ground testing

Reply

  #1  
Old 05-03-04, 03:53 PM
cmv
Visiting Guest
Posts: n/a
ground testing

On a 120v outlet, what should the voltage be between the hot and ground wire?

Thanks,

cmv
 
Sponsored Links
  #2  
Old 05-03-04, 03:58 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
120 volts, more or less.

If you don't have a true ground connection, however, your digital voltmeter could read anything between 0 and 120 volts. We often see reports of 35 volts, 47 volts, 63 volts, etc. These readings are all phantom, caused by capacitive coupling of the wires. A meaningful voltage reading with a digital voltmeter can only be made between wires that are not floating. Measuring to a floating wire results in garbage results. For this reason, digital multimeters are often a very poor tool choice for home wiring.
 
  #3  
Old 05-04-04, 07:49 AM
cmv
Visiting Guest
Posts: n/a
testing

some of the receptacle boxes in my home have a bare solid wire, maybe #16 in size that is run from the nuetral bar in the breaker box to the back of the receptacle box. When I test with the plug in type tester that checks for correct wiring, the bulb that lights up for proper ground is dimmer than the other amber light. When using a voltmeter from hot to ground I get 108 volts on some and 35-60 volts on other plugs. What does this mean? On all of the plugs so far that have been changed out to 3-prong, the tester will light up as correct, however when testing some of the receptacles the second light that lights up on the tester is very dim.
 
  #4  
Old 05-04-04, 08:35 AM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
Received 0 Votes on 0 Posts
My guess is that the dim light is really an off light which is getting some bleed-over from the adjacent light. These outlets are probably ungrounded. This hypothesis is supported by your less-than-100-volt readings. This is likely because the grounding connection is not continuous back to the panel. The connection could have never been completed in the first place, or it could have become disconnected somehow.

By the way, your grounding wire should never be 16-gauge, so I hope you are incorrect about that.

Also, on those outlet where you get 108 from hot to ground, what do you get from hot to neutral?
 
  #5  
Old 05-04-04, 10:16 AM
cmv
Visiting Guest
Posts: n/a
hot to nuetral is 119v. Here is the set up. Meter is on a pole outside, square d disconnect box below the meter with 200 amp fuses. 2/0 cable then goes into conduit underground and comes up in garage to a federal pacific breaker box (house built in 1968). I see that the ground wire that is stapled to the pole goes into the meter box. There is also the same diameter wire in the disconect that is tied into a lug with one of the wires from the meter, how ever this wire sticks out of the disconnect about an inch and has been cut. I have no idea if this needs to be connected to a ground rod or not. Inside the FP breaker box, there are many small bare copper wires that are twisted together and tied into the nuetral bar. The house has 10 gauge and 12 gauge wiring throughout, the bare wire is smaller so I am assuming 16 or so gauge. I can actually see the bare wire (two of them comming out of the romex) in some of the receptacle boxes. When testing across these I get the 108 voltage. The other boxes I am assuming the must have connected the bare wire to the back somewhere during construction.
Another thing I am wondering is how this breaker box is supposed to be grounded in this situation, I have not looked hard enough yet to see if it is or not.

thanks
 
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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: