Portable generator and 702.10

[JOEE]

If I'm understanding 702.10 correctly, 702.10(A) discusses separately derived systems where the neutal gets switched in the transfer switch and the neutral and ground on the portable generator are bonded. In a non-separately derived system, the neutral does not get switched and the neutral and ground on the generator are not bonded.

A customer picked up a portable generator with the neutral and ground bonded together from the factory. They plan to feed lights and the frig with extension cords only. They didn't want to main transfer switch installed at the panel (residential home), but ordered a 15A furnace transfer switch to have just the boiler hardwired. It has a male inlet for an extension cord feed. The TS only breaks the hot leg of it's 120V branch and not the neutral.

My confusion is since the neutral for the TS remains unswitched going back to the panel, then should the bonding jumper be removed on the generator? If yes, now we have a floating neutral for the lights and frig that will be fed with extension cords. We left the bonding jumper on the generator since the recepatcles are not GFCIs, but I don't want to create a potential shock hazard. My suggestion was to install a seperate ground rod for the generator, but the customer questioned it.

Is a ground rod needed? Any thoughts?

 

[ceb58]

If I'm understanding 702.10 correctly, 702.10(A) discusses separately derived systems where the neutal gets switched in the transfer switch and the neutral and ground on the portable generator are bonded. In a non-separately derived system, the neutral does not get switched and the neutral and ground on the generator are not bonded.

A customer picked up a portable generator with the neutral and ground bonded together from the factory. They plan to feed lights and the frig with extension cords only. They didn't want to main transfer switch installed at the panel (residential home), but ordered a 15A furnace transfer switch to have just the boiler hardwired. It has a male inlet for an extension cord feed. The TS only breaks the hot leg of it's 120V branch and not the neutral.

My confusion is since the neutral for the TS remains unswitched going back to the panel, then should the bonding jumper be removed on the generator? If yes, now we have a floating neutral for the lights and frig that will be fed with extension cords. We left the bonding jumper on the generator since the recepatcles are not GFCIs, but I don't want to create a potential shock hazard. My suggestion was to install a seperate ground rod for the generator, but the customer questioned it.

Is a ground rod needed? Any thoughts?

As long as you are cord and plug connected 250.34 doesn't require a ground rod BUT with throwing in this transfer switch for the boiler it would cause it to fall into 250.20 B which deals with premise wireing. and would cause the ground and neutral to be separated. It may be best to change the hard-wire to the boiler to cord and plug and install a receptacle. Then in the event of a power failure the HO could just plug into a drop cord for the boiler. I think 400.7 A 6 would allow this install

 

[erickench]

Okay, because you have both a main bonding jumper at the utility service and a system bonding jumper at the generator, objectionable current will flow through the equipment ground. Might be best to switch the neutrals. If you remove the SBJ and a fault occurs while the generator is activated then there won't be a fault current path back to the generator.

 

[electricmanscott]

Even with the transfer switch you are still cord and plug connecting the genny. No rod needed.

 

[JOEE]

As long as you are cord and plug connected 250.34 doesn't require a ground rod BUT with throwing in this transfer switch for the boiler it would cause it to fall into 250.20 B which deals with premise wireing. and would cause the ground and neutral to be separated. It may be best to change the hard-wire to the boiler to cord and plug and install a receptacle. Then in the event of a power failure the HO could just plug into a drop cord for the boiler. I think 400.7 A 6 would allow this install

I thought of that as an alternative to the boiler TS, but they already had the TS and it makes it look like more of a permanent job too IMHO. This is the unit http://www.reliancecontrols.com/ProductDetail.aspx?TF151W

 

[JOEE]

Even with the transfer switch you are still cord and plug connecting the genny. No rod needed.

That is true, but only the hot leg opens and the neutral and ground are still hardwired back to the panel and if the service drop is still in place back to the utilility co., won't there now be two return paths? Also if the generator had GFCIs, wouldn't they open because of the two return paths? Wouldn't that cause a potential difference?

I didn't want to lift the bonding jumper off the gen. since the other loads will be fed with a cord.

In my mind the generator would need to be bonded to the system ground to keep everything at the same potential and doing that is not a practical task.

What also doesn't make sense it why the furnace TS doesn't switch the neutral as well.

 

[M. D.]

That is true, but only the hot leg opens and the neutral and ground are still hardwired back to the panel and if the service drop is still in place back to the utilility co., won't there now be two return paths? ........

Nope ,.. it is a non separately derived system and theres a whole bunch of them out there ..

You might find this thread interesting Inlet on boiler

 

[electricmanscott]

That is true, but only the hot leg opens and the neutral and ground are still hardwired back to the panel and if the service drop is still in place back to the utilility co., won't there now be two return paths? Also if the generator had GFCIs, wouldn't they open because of the two return paths? Wouldn't that cause a potential difference?

I didn't want to lift the bonding jumper off the gen. since the other loads will be fed with a cord.

In my mind the generator would need to be bonded to the system ground to keep everything at the same potential and doing that is not a practical task.

What also doesn't make sense it why the furnace TS doesn't switch the neutral as well.

Why would the return path be to the utility? Wouldn't the return path be back to the source? The source being the generator.



None of the manual transfer switches/panels switch the neutral.


I think you are thinking too much. :grin:

 

[ceb58]

Even with the transfer switch you are still cord and plug connecting the genny. No rod needed.

I think I may think I disagree.
The OP has stated that the net. and ground are bonded in the gen.set.
He has stated that they will run some equipment from extension cords plugged into the recp. on the gen. set. In that case then, yes, no ground rod needed.
BUT
He is also going to power this transfer switch with a cord. The neutral is connected to the premise wireing neutral which I think would fall under 250.20 B. This would require the neutral - ground bond to be removed and a rod installed.
http://forums.mikeholt.com/showthread.php?t=122291&highlight=ground+needed+generator

I think the only way to do it correctly would be to cord and plug every thing. That way no rod would be needed and the bond would stay in place.