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

Are the 2 mains coming into the panel supposed to be at the same voltage?

Are the 2 mains coming into the panel supposed to be at the same voltage?

Reply

  #1  
Old 02-09-12, 06:07 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Are the 2 mains coming into the panel supposed to be at the same voltage?

Hello. I'm trying to troubleshoot some recent issues and was wondering if both of the "hot" mains that feed the panel should be at the same voltage. What I'm observing is that at times they are close: 119.1v on one , 120.0v on the other (but not exact). Other times they seem to divege, with one line dropping to 115v while the other line increases to 124v. As one drops, the other increases at the same rate. Is this normal behavior?

Regards- Ben
 
Sponsored Links
  #2  
Old 02-09-12, 06:13 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 11,981
Yes. Since the neutral is the mid point of the winding of the single phase transformer, as one side sags the other will rise. Remember, voltage is nominal and will vary 10%. In the case of 120 volts -/+ 12 volts is normal.
 
  #3  
Old 02-09-12, 06:23 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Thanks for the quick reply. That's kinda what I thought.

The underlying issue is that just recently the lights have been dimming under relatively light loads that have never caused the lights to dim before. I can even see them flicker as the coffee pot heating element cycles on and off- which was never an issue before. Larger loads (ejector pit pump) dim the lights significantly more than they have in the past. We had the electrical company out, but they did little and "found" nothing. He seemed to think it was loose neutral.

Any thoughts on that one?
 
  #4  
Old 02-09-12, 06:37 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,213
Yes, it could be a loose neutral, but the power companies responsibility typically stops at the service connection near the weatherhead and the loose connection could be in the meter socket or even your service panel which would be your responsibility. If you have underground service, their responsibility usually stops at the meter socket.
 
  #5  
Old 02-09-12, 06:48 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 11,981
Joe is correct. IF the power company did not find anything on their end then I suggest having an electrician come out and check your service panel. That is unless your comfortable doing it. CAUTION IS A MUST!
 
  #6  
Old 02-10-12, 05:35 AM
Member
Join Date: Oct 2005
Location: USA
Posts: 1,147
It is possible to analyze the neutral connection. Apply a 240v load of 10 amps, and measure the voltage drop. Then apply a 120v load of 10 amps and measure that voltage drop. THey should result in the same voltage drop if the neutral is healthy.
 
  #7  
Old 02-10-12, 05:50 AM
Member
Join Date: Mar 2010
Location: USA
Posts: 2,851
Significant sagging on one side and corresponding rising voltage on the other side is a major problem. The problem is in the neutral and must be repaired to prevent damage to all kinds of electrical equipment and especially electronics.
 
  #8  
Old 02-11-12, 05:06 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Thanks for all the replies. OK, so I've done a bit more troubleshooting and here is what I'm finding.

When I apply a load (microwave) I get a voltage sag of about 5v on one side of the main supply and a corresponding increase of about 4v on the other side of the main supply. This voltage decrease and increase is observed at the panel when monitoring the voltage of the main supply wires coming from the meter. Since this voltage increase/descrease is seen on the main supplies, it's obviously seen throughout the house and all lights dim/ brighten accordingly.

Also- I live in a two flat that has 2 meters (but it supplied by just the 2 wires from the pole). The panel for the other unit is right next to mine and I was also able to observe the same voltage sag/increase on their main supply wires as well when I run a load in MY apartment. They have also reported dim and flickering lights.

So does this help anyone identify where the neutral issue may lie?
 
  #9  
Old 02-11-12, 05:22 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
but it supplied by just the 2 wires from the pole
Are you sure you don't have two insulated around a bare? Two wires would only give you 120v.
 
  #10  
Old 02-11-12, 05:39 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Ray- Yes, sorry I meant supplied by the same 2 "hot" wires from the pole. There is also a third bare neutral wire that supplies both units as well.
 
  #11  
Old 02-11-12, 07:00 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,356
If you notice the same voltage imbalance on your neighbor's side then the poor neutral connection is at the point where the utility's wiring connects to the house wiring, at the weatherhead, OR prior to that point.
 
  #12  
Old 02-12-12, 04:39 PM
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 5
Thanks to all for the help. With the info at hand I was able to convince the ComEd folks that they issue was on their side and they came out today and restrung the service. The guy started by remaking all new connections with the old wire, but that didn't fix the issue. The new wires did the trick- so there must have been some issue internal to the bare neutral wire.

Anyway, issue solved. Thanks again!
 
  #13  
Old 02-12-12, 05:45 PM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,644
Thanks for letting us know how it turned out.
 
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
'