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#100324 - 11/10/06 10:36 AM Space Heater calculations  
WhiteRook  Offline
Member
Joined: Feb 2004
Posts: 48
Republic of Texas
I am looking at a job installing 4 electrical space heaters with fan forced air(hung in the red iron) in a 16000 sq ft unfinished strip mall. The units are 7.5 Kw. The house panel is 208/120 3-phase with 150A main. The spec sheet lists the units as drawing 27A for 208 3-phase. When I was figuring the load, 7500 divided by 360, I get 20.83A...am I correct in figuring the difference in amperage is for the fan portion? I believe the code states that fixed electric space heaters (Art. 424.3(B)are to be considered continuous loads. So would I need 35A breakers for this? And if I put the branch circuit wiring for 2 of these heaters in one conduit the derating for the 7 wires at 70% would mean that I would have to run #6??? If I put all four in one conduit from the panel to a pull box inside then @13 wires I would have to run #4??? This doesn't even take in to account voltage drop. So what do ya'll think, am I right or am I confused.


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#100325 - 11/10/06 04:12 PM Re: Space Heater calculations  
gfretwell  Online Content


Member
Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
I get 6 wires (80%) and 12 (still 50%), you don't count the neutral where it only carries unbalanced current and you never count grounds for derating, only fill.


Greg Fretwell

#100326 - 11/10/06 07:14 PM Re: Space Heater calculations  
George Little  Offline
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Joined: Jan 2004
Posts: 1,489
Michigan USA
I don't think there is a neutral Greg. Maybe he's running an EGC. In either case I agree with your numbers.


George Little


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