General Lighting NEC Demand Factor

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erinkeeney

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In nearly every explanation of Table 220.42, I see people indicating that general lighting that does not fall under dwelling units, hospitals, hotels/motels, or warehouses should have a 125% demand factor applied for continuous loads. I never see the same 125% factor applied to the first 3000VA of dwelling units or the first 12,500VA of warehouses, despite these having the same 100% demand factor within Table 220.42 as the last line of "All Others". Why is it that the continuous loads factor is applied in this seemingly inconsistent way?

Who is to say that a specific other load will certainly be on for more than 3 hours or that a listed load will not? In addition, the continuous load definition is that of a load where the maximum current is expected to continue for 3 hours or more. In an age where the prevalence of easily dimmable LED lighting has made it so that lighting will usually be dimmed and therefore not pulling the maximum current, can we even assume that lighting falls into the continuous load definition anymore?

I'm a new PE trying to wrap my brain around what seems like a disconnect to me in how we as an industry apply this demand factor. Thanks in advance for your help.
 
What lighting load are you talking about to start with? The actual connected load, or the watts per square foot given in table 220.12?

If you are talking about 220.12, I never add an extra 25% to those numbers, although I think others might. I've just never seen where that is required. Now that I think about it, Table 220.42 that you mention seems to indicate that I'm right, and 100% is the largest demand factor I ever need to add to loads from table 220.12.

if you are talking about actual connected load, I do usually add 25%, although it doesn't usually matter, because the numbers from table 220.12 are always larger, and we are supposed to use the larger of the two for feeder and service calculations. So I don't really worry too much if the extra 25% is actually required.

And you do have a good point about dimmable fixtures - less likely they will all be on at 100%, but it is still possible. But again, it just seems the watts per square foot numbers always dominate the calculations.
 
erinkeeney said:
In nearly every explanation of Table 220.42, I see people indicating that general lighting that does not fall under dwelling units, hospitals, hotels/motels, or warehouses should have a 125% demand factor applied for continuous loads. I never see the same 125% factor applied to the first 3000VA of dwelling units or the first 12,500VA of warehouses, despite these having the same 100% demand factor within Table 220.42 as the last line of "All Others". Why is it that the continuous loads factor is applied in this seemingly inconsistent way?

Who is to say that a specific other load will certainly be on for more than 3 hours or that a listed load will not? In addition, the continuous load definition is that of a load where the maximum current is expected to continue for 3 hours or more. In an age where the prevalence of easily dimmable LED lighting has made it so that lighting will usually be dimmed and therefore not pulling the maximum current, can we even assume that lighting falls into the continuous load definition anymore?

I'm a new PE trying to wrap my brain around what seems like a disconnect to me in how we as an industry apply this demand factor. Thanks in advance for your help.
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My opinion: The code states that a continuous load is load where the maximum current is expected to stay on for 3 hours or more. I feel it is our responsibility to err on the side of caution with this. So, if you have a warehouse with constant occupancy and sensors that turn on and off large areas then I would have to consider that continuous, if each aisle is controlled or each light then I would consider it not continuous.
 
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