RTU sizing.

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Chamuit

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
Am I right?

I have an RTU which has a nameplate MCA 17A and Max OCP of 30A.
I can use 12-2 NMB and an 30A breaker.

240.4.G and 440.6.A

This is an old install. I was wanting to just change the breaker since the wire has already been run.
 
RTU = roof top unit?

Would it be considered a continuous load, in which case the circuit ampacity would have to be 125% of the nameplate (21.25 amps)?
 
Chamuit said:
Am I right?

I have an RTU which has a nameplate MCA 17A and Max OCP of 30A.
I can use 12-2 NMB and an 30A breaker.

240.4.G and 440.6.A

This is an old install. I was wanting to just change the breaker since the wire has already been run.
Click to expand...

You have it right, you could actually use 14/2 NM if you wanted too. (That is until your area adopts the 2011 NEC;):))

Chris
 
sd4524 said:
I'm still on 05. What changes in 2011 that will not allow us to use 14 awg?
Click to expand...

Table 310.16 (Re-numbered in the 2011 to 310.15(B)(16)) has dropped the allowable ampacity of #14 copper at 60 degrees C to 15 amps from 20 amps.

Chris
 
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