38 volts with circuit breaker off


  #1  
Old 03-16-21, 03:28 PM
A
Member
Thread Starter
Join Date: Aug 2009
Location: USA
Posts: 217
Received 2 Upvotes on 2 Posts
38 volts with circuit breaker off

My goal is to GFCI protect laundry room receptacles in the basement. The first pic shows a switch and 2 receptacles on the right hand side in one box and a total of 4 receptacles on the left hand side in another box. The 2nd pic shows a close-up of the right hand side box with the cover removed. There are 2 cables running down into the right hand side box. Each cable contains red, black, white and ground wires. The switch is on one circuit breaker, whereas all the other 6 receptacles are on another circuit breaker. All the white wires in the right side box are pigtailed together. A red wire from one of the cables has been previously cut (not by me) and remains open-circuited. Two black wires from the cables terminate at the switch. The right hand side receptacle combo shows one red wire, one pigtailed white wire and one black wire. This black wire seems to run to the receptacle combo on the left hand side box, as does a white wire from the pigtail. So it would appear that replacing the right hand receptacle combo with a GFCI will protect all the outlets shown.

I started off by removing the right side cover plate and noted the wires were live using a digital multimeter and a voltage detector (3rd pic). I turned off the circuit breaker for the receptacles and attempted to verify if indeed the wires were no longer live. The voltage detector continued to show the presence of voltage at the receptacles. Curious, I tried measuring the exact voltage with the multimeter. Inserting the probes into the socket holes showed no voltage. However, I measured 38v from each of the hot terminals to the ground wire. The voltage detector also showed the presence of voltage in the left hand side receptacles. Why am I seeing reduced voltage, meaning it is about a quarter of the normal household line voltage amount? Next, I also turned off the circuit breaker for the switch. This time I measured close to 0 volts. However, the voltage detector did chirp briefly for a second (as opposed to continuous chirp) at each of the receptacles. What might be going on here? Is it safe for me to touch the wires and proceed with GFCI installation? Is it enough to turn off just the receptacle circuit breaker or must I turn off both receptacle and switch circuit breakers? Any help shedding more light on this will be appreciated.




 
  #2  
Old 03-16-21, 04:14 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,277
Received 861 Upvotes on 724 Posts
The voltage you are seeing is from phantom voltage being induced onto the wires because the other wires were still on and current was flowing through them. It is not "real" voltage. This is why the "voltage" disappeared after you turned off the other circuit.

Non-contact testers can be overly sensitive and easily give false positives. They often flash and beep when you turn them on or touch something different. Just for fun turn it on and rub it in your hair. You will find you have a lot of voltage. If it does not continuously flash/beep then you should be safe

If both circuits are off it should be safe to work on the circuit.
 
  #3  
Old 03-17-21, 06:27 AM
B
Member
Join Date: Oct 2015
Location: Ct.,USA
Posts: 3,158
Received 286 Upvotes on 254 Posts
Buy a cheap analog or digital multimeter. Neither is affected by induced voltage from stray magnetism.
 
  #4  
Old 03-17-21, 08:30 AM
A
Member
Thread Starter
Join Date: Aug 2009
Location: USA
Posts: 217
Received 2 Upvotes on 2 Posts
Tolyn and beelzebob, thanks for your comments. I'm already using a digital multimeter. I'm getting the impression that induced voltage is nothing to worry about from a safety point of view. I'd rather not turn off the switch circuit breaker because the overhead fluorescent lamps controlled by the switch sheds plenty of light for me to do the work.
 
  #5  
Old 03-17-21, 05:08 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,277
Received 861 Upvotes on 724 Posts
Many digital meters will detect phantom voltage. Analog meters do not. However, It should be safe to work on.

A headlamp is great for working in a dark space.
 
  #6  
Old 03-18-21, 07:16 PM
A
Member
Thread Starter
Join Date: Aug 2009
Location: USA
Posts: 217
Received 2 Upvotes on 2 Posts
Based on your encouragement, I went ahead to install the GFCI receptacle. The test/reset buttons work correctly and control the intended receptacles. I had ordered a special coverplate which has cutouts for a toggle switch on one side and a GFCI on the other side. The issue I'm running into is that the top and bottom "ears" of the GFCI interfere with the placement of the coverplate and it doesn't fit. The attached pic shows the coverplate resting on the box with the installed GFCI. Suggestions?

 
  #7  
Old 03-18-21, 07:49 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,277
Received 861 Upvotes on 724 Posts
You need to cut off the ears and plate mounting hole as shown in the picture.
The device will be attached to the industrial cover using the 6-32 screws and nuts.
 
  #8  
Old 03-19-21, 07:08 PM
A
Member
Thread Starter
Join Date: Aug 2009
Location: USA
Posts: 217
Received 2 Upvotes on 2 Posts
Tolyn, I followed your advice and it worked! Thank you so much!


 
  #9  
Old 03-20-21, 05:25 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,277
Received 861 Upvotes on 724 Posts
You're welcome. I'm happy you were able to successfully complete your project.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: