80% AMP LOAD LIMIT ON WIRE SIZE

[howardrichman]

I'll be wiring a non continuous load @26 amp 208-230V shop lift. Is #10 gu. copper good for only 24 amps @80% and have to run #8CU on a 30 amp breaker? Under 310-16 chart the 35 amp rating for #10gu is only for derate for conduit fill, and still doesn't meet the minumum amp rating needed.

Please reply;
Thanks, HR...

 

[tkb]

First, the derating is for ampacity and not conduit fill unless more than three wires.
Second, assuming the wire is THHN you can use the 90°c column for derating.
Third, since the load is noncontinuous you do not need to derate.

#10 THHN would be suitable for this load on a 30a circuit breaker.

 

[97catintenn]

You size the wire to actual load. #10 can carry 35amp continous 100% of the time. It's the breaker that would have to be 125% of the current and that's only if you have a continous current on that circuit. (at least I think that's where you are getting 80% from)

210.20(A)

 

[electrofelon]

You size the wire to actual load. #10 can carry 35amp continous 100% of the time. It's the breaker that would have to be 125% of the current and that's only if you have a continous current on that circuit. (at least I think that's where you are getting 80% from)

210.20(A)

Note that the wire is specifically required to be sized at 125% for continuous loads. Specifically, this is for branch circuits, feeders, and service entrance conductors. See 210.19(A)(1), 210.20(A), 215.2(A)(1), 215.3, 230.42. Also note the "small conductor" requirements in 240.4(B), which limit #10 to 30 amps in many situations.

 

[97catintenn]

Note that the wire is specifically required to be sized at 125% for continuous loads. Specifically, this is for branch circuits, feeders, and service entrance conductors. See 210.19(A)(1), 210.20(A), 215.2(A)(1), 215.3, 230.42. Also note the "small conductor" requirements in 240.4(B), which limit #10 to 30 amps in many situations.

Thank you. You are correct. I would edit my post above if I knew how.

 

[howardrichman]

Thanks for reply.
I'll have to check that code. I usually will run a 16 amp max load on a 20 amp breaker,(80%) rule esp. on A/C equipment.
I could be wrong, but safe, esp. if there's an inspection.
I've got an A/C unit to wire next week, and the minimum load is 16.7 amps. Usually I'de run a 10 GU on a 20 amp breaker
HR...

 

[infinity]

A/C units should provide the minimum circuit ampacity (MCA) and the maximum overcurrent protection device (MOCPD) on the nameplate, use the MCA to size the conductors and the MOCPD to size the circuit breaker or fuses. The conductors are not required to be the same size or larger than the MOCPD.