Generator Grounding

Certainly, you always follow the rules and regulations provided by your local Authorities. I have no license to tell you different.

With that said, there is often a bit of confusion as to whether a cross connect is to be made between neutral and ground at the generator head.

We have kicked this topic around a bit in our group, and Bill Rogers has also contributed to this topic as per general guidelines. I apply my Telco training as per ground windows in power distribution systems and find that there is no contradiction to the following answer.

WHEN your generator has power plugs located at the generator AND you are not feeding power panels, it is usually a proper procedure to provide a connection between the neutral and the case ground of the generator.

Many of use use Generators in a stationary setting, and we have wired them in a more permanent way. In this case, we may be feeding a power panel in a shop or home as a single source of AC, or as an alternate source of AC power. In this case we can consider what a grounding system is all about AND we can consider why we have neutrals and grounds. Yes, some think they are the same thing because they go to the breaker panel in a shop or house and see that they are often brought together on one strip inside the fuse box, but there is a simple rule that might help in your understanding.

Grounds are designed to carry FAULT currents, Neutrals are designed to carry current as per normal operation! Now consider the Stationary application, if you run a ground wire between your generator case and the strip in the breaker panel, and then you run a separate neutral between the generator and the same strip in the panel where neutrals are often terminated, there will be no current flowing between the generator case and the ground that is terminated at the panel. The only time this ground will carry current is when there is a FAULT in the generator, a good example might be a 'cut thru' or other insulation failure where a stator winding finds it's way to the outside housing or case. If this happens, we'd expect current to flow in the ground wire that is PROGRAMMED to carry fault current only. It is better that this ground carry this fault current than part of your body when you touch it, and this is what it's all about. IF you were to bond or strap the case ground and the neutral together at the generator head in this all too typical stationary setup, you would assure that the ground would carry current as per normal business, this is USUALLY considered a bad thing in most jurisdictions.

Now a last thing to consider, if you were to take a clamp on amp meter, and use it to monitor for current flow in your grounding system, you might identify wiring errors or insulation problems, this might be a handy idea. You might also investigate how inexpensive ground fault detectors work, and consider making one or more of these part of your design.

Now.. I am aware of at least one case where a Government Authority told an associate of mine that he needed to bond the neutral and ground together in all the generator heads he sold. If this is the direction your authority gives you, you might challenge that order with the information and circumstance on this page, but remember, he's the authority!

In communications buildings; grounding and bonding is of critical importance, we want fault currents to have a far better path to travel than thru the body of a technician working in the building. The efforts include providing a fault path for current flow from lightening strikes, and this type of current, it's fast rise times, and the requirements to handle it best is possibly more complex than the average reader of this page will ever know. I once attended a 40 hour class at Bell Core, there where two students with PhDs in Electrical Engineering in that class of about 20 that also left with the full understanding that we had only covered the basics of building Grounding and Bonding and they too had a lot more to learn. If you know all there is to know about grounding and bonding, you are probably delusional.        

   All the best,

George B.