4000 watt wall heater on #12 Nm 20 amp circuit

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Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
What do you think about a electric wall heater 4000 watts fed from a dedicated 12 guage 20 amp circuit?
Nec says continuous and I calculate 16.67 amps X 1.25% +20.84 amps can ypu still use a 20 amp circuit. I am seeing this quite often done. However does it comply if you replace with a new and different heater?

Thanks
 
Looks like no can do, your fractions are more than 0.5


220.5 Calculations.

(B) Fractions of an Ampere. Calculations shall be permitted
to be rounded to the nearest whole ampere, with decimal
fractions smaller than 0.5 dropped.
Click to expand...
 
No relief from the small breaker rule for this app.

424.22 Overcurrent Protection.
(A) Branch-Circuit Devices. Electric space-heating equipment,
other than such motor-operated equipment as required
by Articles 430 and 440 to have additional overcurrent protection,
shall be permitted to be protected against overcurrent
where supplied by one of the branch circuits in Article 210.
 
I think I'd see if I could swap the guts to a 3500w heater. If it's a Pick-a-watt or Cadet heater, you might get lucky.
 
GlennH said:
Maybe you have 245 volts? :)
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The reality of the situation is probably just that- 245V or 244 either of which would allow the 20 amp circuit. Problem is that 244-245V, even if measured, may not always be that high and cannot be used. That really stinks. The manufacturer should make the units work on 240V on a 20 amp cir.-- a 3840 watt heater...:D

I assume the voltage at the building is 240V.
 
Little Bill said:
:? 4000/240=16.67A, 4000/244=16.39, 4000/245=16.32
How is that drawing more current?:?
Click to expand...

Because your math is incorrect. The 4000 watts is at one specific voltage. If you change the voltage you would change the wattage. You need to first find the resistance at the heater's rated voltage and then use that in your calcuation along with the voltage to determine the current.
 
infinity said:
Because your math is incorrect. The 4000 watts is at one specific voltage. If you change the voltage you would change the wattage. You need to first find the resistance at the heater's rated voltage and then use that in your calcuation along with the voltage to determine the current.
Click to expand...

Nothing wrong with my math, I'm using a brand new "Dollar Store" calculator.:lol: All my divisions are correct. Mis-applied maybe, but correct.:slaphead:
 
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