Continuous Demand Load

[Npstewart]

There are a couple cases in article 220 where they specify the load you are required to use for a given purpose such as for a signage circuit (1200 VA) and for show window receptacles (75 va/ft) etc. These loads by their nature obviously run continuously (greater then 3 hours). In my load calcs, I have always taken these loads at face value and never bothered taking them at 125% because I assumed that when they wrote the NEC it was understood that these loads would run continuously.

I received 2 rejections within 6 months requesting that I take these loads at 125%. I didn't bother arguing with the plan reviewer because it represented such a small load. My question is, if the NEC gives you a fixed VA, should you still apply the demand factor of 125%?

 

[Smart $]

There are a couple cases in article 220 where they specify the load you are required to use for a given purpose such as for a signage circuit (1200 VA) and for show window receptacles (75 va/ft) etc. These loads by their nature obviously run continuously (greater then 3 hours). In my load calcs, I have always taken these loads at face value and never bothered taking them at 125% because I assumed that when they wrote the NEC it was understood that these loads would run continuously.

I received 2 rejections within 6 months requesting that I take these loads at 125%. I didn't bother arguing with the plan reviewer because it represented such a small load. My question is, if the NEC gives you a fixed VA, should you still apply the demand factor of 125%?

First off, 125% factoring for continuous loads is not part of Article 220 load calculations. It is part of conductor and ocpd selection under under 210.19(A)(1) or 215.2(A)(1).

Note these sections state that "conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum ... conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load."

So if the loads are continuous, then yes they are required to be factored at 125% for conductor and ocpd selection.

 

[Npstewart]

So why wouldn't the NEC require you to use 1500 VA for a sign rather then 1200 VA? A building's signage circuit will always be continuous and wont vary between building to building. I understand what you're saying just not sure why the code is written as it is.

 

[GoldDigger]

So why wouldn't the NEC require you to use 1500 VA for a sign rather then 1200 VA? A building's signage circuit will always be continuous and wont vary between building to building. I understand what you're saying just not sure why the code is written as it is.

It is written as it is because the calculated load and the required ampacity are two different things and are discussed in two different sections of the code. The wire has to be able to carry 125%, but the service does not have to be sized to supply 125% of the calculated load.

 

[Npstewart]

So lets say you have just a single 200A panel feeding all the lights, receptacles, signage etc. and you provide a load calculation for the panel which is pretty typical on a project. Are you saying that you shouldn't apply a demand factor of 125% for the lighting etc? Only apply the 125% demand for the branch circuit?

Ie.
Panel "X" Panel Schedule
Lighting: ____va @ 125%
Signage circuit: 1200 VA @ 125 %= 1500 VA
Misc.: _____VA @ 100%
--------------------------------------------

Panel "X" load calculation

Lighting: 3 VA/ft^2 @ 100%
Signage: 1200 VA @ 100%
Misc.: _____VA @ 100%

 

[Smart $]

So why wouldn't the NEC require you to use 1500 VA for a sign rather then 1200 VA? A building's signage circuit will always be continuous and wont vary between building to building. I understand what you're saying just not sure why the code is written as it is.

Not sure what you mean here.
The 1200VA value is a minimum, just like the 75VA/ft for show windows. This value has to be included in the calculation whether there is an actual connected load or not. If the actual connected load is greater, you have to use the connected load value. If the connected load is less or non-existent, it is an allowance for future load addition without requiring upsizing of the service. As to why Code uses these particular values is a moot discussion.

 

[Smart $]

So lets say you have just a single 200A panel feeding all the lights, receptacles, signage etc. and you provide a load calculation for the panel which is pretty typical on a project. Are you saying that you shouldn't apply a demand factor of 125% for the lighting etc? Only apply the 125% demand for the branch circuit?

Ie.
Panel "X" Panel Schedule
Lighting: ____va @ 125%
Signage circuit: 1200 VA @ 125 %= 1500 VA
Misc.: _____VA @ 100%
--------------------------------------------

Panel "X" load calculation

Lighting: 3 VA/ft^2 @ 100%
Signage: 1200 VA @ 100%
Misc.: _____VA @ 100%

Application of 125% for continuous loads is not generalized. In some situations the same load can be noncontinuous. In a commercial environment, some lighting will likely be continuous, some not... but signage and show window loads are rarely noncontinuous.