De-rating conductors

[jbolen]

I have 25 #10 XHHN in 1 1/4 EMT conduit. What is new rating of these wires

 

[infinity]

That depends, you need to know how many are considered current carrying conductors for derating purposes. Worst case scenario 40 amps*50%= 20 amps. Did you mean THHN?

 

[tank728]

That depends, you need to know how many are considered current carrying conductors for derating purposes. Worst case scenario 40 amps*50%= 20 amps. Did you mean THHN?

10-20 CCC is derated with a factor of 50%. I believe the 21-30 CCC is 45%. Based on assumption of thhn or and 90 degree conductor insulation I get a worst case scenario of 40 amps*45%=18 amps.

 

[jbolen]

18 amps

18 amps

If the derating is to 18 amps can I use 20 amp BKR for this #10 THHN

 

[infinity]

10-20 CCC is derated with a factor of 50%. I believe the 21-30 CCC is 45%. Based on assumption of thhn or and 90 degree conductor insulation I get a worst case scenario of 40 amps*45%=18 amps.

You're correct the percentage should have been 45%. :slaphead:

If the loads are not multi-receptacles then you could use the next size up rule to a 20 amp OCPD. I should have the worst case scenario is 15 amp circuits.

 

[kwired]

If the derating is to 18 amps can I use 20 amp BKR for this #10 THHN

If the loads are not multi-receptacles then you could use the next size up rule to a 20 amp OCPD.

And the connected load is no more than 18 amps.