Fixed electric space heating - feeder calc's

[winslowfam]

Hi...we have always performed our load calculations for services and/or feeders with the assumption that area heating loads are continuous and, therefore, included in the calculations at 125% of rated load. We just read in 2005 NEC 220.51 that service/feeder calculations can include fixed electric space heating at 100% of rated load. NEC 215.2(A)(1) says to include continuous loads at 125% for feeder calculations. Which is it? Are heating loads continuous, as we have always thought?

 

[Dennis Alwon]

The difference is that art. 220 is for calculating the load while 215 is calculating the feeder ampacity.

 

[gndrod]

Fixed space heater load calc

Fixed space heater load calc

Hi...we have always performed our load calculations for services and/or feeders with the assumption that area heating loads are continuous and, therefore, included in the calculations at 125% of rated load. We just read in 2005 NEC 220.51 that service/feeder calculations can include fixed electric space heating at 100% of rated load. NEC 215.2(A)(1) says to include continuous loads at 125% for feeder calculations. Which is it? Are heating loads continuous, as we have always thought?

I believe the calculations are for nameplate ratings and not part of the conductor sizing requirement.

 

[gndrod]

The difference is that art. 220 is for calculating the load while 215 is calculating the feeder ampacity.

Hi Dennis,
You type faster than I do. I agree.

 

[winslowfam]

Hi...I think I am missing something about the difference between calculating load and calculating feeder ampacity when I see the load as being fed from the feeder. I don't doubt your answers, just need to get it myslef. I will read more about it and get back to this forum again if it remains unclear. Thanks for your comments.

 

[gndrod]

Hi...I think I am missing something about the difference between calculating load and calculating feeder ampacity when I see the load as being fed from the feeder. I don't doubt your answers, just need to get it myslef. I will read more about it and get back to this forum again if it remains unclear. Thanks for your comments.

Here is a for-instance in optional calculations of fixed space heating;
[220.82(C)(1)...(6)] All six selections state "nameplate ratings" in the heating requirement calculations. The 125% continuous requirement for [215] is not referenced or included.

 

[Dennis Alwon]

Think of it this way-- when you calculate the load for a service the load is going to be -- just that-- the load. A 10kw strip heat is 10 kw not 10kw plus 25%. However for the branch circuit conductor size it is req. to add 25% to keep the conductors from running at maximum temperatures.