white, ground) is likely twisted along it's length to create/increase the induced voltage.

I did up just using the red wire to provide power to the fan and lights at the same time. We will just need to use pull cords to control them individually.

I was using an analog multi-meter, so I guess they can show phantom voltage as well.
 
  #6  
Old 03-21-16, 03:06 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,374
I was using an analog multi-meter, so I guess they can show phantom voltage as well.
Generally they do NOT show "phantom" voltage which is why they are recommended for DIYers.
 
  #7  
Old 03-22-16, 05:56 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,296
Analog meters usually put enough load on the circuit to negate the phantom effect, but it can happen. The only way to be sure you're getting a good reading is to measure in parallel with a resistive load like an incandescent light bulb, but that is really cumbersome to do routinely. A neon bulb tester does a good job to just make a hot-or-not determination because it draws power off the circuit as you're testing it, unlike many multimeters which use a battery to operate the meter itself.
 
Reply

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


Thread Tools
Search this Thread
Display Modes
'