Fixed Heat Calc

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ivsenroute

ivsenroute

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Florida
I am involved in a project for a commercial building that wants to add BB heat in the offices and common areas.

Without using a design, engineer, they spec'd out adding a 120/240 20 circuit, 100A single phase sub panel from an existing 3ph 120/240 225A panel then adding heat from there.

The total calculated load is going to be 95.8A for the 23,000w of 92 lin.ft. of baseboard that they plan on adding.

This is too close for comfort but it is the way they are having everyone bid on it.

Although the conductors and overcurrent protection can't be any less than 125% of the load served for the branch circuit. The feeder only has to be 100%.

Anything that I am overlooking to be able to point out a problem with their specs?
 
ivsenroute said:
I am thinking that 215.3 will apply and if we talk them into using a 3ph sub panel, this will eliminat the problem.
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Given the fact that it will be unlikely that all the units will be on at the same time for 3 hours or more I would tend to think that 100% is all that is needed. I know I will hear grief about this but art. 220.51 tells us some interesting info at least for calculation purposes. Since you are calculating the loaf for a feeder for fixed electric heat I think this article applies.
 
220.51 is what my problem is. I read it multiple times but then I looked back at 215.2 & 215.3.

Deciding which one takes priority is my problem since they don't jive.

I can agree with the fact that you don't think they will all be on at the same time but fixed heating equipment is considered continuous.
 
Not a popular thread but we have it figured out.

220.51 is there to let you know that you must use 100% of the electric heat when doing the calculation unless you meet the exception of course.

215.3 says it all so in this case, they will not be able to feed a 96A load from a 100A panel.

Panel, feeders and OCPD must be upsized to 125A.
 
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