Neutral to Ground Voltage

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Jeffoix

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Westchester, NY
I have a camera installation where I recently had some equipment go bad.
I read 8 volts AC between ground and neutral in the electrical panel (also in the outlets.
I have 3 cameras running about 900' over twisted pair cabling.
recently I had the service visit where I found the GFI outlet I was plugged into was blown. three video distribution amplifiers in the guard house were blown. one channel of my recorder in the house was blown.
I am thinking the N-G voltage is the cause of my problem.
The property is mostly ledge. The electrician is going to look into getting a better ground to get rid of the N-g voltage.
I am looking for some backup to support my case to the client....
Thanks
 
The blown equipment sounds like the problem resulted from an open neutral event on a multiwire branch circuit. You should have an electrician check out the wiring before connectiing any more equipment to that circuit. Another tell tale sign of that would be an unexpected voltage reading between the hot and the neutral or hot and ground, either too high or too low.
 
Neutral to ground voltage (assuming there is not an open neutral) is due to voltage drop on the lines. The further you get away from the Main Neutral to Ground Bond the higher the voltage, depending on load and conductor size.

I have a site that had 120 VAC between neutral and ground (accidental ungrounded system with a ground fault on a phase conductor). HIGHLY SENSITIVE ELECTRONIC equipment ran this way for an extended period of time with no equipment issues.
 
Well actually excessive N-G voltage can damage some electronics as many of these items have components installed between N-G in the circuitry like Filters and MOV's.

As Brian mentioned the N-G voltage is normal and is a result of I*R voltage drop developed in the neutral conductor. You can do anything you want to the grounding circuit and it will not do a thing to reduce the voltage between N-G becuase the cuase is in the neutral circuit and a function of current, resistance, vs distance.

Since your circuits are so long there is not much you can do except to form a new N-G bond point near where the equipment is being used. One of the best and siplest ways to do this is a simple isolation or step down transformer.
 
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Jeffoix said:
I have a camera installation where I recently had some equipment go bad.
I read 8 volts AC between ground and neutral in the electrical panel (also in the outlets.
I have 3 cameras running about 900' over twisted pair cabling.
recently I had the service visit where I found the GFI outlet I was plugged into was blown. three video distribution amplifiers in the guard house were blown. one channel of my recorder in the house was blown.
I am thinking the N-G voltage is the cause of my problem.
The property is mostly ledge. The electrician is going to look into getting a better ground to get rid of the N-g voltage.
I am looking for some backup to support my case to the client....
Thanks
Click to expand...

Do you mean blown as in fried/charred? If so, I don't think the levels of neutral to ground voltage you measured would cause that kind of damage.
 
Well actually excessive N-G voltage can damage some electronics as many of these items have components installed between N-G in the circuitry like Filters and MOV's.
Click to expand...

I do not deny this is possible, but I have seen as high as 7.2 VAC under a properly installed 208/120 VAC distribution system.

And as 120 VAC as noted above.

Additionally had manufactures screaming about anything above 1.5 swearing it voids the warranty. Which I do not mind as I just sell them a Isolation Transformer.

Field service engineer told me I was crazy and that this other site had 0.5 VAC neutral to ground through out and if they could do it there why couldn't this site. The site he was talking about was a customer of mine that surprisingly hand neutral ground issues downstream of the SDS.
 
Jeffoix said:
I have a camera installation where I recently had some equipment go bad.
I read 8 volts AC between ground and neutral in the electrical panel (also in the outlets.
I have 3 cameras running about 900' over twisted pair cabling.
recently I had the service visit where I found the GFI outlet I was plugged into was blown. three video distribution amplifiers in the guard house were blown. one channel of my recorder in the house was blown.
I am thinking the N-G voltage is the cause of my problem.
The property is mostly ledge. The electrician is going to look into getting a better ground to get rid of the N-g voltage.
I am looking for some backup to support my case to the client....
Thanks
Click to expand...

if the electrician is going to drive a ground rod to get a better ground that would be a waste of time. i think an isolation transformer would be your best bet...if power quality is the problem.
 
080624-1956 EST

Jeffoix:

Over long or short distances you can get some large voltage differences.

Electronic equipment that does not use electrical isolation for communication paths between equipment usually has its communication path referenced to the equipment chassis. In turn this means the chassis is usually connected to the grounding pin of the AC power cord and thus is connected to the AC outlet EGC.

Have two of these equipments 6 ft apart but supplied from different branch circuits and thus two different EGC wires back to the main panel. Next make the EGC conductor the same wire size as the hot wire. Assume 120 V source. The sine wave peak voltage is +/-170 V relative to the grounding point in the main panel. Assume a stiff source voltage at the main panel. At one piece of equipment place a dead short between hot and EGC. The voltage difference between the chassis of two pieces of equipment will approach 170/2 = 85 V. This will be enough to destroy at least some of the directly connected electronic components at either or both ends.

This is why we make RS232 electrical isolators. I tell this same story at my web site with slightly different words www.beta-a2.com .

We do not make video isolators, but look for a source that makes video fiber optic isolators. Fiber optic would be ideal for very long path lengths.

.
 
brian john said:
I do not deny this is possible, but I have seen as high as 7.2 VAC under a properly installed 208/120 VAC distribution system.

And as 120 VAC as noted above.

Additionally had manufactures screaming about anything above 1.5 swearing it voids the warranty. Which I do not mind as I just sell them a Isolation Transformer.
Click to expand...
Well Brian 7.2 N-G may have been properly installed I would question if it were properly engineered if N-G voltage is an issue because if you have 7.2 N-G voltage also means you have about 12% voltage drop becuase if you have that much between N-G tells me you are also dropping that much on the line conductors giving you in the neighborhood of 14.5 volt drop L-N.

The IEEE recomendation for N-G is 2 v p-p for sensitive equipment at the point of connection.
 
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