Problem: I have a 12/2 NM-B wire I'd like to use to power an inverter Ductless unit with a nameplate MCA of 22.1, and a MOCP of 25.
240.4(D)(5) states that 12 gauge copper be limited to 20 amps, unless specifically permitted by 240.4(G). That takes us to Article 440 Part III and VI
Table 310.15 Does show that 12 gauge copper at 75 degrees is fine for 25amps.
334.80 insists that type NM must be rated on the 60 degree column, though we can use the 90 degree column for derating. That would limit us to 20 amps.
Within 440 is where I start to get confused, and was looking for help clarifying.
Does 440 even matter if 334.80 states 60 degree rating no matter what?
Adding all F.L.A of all motors in the system together, I get a total F.L.A draw of 15.95 amps.
I've seen a few posts mention that 12/2 NM-B can be used on 25amp circuits for A/C here on this forum, but I want to confirm.
Seems like most of 440 is based on sizing for inductive loads on start up, which we just don't have on these Inverter based ductless systems. I couldn't get this thing to draw close to F.L.A on the coldest day of the year at maximum capacity, because while the compressor motor claims to be able to run at 12 amps F.L.A this unit applies its own overcurrent protection around 9 amps, and throttles back.
240.4(D)(5) states that 12 gauge copper be limited to 20 amps, unless specifically permitted by 240.4(G). That takes us to Article 440 Part III and VI
Table 310.15 Does show that 12 gauge copper at 75 degrees is fine for 25amps.
334.80 insists that type NM must be rated on the 60 degree column, though we can use the 90 degree column for derating. That would limit us to 20 amps.
Within 440 is where I start to get confused, and was looking for help clarifying.
Does 440 even matter if 334.80 states 60 degree rating no matter what?
Adding all F.L.A of all motors in the system together, I get a total F.L.A draw of 15.95 amps.
I've seen a few posts mention that 12/2 NM-B can be used on 25amp circuits for A/C here on this forum, but I want to confirm.
Seems like most of 440 is based on sizing for inductive loads on start up, which we just don't have on these Inverter based ductless systems. I couldn't get this thing to draw close to F.L.A on the coldest day of the year at maximum capacity, because while the compressor motor claims to be able to run at 12 amps F.L.A this unit applies its own overcurrent protection around 9 amps, and throttles back.
