Why do you need to have a 4-pole ATS when the ATS has its sources coming from both the utility and emergency generator both of which are solidly grounded? I believe it has something to do with the ATS breaker seeing less of a ground fault magnitude to interrupt the ground fault?
ATS Neutral connection for Utility and generator source
- Thread starter philly
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ohmhead
Senior Member
- Location
- ORLANDO FLA
You dont need a 4 pole ATS you can use a 3 pole ATS but you must not use a neutral main bonding jumper in the generator its already done in the switchboard .
If you have a solid neutral connection in your ATS most jobs we do call out for a 4 pole so we install a 4 pole .
But it depends on what your doing and your project best interest .
It best to ground the frame of genset only with a 3 pole ATS with a solid neutral but not the neutral .
This will not effect the GFI but if you ground twice it will .
Lets see what others have to say
If you have a solid neutral connection in your ATS most jobs we do call out for a 4 pole so we install a 4 pole .
But it depends on what your doing and your project best interest .
It best to ground the frame of genset only with a 3 pole ATS with a solid neutral but not the neutral .
This will not effect the GFI but if you ground twice it will .
Lets see what others have to say
- Location
- Massachusetts
If the you have GFP breakers, not switching the neutral can cause nuisance tripping of the GFP regardless of how it is bonded.
Check out this document from Cummings Power, specifically Figure 3.
http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf
Check out this document from Cummings Power, specifically Figure 3.
http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf
ohmhead
Senior Member
- Location
- ORLANDO FLA
Yes it can but rare our engineer takes good care with breaker corr/sel when and if we use a 3 pole not often but we dont install a GFI on genset when a 3 pole is used and we dont double bond we kinda dont want that generator to trip out .
We monitor whats going on during the emergency cycle but then suppiers like to sell them 4 poles we like to install them also .
4 pole mostly but on some low budget jobs kinda what were seeing today there going 3 pole to save cost .
please explain in detail how it would trip if generator did not have a GFI and emergency power was online with a solid neutral in that 3 pole ATS as cummings did not go into detail iam interested in finding out how .
We monitor whats going on during the emergency cycle but then suppiers like to sell them 4 poles we like to install them also .
4 pole mostly but on some low budget jobs kinda what were seeing today there going 3 pole to save cost .
please explain in detail how it would trip if generator did not have a GFI and emergency power was online with a solid neutral in that 3 pole ATS as cummings did not go into detail iam interested in finding out how .
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
When discussing 2p-vs-3p-vs-4p ATS switching, I find that it can be confusing without specifying whether we're talking about 1ph or 3ph services.
In my opinion, it would be helpful to mention the real question: whether to switch the neutral. Does 3p switching mean 1ph w/ neutral or 3ph w/o neutral?
In my opinion, it would be helpful to mention the real question: whether to switch the neutral. Does 3p switching mean 1ph w/ neutral or 3ph w/o neutral?
- Location
- Massachusetts
Seeing as the OP was asking about 4 pole I think we can deduce he was talking about 3 phase 4 wire.
That said when ordering an transfer switch I would specify 'solid neutral' or 'switched neutral' along with the number of poles and if it is an ATS you had better also specify the voltage system / phase voltage etc.
An ATS designed for a Wye system may have trouble with a delta supply.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I grok. I had more than this one thread in mind when I posted above. Of course, you couldn't know that.Seeing as the OP was asking about 4 pole I think we can deduce he was talking about 3 phase 4 wire.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Yes 3 phase 4 wire 480 volts solid neutral with a 3 pole ATS how does it effect the GFI if the generator doesnt have a GFI .
How would it effect the main GFI in the normal switchboard if generator is running and online its not needed at this point .
Why is a 3 pole ATS not good per cummings thats what were asking .
How would it effect the main GFI in the normal switchboard if generator is running and online its not needed at this point .
Why is a 3 pole ATS not good per cummings thats what were asking .
- Location
- Massachusetts
It is fully explained in the paper I linked to.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
In the simple case (ie no GFP) you dont, as long as the single installation N/G bond is after the ATS, a three pole transfer switch is all thats needed.
The most common case that requires (ie for regulatory reasons) a four pole transfer switch is where one genset feeds two or more installations, where each installation has its own service. The four pole switch is necessary to prevent the ground wiring being a parallel path to the neutral, as there are multiple N/G bonds.
The presence of GFP on its own doesn't require (for regulatory reasons) a four pole transfer switch, but (and I'm off personal experience here, relying on the opinions of others) generally, the installation works much better with a four pole transfer switch, much better being defined as avoiding nuisance tripping.
I guess anytime I see reference to an "Automatic" transfer switch, I assume its a commercial installation, and from that, I assume its a 3 phase service.
Maybe I assume too much
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Maybe.I guess anytime I see reference to an "Automatic" transfer switch, I assume its a commercial installation, and from that, I assume its a 3 phase service.
Maybe I assume too much
You've never installed, or seen, a residential genny with an ATS?Maybe.
No, we do very little residential. The only residential gen sets I've seen had manual switches to keep the generator size small - the owner could turn off circuits before the generator kicked on.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well we read it kinda tells me about current paths and loops and may trip if you have a ground fault during a emergency run not going to happen everyday and it did stress that the bonding jumper in generator would not be connected so that kinda matters which is what i said in my original post .
We see it but its rare and i dont do residential work so a 3 pole is not what we normally see .
But we did do one job this year with two ATS 800 amp 3 phase 3 pole and one 600amp 3 pole ATS no bonding in the generator the bond in the switchboards were done .
Did not have any GFI issues this was a large court house and electrical engineer designed it that way .
I see a 3 pole ATS ok to use in my book if grounded correctly and breakers and loads are set up to trip correctly .
If a 4 pole 3 phase had a ground fault during a transfer of power what would it do same thing .
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