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am9518 01-05-2007 11:26 PM

12v diff between ground and neutral at panel

I have too much voltage (12v) between ground and neutral when my dryer is running. Do I have a loose neutral at the panel? Or is my house ground not good when under a heavy load? I would really appreciate some help! Here's what I know:

When my dryer (240v, 3 wire, 10 guage, 30 Amp) runs there is a 12v difference between ground and neutral at the main panel. I have no sub panels. and all other breakers are off.

While the dryer is running I measure 120v between the neutral (at the panel) and one of the 2 screws on the 30 Amp circuit breaker (at the panel). I also measure 120v between neutral and the 2nd screw on the on the 30 Amp circuit breaker.

While the dryer is running I measure 113v between the ground (at the panel) and one of the screws on the 30 Amp circuit breaker. I also measure 127v between ground and the 2nd screw on the 30 Amp circuit breaker.

Here's what else I know:
All of the scews in the entire panel are tight.
Without the dryer running (but 15 other circuits on), the ground in the panel is .5 ohm different than the main copper water pipe shut off
The wire for the dryer is brand new
The 30 amp circuit breaker is brand new
The outlet for the dryer is brand new
All tests were done with a Fluke 77 III

Thanks in advance for any help!

am9518 01-05-2007 11:31 PM

Also, when the main circuit is off for the entire house there is 1meg ohm difference between ground and neutral. I took this measurement at the main panel with my Fluke (ground buss and neutral large screw).

Shouldn't there be 0hm difference between ground and neutral at the panel?


vpina 01-06-2007 12:30 AM

Sounds like a loose neutral wire, where? is another question,
The simples thing to do is tighten up all your neutrals inside your CB panel zand anywhere else you have a hunch they may be loose, and/or you may try temporarily -like for 5 minutes running an extra neutral wire into the back of the dryer receptacle (have power off when you do this). Then turn the power on. If the 12volts goes away then it is definetley a loose neutral problem. There's also a small chance you have a slight short to ground inside your dryer to check this you will have to check for potential difference between your dryer's frame and your good receptacle box ground.

jwhite 01-06-2007 06:42 AM

am, it sounds like your first test (of voltage) is showing that the bonding strap or bar between the neutral and ground buss in the main panel is loose or corroded. there should be a wire, or buss bar here which electrically makes the two bars one in the same.

Be sure that while testing you are using the bar and not the panel can as your ground. this can throw off the test results, as you will not get a good connection at the can (panel enclosure)

from the ground to neutral at the main panel should read in the mili ohm range, with a good meter. zero with a cheeper. reality is that zero ohms does not exist. neither does open load OL. those are just indicators that the measurement is out of the range of the instrement that you are using.

joed 01-07-2007 10:41 AM

Is the new cable to the dryer 3 wire + ground? When you have the dryer running and are measuring the different voltages to ground, what are the hot to neutral measurements? What the voltage measurements on other breakers?
The voltage measurements you gave indicate a loose neutral. The question is if it is only the dryer circuit or if it is the entire panel.

wire_twister 02-24-2008 03:57 PM

I agree with jwhite the bond between neutural and ground in the service panel(main bonding jumper) is loose, coroded, or not there at all. The measurement between neutural and ground should be near zero with the power off.

lg 38 02-25-2008 06:02 PM

Have you checked voltage between neutral bar and all breakers? You could see a similar voltage difference throughout the breakers that share the two phases, meaning you could have voltage drop in one of the buss bars.

Just a hunch! Jwhite's hunch sounds pretty good though!

HouseHelper 02-25-2008 06:28 PM

This post is over a year old. I'm sure the OP is long gone from here.

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