Automatic Transfer Switch

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kriverswaters

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I have an installation of a 125KW, 120\208 Volt, three phase emergency generator & a "Service Entrance Rated" 400 Amp, Nema 1, Automatic transfer switch. They are planning on upgrading the existing 225 Amp, 120\208 Volt, three phase utility service to a 400 amp service within the next couple of years. As it is currently wired, the exsisitng 225 amp service comes in to a 400 Amp rated CT can, and then nipples to a 225 Amp main breaker distribution panel. The generator comes supplied with a 400 Amp breaker on the generator itself. The SER rated transfer switch has a 400 Amp Emergency generator breaker as well as a 400 Amp Normal Utility breaker. Do I have to add a 225 Amp disconnect between the transfer switch output and the Main Distribution panel (15'), or does the NEC 240.21 (2) cover this??? Paragraph "1" on this rule states that "the ampacity of the tap conductors is not less than one third of the rating of the overcurrent device protecting the feeder conductors." There never has been a "protecting device" on the feeder conductors, except the 225 Amp main in the distribution panel. Please clarify!!! Thanks
 
Your saying you are going to be putting in an ATS in the future and the load of the ATS will be the existing 225 amp MB panel. The tap rule is good if the conductors are 25' or less.
Rick
 
We are planning on installing the SER 400 Amp transfer switch now with the Generator. It appears that I don't need to install a 225 Amp disconnect between the output of the Transfer switch and the MP (15'), because the MP already has a 225A main, even though the Transfer Swith breakers are both 400 Amp. (Utility & Emergency)
 
kriverswaters said:
Transfer Swith breakers are both 400 Amp. (Utility & Emergency)
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I agree that 240.21(2) would allow the install you describe. But the above quote makes me wonder. This transfer switch has a 400A breaker on the E side, not a switch? What make? Does the genny have a factory breaker installed?
 
chris kennedy said:
I agree that 240.21(2) would allow the install you describe. But the above quote makes me wonder. This transfer switch has a 400A breaker on the E side, not a switch? What make? Does the genny have a factory breaker installed?
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Chris, I bet it is a molded case switch, instead of a breaker, Most of the 1600 amp and 2000 amp service rated t'switches I've installed are, this one is likely the same. What do you think?
 
hillbilly1 said:
Chris, I bet it is a molded case switch, instead of a breaker, Most of the 1600 amp and 2000 amp service rated t'switches I've installed are, this one is likely the same. What do you think?
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Agreed, I don't recall ever seeing a breaker on the E side.
 
The emergency generator does have a factory Square D 400 Amp breaker installed. The SER Transfer switch does have 400 Amp breakers (not a switches) installed on the "Normal" and "Emergency" inputs.
 
kriverswaters said:
The emergency generator does have a factory Square D 400 Amp breaker installed. The SER Transfer switch does have 400 Amp breakers (not a switches) installed on the "Normal" and "Emergency" inputs.
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Molded case switches look just like breakers, but do not have overcurrent protection built in, usually there is a small sticker or label on them stateing this, really doesn't make a difference unless generator does not have OCP. Just cheaper for the manufacture to produce.
 
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