I am confused by the next size up rule (240.4(B)). Lets say I have 6 current carrying conductors (THWN-2 - 90 deg C wire) in a raceway and my cont. currents are 38 A. The wiring is all indoors so no temp. adjustments are needed.
1) Cont. currents x 1.25 = 47.5 A so I would select a 50 A breaker - This would require a #8
2) Cont. currents / 0.8 (for more than three conductors in raceway) = 47.5 A - This also requires a min #8
So by 690.8 (B) both items 1 & 2 require a #8 minimum
Also, checking my 75 deg C terminals #8 is rated at 50 A so my 50 A breaker still protects my terminals
So everything should be ok to use #8 THWN-2/THHN according to 690.8(B)(2)
Ok here is where I am confused. If I multiply #8 at 55 A (90 deg C rating) by 0.8 (6 conductors in raceway) this comes out as 44 A. This is greater than my continuous currents as allowed by 690.8(B)(2) and this should be ok. But wouldn't 240.4 say that the maximum breaker size I can use to protect this wire at these conditions of use is the next size up 45 A breaker? What am I missing here?
Am I ok to use a 50 A breaker?
1) Cont. currents x 1.25 = 47.5 A so I would select a 50 A breaker - This would require a #8
2) Cont. currents / 0.8 (for more than three conductors in raceway) = 47.5 A - This also requires a min #8
So by 690.8 (B) both items 1 & 2 require a #8 minimum
Also, checking my 75 deg C terminals #8 is rated at 50 A so my 50 A breaker still protects my terminals
So everything should be ok to use #8 THWN-2/THHN according to 690.8(B)(2)
Ok here is where I am confused. If I multiply #8 at 55 A (90 deg C rating) by 0.8 (6 conductors in raceway) this comes out as 44 A. This is greater than my continuous currents as allowed by 690.8(B)(2) and this should be ok. But wouldn't 240.4 say that the maximum breaker size I can use to protect this wire at these conditions of use is the next size up 45 A breaker? What am I missing here?
Am I ok to use a 50 A breaker?