Sizing ocpd

[Naterfrechette]

Hello I’m have a little confusion on selections an ocpd for a 100 amp continuous load. I know the code for 125% and it comes out to 125 amps. My wire size for 75 degrees would have to be a number 1 copper which is 130 amps. So my question is it a 125 amp breaker or size the breaker to wire at 130 and use a 150 amp per 240.B.? Any help would be great

 

[Jraef]

Hello I’m have a little confusion on selections an ocpd for a 100 amp continuous load. I know the code for 125% and it comes out to 125 amps. My wire size for 75 degrees would have to be a number 1 copper which is 130 amps. So my question is it a 125 amp breaker or size the breaker to wire at 130 and use a 150 amp per 240.B.? Any help would be great

Size the conductor to the load, size the OCPD to the conductor. If the conductor is rated for only 130A, a 150A breaker is too large.

 

[pv_n00b]

Hello I’m have a little confusion on selections an ocpd for a 100 amp continuous load. I know the code for 125% and it comes out to 125 amps. My wire size for 75 degrees would have to be a number 1 copper which is 130 amps. So my question is it a 125 amp breaker or size the breaker to wire at 130 and use a 150 amp per 240.B.? Any help would be great

Size the conductor to the 100A continuous load with deratings for conditions of use, terminal temp, etc. Then choose an OCPD to protect that conductor.

NEC 240.4(B) allows the use of the next larger OCPD listed in Table 240.6(A) as long as specified conditions are met. So if you have a conductor that is rated for 125A you use a 125A OCPD. If your conductor is rated for 130A you can use a 150A OCPD if you meet the requirements in 240.4(B).

 

[JFletcher]

What is the nature of your continuous load? Lighting, heating, motor, Etc?

Also, what is your ambient temperature? And will you have more than three current carrying conductors in a raceway supplying this load?

 

[kwired]

Size the conductor to the load, size the OCPD to the conductor. If the conductor is rated for only 130A, a 150A breaker is too large.

Well if all of the 130 ampacity of the conductor is needed it can still be protected by a 150 amp device, but if 131 ampacity is needed then you need a larger conductor.