NEC 110.26(C)(2) ...Egress from Working Space for Large Equipment "Rated" 1200 Amperes or

[milwaukeebob]

I have a question related to NEC 110.26(C)(2) and an existing electrical MCC room installation. The installation has an MCC with a 1200AF main incoming circuit breaker (CB) that is set at 800AT. The MCC is labeled and rated 1200A but set to trip at 800A. The upstream CB feeding this MCC main circuit breaker is also 800AT. By virtue of this, is it fair to say the MCC is "rated" 800A? or would the Code consider this "Rating" as defined by the 1200AF CB? This may seem nitpicky but I'm getting a bit hung up on the wording in NEC 110.26(C)(2) which defines the Entrance to and Egress from Working Space for Large Equipment "Rated" 1200 amperes or more. In the most literal sense, the equipment (MCC) is "rated" 1200A but it's essentially been derated to 800A. Any Thoughts?

 

[dpc]

If the feeder is sized for 800 A and the 800 A breaker settings cannot be increased by a simple adjustment at the breaker, then I think it would be considered an 800 A board. But the only opinion that matters will be the AHJ. If you can simply crank up the 800 A to 1200 A by a screwdriver or knob adjustment, then it would be a 1200 A board, imo.

I would probably ask the AHJ about before assuming it will be accepted. Or figure out a second exit.

 

[milwaukeebob]

Thanks dpc. I agree with your assessment. Unfortunately, there's no traditional AHJ on this very unique project.
Regardless of the situation, if I had been responsible for the design, I would've put a second exit in the room on opposite sides of the gear regardless of the rating. Unfortunately they didn't do that here.
Thanks again

 

[waross]

Can you contact the manufacturer and request a replacement 800 Amp breaker and a new 800 Amp rating plate?


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr. milwaukeebob (Electrical)(OP)26 Sep 23 16:10
"...#1. I have a question related to NEC 110.26(C)(2) and an existing electrical MCC room installation. The installation has an MCC with a 1200AF main incoming circuit breaker (CB) that is set at 800AT. The MCC is labeled and rated 1200A but set to trip at 800A. ...#2. The upstream CB feeding this MCC main circuit breaker is also 800AT. By virtue of this, is it fair to say the MCC is "rated" 800A? or would the Code consider this "Rating" as defined by the 1200AF CB? .....#3. This may seem nitpicky but I'm getting a bit hung up on the wording in NEC 110.26(C)(2) which defines the Entrance to and Egress from Working Space for Large Equipment "Rated" 1200 amperes or more. In the most literal sense, the equipment (MCC) is "rated" 1200A but it's essentially been derated to 800A" .
You had received knowledgeable and valuable advice already. I would like to add my personnel opinion based on old publication for your consideration. Please reference the latest NEC Art 110.26(x)(x) .
1. The breaker is considered 1200A if the current trip unit can be set up from 800A to 1200A by a simple tool or dial. However, if the trip unit is say range from <800A to 800A max, it can be considered as a 800A breaker, even it is a 1200AF .
2. The upstream breaker rated set at 800A is immaterial as there is no control that it may reset to >800A.
3. Reference old publication NEC 110.26(3)(C):
a) For boards 1200A and above with width >6ft., shall be one entrance not less than 24 in. width and 8.5 ft high at each end of the working space. Exception No. 1: where the location permits a continuous and unobstructed way of exit travel, one means of access shall be permitted.
Che Kuan Yau (Singapore)