a/c question

[normbac]

I am doing 120 apt. to condo conversions the existing a/c condensors are wired with #12 and a 30amp cb in each panel board. I get confused with some of these a/c applications. min. circuit amps is 18.5 max ocpd 30 but does that permit you to apply #12 to 30amp cb I do not understand how that would be permitted. Inspector isnt saying anything about it.
any advice would be helpful TIA

 

[Kessler4130]

Yes you must wire and protect according to the name plate.

 

[JJoyce]

Yes thats fine. You only have to size the wire to the minimum circuit ampacity. section 430. and twelve wire is good for 25 amps on a 60 or 75 terminal. And you only needed 18.5 amp rated wire.

 

[normbac]

Yes thats fine. You only have to size the wire to the minimum circuit ampacity. section 430. and twelve wire is good for 25 amps on a 60 or 75 terminal. And you only needed 18.5 amp rated wire.

It is hard for me to understand this I always rate the conductor to the cb 30a #10 how is it permitted for a #12 to be protected by a 30a tia

 

[jtester]

The idea that #12 is good for only 20 amps comes from the * in the first column of Table 310.16 which refers you to 240.4(D).

240.4(D) gives a general rule of 20 amps max and numerous exceptions including (G) which lists airconditioners and appliances.

Jim T

 

[normbac]

The idea that #12 is good for only 20 amps comes from the * in the first column of Table 310.16 which refers you to 240.4(D).

240.4(D) gives a general rule of 20 amps max and numerous exceptions including (G) which lists airconditioners and appliances.

Jim T

Got it! Thanks! still confusing though, I will do what the code says not what my limited brain tells me.

 

[benaround]

normbac,

You can only do this for motor loads. When a motor starts it will draw approx

six times the running amps,so,in your example that would be 108amps and

that 'might' trip a 20a breaker. The manafactures' nameplate info has been

tested and is mandatory to follow,so the 30a breaker should hold during the

start of the motor.

The main thing is that the motor has overload protection,usually built in, and

it is set fairly close to the running amps of the motor,thats why you can use

the #12 wire.

The circuit from the 30a breaker in the panel to the motor protection is for

short circuit protection, and that will kick a 30a just as fast as a 20a.

Hope this helps you see why everything is safe. There is nothing else on the

circuit to overload the #12.

 

[normbac]

normbac,

You can only do this for motor loads. When a motor starts it will draw approx

six times the running amps,so,in your example that would be 108amps and

that 'might' trip a 20a breaker. The manafactures' nameplate info has been

tested and is mandatory to follow,so the 30a breaker should hold during the

start of the motor.

The main thing is that the motor has overload protection,usually built in, and

it is set fairly close to the running amps of the motor,thats why you can use

the #12 wire.

The circuit from the 30a breaker in the panel to the motor protection is for

short circuit protection, and that will kick a 30a just as fast as a 20a.

Hope this helps you see why everything is safe. There is nothing else on the

circuit to overload the #12.

Now I get it thanks for the clear explanation!