Motor Home Ground Rod?

[d]

I have a motor home with a 12kW 120/240V 50A vehicle mounted generator. The ground and neutral are bonded together at the generator as well as a ground to the vehicle frame. There is also a 120/240V 50A "shore" input option. It is 4 wire and brings the ground and neutral from whatever source is providing the shore power. The transfer switch between these 2 sources are 2 3 pole breakers that switch the neutral. There is a slider bar that prevents them both from being energized at the same time.

My customer has a requirement to always drive a ground rod. By code with this motor home I do not have to drive one. My question is does it hurt to have the vehicle frame tied to the ground rod while running on generator power? It does however seem like a bad idea to have the bond to the ground rod while running on shore power? Any thoughts.

 

[dereckbc]

Pointless but there is no harm having a supplemental ground rod on the trailer.

As long as the transfer switch is configured properly as you describe, no load or fault current will ever flow or try to flow on the ground rod. Well whatever leakage there might be, but the impedance will be so high any current from shore power can be ignored.

 

[d]

Motor Home Ground Rod?

dereckbc,

So you are saying that it will not hurt while connected to shore power as well? What about ground loops between the ground at the shore location and the ground at the motorhome?

 

[dereckbc]

dereckbc,

So you are saying that it will not hurt while connected to shore power as well? What about ground loops between the ground at the shore location and the ground at the motorhome?

While a loop does exist, it is the exact same loop on any residence and meaningless.

What is the impedance of a single ground rod? Let's say you get the miracle 25 ohm's of the NEC. So what? You will have 25 ohms plus the resistance of the shore ground electrode system. So let's say that equals 50 ohms OK.

Now what is the impedance of the grounded circuit conductor from the shore power. My guess is some much less than say a 1/10th ohm. So now you have something less than a 1/10th ohm in parallel with 50 ohms. So what? Well for every 1000 amps of power returning on the grounded circuit conductor (neutral) you might get 1 amp max on the ground rod return. Who cares, it is not significant or realistic?

EDIT. Excuse me, the answer is what loop exist? Since the N-G bond is only at the shore power, all load current flows on the grounded circuit conductor, none on the EGC or ground rod. Point is still the same, it is harmless but does nothing.

 

[d]

Thanks for the help