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hhsting

Senior Member
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Glen bunie, md, us
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Junior plan reviewer
Calculated demand load comes to 122A. The breaker used is 125A.

Would the cable size be 1/0 awg Al or 2/0 awg Al at 75C? I think its 1/0 awg Al but engineer says 2/0 awg Al should be the size
 
If it meets the requirement of 310.15(B)(7) then 1/0. If not, 2/0

Why do you think 1/0 ?
 
Why do you think 1/0 would be acceptable at 75C?

Also, if this is under your work as a plan reviewer, why would you care if the conductors were upsized?
 
hhsting said:
Two reasons:

1. NEC 2017 section 240.4(B)
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Not applicable in this case. You have a 122 amp load so your conductor must be rated at at least 122 amps 215.2
hhsting said:
2. I am not sure but this is five stories building with dwelling units. Would 310.15(B)(7) apply? Is it multi family dwelling unit?
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If it's a dwelling unit, 310.15(B)(7) applies
 
augie47 said:
Not applicable in this case. You have a 122 amp load so your conductor must be rated at at least 122 amps 215.2

If it's a dwelling unit, 310.15(B)(7) applies
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The cable is feeding 208/120V three phase panelboard.


I am confused by 310.15(b)(7) as to how it applies? Would it apply even if its 5 stories building with dwelling units? Also how would it apply to three phase?
 
Do restaurant menus confuse you :)

For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, single-phase feeder conductors consisting of 2 ungrounded conductors and the neutral conductor from a 208Y/120 volt system shall be permit‐ ted to be sized in accordance with 310.15(B)(7)(1) through (3).

sounds like it is a dwelling unit in a multi-family dwelling so at that point it meets the requirements BUT, now that you added info (Sting SOP) that it is a 3 phase feeder it does not meet the requirement .... so 2/0 !
 
hhsting said:
The cable is feeding 208/120V three phase panelboard.


I am confused by 310.15(b)(7) as to how it applies? Would it apply even if its 5 stories building with dwelling units? Also how would it apply to three phase?
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Please try reading all of the words in the section that you have cited. The code language in that section very clearly answers your questions.
 
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