mbarkleysr
New member
what is the proper method for derating multiple current carrying conductors in a single conduit. do i use the breaker rating or the ampacity of the conductors when determining the conductor sizes?
derating
- Thread starter mbarkleysr
- Start date
- Status
bradleyelectric
Senior Member
- Location
- forest hill, md
Re: derating
rating of the conductors. That is why #12 THHN is rated on 310-16 as higher than 20 Amps with the note it can't be used as higher than 20 amp. You can derate and still come up with it being good for 20 amp. It is a heat disapation thing. More conductors bundled together disapate less heat.
rating of the conductors. That is why #12 THHN is rated on 310-16 as higher than 20 Amps with the note it can't be used as higher than 20 amp. You can derate and still come up with it being good for 20 amp. It is a heat disapation thing. More conductors bundled together disapate less heat.
stew
Senior Member
- Location
- federal way,washington
Re: derating
use the conductor ampacities from the 90 deg table
for say thhn and then use the derating tables based on number of conductors. ex: #12 thhn @90 deg =30 amps derated @70% = 21 amps thus good to go fo a 20 amp circuit and breaker. make sense?
use the conductor ampacities from the 90 deg table
for say thhn and then use the derating tables based on number of conductors. ex: #12 thhn @90 deg =30 amps derated @70% = 21 amps thus good to go fo a 20 amp circuit and breaker. make sense?
- Status