Noncontinuous lighting loads

[taes7t@yahoo.com]

Where in the NEC are lighting loads for dwellings and motel rooms defined as noncontinuous?
Thank you.

 

[jcole]

Electrical apparatus get a continuous load rating when it is on for 3 hours or more under normal operating conditions. I dont think code directly states lighting to be continuous or noncontinuos. So basically, you, ahj, and engineers need to determine if the lighting load meets the definition of continuous.

 

[Dennis Alwon]

Where in the NEC are lighting loads for dwellings and motel rooms defined as noncontinuous?
Thank you.

It is not defined in the NEC. The NEC give a definition of continuous loads. Generally speaking the dwelling units are not considered continuous but you and I know that flood lights and kitch lights can be on for more than 3 hours. I would recommend not filling those circuits to capacity.

 

[iwire]

It is not defined in the NEC. The NEC give a definition of continuous loads. Generally speaking the dwelling units are not considered continuous

I agree

but you and I know that flood lights and kitch lights can be on for more than 3 hours.

Unless that flood light is the only load on the circuit it would not be a continuous load if left on 24/7.

The definition of continuous load includes maximum.

"A load where the maximum current is expected to continue 3 hours or more."

IMO if the flood light is on a circuit with other outlets that will not be on for the same 3 hours we do not have a continuous load.

I also want to mention that it says 'expected' not 'it might happen'

I would recommend not filling those circuits to capacity.

How do I know when a GP branch circuit is full? :grin:

 

[Jim Shorts]

Look at table 220.42. It allows you to de-rate the lighting in the motel rooms and dwelling units when calculating service or feeder loads. If they were considered continuous loads you would not be able to do this.

 

[Dennis Alwon]

IMO if the flood light is on a circuit with other outlets that will not be on for the same 3 hours we do not have a continuous load.
How do I know when a GP branch circuit is full? :grin:

Well if you wire a branch circuit as I do it will usually have all lighting on it. I would then figure the maximum wattage allowed by each fixture. This will give me the max. load.

I agree if the load is a mixed load then the continuous load does not come into play.

 

[iwire]

Well if you wire a branch circuit as I do it will usually have all lighting on it. I would then figure the maximum wattage allowed by each fixture. This will give me the max. load.

I agree, but everyone of those fixtures would have to be expected to be on for more then 3 hours at the same time.:smile:

 

[Dennis Alwon]

I agree, but everyone of those fixtures would have to be expected to be on for more then 3 hours at the same time.:smile:

Correct.

I say this because I ran into this issue at a very expensive estate that some other EC wired. All the kitchen cans, dining room and floods were on the same circuit. Thus when the ho entertained she had all the lights on. The chandelier itself, I believe had about 600 watts. I had her reduce the wattage on the chandelier and the floods since she did not want to run a new circuit.

 

[Smart $]

Correct.

I say this because I ran into this issue at a very expensive estate that some other EC wired. All the kitchen cans, dining room and floods were on the same circuit. Thus when the ho entertained she had all the lights on. The chandelier itself, I believe had about 600 watts. I had her reduce the wattage on the chandelier and the floods since she did not want to run a new circuit.

This is a fine line, but all the same, I'm going to have to disagree with the correctness :grin:

A continuous load is a continuous load regardless of whether other loads on the circuit are non-continuous. When you "load up" a circuit, you are permitted up to 80% for continuous loads on the circuit, and 100% for the non-continuous. If they are mixed, continuous load still adds up at 125% and non-continuous at 100%, and doing so [accurately] would prevent overloading the circuit.

When the code defines continuous load as "A load where the maximum current is expected to continue 3 hours or more", it is referring to the load's current, not the circuit's maximum permitted current.

Aside from that, we can debate on exactly what is meant by "expected" 'til we're blue with frustration and without resolution :roll: ...but I do feel at times we should take into consideration what may happen.

 

[charlie b]

. . . I'm going to have to disagree with the correctness.

And if you don't mind, I am going to disagree right back.

Riddle me this: If we are allowed to lump general lighting loads (e.g., 3 VA/Ft2) with certain receptacle loads (e.g., 1500 VA laundry circuit), and then we are allowed to reduce the total by applying demand factors after the first 3000 VA, then how exactly are we to insert a 125% factor for the lighting? Indeed, if we needed to add some VA to account for lights being continuous, then why do they let us deduct anything from the total VA (i.e., the total you get by multiplying 3 VA/Ft2 times the square feet)? Why don't they tell us to multiply 3 times the square feet, and then multiply by 125% at that point?

 

[iwire]

When the code defines continuous load as "A load where the maximum current is expected to continue 3 hours or more", it is referring to the load's current, not the circuit's maximum permitted current.

So by your account if I have a circuit with 10 'loads', 9 of which only run 30 seconds at a time but the 10th load is a 24/7 - 5 watt night light the entire circuit must now be treated as a continuous load?

I think that is a stretch. :smile:

 

[iwire]

It seems that for my example of 9 non-continuous loads and a 10th continuous load we would count the first 9 at 100% and the 10th at 125% so it is not the entire circuit that is a continuous load.

What Charlie brings up is definitely a wrench in the works and why I asked Dennis how do we know when a GP branch circuit is 'full'?

 

[Smart $]

It seems that for my example of 9 non-continuous loads and a 10th continuous load we would count the first 9 at 100% and the 10th at 125% so it is not the entire circuit that is a continuous load.

Exactly what I was attempting to point out :grin:

What Charlie brings up is definitely a wrench in the works and why I asked Dennis how do we know when a GP branch circuit is 'full'?

I agree with the former part of your comment, and cannot give a concise answer on the latter regarding the design stage... in the usage stage I believe the answer is rather obvious. However, I do believe one can make an experience-coupled-with-calculated guess for lighting-only circuits...

 

[Smart $]

And if you don't mind, I am going to disagree right back.

Riddle me this: If we are allowed to lump general lighting loads (e.g., 3 VA/Ft2) with certain receptacle loads (e.g., 1500 VA laundry circuit), and then we are allowed to reduce the total by applying demand factors after the first 3000 VA, then how exactly are we to insert a 125% factor for the lighting? Indeed, if we needed to add some VA to account for lights being continuous, then why do they let us deduct anything from the total VA (i.e., the total you get by multiplying 3 VA/Ft2 times the square feet)? Why don't they tell us to multiply 3 times the square feet, and then multiply by 125% at that point?

Nah!! I don't mind... but I do believe you are taking the issue way beyond the context of my post :smile:

 

[charlie b]

... but I do believe you are taking the issue way beyond the context of my post :smile:

Not my intent. Sorry. I was bringing us back to the original question. In a dwelling unit, we start accounting for lighting by taking 3 va per square foot. Then we get to make the number smaller. My intended message to the OP is that we don't treat that as a continuous load. My reply to your post was a way of backing up my claim that such loads are not to be multiplied by 125%.

 

[Jim W in Tampa]

You need apply thinking in residential. I would never have lights only on a circuit. Doing so will cause a problem sometimes. Think in terms of all lights on. My method was 1800 watts could cover 2 bedrooms and perhaps a hall. Never had a problem. Putting a full load on cans and fixed lighting is just stupid. With added cost today of afci i can only imagine what is out there. Be sure to thank them boys that caused all this. It's your name on display ,legal is not every thing but to get job you might need get cheap. NEC is about safe not GOOD.

 

[Smart $]

...such loads are not to be multiplied by 125%.

Correct when calculating feeder and service load, but when considering the number of and loading of required branch circuits we must multiply by 125% for bona fide continuous lighting loads (perhaps even borderline continuous in some cases). This falls under the general requirement for all branch circuits. Consideration as such should in no way be construed to change any Article 220 calculation.

 

[charlie b]

So you are implying there is no relationship between 210 and 220, eh? Never the twain shall meet, eh? The one is about picking a large enough service or feeder size, and the other is about installing branch circuits, eh? I have been pushing that agenda for a while now.

 

[Smart $]

So you are implying there is no relationship between 210 and 220, eh? Never the twain shall meet, eh? The one is about picking a large enough service or feeder size, and the other is about installing branch circuits, eh? I have been pushing that agenda for a while now.

I'm not saying there is no connection... 220 calculations provide the value of minimum required available current on service and feeder conductors serving an area. When dividing that value up into the minimum amount of branch circuits needed to distribute the required available current per 210, we need to consider loads as continuous and non-continuous regardless of the value transposed from 220.

For example, say we have 10 lighting loads drawing 1 amp each on one circuit. By our reckoning, 5 of the loads are likely to be "continuously" operated. So we have 5 ? 1A ? 125% + 5 ? 1A (? 100%) = 6.5A + 5A = 11.25A of circuit loading. If this is a 15A circuit, we will have made available 15A ? [11.25A ? (10 ? 1A)] = 13.75A of the Article 220 value with this circuit. What this amounts to is any time we consider a load as continuous and multiply by 125% to determine circuit loading, the extra 25% is not counted towards the current that must be made available if it was not considered a continuous load in Article 220 calculations.

210.11 Branch Circuits Required. Branch circuits for
lighting and for appliances, including motor-operated appliances,
shall be provided to supply the loads calculated in
accordance with 220.10. In addition, branch circuits shall
be provided for specific loads not covered by 220.10 where
required elsewhere in this Code and for dwelling unit loads
as specified in 210.11(C).

(A) Number of Branch Circuits. The minimum number
of branch circuits shall be determined from the total calculated
load and the size or rating of the circuits used. In all
installations, the number of circuits shall be sufficient to
supply the load served. In no case shall the load on any
circuit exceed the maximum specified by 220.18.

(B) Load Evenly Proportioned Among Branch Circuits.
Where the load is calculated on the basis of voltamperes/
square meter or volt-amperes/square foot, the wiring
system up to and including the branch-circuit panelboard(s)
shall be provided to serve not less than the calculated
load. This load shall be evenly proportioned among
multioutlet branch circuits within the panelboard(s).
Branch-circuit overcurrent devices and circuits shall be required
to be installed only to serve the connected load.

(C) ***Omitted for brevity


???????????????????????????????????
210.19 Conductors? Minimum Ampacity and Size.

(A) Branch Circuits Not More Than 600 Volts.

(1) General. Branch-circuit conductors shall have an ampacity
not less than the maximum load to be served. Where
a branch circuit supplies continuous loads or any combination
of continuous and noncontinuous loads, the minimum
branch-circuit 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.

***Remainder omitted for brevity


???????????????????????????????????
220.18 Maximum Loads. The total load shall not exceed
the rating of the branch circuit, and it shall not exceed the
maximum loads specified in 220.18(A) through (C) under
the conditions specified therein.

(A) Motor-Operated and Combination Loads. Where a
circuit supplies only motor-operated loads, Article 430 shall
apply. Where a circuit supplies only air-conditioning equipment,
refrigerating equipment, or both, Article 440 shall
apply. For circuits supplying loads consisting of motoroperated
utilization equipment that is fastened in place and
has a motor larger than 1⁄8 hp in combination with other
loads, the total calculated load shall be based on 125 percent
of the largest motor load plus the sum of the other
loads.

(B) Inductive Lighting Loads. For circuits supplying
lighting units that have ballasts, transformers, or autotransformers,
the calculated load shall be based on the total ampere ratings
of such units and not on the total watts of the lamps.

(C) Range Loads. It shall be permissible to apply demand
factors for range loads in accordance with Table 220.55,
including Note 4.

 

[erickench]

Although the code does'nt say so lighting inside a dwelling is treated as non-continuous when performing the calculation. Using NEC table 220.12 the receptacle and lighting loads are calculated together from the area square-footages. Because you cannot separate the lighting from the receptacle loads the value obtained is treated like noncontinuous load in that the 125% factor does not apply as evidenced by the sample problems in the back of the NEC. In all other occupancies like a restaurant or a factory lighting is expected to operate far longer than the minimum three hour limit. Therefore the receptacle load is calculated separately in such occupancies.