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Joined: Jan 2007
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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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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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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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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: 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. 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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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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You also need to check the generator. Some come with the neutral bonded, others, particularly Honda, don't.
Greg Fretwell
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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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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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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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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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