Generator Question

[JDGREEN4ME]

Is a "earth ground" required for a portable generator? recently bought a generator and it shows one in the manual but I was told by dealer it isn't needed. Is that true?

 

[snowman]

According to my electrician, you do not need to use the ground on the generator, as the "plug" from the generator to the house is grounded.

My generator also has a ground "screw" that I dutifully hooked up a ground wire to and stuck in the ground when I used it.

A few months ago, I had the electrician come out and move my generator hookup box and add more circuits to the box that the generator was feeding. He saw my ground wire that I had on the generator and said that it wasn't needed per the above explanation, so I ripped it off and won't use it.

 

[_RaT_]

Grounds can present many tricky situations. Out here in the West where the ground is typically quite dry, a 8 foot rod driven into the ground may have enough resistance that it cannot ground out a 20 amp breaker. The preferred way is a ufer ground, a ground buried in the top 3" of the bottom of a concrete footing. It is typically a piece of 1/2" rebar 20 feet long. Your generator will be grounded when tied to the house ground. In some areas, adding another ground for equipment like a generator can actually create a problem when tied to the house ground. You can develop a differential voltage simply because one ground will be of less resistance then the other. It's one of those areas I am certainly not to sure of as its difficult in real life to ever have this scenario occur and evaluate it. Suffice it to say, if you have a 120V/240V generator, you will need a 4 prong male/female plug/receptacle to adequately transfer power and ground the generator.

 

[Docsknotinn]

Rat, sorry to be off topic but I cant help but enjoying a good laugh at the "no Vote State". My generator has a spot for a extra ground as well. I had the transfer switches installed by the main breaker box in the basement and the plug in the garage. I can set the generator just outside but under the eaves and plug in. The electrician didn't say any thing about a extra ground so I have never used one. Dave

 

[snowman]

I forgot to mention the fact that my generator connects to the house via a 30 amp plug, which is why the electrician said that I did not need the generator's ground.

 

[JackIL]

When hooked up to your house for emergency power there is no need for a supplemental ground as others have pointed out. But if you are using the generator in a remote location to provide stand alone power for lights, tools, etc. then it would be a good idea to use the ground wire. I bought a copper ground rod and a short length of heavy wire for this purpose.

JackIL

 

[herbenus]

This is probably outside the usage of most generators. But I have used generators for powering sensitive electronics, with multiple sensors. I had the strangest noise problems that I couldn't track down until we properly grounded all equipment, including generator. Noise problem went away. But for running a drill or saw the ground is probably not needed.

 

[mountain_man]

Ground rods (grounding electrodes) are only required if the generator is a "separately derived system". (For the complete text of sections cited please see the 2002 NEC)

What is a Separately Derived System?

The NEC in Article 100 defines a Separately Derived System as:

A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection , including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

The key to knowing if a generator is a "Separately Derived System" is not the generator, but rather the transfer switch. If the transfer switch does not transfer the neutral (grounded conductor), then the generator has a “solidly connected” grounded circuit conductor and the generator is not a separately derived system.

Bottom line, if connecting to your existing panel thru a transfer switch (that does not transfer the neutral), no ground rod is needed. If generator is sole power source (i.e. job site construction), ground rod is needed.

Here a link for further info --> Generator grounding

 

[Inspector507]

The grounding lug, on the most of the gensets that they are concerned with, have no connection to the neutral. It's just simply a lug on the case. I have purchased, but not yet installed,a 12KW generator. It has an external lug and WILL get a connection to a grounding electrode, if for nothing more than to dissipate transient voltage, i.e. lightning. The NEC® does allow a "supplemental electrode". I'll feel better spending the $10 to install one.

Jerry

 

[mountain_man]

Jerry - I certainly don't have your knowledge and experience, however I have installed a few of these previously and was familiar with the NEC code (about gensets from previous research). BTW - I've seen gensets internally wired both ways - with neutral grounded to the chassis and not. I agree an extra ground wouldn't hurt.