Derating conductors passing through window (from gear to gear)

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mpwasco

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Curious to know if i would have to derate the conductors that are originating from a Transformer to a piece of switch gear. i will be planning on cutting a pass through window from a SQD transformer to feed a 5000amp Eaton MLO panelboard with (5) 1000 amp breakers. see attached drawing for reference. This application will have (15) 600 kcmil AL conductors per phase.
any input would be appreciated- Thank You

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When we do this type of design, considering that we have 100% rated breakers, a very high load factor and where the feeder is very short and the net ampacity when calculated per Table 310.16 results in a value very close to the protection setting (5000A vs 5100), we often add one set of conductors extra, due to the high likelihood that there will be a compliance issue with 310.10(G)(2)(1). The shorter conductor(s) will carry more current that it is rated to carry.

310.10(G)(2) Conductor and Installation Characteristics.
The paralleled conductors that comprise each ungrounded conductor, grounded conductor, neutral conductor, equipment grounding conductor, equipment bonding jumper, or supply-side bonding jumper shall comply with all of the following:
(1) Be the same length
 
On a seperate note, I'm guessing you have some method that you are doing primary protection only, because you have no method to comply with Note 2 of Table 450.3(B)

Where secondary overcurrent protection is required, the secondary overcurrent device shall be permitted to consist of not more than six circuit breakers or six sets of fuses grouped in one location. Where multiple overcurrent devices are utilized, the total of all the device ratings shall not exceed the allowed value of a single overcurrent device.
 
ron said:
When we do this type of design, considering that we have 100% rated breakers, a very high load factor and where the feeder is very short and the net ampacity when calculated per Table 310.16 results in a value very close to the protection setting (5000A vs 5100), we often add one set of conductors extra, due to the high likelihood that there will be a compliance issue with 310.10(G)(2)(1). The shorter conductor(s) will carry more current that it is rated to carry.

310.10(G)(2) Conductor and Installation Characteristics.
The paralleled conductors that comprise each ungrounded conductor, grounded conductor, neutral conductor, equipment grounding conductor, equipment bonding jumper, or supply-side bonding jumper shall comply with all of the following:
(1) Be the same length
Click to expand...
how does adding a set of conductors allow you to violate the requirement to make all the paralleled conductors be the same length?
 
petersonra said:
how does adding a set of conductors allow you to violate the requirement to make all the paralleled conductors be the same length?
Click to expand...
As pointed out by Don, 310.10(G)(2)(1) provides for no flexibility, which is not real life, especially for a feeder that might be 5 or 10 feet long. There will a set of the paralleled feeder that might be 5% longer than the shortest set, which means that the shorter set will carry that much more current in direct proportion.
 
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