Voltage loss

Reply

  #1  
Old 02-19-12, 09:30 AM
Member
Thread Starter
Join Date: Feb 2012
Location: usa
Posts: 5
Voltage loss

My Microwave, a wall mounted unit, stopped working.

I verified it worked in another outlet so i took some voltages at the plug and after i pulled the socket at the wires.

Black to Grnd - 123V
White to Grnd - 12V
Black to White - 79.5V

I replaced the socket with a new heavy duty version - no change.

The breaker didn't trip open. I reset it several times with no change in condition. The microwave is serviced by a dedicated 20A breaker.

Most of my electrical experience is with Navy 3 phase A/C. I feel like i lost a phase but i don't think home wiring is the same.

No other outlet is behaving like this - all others are B-Grnd 123V; White-Grnd 1V; B-W 123V.

Any ideas? I am thinking of swapping/replaceing the breaker to see if that helps.
 
Sponsored Links
  #2  
Old 02-19-12, 09:53 AM
Justin Smith's Avatar
Member
Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
I think you either have a loose connection or an open neutral.
 
  #3  
Old 02-19-12, 09:54 AM
Member
Join Date: Dec 2008
Location: Northeastern, MN
Posts: 175
Maybe a loose netural in braker box.
 
  #4  
Old 02-19-12, 09:57 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
Black to White - 79.5V That is a classic sign of a poor neutral connection. Since you replaced the receptacle it is unlikely a connection at the receptacle. Assuming a cable direct to the breaker box then next check the neutral connection at the breaker box.
 
  #5  
Old 02-19-12, 10:01 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 11,982
The white to ground volts mean nothing. It is likely phantom voltage so ignore that.
Swapping out the breaker will also do nothing.

I think you might be on to something about losing a phase. While single phase in a home is not the same as three phase is it quite similar. They just take a single 240v transformer and center tap the coil for the neutral for your 120 volts between legs.

Is this circuit dedicated to the microwave? You might have an open neutral on a multiwire circuit. Do you know if this is a multiwire circuit?
 
  #6  
Old 03-01-12, 06:44 AM
Member
Thread Starter
Join Date: Feb 2012
Location: usa
Posts: 5
Breaker good

Thanks for the patience i am in the military and had to leave for a few days.

I verified the breaker continuity is good (it opens to infinite and closes to .04 ohms).

I verified the power to the breaker was 124V. I traced out the white and ground wires - both are tight to the main terminal nothing seems wrong out in the main panel.

I still have the original voltages at the socket.
 
  #7  
Old 03-01-12, 07:48 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
Are you sure there aren't any Jboxes or other fixtures between the breaker and microwave oven?
 
  #8  
Old 03-01-12, 08:53 AM
Member
Thread Starter
Join Date: Feb 2012
Location: usa
Posts: 5
J-boxes

There are none i can find.
 
  #9  
Old 03-01-12, 09:34 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
Maybe others have a better idea but in a case like this if it was relatively easy to run a new cable that is what I would do.

I verified the breaker continuity is good (it opens to infinite and closes to .04 ohms)
To test the breaker you measure the voltage at the breaker. Is that what you meant by:
I verified the power to the breaker was 124V
I know I sound like a little old gray haired English teacher but you said "to" not "from".
 
  #10  
Old 03-01-12, 12:21 PM
SeaOn's Avatar
Member
Join Date: Dec 2011
Location: USA
Posts: 351
The white to ground volts mean nothing. It is likely phantom voltage so ignore that.
Swapping out the breaker will also do nothing.
Do you mean in this case?
 
  #11  
Old 03-01-12, 12:41 PM
SeaOn's Avatar
Member
Join Date: Dec 2011
Location: USA
Posts: 351
I believe ray is on to something. I believe you have a junction somewhere between the load, and the service panel. With the proper skill and knowledge, you could find a splice point, buried electrical box or cable, or damage conductor.

Good luck, as troubleshooting a problem online is limited.
 
  #12  
Old 03-01-12, 03:34 PM
Member
Thread Starter
Join Date: Feb 2012
Location: usa
Posts: 5
I was measuring from the input to the house to the breaker.
 
  #13  
Old 03-01-12, 04:50 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,659
What "input to the house", the neutral bar?
 
  #14  
Old 03-01-12, 05:12 PM
SeaOn's Avatar
Member
Join Date: Dec 2011
Location: USA
Posts: 351
Lost me on the input comment as well. When I here input, I somewhat think motor loads
 
  #15  
Old 03-01-12, 06:07 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,213
The white neutral conductor and the bare ground conductor both originate from the same neutral bar.

Black to Grnd - 123V
Black to White - 79.5V
Most of my electrical experience is with Navy 3 phase A/C. I feel like i lost a phase but i don't think home wiring is the same.
Regardless of where you got your experience, if you have electrical experience at all I think you'll agree that black to white and black to ground should be almost identical.

I am thinking of swapping/replaceing the breaker to see if that helps.
Replacing the breaker won't help because you already verified the breaker is providing the proper voltage at the outlet through the black conductor. Be it 1 phase or 3 phase makes no difference. You have a bad neutral connection either at the neutral bar or in a splice you haven't yet found.
 
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
'