Emergency Back Up Generator

[A/A Fuel GTX]

When connecting an emergency generator to a sub panel intended for that purpose, I understand that the floating neutral can be unswitched, and solid connecting to the sub panel, main panel and generator neutral terminal. I'm trying to visualize what happens to the current being back fed to the poco transformer via the grounded conductor. Wouldn't that pose a hazard to the unsuspecting lineman downstream just as a backfeed on an ungrounded conductor would?

 

[charlie b]

Re: Emergency Back Up Generator

At that point in time, the "source" to which all current is trying to return is the generator. There is no complete path from a generator hot back to the generator neutral, that includes the hot wire coming from the POCO. The switch takes care of that by switching all ungrounded conductors. No, there is no hazard here.

 

[jbwhite]

Re: Emergency Back Up Generator

That neutral is not floating.
It is grounded at the main panel.
It is not bonded at the generator, so as to not create a parallel path for the neutral current.

A floating neutral is when the grounding bond becomes open.

 

[A/A Fuel GTX]

Re: Emergency Back Up Generator

There is no grounding bond at the transfer switch or the sub panel so it is a floating neutral isn't it?

 

[LarryFine]

Re: Emergency Back Up Generator

Originally posted by m73214:
There is no grounding bond at the transfer switch or the sub panel so it is a floating neutral isn't it?

But, you said:

Originally posted by m73214:
When connecting an emergency generator to a sub panel intended for that purpose, I understand that the floating neutral can be unswitched, and solid connecting to the sub panel, main panel and generator neutral terminal.

There seems to be a contradiction.

"I'm so confused!" - Vinnie Barbarino

 

[A/A Fuel GTX]

Re: Emergency Back Up Generator

Yes, the neutral is bonded to the GEC at the main service but not at the generator sub panel so wouldn't the sub panel neutral be considered floating?

 

[charlie b]

Re: Emergency Back Up Generator

Originally posted by m73214: Yes, the neutral is bonded to the GEC at the main service but not at the generator sub panel so wouldn't the sub panel neutral be considered floating?

It would not. The neutral at the sub-panel is connected to planet Earth, even if it is with a long wire. There will be a measurable voltage between neutral and ground at the sub-panel, because of the current flowing in the neutral wire from the sub-panel to the main panel. That voltage may well vary from moment to moment, but it is not free to "float," as though it were a leaf blowing in the wind. Rather, that voltage is firmly established as being equal to the resistance of the neutral wire times the current that it is carrying.

 

[A/A Fuel GTX]

Re: Emergency Back Up Generator

OK...I understand that now so would the neutral at the sub panel be considered " isolated " ?Thanks Charlie...

 

[charlie b]

Re: Emergency Back Up Generator

I don't know what you mean by saying the neutral would be "isolated." That's a word that is not commonly used in conjunction with the word "neutral." I have heard of an "isolated ground," but that is an entirely different animal. If you mean that the neutral bus and the ground bus are not to be connected to each other at the sub-panel, you are right.

 

[allenwayne]

Re: Emergency Back Up Generator

Charlie we can`t install a sub panel with the neutral and grounding conductors together at the sub panel.So to say that is redundent.Once past the first OCPD in the service all panels are isolated IE :4 wired.

 

[roger]

Re: Emergency Back Up Generator

Originally posted by allenwayne:
Charlie we can`t install a sub panel with the neutral and grounding conductors together at the sub panel.So to say that is redundent.Once past the first OCPD in the service all panels are isolated IE :4 wired.

Allen, read 250.32(B)(2) to see where you're wrong

Roger