How to determine hot supply wire

Reply

  #1  
Old 06-27-16, 05:13 PM
R
Member
Thread Starter
Join Date: Jun 2016
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
How to determine hot supply wire

I've acquired an old house - no ground wires. A switch box has two black wires and two white wires which have black tape on them. Without a ground wire, I'm not sure how to determine which wires are hot.
 
  #2  
Old 06-27-16, 05:23 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,824
Received 1,330 Votes on 1,229 Posts
Welcome to the forums.

With or without a ground wire.... the hot and neutrals are the same.

You have two cables. One cable is probably power in and the other cable is light out. That would mean that the two whites would be combined together and you would have the two black wires on the switch.

If you opened the white connection..... you would check from white to black on either cable to see which one was hot.

Just for your information.... by code.... you cannot modify or add a receptacle to an ungrounded circuit.
 
  #3  
Old 06-27-16, 05:26 PM
R
Member
Thread Starter
Join Date: Jun 2016
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
Sorry, I left out one detail. It's a double switch that fits in a one-gang box. One controls a light in one bedroom and the other controls a light in another bedroom. Not sure what you call that kind of switch.
 
  #4  
Old 06-27-16, 05:26 PM
C
Member
Join Date: May 2015
Location: USA
Posts: 3,138
Received 2 Votes on 2 Posts
You can connect one side of your meter to any ground, using a length of wire if necessary. In an older house, a water pipe would be a good bet for a ground.

Failing that, you can use a non-contact voltage sensor. They are not totally reliable, but better than nothing, and when they give a misleading indication it's almost always telling you a wire is hot when it's not.

Are there two switches in the box? Sounds like two switch loops....
 
  #5  
Old 06-27-16, 05:38 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,583
Received 13 Votes on 11 Posts
It's a double switch that fits in a one-gang box. Not sure what you call that kind of switch
It is a duplex switch. One controls a light in one bedroom and the other controls a light in another bedroom. As C.T. said it is probably two switch loop. If the tab on the switch was broken that is further proof.
two white wires which have black tape on them.
And that is more proof. By code they were remarked with tape to indicate they are "hots" not neutrals.

Here is a single simple switch loop. You probably have two in the box.

Name:  Sw_Loopb-pre-2011.jpg
Views: 280
Size:  24.5 KB
 
  #6  
Old 06-27-16, 05:54 PM
Handyone's Avatar
Member
Join Date: Aug 2000
Location: U.S.
Posts: 5,450
Received 0 Votes on 0 Posts
I think the OP is referring to a stacked switch, 2 switches in a single gang box.

Either way, Ray is probably right. Pick a cable and connect the white and black together, one of the lights should turn on.
 
  #7  
Old 06-27-16, 06:01 PM
R
Member
Thread Starter
Join Date: Jun 2016
Location: USA
Posts: 3
Received 0 Votes on 0 Posts
Thanks to all. I'll try that.
 
  #8  
Old 06-27-16, 06:06 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,583
Received 13 Votes on 11 Posts
To answer your original questions all wires are hot. If you wanted to power something from the box you couldn't even if there was a ground because there is no neutral.
 
  #9  
Old 06-27-16, 07:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,824
Received 1,330 Votes on 1,229 Posts
Thanks Ray... I missed the part about the whites being taped black. Definitely switch loop situation.
 
 

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