electric heat calculations

[elecmen]

Hi, How do you calculate the load on the service feeder for electric heat? Thanks for any info

 

[Dennis Alwon]

art. 220.51 is for fixed electric space heating

 

[elecmen]

Thanks Dennis. Next dumb question. If you have to wire 2 baseboard heaters from the same wall thermostat will 2 12/2 romex fit in the heaters junction box?

 

[LarryFine]

Thanks Dennis. Next dumb question.

I'm not Dennis, but we don't allow dumb questions. Luckily, we also don't recognize them.

If you have to wire 2 baseboard heaters from the same wall thermostat will 2 12/2 romex fit in the heaters junction box?

Every one I've seen had plenty of room for more than one cable in the wiring compartment.

 

[elecmen]

Thanks Larry, Thats what I thought.

 

[jbelectric777]

lmfao !!!! I think what he means is baseboard calcs: No matter what type of inductive heating load you must multiply by 1.25 and remember to omit from the service or feeder calculation the smaller of the Air conditioning and heat. Example AC air handler with compressor 7.2kw with heat at: 20kw drop the 7.2 all together and take 20k X 1.25 = 25kw

If your sizing branch circuits for baseboard you can use 15, 20, or even 30 amp branch circuits so for a branch circuit with 5 - 1250watt units it's 5X1250 = 6250 plus 125% = 7812 / 240 = 32 amps serve with 2 20 amp 240v branch circuits, if your load came just under 30 after your multiplier like 29.3 amps, you could use (1) 30 amp 240v branch circuit. Jim

Note: Using #10 in the stats boxes sucks and takes up a lot more cubic volume and would in some cases cause box over fill.......

 

[brother]

lmfao !!!! I think what he means is baseboard calcs: No matter what type of inductive heating load you must multiply by 1.25 and remember to omit from the service or feeder calculation the smaller of the Air conditioning and heat. Example AC air handler with compressor 7.2kw with heat at: 20kw drop the 7.2 all together and take 20k X 1.25 = 25kw

If your sizing branch circuits for baseboard you can use 15, 20, or even 30 amp branch circuits so for a branch circuit with 5 - 1250watt units it's 5X1250 = 6250 plus 125% = 7812 / 240 = 32 amps serve with 2 20 amp 240v branch circuits, if your load came just under 30 after your multiplier like 29.3 amps, you could use (1) 30 amp 240v branch circuit. Jim

Note: Using #10 in the stats boxes sucks and takes up a lot more cubic volume and would in some cases cause box over fill.......

Oh my here we go again, this thread sounds like I heard it before LOL. Remember that when sizing branch circuits NEC 2008 424.3(B) you have to size 125% of the rated load. When sizing for feeders or services NEC 2008 220.51 it is allowed/can be sized at a 100% of the rated load, however in no case shall the feeder or service load be less than the largest branch circuit supplied.
check out this link

http://www.ecmag.com/?fa=article&articleID=7781

 

[tomwible]

So for load calculations, electric heat is taken at 100% and for circuit sizing it is taken at 125%????

-Tom

 

[Dennis Alwon]

So for load calculations, electric heat is taken at 100% and for circuit sizing it is taken at 125%????

-Tom

That is correct.