roc1
Member
- Location
- Lubbock Tx
One thought I have.The code says you can size conductors by the 90 deg chart for Thhn as long as you derate and for terminations not to exceed the 75 deg chart over 100 amps.I say this because if you size a motor wire,you multiply by 125% to get amp rating of wire and then by NEC you go by 75 deg chart.Why can you not size by 90deg as long as load is not in excess of 75 deg chart?Ex 200hp 460 volt three phase motor FLC 240 amps.Wire size by charts Square D for example is 350mcm.The FLC x 125% is 300amps.By 310.16 chart 300mcm 90deg is rated at 320 amps derate by 75deg is 285 which is more than the 240FLC of motor?I am just curious I know if wire is underground then it is not rated at 90deg but 75deg.I was wondering why you can not derate this like a service when wire ampacity is same no matter what.
Thanks
roc1
Thanks
roc1