Dwelling Unit Continuous Loads

[iggy2]

A feeder serves a dwelling unit, say an apartment.
215.3 requires a feeder to be sized with 125% of continuous load, and 100% of non-continuous load.
Lighting is, arguably, a continuous load.

Why do none of the dwelling unit examples in annex D account for the 125% continuous load?
Is continuous vs. non-continuous irrelevant for dwelling units?
Why? Code reference?

Thanks.

 

[augie47]

Although the Code requires certain loads such as storage water heaters, to be considered continuous loads, service calculations do not have the same requirements.
Few, if any, residential loads are considered to be continuous for service calculations.
When you think of it, what residential loads run for more than 3 hours at full capacity (as compared to commercial lighting)

 

[iggy2]

Although the Code requires certain loads such as storage water heaters, to be considered continuous loads,

Storage water heaters are only continuous as far as branch circuit load calcs.

When you think of it, what residential loads run for more than 3 hours at full capacity

I think dwelling unit lighting could be on for 3 hours - perhaps not 100% of the dwelling unit lighting, but certainly some or most of it. Or a TV (receptacle load) could easliy be on for 3 hours +. But I'm not seeing any accounting for these in the examples.

Can you identify a code reference to overcome 215.3? I can't....

 

[augie47]

I can't think of a specific Code reference....During discussions, most often the references I see simply note example D-3. It might be a good project for someone wanting to submit a "change".
It's an area that seems to be more of a "common-sense" issue. As I referenced and you elaborated upon, certain items such as storage water heaters require branch circuits to be continuous but rely on our everyday knowledge to understand that, from a service standpoint, they don;t actually operate a fll load for 3 hours or more.
On such items as the TV, I think D-3 somewhat addresses that in noting that they used the larger or the actual loads vs the Table 220.12 loads to determine the lighting load.
In a residential situation, any continuous load, such as a TV or a specific light, is less than the 3 VA per sq ft already allowed.

 

[Dennis Alwon]

I think dwelling unit lighting could be on for 3 hours - perhaps not 100% of the dwelling unit lighting, but certainly some or most of it. Or a TV (receptacle load) could easliy be on for 3 hours +. But I'm not seeing any accounting for these in the examples.

Can you identify a code reference to overcome 215.3? I can't....

There may be some lights in a residence that may be continuous but generally not the entire branch circuit. I think this is more of a design issue. Generally most contractors do not load a lighting circuit at 100% anyway. Where they may be a few lights that are continuous certainly the entire feeder or service is not continuous at the max. load for them.

A TV does not draw much so unless the circuit is loaded to 100% or so I don't see an issue.

Frankly I want to contest the water heater as being continuous. I would bet that it would be a rare , if not impossible, situation where the water heater is on for 3 hours.

 

[jumper]

Frankly I want to contest the water heater as being continuous. I would bet that it would be a rare , if not impossible, situation where the water heater is on for 3 hours.

Yeah, I always wondered about that one also, but it is an old rule-it is in my 1978-so it is unlikely that it would get changed.

 

[charlie b]

Regarding dwelling unit lighting load, I see the "3 VA per square foot" as having already taken into account the possibility of the circuit being on for more than 3 hours. If the CMP wanted us to add 25% to account for it being a continuous load, they would have assigned the value of 3.75 VA/SF, instead of 3.00.

Regarding the water heater, I can only guess that some of the older style equipment might take more than three hours to heat up the entire tank from a completely cold condition (e.g., after a series of showers by teen agers).