Issue running a breaker at 90% of rating?

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Old 08-17-19, 09:12 AM
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Issue running a breaker at 90% of rating?

this is for a 240v air handler 10kW and a 3A motor. Works out to about 45 Amps. Wondering if a 50A breaker will hold reliably. TIA. Cable is nm awg 6.
 
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Old 08-17-19, 09:33 AM
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You just need to follow the circuit requirements on the data plate of the unit. The proper sizes are already calculated for the unit.
 
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Old 08-17-19, 02:47 PM
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Very doubtful it will hold. You are talking about a continuous resistive heating load. If it does hold it will be hot. #6 cable is rated for 55A maximum.

What is the size of the disconnect breaker inside the air handler ?
 
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Old 08-17-19, 03:16 PM
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There is a placard with a max overcurrent of 60 amp, no local disconnect. Although the load center is in site. No 55A breaker avail, but i think a 60 is therefore allowed. I have an extra 50, thus my question.
 
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Old 08-17-19, 03:23 PM
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Nearest size to the required so yes..... 60A is allowed.
 
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Old 08-19-19, 05:19 PM
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this is for a 240v air handler 10kW and a 3A motor.

Sounds like a basic 10 KW electric furnace. Manufacturers have recommended a 60 amp circuit on these practically forever and many manufacturers actually install a 60 amp breaker in the unit as a disconnect. Many years in the past, I wired many 10 KW, 15 KW, 20 KW, quite a few 25 KW and a couple 7.5 KW furnaces.
 
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Old 08-19-19, 05:50 PM
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I will use the 60A. One interesting note, the Leviton breakers are hydraulic/magnetic, not the common thermal/magnetic. They claim much more consistent trip levels.
 
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Old 08-19-19, 05:57 PM
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Hydraulic ? Curious to see how well that works out.
 
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