I’m a homeowner and am thoroughly confused after reading this and other articles about grounding a generator. (I'm not an electrician, but am a licensed ham radio operator, so I know a little more about electricity and electronics than most homeowners, but honestly, not that much).
I just bought a new 6700-watt (7300-watt surge) portable generator. Before I bought it, an electrician installed an interlock kit (UL listed) to enable me to legally connect the generator to my house wiring. In tests, including a 2-hour test during an outage a week after this was connected, the generator was able to power my well pump, two furnaces, two fridges plus some miscellaneous low power items (lights, APC SmartUPS protected computers) without getting overloaded. It ran at 114 to 116 volts, with a frequency of 61.8 hertz. Voltage varied only 2 to 3 volts when a furnace turned on or some other appliance surged. I can very easily turn breakers on and off to reduce strain on the generator if need be, and with our woodstove, can get by with one or even no furnaces on.
The generator neutral is bonded to the ground at the generator. It is connected via a 40-foot cord. The interlock kit does not shift the neutral. I asked the electrician if I should install a ground rod at the generator, and he said that the generator is using the house ground, so I shouldn’t need it. He also said that some inspectors require that you install a ground rod in such installations, and about half the articles that he reads about generators say that the generator should be grounded at its site, and the other half say that this is second ground is unnecessary.
I haven’t installed a ground rod at the generator.
I was speaking to the engineering manager at the manufacturer (manufacturer's name undisclosed, because he told me some things out of school) about another issue about the generator, and while doing so, he brought up the grounding issue (which started me on this wild goose chase across the internet). He said that he disagrees with UL about requiring bonded neutrals. He told me that it is best if I have an electrician convert the generator to a floating neutral if I am going to connect it to my house wiring.
At the same time, he said that there has never been a record of a fatality caused by having a bonded neutral generator hooked up (legally) to house wiring. He also said that the GFCI’s will no longer work if I was to use the generator in some other way if I changed it to a floating neutral.
I don’t plan on using the generator in any other place than where it is, which is inside a shed I custom-built for the generator (plenty of ventilation, and very dry, by the way). I don’t really have the need for the 120 volt outlets.
What should I do?
1) Leave the generator as is, without a ground rod, and continue to use the house ground point at the main breaker box as the generator ground?
2) Install a ground rod next to the generator and wire it to the generator?
3) Convert the generator so it has a floating neutral, and connect it to the house wiring without a ground rod at the generator?
My preference would be not to have the generator’s innards altered, as it may void the warranty. I can install a ground rod in half an hour, but I’ve also heard that this can do more harm than good.
I'm also more concerned with safety than with complying with code, if code outlines an unsafe situation. (Please don't suggest extension cords - I can't run 240 v appliances with them, and don't feel that having extension cords running thoughout my house is safe).
An IEEE article I read about generator grounding went through a series of real-life situations, and found significant variance in systems. Some had problems with current intermingling and “[some] installations, whether code-complying or non-code complying, may show little deleterious effect, because of favorable system impedances which tend to attenuate ‘stray’ currents.” Read the entire article for total confusion:
http://mercedeelectric.com/Documents/00585847.pdf
By the way, JW Electric, I would be interested to know more about the refueling fire. Was he refueling a hot generator that had been running and had just run out of gas (could the fire have been caused by heat?), or was it a cold generator that was hooked into his panel through a transfer switch, and the cause of the fire was unclear, but pointed to an electrical issue? Could an undischarged capacitor in the generator have caused the fire? Was he refueling a generator while it was running?