45V neutral to ground

[shangoman]

Residential house, built in 1970. 20A cct, one BR (ceiling fan and light and 3 receptacles),TV Rm (5 receptacles), garage (2 GFCI receptacles for garage door openers), and attic (1 receptacle switch combo, 2 60W lights on switch, another 60W light on another switch) on cct.

Problem:
Receptacles in garage are frying garage door opener circuitry, checked voltage across receptacles, there is a 45V neutral-ground, 75V hot-ground, 120 hot-neutral. Receptacles were replaced, wiring was checked and wire correctly and tight. All other receptacles on cct reads within normal limits (basically 0V neutral-ground). Any suggestions on what the problem could be?

 

[bennie]

Re: 45V neutral to ground

Are the openers plugged in when taking the reading?

 

[hurk27]

Re: 45V neutral to ground

This is a ground that has a load to it and the neutral to ground bond has been lost. look in the panel for neutrals on the grounding bar and then look for loss connection between the grounding bar and the main service neutral. by bonding this you will loose this voltage on the grounds. but this could be caused by someone useing the grounds as a neutral and the ground was lost at a device or fixture. this would explain the two voltages adding up to 120 volts (45+75=120), check the ground terminations in the panel and at each device as the home runs could go to switches or even the light box's first befor going to the receptacle's.

 

[hurk27]

Re: 45V neutral to ground

A good way to determine where the loss has occured is plug in a extention cord to a known good receptacle then use it to get your readings you will find that the ground is 45 volt elevated above ground at the panel most houses are fed to the light fixtures then to the switch's.

[ June 25, 2003, 11:49 PM: Message edited by: hurk27 ]

 

[sno]

Re: 45V neutral to ground

I had the same problem.. twice, ended up rewiring the whole circuit both times. Problem was then gone.

In both cases a 3 way switch was involved, and disconnected grounds somewhere between the problem and the service.

My feeling was always that a neutral was being switched or a common neutral was shared somewhere in a junction box that I could not find.

Sometimes it's just as fast to start from the begining and rewire it as try to trace someones mess up so I never got to the bottom of it.

I just rewired it and knew it was right. I cant see whats behind the walls.

 

[templdl]

Re: 45V neutral to ground

Also, don't overlook that fact that most of own the latest and greatest digital meters which have a most awesome ohms per volt value. What this means is that it is common to measure a voltage across just about anything because they draw an insignificant amount of current from the circuit being measured to measure a voltage unlike the good ol' analog meter. Digital meters are an excellent tool but we also must interpret what we are seeing when we are using them.
Put a load, such as a small 120v light bulb, across the points you are measuring while you are measuring the voltage. You may find that the bulb will not light and the voltage will fall to zero. This doesn't mean that you should accept the EGC but what it does mean is that is enough resistance in the EGC to cause a potential difference between it and the grounded neutral conductor which can be measured with a digital voltmeter.
In a series circuit with (2) resistors, the EGC and the meter, the one with the highest resistance will have the greatest voltage drop across it, i.e. the digital meter with its very high ohms/volt value. This voltage reading will decrease, most likely significantly, when an inexpensive analog meter is used.

 

[karl riley]

Re: 45V neutral to ground

I question dismissing digital voltmeter readings. I often measure the millivolts between neutral and ground when trouble-shooting. I see millivolts, and occasionally 1+ volts. I don't see 45 volts! If I did, I would trace the problem. I do not use the analog meter because of its insensitivity. Even if the 45 V has little amperage behind it, I want to see it, because it should not be there.
Karl

 

[brian john]

Re: 45V neutral to ground

Karl:

I don't think anyone is saying dismiss the reading, BUT one should be aware that with the better digital multimeters it is possible to read voltage when the line is dead. The most likely cause of this in the instance would be an open ground. In this case the source of the voltage should be looked into, BUT the tech should be aware of inherent problems with some meters.

 

[dereckbc]

Re: 45V neutral to ground

I agree with Karl, a digital DMM will read strange voltages on open circuits due to the high input impedance. However on a complete circuit it is accurate. If the N-G bond is in place, milivoltage up to 3 volts should be observed depending on the circuit load and distance. 45 indicates open or improper wiring whether your using a digital or analog meter.

[ July 02, 2003, 05:41 PM: Message edited by: dereckbc ]