Electronic Breaker and Conductor Wiring

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anbm

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We have 1,200A (100% rated electronic breaker) in a switchboard, according to NEC, we have to run (3) sets of 4#600kCM out of this breaker.

Contractor proposes to run (3) sets of 4#500kCM out of this breaker, in order to do this, he will adjusts the setting at the breaker lower than 100% (I guess around 1,100A).

(3) sets of 500KCM will be good for 1,140A so it should be okay with 1,100A load setting, I guess.


Will this be acceptable with NEC?
 
anbm said:
We have 1,200A (100% rated electronic breaker) in a switchboard, according to NEC, we have to run (3) sets of 4#600kCM out of this breaker.

Contractor proposes to run (3) sets of 4#500kCM out of this breaker, in order to do this, he will adjusts the setting at the breaker lower than 100% (I guess around 1,100A).

(3) sets of 500KCM will be good for 1,140A so it should be okay with 1,100A load setting, I guess.


Will this be acceptable with NEC?
Click to expand...

You may be able to run the 3 sets of 4#500KCM and leave the 1200A plug there if your calculated load doesn't exceed the ampacity of the wire(1140A). If not just change the plug to a lower setting.
 
chevyx92 said:
You may be able to run the 3 sets of 4#500KCM and leave the 1200A plug there if your calculated load doesn't exceed the ampacity of the wire(1140A). .
Click to expand...

Do you not think that contradicts 240.4(C) ?
MLO, I can see by load calculations but MB ?????
 
anbm said:
We have 1,200A (100% rated electronic breaker) in a switchboard, according to NEC, we have to run (3) sets of 4#600kCM out of this breaker.

Contractor proposes to run (3) sets of 4#500kCM out of this breaker, in order to do this, he will adjusts the setting at the breaker lower than 100% (I guess around 1,100A).

(3) sets of 500KCM will be good for 1,140A so it should be okay with 1,100A load setting, I guess.


Will this be acceptable with NEC?
Click to expand...

  • You are allowed to use the next highest standard size device, so you are allowed to leave it at 1200A.
  • What is your ambient at the breaker?
  • What is the temperature rise alowance for the breaker lugs? Other end of the cables?
  • Does the cable stays at the same ambient or does it go from inside to outside where you would need to adjust for maximum ambient.
 
weressl said:
You are allowed to use the next highest standard size device, so you are allowed to leave it at 1200A.
Click to expand...
If I am understanding you correctly, that's true for 800A or less.

As augie noted, (2002) 240.4.C, over 800A, ampacity has to be equal or greater than the device rating.

cf
 
I agree that condutor size needs to be equal or greater than breaker rate.

However, when they adjust the setting on breaker (1,200A) to a smaller full load rating (i.e: 1,100A; 1,000A; 900A, etc), can we consider these smaller rates as breaker rating and run with smaller wiring accordingly?
 
anbm said:
I agree that condutor size needs to be equal or greater than breaker rate.

However, when they adjust the setting on breaker (1,200A) to a smaller full load rating (i.e: 1,100A; 1,000A; 900A, etc), can we consider these smaller rates as breaker rating and run with smaller wiring accordingly?
Click to expand...

I was incorrect, the cutoff rating is 800A for allowing the next higher standard size to be used.

Adjustable setpoint can be only utilized if access to the means adjustability is restricted.

240.6 Standard Ampere Ratings.
​
​

.....(C) Restricted Access Adjustable-Trip Circuit Breakers.​
A circuit breaker(s) that has restricted access to the
adjusting means shall be permitted to have an ampere rating(
s) that is equal to the adjusted current setting (long-time
pickup setting). Restricted access shall be defined as located​
behind one of the following:
(1) Removable and sealable covers over the adjusting
means
(2) Bolted equipment enclosure doors​
(3) Locked doors accessible only to qualified personnel
 
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