ATS

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medinajuli

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Good afternoon; Recently, I have been on a project that has an automatic transfer switch (ATS) of 480V/1200A. This ATS is fed from two switchboards and feeds a panel with a main of 1200A. My question is, Who protects the section of cable (#3) that goes from the ATS to the panel? ATS uses contactors. Tks. What does the NEC say? Tks.ATS.jpg
 
What Augie said. The conductors for 1,2, and 3 will all be rated for at least 1200 amps.
 
infinity said:
What Augie said. The conductors for 1,2, and 3 will all be rated for at least 1200 amps.
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I am not disagreeing; I'll just add that for 1200A OCPD the conductors have to be rated at the full 1200A - no "next size up" rounding per 240.4(B) for OCPD of greater than 800A.
 
The 1200 amp breakers protect #1 & #3 when on Normal power and the other 1200 amp breaker protects #2 & #3 when on Emergency Power. As was stated earlier, the conductors must be a full 1200 amps. I'm assuming Panel EHDP is either MLO or MB at 1200 amps.
 
tshea said:
The 1200 amp breakers protect #1 & #3 when on Normal power and the other 1200 amp breaker protects #2 & #3 when on Emergency Power. As was stated earlier, the conductors must be a full 1200 amps. I'm assuming Panel EHDP is either MLO or MB at 1200 amps.
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Okay, NEC says anything about this arrangement. Are there any restrictions?. Tks =)
 
Simply 240.4. Conductors must be protected at their ampacity and your 1200 amp breakers 1 and 2 provide that protection.
The ATS is simply a switch.
In it's simplest form this is no different than a light switch on a 20 amp circuit. The 20 amp OCP protects the conductor on both sides of the switch
 
Just a correction on the terminology: the ATS would have a SCCR not a AIC rating. Typically, the ATS will have a chart with different SCCR ratings based on different types and sizes of OCPD's and their clearing times - it's not a simple single rating.
 
electrofelon said:
Just a correction on the terminology: the ATS would have a SCCR not a AIC rating. Typically, the ATS will have a chart with different SCCR ratings based on different types and sizes of OCPD's and their clearing times - it's not a simple single rating.
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Great point. I had overlooked that.
 
electrofelon said:
Just a correction on the terminology: the ATS would have a SCCR not a AIC rating. Typically, the ATS will have a chart with different SCCR ratings based on different types and sizes of OCPD's and their clearing times - it's not a simple single rating.
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Since we are correcting terminology, it is actually a WCR, Withstand and Close On Rating. It is different than SCCR because the ATS needs to be able to withstand the fault current and be able to close into that fault current rather than just survive the fault current.
 
d0nut said:
Since we are correcting terminology, it is actually a WCR, Withstand and Close On Rating. It is different than SCCR because the ATS needs to be able to withstand the fault current and be able to close into that fault current rather than just survive the fault current.
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Yes, thanks for the correction.

a slight aside: Although WCR is the industry standard term, and exactly the words used in UL 1008 (or is it "closing":unsure:) I have a few nitpicks with it. I dont like the word "withstand" as it is considered an outdated term in pretty much all other contexts. Also "withstand AND closing rating" implies there are two different ratings, and although there are indeed two tests, there is only one rating.....Although Im not sure what I would call it if I were king. Maybe I could be convinced to stick with "WCR" and focus on more important matters ;)
 
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