45 Amp Air Handler ?

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davedottcom

davedottcom

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Is #8 on a 45 Amp Breaker acceptable for an Air Handler that has a 7.68 KW Heat Strip (32 Amps @ 240V)

The Unit (Trane1408) lists the following specs:

240 V
7.68 KW
Heater Amps: 32
Minimum Circuit Ampacity: 43
Maximum Over current: 45
(Motor specs are not listed)

According to 2002 NEC: 424.3 (B)......conductors....shall not be less then 125 percent of the total load of the motors and the heaters

Since #8 is listed for 45 Amps @ (75o)
The 45 Amp Breaker is listed for (75o)
Wirenuts used to terminate #8 are rated @ (105o)
Is #8 ok?

I wasn't aware the Air Handler had a higher KW rating than the ones they usually install in this model home until now! I plan on replacing the 30' of 8/2 with 6/2 but I was trying to determine if it was actually necessary or not.

Anyone?
 
Re: 45 Amp Air Handler ?

My experience with these is that the maximum overcurrent protection device rating already has the 125% factored into it.

Also, I read 310.16 as stating that a #8 at 75 degrees is worth 50 amps, not 45.
 
Re: 45 Amp Air Handler ?

Ryan, you're right, #8 is rated for 50 Amps @75o.
Thanks, I'm not sure why I said 45!?
I agree with you that the Manufacturer's listing for the Max Breaker size already takes the 125% into consideration but my question is in the size of the branch circuit conductor.
Is #8/2 NM allowed to be on a 45 Amp breaker in this situation?

Thanks, Dave
 
Re: 45 Amp Air Handler ?

1999 336-26 Ampacity
2002 334.80 Ampacity
Steve, you're right, thanks. 40 Amps it is!
6/2 to the rescue!
Thanks again,
Dave
 
Re: 45 Amp Air Handler ?

Ryan_618

It's my impression that NM is ALWAYS figured from the 60C column regardless of the application. The only exception is that the 90C column can be used for de-rating as long as the final derated amperage does not exceed that for 60C rated conductors. (336-26.) If you're using NM-B, NMC-B or NMS-B the conductors are rated for 90C (336-30(b)), but you MUST still use the 60C column for the ampacity.
steve
 
Re: 45 Amp Air Handler ?

Davedottcom:

I've got to start referring 2002 code numbers. It's just that I'm old and lazy and more familiar with the 99 model. I need to get the 2002 on CD for quick searches.
steve
 
Re: 45 Amp Air Handler ?

Hillbilly, yes that is my impression as well. I didn't see that he was using NM cable, so I went right to 310.16. I skimmed over the fact that this is for a model home, and therefore NM cable was the probable wiring method. Thanks.
 
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