Decoding Equipment Specs: Please help me understand this Equipment Spec??????

[dionysius]

Optimal Solution to Date.........

Optimal Solution to Date.........

3 sets of #12 derate to 21A (with no other derating), should sufficient for a 21.10 MCA. 220.5 permits us to round fractional ampere values to the nearest whole number. However, there may be some question whether that stipulation carries to other articles, or more specifically where no calculation is performed, such as in this case the MCA being a rating, not a calculation. Opinions?

I am amazed at the fine detail I pick up here with you folks. Thank you all so much. This is a big improvement on my initial solution.

Optimal solution so far is:

To install 5 Outside Units about 50 ft from the 480/277 panel:​

• 
  [*=2]Run 2 3/4" EMT's
  
  [*=2]Pull 3 sets (A,B,C) of #12's in first (9 wires)
  
  [*=2]Pull 2 sets (A,B,C) of #12's in second (6 wires)
  
  [*=2]Use 3 pole 25 amp common trip circuit breakers for each set (5 x 3-pole breakers)
  

Note 1: No neutrals are to be run​

Note 2: Because it is a/c compressor equipment the small conductor rule is ignored so #12 is rated for 30A
Note 3: EMT conduit used as ground

​

Any corrections or comments????

 

[infinity]

I am amazed at the fine detail I pick up here with you folks. Thank you all so much. This is a big improvement on my initial solution.

Optimal solution so far is:

To install 5 Outside Units about 50 ft from the 480/277 panel:​

• 
  [*=2](1)-Run 2 3/4" EMT's
  
  [*=2](2)Pull 3 sets (A,B,C) of #12's in first (9 wires)
  
  [*=2](3)Pull 2 sets (A,B,C) of #12's in second (6 wires)
  
  [*=2](4)Use 3 pole 25 amp common trip circuit breakers for each set (5 x 3-pole breakers)
  

Note 1: No neutrals are to be run
​

Note 2: Because it is a/c compressor equipment the small conductor rule is ignored so #12 is rated for 30A
Note 3: EMT conduit used as ground

​

Any corrections or comments????

#1-Good.
#2-Spliting hairs, technically the #12's after adjustment for 9 CCC's (30*70%=21 amps) are .1 amps too small so #10's are required.
#3-Good.
#4-Good.
Note#1-Yes.
Note#2-You would size the #12 according to the 75° C column which is 25 amps not 30 amps.
Note #3- Yes EMT is a listed EGC in 250.118.