Store/Show Window Lighting Calculations

[erickench]

Just reading my "Stallcups Electrical Calculations Simplified" and I've come across two examples that I find a little puzzling. Here's the first:

A store with an area of 6000 sq-ft is to have 90 lighting outlets

The load calculation is performed like this:

6000 x 3 = 18,000 VA
18,000 x 125% = 22,500 VA

90 x 180 = 16,200 VA
16,200 x 125% = 20,250 VA

The load is 22,500 VA based on the larger calculation.

However, NEC 220.14(I) state's that receptacle outlets are calculated on the basis of 180 VA per yoke. I was under the impression that with the exception of residences all receptacle loads are calculated separately from the lighting loads. Why is the book applying NEC 220.14(I) to lighting outlets?

 

[Dennis Alwon]

What was the question? I don't know why the receptacles are figured at 125% nor do I know why you choose between the two.

 

[steve66]

I'm not exactly sure what your are asking either, but does the first sentence of 220.44 help any?
Steve

 

[david luchini]

I don't see anything in the question that mentions the word "receptacle."

It appears to me that second part of the example is related to 220.14(D) Luminaires, with each lighting "outlet" being figured at 180VA based on the fixture.

If the max VA of the fixture was 210VA, then the lighting load would be:
9x210=18900VA
18900VA x 125% = 23,625VA, which is larger than the 3VA/sf calculation.

The load from 220.12 constitutes the "minimum" lighting load. If the actually load (from 220.14(D)) is higher, it must be used.

 

[erickench]

Stallcups is assuming that the lighting outlets are rated at 180 VA each. I just want to know where he got this assumption from.

 

[Dennis Alwon]

Stallcups is assuming that the lighting outlets are rated at 180 VA each. I just want to know where he got this assumption from.

I agree unless you know what the wattage of the unit is you can only use the sq.ft.

One other thing is the heading says show window????? where is that calculation or info

 

[erickench]

Here's the second example. It's very similar:

80 feet of show window lighting or 71 medium-base lamps at 180 VA each.

The load calculation is performed like this:

80 x 200 = 16,000 VA
16,000 x 125% = 20,000 VA

71 x 80 = 12,780 VA
12,780 x 125% = 15,975 VA

The 20,000 VA calculation is used for it's greater than 15,975 VA

 

[steve66]

Stallcups is assuming that the lighting outlets are rated at 180 VA each. I just want to know where he got this assumption from.

Now I think I know what you are asking. I think it comes from 210.62 - one receptacle required every linear foot in show windows. I should of read a little slower the first time.

Steve

 

[david luchini]

Now I think I know what you are asking. I think it comes from 210.62 - one receptacle required every linear foot in show windows. I should of read a little slower the first time.

Steve

I think 210.62 says one receptacle for each 12Ft or major fraction thereof. That would be seven (7) receptacles. But the show window receptacle requirement and lighting requirement are separate issues.

 

[david luchini]

Here's the second example. It's very similar:

80 feet of show window lighting or 71 medium-base lamps at 180 VA each.

The load calculation is performed like this:

80 x 200 = 16,000 VA
16,000 x 125% = 20,000 VA

71 x 80 = 12,780 VA
12,780 x 125% = 15,975 VA

The 20,000 VA calculation is used for it's greater than 15,975 VA

The show window example is little more clear. 220.14(G) says the windows shall be computed at either 200VA/ft of window, OR the unit load per outlet as specified in other section of 220.14. Not knowing the actual VA of the luminaire, I think 220.14(L) Other Outlets would apply, which is 180VA per outlet.

However, I don't see anything in 220.14(G) that requires the larger of the two options to be taken.

I wonder if they are not also using 220.14(L) for the "lighting outlets" in the first example. But I think this would be incorrect, as 220.14 says it is for outlets "NOT used for general illumination." The example seems to be about general illumination.

 

[erickench]

I wonder if they are not also using 220.14(L) for the "lighting outlets" in the first example. But I think this would be incorrect, as 220.14 says it is for outlets "NOT used for general illumination." The example seems to be about general illumination.

Thanks Dave. That's what I was looking for. NEC 220.14(L).