Dwelling Calculations

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OscarO

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I am a bit confused about article 220, more specifically the dwelling portion of the article. When you do a dwelling calculation are you to include the basement even though it will not be finished. If the answer is yes does this mean it is safe to assume that all existing homes have been calculated this way. I would also like clarification on article 220.16(A)(1). Does this section of the article mean that when finishing a basement you don't have to recalculate the whole dwelling unit? Or do you recalculate the whole dwelling unit just to be safe.
 

Dennis Alwon

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Art. 220.14 states if the space is not adaptable for future use then the basement does not get calculated however if it can be finished and used as habitable space then it must be considered in the calculation.

If the basement was capable of being finished then it should have been calculated originally so no need to recalculate according to 220.16 except for loads other than the 3 watts/ sq.ft. For example heating loads, another kitchen, etc
 

Rewire

Senior Member
For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.

The key wording is adaptable for future use the idea being that you would be adding additional load when the area is finished.
 

Smart $

Esteemed Member
Location
Ohio
For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.

The key wording is adaptable for future use the idea being that you would be adding additional load when the area is finished.
When you get right down to it, there is no space which is not adaptable for future use. :p
 

GoldDigger

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For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces not adaptable for future use.

The key wording is adaptable for future use the idea being that you would be adding additional load when the area is finished.
And if the basement floor space is included in the floor area for the initial load calculation and you finish or remodel the basement, you will not need to recalculate any general load which is figured just from the square footage, but any specific loads which end up in the basement (that did not move there from another part of the house) can still force a recalculation.
 

Rewire

Senior Member
And if the basement floor space is included in the floor area for the initial load calculation and you finish or remodel the basement, you will not need to recalculate any general load which is figured just from the square footage, but any specific loads which end up in the basement (that did not move there from another part of the house) can still force a recalculation.



only added loads that would have need included in an initial calculation such as an additional range or added dryer etc..
 

OscarO

Member
Thank you everybody for the replies. I have another question about calculations. According to article 210.52 there are receptacle outlets in addition to the general lighting/receptacle loads. Included is a receptacle for the bathroom. In some calculation examples I have seen the small appliance receptacles from article 210.52(B)(1) added to the calculation but never the bathroom receptacle. Should the bathroom receptacle always be omitted or do we have to include it in the calculation?
 

kwired

Electron manager
Location
NE Nebraska
When you get right down to it, there is no space which is not adaptable for future use. :p

:happyyes::happyyes:

Garages get made into living space, porches get enclosed and made into living space, unfinished areas get finished off - even if at one time they never thought they would finish them in any way, attics even get made into living space sometimes, then of course there is the completely new additions. The lot next door gets purchased and the space (whether living space or not )grows into the orginal area....
 

suemarkp

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Kent, WA
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Some just get omitted. You could argue that bathrooms are covered by the 3 VA per sq-ft rule. However, garages and outside receptacles are not covered by that, so those are receptacles with a 0 for the load calc. It would be prudent to include receptacles for things you're fairly sure are going to be there (e.g. two fridges in the garage). You do need to include outlets for specific appliances (e.g. outlets listed for tools such as an air compressor, table saw, dust collector, or welder). I would think you need to cover garage door openers, but I've never seen calc examples with those. I wish the examples in the NEC were more thorough and cover things most people have today. That way, if you don't see it on the list, it may be covered elsewhere (e.g. bathroom fans -- is that a light, a separate fastened-in-place appliance, and covered in the 3VA per sq-ft rule or not?).
 

Smart $

Esteemed Member
Location
Ohio
Thank you everybody for the replies. I have another question about calculations. According to article 210.52 there are receptacle outlets in addition to the general lighting/receptacle loads. Included is a receptacle for the bathroom. In some calculation examples I have seen the small appliance receptacles from article 210.52(B)(1) added to the calculation but never the bathroom receptacle. Should the bathroom receptacle always be omitted or do we have to include it in the calculation?
See 220.14(J)(1)... included in dwelling general lighting, general-use receptacles including receptacles connected to circuits in 210.11(C)(3)?which covers bathroom branch circuits.
 

kwired

Electron manager
Location
NE Nebraska
Some just get omitted. You could argue that bathrooms are covered by the 3 VA per sq-ft rule. However, garages and outside receptacles are not covered by that, so those are receptacles with a 0 for the load calc. It would be prudent to include receptacles for things you're fairly sure are going to be there (e.g. two fridges in the garage). You do need to include outlets for specific appliances (e.g. outlets listed for tools such as an air compressor, table saw, dust collector, or welder). I would think you need to cover garage door openers, but I've never seen calc examples with those. I wish the examples in the NEC were more thorough and cover things most people have today. That way, if you don't see it on the list, it may be covered elsewhere (e.g. bathroom fans -- is that a light, a separate fastened-in-place appliance, and covered in the 3VA per sq-ft rule or not?).

Many people doing projects at home in the garage or workshop often get the table saw, dust collector and welder all fully loaded at the same time, while doing that they also have every light on in the house and all the cooking equipment going as well as a hair dryer or two and the laundry.:happyno:

Sorry, but I hate it when people think you have to include every item imaginable in these load calcs including portable power tools or other "occasional use" appliances. I think the 3VA/Sq Ft usually covers most miscellaneous items pretty well. Anything that is heavier load and operates rather continuously deserves additional consideration.
 

ActionDave

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Many people doing projects at home in the garage or workshop often get the table saw, dust collector and welder all fully loaded at the same time, while doing that they also have every light on in the house and all the cooking equipment going as well as a hair dryer or two and the laundry.:happyno:

Sorry, but I hate it when people think you have to include every item imaginable in these load calcs including portable power tools or other "occasional use" appliances. I think the 3VA/Sq Ft usually covers most miscellaneous items pretty well. Anything that is heavier load and operates rather continuously deserves additional consideration.
Loaded my house with everything I could except power tools- lights, double oven, dryer (both electric), washer, micro, exhaust fan, popcorn popper, coffee pot, toaster, hair dryers in all three bathrooms, stereo and tv, opened the door on the fridge and freezer.....seventy-two to seventy-six amps.

Went back and cranked up the stereo and found a couple of more things to turn on....managed to read seventy-eight amps plus or minus.

Was trying to plug in my air compressor when my grabbed my arm and said, "What are you doing?!!!"

"Research", I said. She clearly did not see it as valid because she went back in the house and started turning things off.

Never did crack eighty amps. I might have got there if I had tried the compressor first instead of cranking I up the stereo.......
 

suemarkp

Senior Member
Location
Kent, WA
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Retired Engineer
Many people doing projects at home in the garage or workshop often get the table saw, dust collector and welder all fully loaded at the same time, while doing that they also have every light on in the house and all the cooking equipment going as well as a hair dryer or two and the laundry.:happyno:

Sorry, but I hate it when people think you have to include every item imaginable in these load calcs including portable power tools or other "occasional use" appliances. I think the 3VA/Sq Ft usually covers most miscellaneous items pretty well. Anything that is heavier load and operates rather continuously deserves additional consideration.

While I agree that the dwelling calculations seems to be overly conservative, to properly do a load calculation how do you ignore:
220.14(A) circuits for specific appliances or loads (use nameplate value) that are hard wired or uses receptacles over 20A
220.14(C) motor loads that are hard wired or uses receptacles over 20A
220.40 - service and feeder loads shall include the items above
220.50 service/feeder to include motor loads (seems a bit redundant to 220.14(C)
220.53 - you can use a 75% demand factor for 4 or more appliances fastened in place

It does seem that 220.14(J)(1) seems to let you lump in outlets of 20A or less into the general lighting load unless it is named elsewhere in the code. So that gets rid of the bath fans and garage door openers when using the Standard calculation. But it won't get most welder circuits or some of the larger saws or air compressors.

If using the dwelling Optional calculation instead:
220.82(B)(3)(a) requires you count "All appliances that are fastened in place, permanently connected, or located to be on a specific circuit"
 

jumper

Senior Member
Loaded my house with everything I could except power tools- lights, double oven, dryer (both electric), washer, micro, exhaust fan, popcorn popper, coffee pot, toaster, hair dryers in all three bathrooms, stereo and tv, opened the door on the fridge and freezer.....seventy-two to seventy-six amps.

Went back and cranked up the stereo and found a couple of more things to turn on....managed to read seventy-eight amps plus or minus.

Was trying to plug in my air compressor when my grabbed my arm and said, "What are you doing?!!!"

"Research", I said. She clearly did not see it as valid because she went back in the house and started turning things off.

Never did crack eighty amps. I might have got there if I had tried the compressor first instead of cranking I up the stereo.......

:lol:

PS. Ya forgot to jack up the t-stats on the WH, that's like another 17A.

PPS. The highest I ever got in a standard resi was around 110-130, yet everyone knows you need a 200A service minimum, right?:cool:
 

kwired

Electron manager
Location
NE Nebraska
While I agree that the dwelling calculations seems to be overly conservative, to properly do a load calculation how do you ignore:
220.14(A) circuits for specific appliances or loads (use nameplate value) that are hard wired or uses receptacles over 20A
220.14(C) motor loads that are hard wired or uses receptacles over 20A
220.40 - service and feeder loads shall include the items above
220.50 service/feeder to include motor loads (seems a bit redundant to 220.14(C)
220.53 - you can use a 75% demand factor for 4 or more appliances fastened in place

It does seem that 220.14(J)(1) seems to let you lump in outlets of 20A or less into the general lighting load unless it is named elsewhere in the code. So that gets rid of the bath fans and garage door openers when using the Standard calculation. But it won't get most welder circuits or some of the larger saws or air compressors.

If using the dwelling Optional calculation instead:
220.82(B)(3)(a) requires you count "All appliances that are fastened in place, permanently connected, or located to be on a specific circuit"

I don't disagree with what is in art 220.

A welder on a dedicated branch circuit, is maybe a little harder to say is included in the general lighting load of 3 VA sq Ft. Most of your 120 volt tools that plug into a 15 or 20 amp receptacle are exactly what I am getting at. Why are they any different than trying to account for say a vacuum cleaner, or knowing someone will use a hair dryer in a bedroom instead of the bathroom? Even though some of these things are a heavy load for a 15 or 20 amp circuit, they likely are not as significant of a load to the total VA on the feeder or service as they often have limited demand time.

The garage door opener - time for a reality check. I agree as code is written it should probably be considered an appliance fastened in place. Now how many of these have you seen that run for more than 10-20 seconds? Not really a significant load at all on a service or feeder, unless you maybe you have 15 or more doors and at least one is almost always running.

Even if you constantly cycle one open and closed (I have done this when trying to make repairs before) they often are not rated for that kind of duty and thermal overload only allows so much and it is going to trip, it will not run until it cools down again.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
I can't disagree with what you say. It is the code that is lacking in providing an exception for these items (might as well add garbage disposals and most sump pumps too). Any intermittent use motor or tool should be mostly insignificant to the overall load calculation. There isn't a legal way to exclude them, but there should be (or put them in with a very low demand factor).

I have a house with a 400A service. I struggled to get everything to fit within that limit and took some liberties with non-coincidental use. I think the highest I've ever measured was a bit under 200A when the heat pump kicked in the 20KW of Aux heat. The power companies know this, as I have a 1/0 aluminum service drop and it hasn't melted yet.
 

kwired

Electron manager
Location
NE Nebraska
I can't disagree with what you say. It is the code that is lacking in providing an exception for these items (might as well add garbage disposals and most sump pumps too). Any intermittent use motor or tool should be mostly insignificant to the overall load calculation. There isn't a legal way to exclude them, but there should be (or put them in with a very low demand factor).

I have a house with a 400A service. I struggled to get everything to fit within that limit and took some liberties with non-coincidental use. I think the highest I've ever measured was a bit under 200A when the heat pump kicked in the 20KW of Aux heat. The power companies know this, as I have a 1/0 aluminum service drop and it hasn't melted yet.

Like I said, power tools in somebody's garage or workshop are just as intermittent of a load as say a vacuum cleaner in the house and maybe a similar amount of load in many cases.

Just how often when doing a load calculation do we know just exactly what power tools will be used in the garage? Things like a garage door opener or a disposer at least are fastened in place and are more easily determined whether or not they will be there even if it is questionable how much demand they actually put on the service.

But I certainly wouldn't include table saws, jointers, planers, and things of that nature in a dwelling load calculation, or even a welder (which I agree maybe crosses the line farther than the other mentioned items but welders are a different breed of load also and the type of welding done at a dwelling garage or shop is not likely to be high duty cycle type of welding either).

I would include all those items if I were calculating the load for a commercial shop where these items are used quite frequently and especially if use of many of them simultaneously is common.

I have seen overloaded branch circuits in home shops or garages but never seen a service that is overloaded because they do some woodworking or metalworking in their garage on occasion, or even on a fairly regular basis.

My grandfather took up woodworking in his basement after he retired. Had a fair amount of power tools. Aside from maybe a fan or dust collector that ran simultaneously he did not run the table saw and the planer at same time - he just didn't have enough hands to do so for one thing. When he was doing his woodworking he wasn't also in another part of the house running other items. Adding all those loads that just will never run together into the load calc just doesn't make sense.
 

Dennis Alwon

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