generator ground/neutral/hot variance

Merry Christmas
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New member
Hello all,

Setting up a EOC (Emergency Operations Center) trailer recently, I ran into a problem where the APC UPS wouldn't accept the "building wiring". The UPS is a APC SmartUPS 800, running not more than a satellite modem and a Linksys router. Running off of a brand new Honda 6KW generator, it would not turn on. Another UPS running 3 laptops did the same thing. I wired the trailer myself, keeping the neutral/ground separate, and running into a GFI. The GFI didn't trip.

With two different meters, I had around 40V difference between neutral and ground, and 60V difference between hot and ground. However, I still had almost 130V between N/G. (normal) But the UPS refused to fire up. Thought it was the new generator, so another was brought in, same result.

Ground rods at both the trailer and gen. Can anyone explain why it is the way it is? I question this, as well as pretty much need an answer, since we are setting up the trailer to run off of both commercial, and various generator power. (depending on situation) I took a chance and hooked up the old LJ-4 printer, without the UPS, and it works, so I plugged in the laptops, and all worked there as well. Just don't know why the V difference is so great. All cords are 12GA 3 wire, longest run of the two is 100'.

Also, the tests were run at the gen, without a load, and the gen outlets gave me the same readings.

I'm not a licensed electrician, but I'm sure I rewired my kitchen to better standards than most contrators, including adding a sub-panel, and having to rewire the bathrooms and laundry room at the same time. (such FUN!) And I may be posting this from my garage, but the house is still there... REALLY!

Thanks in advance,

I would call a licensed electrician/EC to take a look at this installation. You may find that his/her career experiences may find/see something that you missed and thus could not explain to us here.
He may also take the readings in a different method than you...


Senior Member
Delray Beach, FL
Equipment Not Working

Equipment Not Working

We just ran into a similar problem at an installation for a small data center.
The customer had one of those tan generators installed and could not get their servers to boot up.
We brought in a high quality portable generator that produced nice clean power and everything worked just fine.
The small portable generators sometimes just have too much harmonic wave distortion for modern electrical components.
For a read on this issue, see this link:


Senior Member
Antipolo City
I have been with the power sector for ehem, a long time, ehem, and I have yet to see a generator producing harmonics. most porbably, there is a problem in voltage regulation, especially if the generator hasn't been tried out or field tested yet. but certainly not harmonics.


Senior Member
new york


If this untrained person is reading 130 volts ground to neutral he probably has a better chance of electrocuting himself.

Even worse someone else could die from harry the homeowners dabbling.

This is a serious buisness with tremendous responsibility and not a place for someone with absolutely zero training.

Get him a scalpel so he can try surgery too there is a do it yourself section on Web MD.

Maybe send him to the do it yourself lightningrod website.

You just cant make this stuff up.
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tom baker

First Chief Moderator
Staff member
We often run traffic signal cabinets from portable generators and some generators don't have the regulation on the sine wave, so the conflict monitor will trip the signal to flash.
This seems like a DIY question so I'll close this
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