Portable Generator Grounding, why not required?

[wcunningham]

Why are portable generators not required to have the frame grounded to a ground rod? Per NEC 50.34 (A) they are not required to be grounded, but why would they provide grounding posts on the unit then?

 

[KaBoom!]

Those are two completely different entities. The manufacturer could put whatever they want on the unit. The existence of a log doesn’t mean that code will automatically require you to use it.


Code is also different everywhere. There might be one area that requires it to be bonded.

 

[jaggedben]

Just because it's not required doesn't mean it's a bad idea, especially for a 'semi-permanent' setup. But certainly not all portable generators have grounding posts, in my experience.

 

[ActionDave]

There is no requirement for a ground rod because there is no reason for one. It would not do anything to make the generator safer or perform better.

 

[KaBoom!]

Just because it's not required doesn't mean it's a bad idea

Personally, I think it's a bad idea. It's just as bad of an idea as driving a ground rod and connecting it directly to your fridge.

 

[infinity]

There is no requirement for a ground rod because there is no reason for one. It would not do anything to make the generator safer or perform better.

I agree, once you've decided to make it a non-SDS the grounding electrode system for the structure will do the job just fine.

 

[mbrooke]

Why are portable generators not required to have the frame grounded to a ground rod? Per NEC 50.34 (A) they are not required to be grounded, but why would they provide grounding posts on the unit then?

Because there is generally no lightning risk and no incidental contact with higher voltages. As is if feeding into a building there will already be ground rods but they will not matter in terms of the generator itself.

 

[JPinVA]

Just because it's not required doesn't mean it's a bad idea, especially for a 'semi-permanent' setup. But certainly not all portable generators have grounding posts, in my experience.

But it CAN be a bad idea in some instances. Current can use a ground rod to flow in either direction! We design our systems so lightning induced current flows from the structure to the ground in an organized (well bounded) fashion. This is best achieved by bonding everything together and directing it to ground via the GEC. When multiple ground rods are in play, especially when separated by distance, one must carefully evaluate how the entire system is bonded together. If lightning strikes the ground near the structure, a voltage gradient is created. If two rods exist across this gradient, and both are connected via the EGCs in the structure, then current can flow between the two rods running through the EGCs. Instead of shunting current to ground, the extra rod becomes an enabler in energizing enclosures in the structure. Bad idea.

 

[ActionDave]

But it CAN be a bad idea in some instances. Current can use a ground rod to flow in either direction! We design our systems so lightning induced current flows from the structure to the ground in an organized (well bounded) fashion. This is best achieved by bonding everything together and directing it to ground via the GEC. When multiple ground rods are in play, especially when separated by distance, one must carefully evaluate how the entire system is bonded together. If lightning strikes the ground near the structure, a voltage gradient is created. If two rods exist across this gradient, and both are connected via the EGCs in the structure, then current can flow between the two rods running through the EGCs. Instead of shunting current to ground, the extra rod becomes an enabler in energizing enclosures in the structure. Bad idea.

You are my new best friend. I wish more people understood this.

 

[JPinVA]

You are my new best friend. I wish more people understood this.

Well, this is the Mike Holt forum...and he is my teacher!!!!

 

[mbrooke]

But it CAN be a bad idea in some instances. Current can use a ground rod to flow in either direction! We design our systems so lightning induced current flows from the structure to the ground in an organized (well bounded) fashion. This is best achieved by bonding everything together and directing it to ground via the GEC. When multiple ground rods are in play, especially when separated by distance, one must carefully evaluate how the entire system is bonded together. If lightning strikes the ground near the structure, a voltage gradient is created. If two rods exist across this gradient, and both are connected via the EGCs in the structure, then current can flow between the two rods running through the EGCs. Instead of shunting current to ground, the extra rod becomes an enabler in energizing enclosures in the structure. Bad idea.

The ground is no different then a person swimming in energized water, voltage gradients form and anything spaced across that mass (water/dirt) will pass current due to that potential gradient.

 

[JPinVA]

The ground is no different then a person swimming in energized water, voltage gradients form and anything spaced across that mass (water/dirt) will pass current due to that potential gradient.

Yes...however, two ground rods with EGC connections provide a very low impedance path across the gradient. Without the rod, the gradient current will be limited to the ground resistance and any resistance coupling of the structure. With the rod, you literally provide a short circuit across the gradient...THROUGH the EGCs (to include all the enclosures so bonded).