Show windows - feeder calcs

[JDBrown]

I'm having a little difficulty figuring out how to apply 220.43(A). I'm designing for a small retail space with a 100 Amp, 208Y/120V panel. There's one show window, which is about 6-1/2' wide. The owner does not plan to put any load in the show window, other than a light fixture across the top, but I've provided a duplex receptacle at the top of the window per 210.62. Since there's no specific load associated with that receptacle, I've assigned the branch circuit 180VA. So far, so good.

Here's where the confusion sets in. When calculating the feeder, 220.43(A) says I have to use 200VA/ft, rather than 180VA/duplex. Okay, I understand that. Since my window is 6-1/2' wide, I calculate 7' x 200VA = 1400VA. Now, do I apply that 1400VA to Phase B, since that's the phase that's feeding my show window receptacle, or do I split the 1400VA evenly between the three phases? This is my first time dealing with a show window, and I want to make sure I get it right.

Normally, I add up each of the three phases separately and then size the feeder based on the largest of the three. In this case, however, since the 1400VA is more of an allowance, rather than an actual load, I'm unsure how it should be handled.

 

[JDBrown]

Bump. Really, no input?

 

[GoldDigger]

Normally, I add up each of the three phases separately and then size the feeder based on the largest of the three. In this case, however, since the 1400VA is more of an allowance, rather than an actual load, I'm unsure how it should be handled.

I would say that since it is used in the expected load calculation, you need to apply it to the phase that is actually feeding it. Hopefully this will not create enough imbalance to force you into a larger feeder size.

 

[RB1]

The feeder or service load is permitted to be distributed across the phases of the system.

 

[Volta]

Well, the feeder is to include the calculation of the show-window length per 220.40(A), and as such I suppose that it may well be compliant to split such across the available phases of the system. I think that would be a poor design, however, as the NEC expects 1400 watts to eventually be likely to be used, from a historical perspective.

But does Section 220.14(G) even allow us to use sub-section (I) to satisfy (G)(1)? I would be skeptical, as (G)(1) allows us to use "The unit load per outlet as required in other provisions of this section", not those permitted. I interpret that to mean appliances intended to be installed or used there (A), luminaires (D), or even a motor for some type of display (C). I cannot believe that 'loads required" in other parts of that section in meant to reduce the load capacity if it is as yet unknown.

I would expect that the show-window receptacle installed would be able to deliver 200 watts per foot of window without overloading "B" phase.