Continuous load in Dwelling?

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mweaver

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Greetings from Kansas,

For many years I have always heard and believed that the NEC does not consider any loads in a dwelling to be continuous loads.

I have searched this forum and the 2002 NEC to back this up but am unable to actually find anything that specifically states or even clarifies that loads in a dwelling are not considered continuous.

My original substantiation for this may have come from Example D1(a) on page 667 of the 2002 NEC which makes no additional calculation for lighting in a dwelling which would certainlay most generally be continuous. If the lighting is not considered continuous why would a pool pump or a whole house fan or anything else be considered continuous in a dwelling?

I appreciate any thoughts or comments you may have regarding continuous loads in a dwelling.

thanks

mweaver
 
Re: Continuous load in Dwelling?

The Code doesn't say that dwelling unit loads are non-continuous. You are required to make that determination and apply the proper rules for continuous and non-continuous loads. Generally, dwelling unit loads are indeed non-continuous but some loads are continuous and should be accounted for during the load calculations. :D
 
Re: Continuous load in Dwelling?

I think that if you use the ?3 watts per square foot? for general lighting (and some receptacles), then any consideration of the lights being continuous is built into the ?3 watts? number. You don?t have to add a 25% factor to the ?3 watts.?
 
Re: Continuous load in Dwelling?

I agree with Charlie. The calculations for lighting, for example at the service, don't require a consideration of continuous vs noncontinuous. The sizing of an individual branch circuit in a house should include thoughts about continuous vs noncontinuous. An evaporative cooler, for example is usually on for 3 hours or more. Individual lights in my home are on for 3 hours or more.

Jim T
 
Re: Continuous load in Dwelling?

I should have been more clear in my question (sorry). I was only referring to service and feeder calculations of Article 220 as they would apply to a dwelling.

I agree the NEC does not specifically say one way or the other what is or is not a continuous load in a dwelling for service and feeder calculations. The NEC examples do not apply continuous load for a dwelling but it does for commercial (go figure!).

I can find no examples in Mike Holt's, Tom Henry's or James Stallcup's books that depict any continuous load in a dwelling service or feeder calculation. They all use 100% not 125%. They all add 125% for commercial continuous loads.

This is what brought about my original question.

mweaver
 
Re: Continuous load in Dwelling?

I think it is probably for some of the same reasons that Table 310.15(B)(6) was develpoed as to why you never see dwellings calculated with continuous loads.

The demand on the service is simply not there for typical single family and even multi-family homes. Considering that a typical electric service to a single family home is commonly 200A, that would permit nealry a 50,000VA demand load. I think most homes fall well below this and adding 25% to 2-3 lighting circuits would make little difference.

Now in commercial buildings where you may have a few dozed lighting circuits, I can see the need for the added demand allowance.
 
Re: Continuous load in Dwelling?

heating circuits in winter (elec heat, furnace motors)

cooling circuits in summer

car heating outlets in Minnesota

freezer circuits in Tuscon

pump circuit for a 5 bedroom house (water heater as well)

some are always in use

paul
 
Re: Continuous load in Dwelling?

Originally posted by apauling:
heating circuits in winter (elec heat, furnace motors)

cooling circuits in summer

car heating outlets in Minnesota

freezer circuits in Tuscon

pump circuit for a 5 bedroom house (water heater as well)

some are always in use

paul
Click to expand...
Paul I do not see that any of those are continuous loads.

All that separates a continuous load from a non continuous load is the opening of the circuit at least once within 3 hours.

If your heating or cooling truly runs continuously the units are not sized correctly to begin with.

I live in the Northeast I would be very upset (and poor :)
 
Re: Continuous load in Dwelling?

without looking it up, I thought a load was considered continuous if opped for three hours, not if it took a break every 2:59. And that didn't mean for residential that it was 125% unless a motor load, just that it was in addition to the sq. ft calcs at 100%.

but i may be wrong

paul
 
Re: Continuous load in Dwelling?

I believe Mr. Badger is correct when he states that the loads Paul listed are not continuous.

Thermostatically controlled loads (which certainly can operate for three hours or more) are not continuous by their design.

I have two loads at my house that most generally operate for three hours or more. They are the lighting and my pool pump.

The lighting is specifically exampled as non-continuous in a dwelling by Example D1(A) on page 667 of the 2002 NEC. While these examples are not adopted code they are definitely representative of how the NEC intends for those calculations to be made.

If the lighting is obviously continuous in a non-dwelling but is non-continuous in a dwelling why would my pool pump (or any other load) be continuous in a dwelling?

mweaver
 
Re: Continuous load in Dwelling?

Don't the application of table 220.12 coupled with the application of table 220.42 ensure that, while lighting may be continous in a dwelling unit, from a service perspective that these loads are covered? What if a poll of average houses in a testing area showed 2.5 VA/sq.ft of lighting load on average, and this was increased to 3 VA in table 220.12 to accomodate continous lighting?

Also, I haven't seen an example where recessed cans are included in an example for a load calc of a house. Are we required to add recessed cans on a load calc for a dwelling unit? Cans are more and more popular, and are frequently used for general lighting in a house. Just wanted to see some thoughts on this.
 
Re: Continuous load in Dwelling?

Further compounding the can issue: It disappeared in NEC 2005???

Now all I find is 220.14(D), Luminaires, which seems just as stinking ambiguous as 2002 was on the subject... :(

220.14(J) states general use receptacles, outside garage and unfinished outlets, and the lighting outlets required in 210.70 are covered under general lighting. This seems to override (D).

Thoughts?
 
Re: Continuous load in Dwelling?

Mr. Stolz,

As far as recessed cans are concerned they are considered within the 3va per sq ft for a residential calculation.

What the code says is that the lighting load calculation is the greater value of either the known fixture schedule or the va per square foot listed in Table 220.3(A).

I am unable to Find the two tables you listed.


mweaver

[ December 14, 2004, 08:51 AM: Message edited by: mweaver ]
 
Re: Continuous load in Dwelling?

Originally posted by mweaver: I am unable to Find the two tables you listed.
Click to expand...
George was referring to tables in the 2005 version.
Originally posted by georgestolz: 220.14(J) states general use receptacles, outside garage and unfinished outlets, and the lighting outlets required in 210.70 are covered under general lighting. This seems to override (D). Thoughts?
Click to expand...
I don?t think it overrides (D). Certain locations have to have a wall-switched outlet. Those we can lump in with the general lighting loads. But if we install additional lighting outlets, then we could them individually, and use the rating of the luminaire. For most residential applications, I don?t think 220.14(D) will come into play. But a few examples in which I would count the luminaire separately might be outdoor security lights, track lights used for decorative purposes (e.g., pointed at works of art), and special work lights for a auto repair shop built into a garage. But I?ll admit this is wide open to interpretation.

[ December 14, 2004, 11:02 AM: Message edited by: charlie b ]
 
Re: Continuous load in Dwelling?

Mr. Stolz? Good Lord, man! I gotta change my account name! :)

But I?ll admit this is wide open to interpretation.
Click to expand...
That stinks. You'd think three years would bring about more clarity--although I do believe the 2005 is a step up--they define dwelling unit loads better.
 
Re: Continuous load in Dwelling?

Mr. Stolz, (or would you prefer George?)


The problem for me (at my age) is that the code runs all together. I say things without knowing EXACTALY where (or when) I got them from! ??.

The passage I was referring to is actually noted in the example for commercial store calculations. While not part of the code it's presence is intended to clarify NEC intent.


quote:
________________________________________
What the code says is that the lighting load calculation is the greater value of either the known fixture schedule or the va per square foot listed in Table 220.3(A).
________________________________________


meant to say .....

Example D3 Store Building 2002 NEC pg 669:
? ?.. *In the example, 125% of the actual connected lighting load (8500 VA ? 1.25 = 10,625 VA) is less than 125% of the load from Table
220.3(A), so the minimum lighting load from Table 220.3(A) is used in the calculation. Had the actual lighting load been greater than the value computed from Table 220.3(A), 125% of the actual connected lighting
load would have been used. ???


While my own personal interpretation (obvious problems here!); it seems only logical the first part of this statement from example D3 should apply to any calculation that could involve a comparison between actual connected load and Table 220.3(A). For me the NEC?s intent is clear here. The greater value should be used for any lighting calculation that would involve Table 220.3(A).


mweaver

[ December 15, 2004, 05:56 PM: Message edited by: mweaver ]
 
Re: Continuous load in Dwelling?

I buy the reasoning. I don't have the book in front of me, but doesn't the example reference a code? Seems like they usually do. (Then again, I haven't gotten past the first page of the examples. Seeing other people's math doesn't stick in my head! :) )

And yes, George is good.

[ December 15, 2004, 07:02 PM: Message edited by: georgestolz ]
 
Re: Continuous load in Dwelling?

While certain light fixtures will burn for three hours or more in a dwelling, all of the lights should not be on at the same time. In a commercial building the lights are either all on or all off. There are circuits dedicated to supplying lighting loads, so these circuits will see a continuous load. While the reading lamp next to my easy chair may stay on for three hours or more on a winter evening, the other loads on this circuit will be periodic or perhaps non existent. Therefore the entire lighting load will not be "continuous".
 
Re: Continuous load in Dwelling?

Well put. I agree.

In summary, the "general lighting loads" do not need the 125% factor, but special lighting circuits that are not included in Table 220.3()A) do need the 125% factor.
 
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