Should We Figure Lighting As A Continuous Load In Commercial Load Calcs?

[Psychlo]

So I read through a post from '22 that is now closed which discussed this issue. And I question the conclusions drawn there. It seemed to be a consensus that continuous loads were not to be considered for a load calc - only for conductor and OCPD sizing. That sounds right at first....

But what about Table 220.12 [T220.42(A) in 2023]? We are specifically told in the table note that 125% was figured into the minimum lighting load values in the table, due to their continuous nature. It even refers to 210.20(A) as backup.

The STRONG implication is that any lighting load that is on for 3 or more hours at a time requires the extra 25% to be added for the calculation.

This would mean that show window lighting, track lighting, and sign & outline lighting, would require the extra 25% as well.

This could make a big difference on an license exam for someone.

I would appreciate your thoughts.

 

[roger]

See 220.14(G)

 

[tortuga]

what about Table 220.12 [T220.42(A) in 2023]? We are specifically told in the table note that 125% was figured into the minimum lighting load values in the table, due to their continuous nature. It even refers to 210.20(A) as backup.


I would appreciate your thoughts.

I wonder if anyone ever proposed removing the continuous factor from that table.
Seems odd to have it in there when there are situations that do not require the continuous factor.

 

[Psychlo]

See 220.14(G)

220.14(G) doesn't address the continuous load question. Show window lighting is usually continuous, but not always.

 

[Psychlo]

Annex D, Example D3 is anything but easy to follow. However, it indicates three things:
1) Continuous loads DO play a role in load calcs. Otherwise, they wouldn't bother to distinguish between cont. and noncont.
2) All lighting is considered to be continuous (at least in their example).
3) The extra 25% (for continuous loads) is not already included in the 200VA/ft (show window) or the 1200VA (outside sign) values.

So why is this extra 25% figured into the minimum lighting load, but not the other lighting loads? Why wouldn't we do the same for them? I would think we should. But Example D3 seems to throw a monkey wrench in the problem by not including the extra 25% in the calculated load calc (until later on for OCPD, which is rather confusing).

So is D3 incorrect? Or is the NEC insufficient in it's direction on this? Are they expecting us to know something without telling us?

Or is there something right under my nose that I'm just not seeing?

 

[Dennis Alwon]

I see 125% used for the feeder or service calc. They combine the showcase window with the outside sign circuit




Minimum Size Feeder (or Service) Overcurrent Protection




(see 215.3 or 230.90)

 

[Psychlo]

I see 125% used for the feeder or service calc. They combine the showcase window with the outside sign circuit

Agreed. But where in Article 220 do they get the directive to do that?

 

[tortuga]

Agreed. But where in Article 220 do they get the directive to do that?

The calculations are just a step on the way to an end objective such as sizing a service or feeder.
In the late 90's they moved the 'continuous load requirement' out of 220 to 215 and added the requirement for services.
If a test question is just simply asking you to calculate a load then that would be pretty unusual, unless its an engineering exam.
I would think a test electrician question would state something like "What is the minimum Size Service Overcurrent Protection for a store with xyz equipment"

 

[Psychlo]

The calculations are just a step on the way to an end objective such as sizing a service or feeder.

Agreed.

In the late 90's they moved the 'continuous load requirement' out of 220 to 215 and added the requirement for services.

What do you mean by "added the requirement for services"? That's exactly what I'm trying to locate. Where is that?

I personally believe the continuous load requirement should apply to feeder, service, and related OCPD calcs. But I think the CMP's intentions are very vague in 220. They make it clear that the minimum lighting load requires the extra 25% (due to being continuous), but they don't mention other lighting loads having the same requirement. My question is, why not?

 

[Psychlo]

I see 125% used for the feeder or service calc. They combine the showcase window with the outside sign circuit

View attachment 2572407

Here is exactly why I bring this up. Notice that they place the General Lighting, Show Window Lighting, and Outside Sign Circuit all under Continuous Loads. Yet, they include the extra 25% ONLY for the General Lighting. Why?

Minimum Size Feeder (or Service) Overcurrent Protection




(see 215.3 or 230.90)
View attachment 2572408

Yes, they seem to do this ONLY for the OCPD. It seems they are treating the Service different from the OCPD. What would be the purpose of that in a calc such as this?

 

[wwhitney]

What do you mean by "added the requirement for services"?

The word "continuous" as a modifier to loads appears in 210.19, 210.20, 215.2, 215.3 and 230.42.

Cheers, Wayne

 

[wwhitney]

They make it clear that the minimum lighting load requires the extra 25% (due to being continuous), but they don't mention other lighting loads having the same requirement. My question is, why not?

Arbitrary, no good reason.

Cheers, Wayne

 

[Psychlo]

The word "continuous" as a modifier to loads appears in 210.19, 210.20, 215.2, 215.3 and 230.42.

Cheers, Wayne

Right. It doesn't appear in 220, which is where one would expect to find it, if it applies to service load calcs.

 

[Psychlo]

Arbitrary, no good reason.

Cheers, Wayne

And therein lies the problem. When writing a code, nothing should be arbitrary. A lot of confusion surrounds this topic among veterans and newbies alike. Seems it wouldn't be too difficult to clarify it once and for all.

 

[tortuga]

Agreed.

What do you mean by "added the requirement for services"?

The original requirement for adding 125% of the continuous load as it was first proposed in the 1971 NEC was just for feeders and branch circuits. Which seems a little odd but apparently thats what the UL test data suggested.
I think it might have to do with service breakers and disconnects having more cooling that feeder breakers but I never have dug into the old studies, and nobody has studied the continuous factor in decades that I know of.
I do think there is real world experience to back up the requirement for branch circuits, less so for service conductors.
The NEC has gone back and forth a little on the adding 125% of continuous loads for service entrance conductors if I am not mistaken the continuous factor for service entrance conductors was not added till the 1987 NEC, then it was immediately removed in the 1990 NEC, then put back again in 1999 but some say by mistake.
Its still not required for a service lateral or overhead service conductors. (and the service panel itself)

 

[wwhitney]

Its still not required for a service lateral or overhead service conductors. (and the service panel itself)

How's that? If the service panel has a single main OCPD to disconnect all power, that OCPD is the 215.3 OCPD for the feeder supplying power to the entire load, so it requires a 125% continuous use factor unless it is 100% rated.

You might say that only applies when the OCPD supplies a single wire-type feeder, but I will say (a) there is no language in Article 215 exempting bus type feeders and (b) applying it to buses as well as wires gives a more consistent result. So applying it to the internal bus of a panelboard, switchboard, or switchgear is therefore more logical.

Cheers, Wayne

 

[tortuga]

So applying it to the internal bus of a panelboard, switchboard, or switchgear is therefore more logical.

408.30 covers the rating of the panelboard buss, there is no test data I have seen to support sizing them to 125% of a continuous load. Even a meter socket is has alredy factored in a continuous load.

 

[tortuga]

How's that?

Overhead service conductors are sized per 230.23, underground service laterals per 230.31 no continuous requirement in either code section there.

 

[wwhitney]

408.30 covers the rating of the panelboard buss, there is no test data I have seen to support sizing them to 125% of a continuous load.

If I have a 100A continuous load and a 100A non-continuous load, then the service OCPD needs to be 225A. That has the side effect that the busbars must be rated 225A.

Even a meter socket is has alredy factored in a continuous load.

Meter sockets are to be marked with a continuous rating. They may optionally be marked with a larger non-continuous rating, up to 125% of that continuous rating. But if not so marked the maximum load is the same, continuous or non-continuous.

Cheers, Wayne

 

[wwhitney]

Overhead service conductors are sized per 230.23, underground service laterals per 230.31 no continuous requirement in either code section there.

Correct. So in my previous example of 100A continuous and 100A non-continuous load, you could have 200A overhead service conductors (if the service point is aerial), supplying 225A SECs supplying a 225A service OCPD supplying 225A busbars.

Cheers, Wayne