Pulled 10's where 12's were sufficient?

[ritelec]

Yet another AC question.

Unit minimum amps 23.

Using nm cable.

Is the rating taken from the 90 degree because of thhn or 60 degree because it's nm ?

Thank you

 

[infinity]

60° so #10 is required for NM cable. Use MC or conduit and wire and you're good with #12 which is 25 amps @75° C.

 

[ritelec]

Ok

Thank you

 

[domnic]

NM

NM

I thought # 12 NM was rated for 25 amps, why cant I use it for 23 amps . for a/c unite .

 

[curt swartz]

I thought # 12 NM was rated for 25 amps, why cant I use it for 23 amps . for a/c unite .

Where are you getting 25 amps from? Look at the 60C column for #12.

 

[Smart $]

.... Use MC or conduit and wire and you're good with #12 which is 25 amps @75° C.

Maximum 20A OCPD, though.
240.4(D)(5)

However, wiring for an A/C unit falls under Article 440.
240.3

 

[domnic]

nm

nm

NM #12 is rated for 20 amps , looked at wrong table .

 

[Carultch]

Yet another AC question.

Unit minimum amps 23.

Using nm cable.

Is the rating taken from the 90 degree because of thhn or 60 degree because it's nm ?

Thank you

NM cable ("romex") is a special case where the 60C column of the NEC limits the ampacity prior to bundling and ambient calculations, no matter what the temperature ratings of the equipment terminations and wire/cable may be. This is specific to NM cable per 334.80.

 

[dionysius]

60° so #10 is required for NM cable. Use MC or conduit and wire and you're good with #12 which is 25 amps @75° C.

So is this correct??? #12 wire in conduit is good for 25A @ 75 degC???

 

[ActionDave]

So is this correct??? #12 wire in conduit is good for 25A @ 75 degC???

In the context of this discussion, yes. 240.4(D) allows the small conductor rule to be ignored for motors and air conditioners.

 

[MD84]

So is this correct??? #12 wire in conduit is good for 25A @ 75 degC???

Yes that is true. However number 12 wire is limited to a 20A OCPD (excluding motor circuits see 430.52, or welders see 630.12, or A/C see 440.22, etc etc see 240.4(G)). The 25 amps is useful for derating purposes. In that case it is good to 30A at 90C. The 25/30A is good for not more than 3 current carrying conductors in the raceway. Above that and you must start derating. Also you must derate for ambient temperatures above 30C (see 310.15)

 

[dionysius]

Yes that is true. However number 12 wire is limited to a 20A OCPD (excluding motor circuits see 430.52, or welders see 630.12, or A/C see 440.22, etc etc see 240.4(G)). The 25 amps is useful for derating purposes. In that case it is good to 30A at 90C. The 25/30A is good for not more than 3 current carrying conductors in the raceway. Above that and you must start derating. Also you must derate for ambient temperatures above 30C (see 310.15)

Is the neutral in a MWBC in metallic conduit with 4 wires (3 phases A,B,C and a neutral) considered a CCC???? It should not be IMHO!!!!! What is the max allowed in this case. Can I use 8 as opposed to 6 650 kVA/277VAC fixtures per cct????

 

[iwire]

Is the neutral in a MWBC in metallic conduit with 4 wires (3 phases A,B,C and a neutral) considered a CCC????

That depends if the majority of the load is non-linear or not.

If the majority of the load is non-linear than the NEC requires we treat the neutral as a CCC due to harmonic currents on the neutral.