wire sizing

[hienlam]

here is a senerio,
i got an existing spare breaker(100A). i want to use this spare breaker and connect to a new unit equipment(x), which has a load of 70A. i connect this unit with a disconnect switch(100/70) 3poles. i want safe the cost of the wire...
is nec code allow me to size the wire base on 70A fuse???

 

[charlie b]

Re: wire sizing

Yes, unless this load will be running for more than 3 hours at a time. That would make the load ?continuous,? and you would have to size the conductors and the overcurrent protection device for 25% above the load. 125% of a 70 amp load is 87.5 amps, and that would bring you back to a 100 conductor and a 100 amp breaker.

 

[david]

Re: wire sizing

Hienlam

Are you saying you want to start with a 100-amp breaker and feed with a 70-amp conductor to a 100 amp fusible disconnect with 70 amp fuses?

 

[don_resqcapt19]

Re: wire sizing

240.4 will require that you use 100 amp wire on the 100 amp breaker unless you can meet one of the tap rules in 240.21 or unless this is special application circuit such as a motor feeder.
Don

 

[hienlam]

Re: wire sizing

thanks for all the comments....you guys really heldful...again thanks

Davis...yes, that is what i meant...