Central Heating

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jca0108

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Im trying to figure out how to size wire to an air handler. The heat draws more of course, so i size it to the heat. In Table 210.2, it refers me to 422.12. Are there any other provisions to take into account, 125%of load for wire size, etc.? And am I in the right article?
 
jca0108 said:
Im trying to figure out how to size wire to an air handler. The heat draws more of course, so i size it to the heat. In Table 210.2, it refers me to 422.12. Are there any other provisions to take into account, 125%of load for wire size, etc.? And am I in the right article?
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Check out article 424
 
Most air handlers with electric heat are marked with MCA, minimum circuit ampacity, and MOCP, maximum overcurrent protection. The ratings will vary with what size heat strips, 5kw to 15kw for resi, you install and include the fan blower motor. 422.12 applies and yes it is a continuous load.
 
jca0108 said:
so the air handler is considered fixed space heating equip? whats the difference between central heating and fixed heating?
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I think of fixed heating as baseboards as well as all the different heating systems as well as central heating. Central heating , of course, would be a main unit supply the structure thru ducts etc and is a subcategory of fixed heating. This is just my interpretation
 
jumper said:
Most air handlers with electric heat are marked with MCA, minimum circuit ampacity, and MOCP, maximum overcurrent protection. The ratings will vary with what size heat strips, 5kw to 15kw for resi, you install and include the fan blower motor. 422.12 applies and yes it is a continuous load.
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just out of curiosity, what if the unit didnt have mopd marked. what would i use 125%, 150%, 175%, 225% ?
 
jca0108 said:
just out of curiosity, what if the unit didnt have mopd marked. what would i use 125%, 150%, 175%, 225% ?
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I read what Dennis wrote and I think he is right. 424 is where to go. All units that I have seen are marked, see 424.28.

If you had a unit that was not marked, I guess you would size the motor using 430 and then figure out the amps for the heat, then size the total load as continuous and use 125%. I have never had to do this for an air handler, so I am not sure.
 
jumper said:
I read what Dennis wrote and I think he is right. 424 is where to go. All units that I have seen are marked, see 424.28.

If you had a unit that was not marked, I guess you would size the motor using 430 and then figure out the amps for the heat, then size the total load as continuous and use 125%. I have never had to do this for an air handler, so I am not sure.
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i read 424.28 , and your math is right(break it down by section and solve). As far as the opd, 424.28 doesnt address it ,but i would i would just size it for the load to be served
 
I agree with Dennis. Central heat/air is a marketing name for one unit with duckwork as opposed to base board heat and window A/C/heat.
 
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