# Building Load



## Dennis Alwon (May 9, 2009)

Table 250.54 is for dwelling units.... If this is a commercial unit then the diversified loads are very different then a residential load.

Look at Annex D in the back of the NEC. There are examples there that may be of help. If not, then art. 220 is what you use and just use the areas that are not for dwellings. 220.14 gives a lot of info for calculating loads


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## joebanana (Dec 21, 2010)

Are there any prints for this building? Load schedules? Sounds almost like you should consult a licensed EE.


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## Woodland (Jan 21, 2018)

Ok, thanks. I see quite a bit of references for dwelling units but not too much on buildings in general. Where general receptacles are concerned I see the calculation for the first 10,000 VA @ 100% and the remainder of the load at 50% demand factor. From what I have been finding, lighting and heating would be considered continuous duty and thus be factored @125%. I'll have to look over those sections you referenced and see what I can find.


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## Woodland (Jan 21, 2018)

I do have the schedule for the the heat pumps along with total square footage to determine lighting demands. I count seven heat pumps that are single phase 208v variety at a specified amperage for each ranging from 10.4A up to 28A depending on what area they are servicing. Pretty straightforward there and I though I could just add them up. I was under the impression that since this is a commercial building there is not much demand factor reduction to apply here except for maybe the general purpose receptacles since most of those will probably not be utilized.


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## brian john (Mar 11, 2007)

I assume this is an existing building?

What is the reason you need this information?

Rent a power monitor.


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## brian john (Mar 11, 2007)

joebanana said:


> Are there any prints for this building? Load schedules? Sounds almost like you should consult a licensed EE.


I do not understand many members rush to pass work off, especially for work an electrician can do.

Engineers hire us to do this work.


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## frenchelectrican (Mar 15, 2007)

Woodland.,

Did ya ever thought about asking the POCO of that exsting building load?

ask for the history for last 12 months and I am pretty sure they will be happy to give you a copy to ya and you can able see where the peak demand is and when you do the load caluations you will be not too far off on figures if done right. 

The other thing is just watch the figures espcally if you have three phase supply it may get ya if not carefull with the figures. ( ya have to make sure you are aware if this is delta or wye system )


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## paulengr (Oct 8, 2017)

brian john said:


> I do not understand many members rush to pass work off, especially for work an electrician can do.
> 
> Engineers hire us to do this work.


Because it passes blame. In a litigious society the goal is zero liability for anything. What happens though is repeat customers figure out you aren't doing anything and move on. The EE allows for hiring pure conduit runners that can only follow a print. Anyone that has been through a law suit though eventually realizes that you can use anyone, any time, for anything. Lawyering up is a tactic, not prevention. So you man up and do it or learn it.

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## paulengr (Oct 8, 2017)

Woodland said:


> Is there an accurate way to determine the diversified load for a commercial building verses the total connected load? Lets say a building has separate heat pumps located throughout the building including lighting and general receptacles and there is even a small laundry room with some washers and dryers installed. I have a very good handle on this for residential units including multi-unit apartment buildings just not sure how to accurately diversify the load on the building itself. Do I treat the heat pumps as continuous loads and multiply by 1.25? Can I also assume the load to the laundry appliances can be reduced using table 220.54 of the NEC? Since its commercial, the lighting is on for more that three hours at a time. It almost looks like the diversified load would be greater than the connected load but that just does not seem right. Been looking thru the NEC and can’t seem to find a section for this particular question.
> Thanks!
> Frank


Load calculations for continuous duty motors as well as ampacity can definitely exceed name plate. Remember rpughly 6x FLA for large motor stall current up to 10x FLA on small ones? The wiring and everything else has to be a bit oversized for this.. The 125% is a fudge factor that works with lots of similar motors for sizing. With a small number of large motors it doesn't so actual sizes matter. Example two 200 HP motors. Taking .746x1.25x400 = 373 kVA so next size up is 500 but with just one you get 187 kVA and a 250 kVA transformer will NOT work because the voltage drop is too much and the contactor drops out or overload trips. Once you get above 2-3 motors the simple 125% rule works. Engineers often use .746xHP for ALL motors plus 500% of the largest one. That's closer to an exact answer. I have a spreadsheet I use where I calculate both and look at actual voltage drop for transformers but that's for industrial and transformers, not panel sizing. Diversity sort of goes out the window in industrial loads because it's not just lights, receptacles, and kitchens and washers. Code specifies doing it by diversity and connected load using one of a couple options or on existing you can also measure it.on commercial buildings sometimes the square foot factors make the most sense. As you get further from residential it's not so easy. Residential with 200 A panels is usually grossly oversized but still $200 more or less for the panel no matter what the size is. Not so easy with commercial or industrial where generally diversity is a total miss, either over or undersized depending on occupancy and use. It's not uncommon to sort of have meetings with the owner to negotiate or use an EE to go "off the books" when Code doesn't allow for say a dark warehouse.

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## joebanana (Dec 21, 2010)

brian john said:


> I do not understand many members rush to pass work off, especially for work an electrician can do.
> 
> Engineers hire us to do this work.


The OP seemed to be having trouble applying certain code requirements to the task at hand. I'm used to working from engineered plans on large projects, and TI's, that's what the architect gets paid for. If this is a "design and build", depending on the area, the building department may have certain requirements for the design portion to be by a licensed entity. If that's the contractor, then so be it, but, if they have to turn to an internet forum for advice, maybe some consultation is in order.


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## brian john (Mar 11, 2007)

paulengr said:


> Because it passes blame. In a litigious society the goal is zero liability for anything. What happens though is repeat customers figure out you aren't doing anything and move on. The EE allows for hiring pure conduit runners that can only follow a print. Anyone that has been through a law suit though eventually realizes that you can use anyone, any time, for anything. Lawyering up is a tactic, not prevention. So you man up and do it or learn it.
> 
> Sent from my SM-T350 using Tapatalk


OH HORSE HOCKEY, I typically hear this from people that do not understand what they are doing. Professionals do professional work and the rest are just assembly line workers and should stay home and let those that know do the work.


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## telsa (May 22, 2015)

The diversification one can expect in a residence is rare to be found in a commercial structure.

At the beginning of any work day, just about every load imaginable fires up. 

This is the load that one must size for, both the customer's EE and the Poco, too.

You can't treat them like they're apartments.


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## brian john (Mar 11, 2007)

THIS IS FOR WASHINGTON DC but should be typical for any normal 9-5 operation 

Typical commercial office building cruises with a flat line for most of the night, except in extreme cold or heat where chillers or electric heat may be left on.

Around 4:00-6:00 AM chillers or heat are fired up, around *;30 elevators can be seen coming online, and office loads pick up.

Around 9:30 you will see a drop in elevator operation and the load is stable until 11:30-1:30 then stable at 4:30-5:30 same thing.

Around 5:30-6:00 everything winds down.

This will be the same day to day with the exception of Saturdays and Sundays. A power monitor will show this in text Min, Max and Average with a time stamp along with a graphical representation for, Voltage, Amperage, KW, KVA, KVar, PF, Peak Demand additionally if you want you can record VOltage and Current Harmonics.

On monitors
If you rent or buy a decent monitor from Fluke or Dranetz it will come with report writer software and will allow you to export the data to excel to revies the data. The report writer software is well worth the extra cost of a good monitor. Other manufacturers have similar monitors I am just not familiar with them and their report writer capabilities. 

The Fluke 1750 has an excellent youtube instructional video.

If you are not comfortable with this sub the work out, but if you feel an engineer is necessary sub him as well drive the bus and make the money, why give away work?


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## splatz (May 23, 2015)

brian john said:


> If you are not comfortable with this sub the work out, but if you feel an engineer is necessary sub him as well drive the bus and make the money, why give away work?


:thumbsup:


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## Woodland (Jan 21, 2018)

Yea, I see that all the time in commercial buildings. An inspector here was insisting today that a multi-unit apartment building that contained around 16 units where each unit had an electric cook range required that each cook range be added to the total building load even though the chance of each range being on at the same time would be remote. Can this be possible as it does not make sense to me but I cannot seem to find anywhere in the NEC where this applies but I'm still looking into it. Sometimes I seem to have difficulty interpreting those things but I want to be informed about it as I haven't dealt with this before.


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