fixed electric heat

[Matt Mckenzie]

Is a feeder conductor size for fixed electric heat calculated any different than a branch circuit is calculated for fixed electric heat? Branch circuit sizing for fixed electric heat is calculated at 125%. Is it also a 125% for a feeder to fixed electric heat or is it 100%?

 

[ActionDave]

Going off of memory here....the feeders are sized at 100%.

 

[kwired]

2014 215.2(A)(1):

(1) General.


Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. Conductors shall be sized to carry not less than the larger of 215.2(A)(1)(a) or (b).


(a)Where a feeder supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum feeder conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.


(b)The minimum feeder conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.

Not sure what has all changed from 2011, quite a bit of text was highlighted as changed though, but that doesn't necessarily mean the general intentions of the rules changed just that something changed - could just have been editorial changes to help clarify something.

When calculating (a) if you have a 10 amp continuous load it is to be treated as 12.5 amps for the purpose of calculating minimum conductor ampacity. Where demand factors are used in art 220 - I don't think you add 25% to any continuous load - but then you don't really have a demand factor that applies to anything that is continuous in nature either - which includes electric space heating.