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#74650 - 01/30/07 03:38 AM Transfer switch
guschash Offline
Member

Registered: 01/25/07
Posts: 12
Loc: Walbridge,Ohio,wood
I will doing my first residentical transfer switch hook-up. Do I tie the neutrals together at the transfer switch enclosure.

[This message has been edited by guschash (edited 01-30-2007).]

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#74651 - 01/30/07 04:05 AM Re: Transfer switch
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
Yes. There needs to be exactly one ground/neutral connection in the entire system, and the ATS is generally the place to do it. (250.30(A)(1) Exception 1 permits this.

NEC 250.30 will tell you what you need to know. Well, if you can decipher it at least- it's one of the most confusing codes to try to read. Why can't the NEC just use plain english?

[This message has been edited by SteveFehr (edited 01-30-2007).]

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#74652 - 01/30/07 07:15 AM Re: Transfer switch
ShockMe77 Offline
Member

Registered: 06/11/05
Posts: 823
Loc: Rahway, New Jersey
I haven't done many of these but the ones I have done have NOT been seperately dervied systems since the grounded conductor was NOT switched.

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#74653 - 01/30/07 03:31 PM Re: Transfer switch
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
It was my understanding that generators and UPSs are are always a seperately derived source, regardless of how the neutral is handled.

Quoth NEC 2005:
 Quote:
Separately Derived System. A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.


 Quote:
250.30(A)(1) Exception No.1: For separately derived systems that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each power source shall be permitted


[This message has been edited by SteveFehr (edited 01-30-2007).]

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#74654 - 01/30/07 03:54 PM Re: Transfer switch
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
It is up to the installer to decide if it will be a separately derived system or not.

If you switch the neutral and put a bonding jumper at the generator it will be an SDS.

If you do not switch the neutral and do not install a bonding jumper at the generator than it will not be an SDS.

Both ways have advantages and disadvantages.

Primarily non-SDS is cheaper, SDS works better with GFP mains.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#74655 - 01/30/07 04:02 PM Re: Transfer switch
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
You also need to check the generator. Some come with the neutral bonded, others, particularly Honda, don't.
_________________________
Greg Fretwell

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#74656 - 01/31/07 03:24 AM Re: Transfer switch
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Interesting that you mention Honda, with this being a foreign make. By far the majority of generators on the U.K. market are sold with an unbonded neutral, as I believe are most in Europe. Perhaps this accounts for it?

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#74657 - 01/31/07 03:57 AM Re: Transfer switch
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
That's odd, now that you mention it- I'd think it would be the other way around, as PME & shared earth/neutral is illegal in the US but more prevalent in Europe.

Boy that THAT throw me for a loop the first time I saw it! 3W WYE bus duct? Not very common in the US

[This message has been edited by SteveFehr (edited 01-31-2007).]

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#74658 - 01/31/07 03:30 PM Re: Transfer switch
guschash Offline
Member

Registered: 01/25/07
Posts: 12
Loc: Walbridge,Ohio,wood
This is a Honda, so if I don't tie neutrals together, how do the loads that will be running now on the generator get there neutal. From the generator?

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#74659 - 01/31/07 04:57 PM Re: Transfer switch
Roger Offline
Member

Registered: 05/18/02
Posts: 1779
Loc: N.C.
Guschash, here is a diagram from Ed MacLaren that shows a proper hook up for an unswitched neutral transfer switch.

Notice the generator neutral is not bonded to the generator housing.



Roger

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