General Lighting Circuits

[m.pague]

Had a question from an instructor on Continuous Duty. I disagreed when discussing residential/dwelling. I know how the NEC reads, but here is the question. Instructor didn’t like my answer. Help me to understand. Thanks in advance.

 

[infinity]

IMO it's a poorly written question but as a general rule lighting circuits should be considered continuous. Regarding a dwelling is it often that a circuit is used only for lighting?

 

[m.pague]

Thank you. I did ask what about a branch circuit only used for receptacles? If I plug in an alarm clock, use a night light, or computer plugged in but not used, do I need that branch circuit to be considered CDL? Answer was no, then I asked should all the general lighting in my home with all proper conductors be on 20 amp breakers? Answer was also “No.”


Thanks.

 

[HEYDOG]

Had a question from an instructor on Continuous Duty. I disagreed when discussing residential/dwelling. I know how the NEC reads, but here is the question. Instructor didn’t like my answer. Help me to understand. Thanks in advance.

Continuous duty has more to do with motor loads. Continuous load is “A load where the maximum current is expected to continue for three hours or more“. As far as continuous lighting load goes commercial buildings, in a lot of areas in a hospital, schools, industrial buildings are good examples of occupancies where the lighting load would be considered continuous. Lighting loads in residential are not considered a continuous load . The lighting load in residential is not Comparable to buildings where the entire lighting load could even be on 24/7.

 

[m.pague]

Continuous duty has more to do with motor loads. Continuous load is “A load where the maximum current is expected to continue for three hours or more“. As far as continuous lighting load goes commercial buildings, in a lot of areas in a hospital, schools, industrial buildings are good examples of occupancies where the lighting load would be considered continuous. Lighting loads in residential are not considered a continuous load . The lighting load in residential is not Comparable to buildings where the entire lighting load could even be on 24/7.

My understanding in 2020 NEC. Waiting on my 2023 NEC. I asked the instructor if he considered general lighting branch circuit in a dwelling/residential a CDL, what type of branch circuits are now not considered CDL? Been in school 8 months at this point.

 

[Rock86]

NEC Definition " Continuous Load - A load where the maximum current is expected to continue for 3 hours or more." So a clock is a continuous load because it will hopefully be plugged in for 24 hours, a refrigerator is not because your refrigerator is not actually running all day even though it is plugged in. Lighting could easily be kept on for 3 hours if you live in a home with poor natural lighting, or have exterior lighting that is on at night or you just like to leave lights on. Those were things I was taught when I was in ECM school. Does that help?

 

[Rock86]

sorry for the similar repy

 

[HEYDOG]

My understanding in 2020 NEC. Waiting on my 2023 NEC. I asked the instructor if he considered general lighting branch circuit in a dwelling/residential a CDL, what type of branch circuits are now not considered CDL? Been in school 8 months at this point.

In a dwelling unit general purpose receptacles that are not for any specific appliance for instance they may be used for table light, alarm clock, television, etc. are not considered continuous loads. There is a lot of calculations for dwelling units that are different from other occupancies. Article 100 is a very important article to get a grasp on terms and definitions used through out the NEC. You do not need to memorize them….but you do need to be familiar with them and use them when applying the code. First off when the instructor is teaching you about the NEC he or she should be able to tell you where in the Code book it is that he is teaching you that something is required! If he says that the lighting load in Residential is considered a Continuous Load……where in the code does it tell you that.? Again look under definitions in article 100 Continuous Load versus Duty, Continuous. Articles 210 and 220 give you a lot of information!

 

[infinity]

If we go back to the original question:

[22] All lighting circuits must be considered as continuous use.
True
False

The answer is false simply because it uses the word all.

 

[m.pague]

In a dwelling unit general purpose receptacles that are not for any specific appliance for instance they may be used for table light, alarm clock, television, etc. are not considered continuous loads. There is a lot of calculations for dwelling units that are different from other occupancies. Article 100 is a very important article to get a grasp on terms and definitions used through out the NEC. You do not need to memorize them….but you do need to be familiar with them and use them when applying the code. First off when the instructor is teaching you about the NEC he or she should be able to tell you where in the Code book it is that he is teaching you that something is required! If he says that the lighting load in Residential is considered a Continuous Load……where in the code does it tell you that.? Again look under definitions in article 100 Continuous Load versus Duty, Continuous. Articles 210 and 220 give you a lot of information!

Gone over 100, 210, 220 and have understood. i said the question was false, since it said ALL.

 

[m.pague]

If we go back to the original question:



The answer is false simply because it uses the word all.

My exact thoughts.

 

[m.pague]

In a dwelling unit general purpose receptacles that are not for any specific appliance for instance they may be used for table light, alarm clock, television, etc. are not considered continuous loads. There is a lot of calculations for dwelling units that are different from other occupancies. Article 100 is a very important article to get a grasp on terms and definitions used through out the NEC. You do not need to memorize them….but you do need to be familiar with them and use them when applying the code. First off when the instructor is teaching you about the NEC he or she should be able to tell you where in the Code book it is that he is teaching you that something is required! If he says that the lighting load in Residential is considered a Continuous Load……where in the code does it tell you that.? Again look under definitions in article 100 Continuous Load versus Duty, Continuous. Articles 210 and 220 give you a lot of information!

Thank you. Very familiar with NEC, just looking for an article to say ALL.

 

[m.pague]

NEC Definition " Continuous Load - A load where the maximum current is expected to continue for 3 hours or more." So a clock is a continuous load because it will hopefully be plugged in for 24 hours, a refrigerator is not because your refrigerator is not actually running all day even though it is plugged in. Lighting could easily be kept on for 3 hours if you live in a home with poor natural lighting, or have exterior lighting that is on at night or you just like to leave lights on. Those were things I was taught when I was in ECM school. Does that help?

Yes thank you. The part that is misleading in definition is “where maximum current is expected to….” If I leave a LED bulb on in a bedroom ceiling fan (light only), that’s at let’s say 2.5 watts for more than than 3 is that maximum current? Just my thoughts.

 

[HEYDOG]

Yes thank you. The part that is misleading in definition is “where maximum current is expected to….” If I leave a LED bulb on in a bedroom ceiling fan (light only), that’s at let’s say 2.5 watts for more than than 3 is that maximum current? Just my thoughts.

No! I will give you an example of a continuous load in a school! If here is a 20 amp circuit feeding a bank of lights in a school hallway and they burn 12 hours per day and the total load is 16 amps this meets the definition of a continuous load. Because this is a continuous load I can only load the 20 amp circuit to 80%. 20 * .8 = 16 amps. 1.25 *16 = 20 amp overcurrent device. I am not sure how much you have gotten in to calculations in your class. The best way to get good with calculations is to get a book that covers examples for both Dwelling units and other types of occupancies.They will show you the steps to go through and what code articles apply! Mike has several good books. Also there are several example in Annex “D” in the back of the NEC!

 

[infinity]

If there is a 20 amp circuit feeding a bank of lights in a school hallway and they burn 12 hours per day and the total load is 16 amps this meets the definition of a continuous load.

I agree, but just for clarity the 16 amps in your example has nothing to do with it being a continuous load. The load could be 6 amps and it would still be a continuous load if that was the maximum load on the circuit and it continued at the maximum current level for 3 or more continuous hours.

 

[Bill_F]

Good discussion, thanks.
But I've always not fully grasped the intent of the wording "maximum load".

 

[infinity]

Good discussion, thanks.
But I've always not fully grasped the intent of the wording "maximum load".

If the lighting circuit had 10 fixtures connected to it but only 9 fixtures were on at one time for more than 3 hours that would not be considered a continuous load. The max load would be when all connected fixtures were on at one time.

 

[Bill_F]

Thanks very much. Sometimes interpretations are difficult. I realize the notes are very helpful.

 

[HEYDOG]

I agree, but just for clarity the 16 amps in your example has nothing to do with it being a continuous load. The load could be 6 amps and it would still be a continuous load if that was the maximum load on the circuit and it continued at the maximum current level for 3 or more continuous hours.

You are correct! I kind of threw that in to also show that on a continuous lighting load that you can not load the overcurrent device to more than 80%.

 

[infinity]

You are correct! I kind of threw that in to also show that on a continuous lighting load that you can not load the overcurrent device to more than 80%.

Yes, your example was exactly why the total load would be limited to 16 amps.