Percentage of Values question

Status
Not open for further replies.

wbalsam1

Senior Member
Location
Upper Jay, NY
If I elect to run #12 thhn's in an EMT conduit in an environment of between 70-77 F, can I take the 30 ampere rating for #12 thhn from Table 310.16 and multiply it by 1.04 giving me 31.2 amperes and then use between 10 and 20 conductors in a properly sized conduit allowing a 50% reduction in ampacity to 15.6 amperes for several 15 ampere circuits?
I think I'm reading this correctly, but could use a little help....Thanks in advance.:smile:
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
You could. But you don't need to. I have yet to come across a real world installation in which I had to take advantage of an ambient temperature below 30C. I am not sure I would want to try, because it might be tricky to defend my selected value of ambient temperature.

In your case, if you take the 30 amp rating of #12 THHN from the 90C column, multiply it by 50% for the number of conductors in the conduit, and disregard the fact that the ambient is below 30C, you still have an ampacity of 15 amps. So you can still use this wire for 15 amp rated circuits.
 

StephenSDH

Senior Member
Location
Allentown, PA
Makes sense to me. Not sure about your environment, but my guess is the 86 degrees is the NFPA default for most office building ceilings. Even if you don't scale for ambient you still have 15A.
 
Status
Not open for further replies.
Top