3 pole or 4 pole transfer switch

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AEFAC

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I am looking for a little direction on transfer switches. I'm not sure what the reasons why I would need a 4 ploe v.s. a 3 pole. I have more info if need be but every instalation it seems is different so if I knew the reasons you use or don't use 3 or 4 pole transfer switche then i could figure them out in the future by myself. Thanks for any response.
 
The most of the time you would not need to switch the neutral unless you got over 1000amps with gfi protection. Just comes down to cost. What size switch are you using?
 
We are using a 175 Kw generator feeding a 600 amp transfer switch and a 100 amp transfer switch one feeds life saftey and one feeds critcal branch panels in a skilled nursing facility. The generator only has one breaker for the output so we are hitting a 600 amp panel first and breaking it out from there to each transfer switch.
 
There was a short article in ECM Aug. 1, 2000. Also you might want to look at Cummins Power Topic #6005.
 
Anytime the over-current devices include GFP you should switch the neutral.

As ceb58 mentioned this is common over a 1000 amps @ 480 volts I see GFP being specified more often by engineers on smaller breakers.

The reason for the concern with GFP is that under certain conditions the GFP can false trip due to parallel paths for the neutral current.
 
AEFAC said:
We are using a 175 Kw generator feeding a 600 amp transfer switch and a 100 amp transfer switch one feeds life saftey and one feeds critcal branch panels in a skilled nursing facility. The generator only has one breaker for the output so we are hitting a 600 amp panel first and breaking it out from there to each transfer switch.
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Let's see --- You'ere putting in a generator feeding "life safety" and "critical" branch panels in a commercial building.

My first question would be, "What do the stamped drawings show?"

Once we get past that issue, then:
Are the two panel you are going to feed with the transfer switches 3P5W? I suspect they are, but maybe not. Worst case would be if either panel is 3p4w. If so there are definitely major issues.

Give us answers on these two - maybe we can go from there.

Curiousity side issue:
What are the downside issues if this is put in with a poor design? Does someone's iron lung get shut off - or the operating room lights go out?

I guess I am not clear on the what exactly "life safety" or "Critical Circuits" mean in this context.

ice
 
Our main service is a 1200 amp and it does have GFP on the main service. The generator is only backing up half of the building. So if I understand right we would need to use the 4 pole transfer switch. Please correct me if i'm wrong.
 
AEFAC said:
The generator only has one breaker for the output so we are hitting a 600 amp panel first and breaking it out from there to each transfer switch.
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I was under the impression the generator would need two breakers?

When we use one generator for emergency and optional standby loads we will order the generator with two or more breakers.
 
iceworm said:
Let's see --- You'ere putting in a generator feeding "life safety" and "critical" branch panels in a commercial building.

My first question would be, "What do the stamped drawings show?"

Once we get past that issue, then:
Are the two panel you are going to feed with the transfer switches 3P5W? I suspect they are, but maybe not. Worst case would be if either panel is 3p4w. If so there are definitely major issues.

Give us answers on these two - maybe we can go from there.

Curiousity side issue:
What are the downside issues if this is put in with a poor design? Does someone's iron lung get shut off - or the operating room lights go out?

I guess I am not clear on the what exactly "life safety" or "Critical Circuits" mean in this context.

ice
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The drawings do not clarify what is to be installed for the transfer switch and it is design build so we are responsible for putting in what is required. The "Life Saftey" panel feeds emergency lighting and that sort of stuff. The "Critical Branch Circuit Panel" feeds patient beds and other stuff to keep people alive. Being that this is up to us to pick which one price is not the issue here. We just want to put in what is the best choice. Just trying to figure it out before we install it.
 
iwire said:
I was under the impression the generator would need two breakers?

When we use one generator for emergency and optional standby loads we will order the generator with two or more breakers.
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We were told by our generator supplier that two breakers were not an option so we are going to do it this way, we did think it was odd that it could not be done that way. Maybe we should put some heat on them about it.
 
AEFAC said:
We were told by our generator supplier that two breakers were not an option so we are going to do it this way, we did think it was odd that it could not be done that way. Maybe we should put some heat on them about it.
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Or find a new supplier
 
AEFAC said:
We were told by our generator supplier that two breakers were not an option so we are going to do it this way, we did think it was odd that it could not be done that way. Maybe we should put some heat on them about it.
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Buy it with no CB. The generator doesn't need one on the gen skid. Put a main CB for the generator incomer, in the 600A panel you are installing.

Pull the N-G bond out of the generator and bond the NG at the 600A panel. The two feeders to the transfer switches are 5wire. As iwire and others had said the transfer switches will need to be 4wire. However, for this to work the two panels you are feeding with the transfer switches have to be 5wire. They probably are but you have not verified.

Personally I would be very leary of doing any design work on life safety or critical circuits relying on internet post (even mine :)) or a Cummins paper. We can have all the best intentions, but we still can not see your equipment nor your one-lines.

You do have the one-lines, don't you?

ice
 
AEFAC said:
xxx Being that this is up to us to pick which one price is not the issue here. We just want to put in what is the best choice. xxx.
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That is always a a good design choice. Price is always important - but you have to meet spec and regulation first. After that one does the most cost effective methods available.

ice
 
iceworm said:
Buy it with no CB. The generator doesn't need one on the gen skid. Put a main CB for the generator incomer, in the 600A panel you are installing.

Pull the N-G bond out of the generator and bond the NG at the 600A panel. The two feeders to the transfer switches are 5wire. As iwire and others had said the transfer switches will need to be 4wire. However, for this to work the two panels you are feeding with the transfer switches have to be 5wire. They probably are but you have not verified.

Personally I would be very leary of doing any design work on life safety or critical circuits relying on internet post (even mine :)) or a Cummins paper. We can have all the best intentions, but we still can not see your equipment nor your one-lines.

You do have the one-lines, don't you?

ice
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Very good advice. You may want to seriously think about getting a EE involved. If you decide to go with the no breaker on the gen. as Ice has suggested then do not forget about 445.13. Your conductors to the first disco. will need to be sized at 115% of the name plate rating.
 
To answer a few questions. Yes we do have the one line's but it does not specify what transfer switch to use and yes the two panels are 5 wire panels. Sounds like we will be going with 4 pole switch based on the GFP that is going in. Thanks for all of the help.
 
Old man

Old man

There are other reasons requiring 4 poles ATC.
Backing up two separate buildings (separately derived electrical systems) from the same generator for example. You may need to switch the neutral so you will not create a difference of potential in the emergency neutral wire.
 
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