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Generator neutral bonding #91399 01/15/05 03:22 PM
Joined: Oct 2003
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Darryl Offline OP
Member
Ok, I'm sure you have all dove into this topic before but I want to get it straight before hooking something up.

Using a portable Generator, Generac 5500, to back up a residential home, I need to have a three pole Transfer switch to isolate the neutral as well, right?

Then my question is, Is the bonding jumper in the generator suffcient to serve for the new bonding conductor? As far as I am aware the only jumper in this Generator is a #12 or #14 between the neutral and ground on the back of one of the receptcles? Which to me sounds like it is not sized appropriately, should be #6 ?

Your Feedback is appreciated...

2017 / 2014 NEC & Related Books and Study Guides
Re: Generator neutral bonding #91400 01/15/05 04:36 PM
Joined: Jan 2004
Posts: 1,507
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George Little Offline
Member
Based on the information you've provided, the # 12 probably is adequate. I say this based on the fact that you probably are using the 120/240 part of the generator. I wonder if you are using a "Gentran" type connection where you selectively connect loads. As a rule the inspector has no control of a portable generator and whether or not the neutral is bonded to the frame of the generator. If the neutral and the frame are bonded together, you are doing the right thing by using a 3 pole switch to eliminate the bonding in two places problem. Now for the real world: We have an emergency, the utility has failed, we have a portable generator that has the neutral bonded to the frame, - I'm using it for power and the size of the bonding conductor that came with the generator is appropiate based on the factory specs.
One side note, Honda generators will trip the GFCI if the bonding jumper is not removed and you try to use them as a back-up for a utility and the Neutral is also at the utility.


George Little
Re: Generator neutral bonding #91401 01/16/05 01:20 AM
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Darryl Offline OP
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How do you figure a #14 or #12 jumper is big enough? Doesn't the bonding jumper need to be #6 minimum for a 120-240V 60a system?

Re: Generator neutral bonding #91402 01/16/05 02:50 AM
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George Little Offline
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Sizing of bonding conductors for Service is covered in 250.102. (C) covers Supply side of Service and (D) covers Load side of Service. I don't know that this is the proper place to look because a generator is not Service. But it appears that in some cases even for Service Load size the bond can be as small as #14 AWG. The Bond that you mentioned that was on the generator is probably sized per manufacturer's specs. If there is any labeling, UL, CSA, etc I'm sure you don't have to worry about the bond being sized properly. Now you had indicated that it was a 120/240v. 5500 va generator so the capacity of the generator is 23a. on 240v. or if your are running it straight 120v. you might, I stress might, get 43a, I question if you could even do that at all. So 60a. is not what you can expect from this unit.


George Little
Re: Generator neutral bonding #91403 01/16/05 12:26 PM
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gfretwell Offline
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Don't most small transfer switches simply switch the phases? If you don't switch the neutral you float it in the generator. (the way it is usually shipped)


Greg Fretwell
Re: Generator neutral bonding #91404 01/16/05 03:13 PM
Joined: Oct 2003
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Darryl Offline OP
Member
But George... if you are supplying the circuits soley from the generator... it IS a seperately derived service by definition and would need a service rated bonding jumper.

Gfretwell, if you REMOVE the bonding jumper in the generator it is no longer safe to use as a seperate unit for just the 120v receptacles at another time!? Right? Should I make up a jumper to fix that and instruct some ignorant homeowner to use this thing everytime you want to use your generator for the receptacles only... That's NOT safe either!!

Finally, I have yet to find online, and havn't checked at wholesale house yet, a Trasnfer switch made for switching the neutral. In these units are the individual circuit neutrals brought to a isolated bar in the transfer switch and then a pole of the switch transfers which neutral feeds it? (all while keeping it isolated from the transfer switch can since it has to go back to gen for bonding)

Re: Generator neutral bonding #91405 01/16/05 06:01 PM
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George Little Offline
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A few facts are in order:

1. Just because a 2 pole or a 3 pole double throw switch is being used to transfer a load from utility to generator does not make it a "Transfer Switch" Needs to be Listed as a transfer switch to be called a transfer switch.

2. If you are going to use the generator as a separately derived system you must break the grounded as well as the ungrounded conductors when using it in conjunction with a utility Service.

3. A Generator is not a "Separately Derived Service".

4. Kohler ship all of their generators from the factory with the common conductor bonded to the frame.

5. Generac and Onan and probably more, float the common conductor from the frame and their systems are shipped knowing they will be using them as backup for a utility.

6. Most portable generators say <7KW are shipped with the common conductors bonded to the frame and it is almost impossible to change them. Just put your ohm meter between the neutral terminal of an outlet on the generator and the frame and you see what I mean.

7. Most small generators are portable and the inspector has little to say about what homeowners do with them. Its the permanent installations that get inspected and these bonding issues are addressed.

8. If your going to use a ligit transfer swith your going to spend some serious cabbage. You'd be better off installing what they call a generator panel that has the interlock built in.


George Little
Re: Generator neutral bonding #91406 01/16/05 06:24 PM
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Darryl Offline OP
Member
According to the code a generator CAN be a seperately derived system...

Another Electrician has steered me to a Siemans model of transfer switch that is three pole to switch the neutral.
SIE-EQG660D
Here is a link: http://hillsupplies.com/cgi-bin/search/subproducts.pl?qs=5803&sb=commodit&d=00&ft=1

This discussion is only referring to small portable generators used for Home back-up... Most gen's have the neutral bond to use with the recep. but HONDA is now putting them out without a bonded neutral, probably for the home back-up reasons, but isn't that electricaly unsafe? for use as the stand alone 120v recep's go?

Re: Generator neutral bonding #91407 01/16/05 07:02 PM
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George Little Offline
Member
Darryl- That was my point earlier, a generator is not a Service but a System. Hence the bonding jumper talked about in 250 for services is not applicable to generators. I'm not quite sure how youn size it. I'd have to research it. I've never had to size the bonding jumper for a generator but it's probably based on 12.5 % of the phase conductors. The Seimens panel looks like a good choice and I guess as long as your not ending up bonding the common conductor in two places your approved [Linked Image]


George Little
Re: Generator neutral bonding #91408 01/17/05 12:15 AM
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Darryl Offline OP
Member
"George Little
Member posted 01-16-2005 07:02 PM
--------------------------------------------------------------------------------
Darryl- That was my point earlier, a generator is not a Service but a System. Hence the bonding jumper talked about in 250 for services is not applicable to generators. I'm not quite sure how youn size it. I'd have to research it. I've never had to size the bonding jumper for a generator but it's probably based on 12.5 % of the phase conductors. "


I THINK YOU MEANT 125% OF THE PHASE CONDUCTORS IS WHAT THE BONDING JUMPER SHOULD BE SIZED AT? SO THE #14 OR #12 JUMPER WOULD NOT SUFFICE, WHICH WAS MY ORIGINAL POINT... AND WHAT ABOUT THE FACT THAT SOME GEN'S ARE BEING SOLD WITH ISOLATED NEUTRALS... IF THAT IS A CODE VIOLATION AS WE SEEM TO AGREE, HOW ARE THEY GETTING AWAY WITH IT... I KNOW THE NEC ISN'T APPROVING THEIR PRODUCT BUT CERTAINLY THE U.L. SHOULD BE CONSIDERING THE SAME SAFETY PROBLEMS IF THEY ARE MONITORING AND APPROVING PRODUCTS????

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