Sizing a New Commercial Building

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Newb question:
Was wondering if anyone has a handy excel spreadsheet for calculating initial loads of a new commercial building...ie for roughly sizing your main switchgear. I have one that i made up but I'm sure someone here has a better one.
I guess when you are in this early phase of a new design, you size everything based on square footage?
Lighting~1-3 VA/sq ft.
Recptacles~3VA/sq ft.
HVAC~? VA/sq ft.

Any other good pointers for starting a new commercial building?
 
I've usually heard 10VA per square foot for a rough estimate of service size on an air conditioned office building. I think it might be a little bit smaller. Like 9VA per square foot.

I think your lighting estimate is too high. I would use 1 - 1.4VA per square foot for office lighting.
 
I use 8VA/SQFT for rough load calculation. Sometimes I use 10VA/SQFT for certain building with possible more equipment.
 
Be careful... the connected load in San Diego can easily reach 18-20VA per SF in a commercial/educational building.
 
I used to use, 10 years ago, 10 watts/sf mech
3 watts/sf lighting
2 watts/sf power

Since then power is going up and lighting is going down.

Of course this is just for a starting point and could go higher if it is electric heat.
 
All good points. This is a 42,000 sq-ft. office building in FL, so the HVAC would be pretty high i believe (another engineer here quoted around 18VA/sqft.).
Suppose after i added up the rough VA numbers, I came to around 1200A main service. Now how do i know how many panels i need? And when are you supposed to use MLO panels vs. panels with an MCB?
 
The number of panels is a design issue, not an NEC issue. How many panels will make a reasonable wiring pattern? One is acceptable, but it may be financially beneficial to distribute sub-panels through the installation to eliminate some of the long "home runs". You would only need a main disconnect in the service panel. The sub-panels may be MLO.
 
haskindm said:
The number of panels is a design issue, not an NEC issue. How many panels will make a reasonable wiring pattern? One is acceptable, but it may be financially beneficial to distribute sub-panels through the installation to eliminate some of the long "home runs". You would only need a main disconnect in the service panel. The sub-panels may be MLO.
Click to expand...

Without knowing the voltage how can you assume that all other panels except the main can be MLO?
 
Why not just ask the person that is signing your plans? They are supposed to be directly supervising your work. That is the purpose of working under someone with more experience for a few years before you can take the PE exam.

Learning how to do electrical design from the internet is a bad idea.
 
sceepe said:
Why not just ask the person that is signing your plans? They are supposed to be directly supervising your work. That is the purpose of working under someone with more experience for a few years before you can take the PE exam.

Learning how to do electrical design from the internet is a bad idea.
Click to expand...

I did ask him......and it's definatily a design preference.
Just getting various opinions my friend....
 
necnotevenclose said:
Without knowing the voltage how can you assume that all other panels except the main can be MLO?
Click to expand...


I was not aware that supply voltage would effect the requirement for a panelboard to have a main disconnect or be MLO. Where is this found? I am ready to learn.
Thanks,
 
Of course, the supply voltage will impact panelboard to have main break. If the supply voltage is 480/277v, you need a step down transformer to get 208/120v, the low voltage panels after the transformer probably have to have a main breaker. SEE 240.21(C).
 
I think the point he was trying to make was that the secondary side of the transformer may have a fused disconnect switch and then could go to a main lug on a panelboard. A main circuit breaker may be standard design after a transformer but it is not absolute.
 
At the electric utility, we always find that NEC requires much larger sizing of main switchgear than we see as actual load. Our service wire is usually always lower ampacity than the wiring past the meter, many times very significantly smaller (300A meter for an 800A disconnect). I don't know if this is because the designer who specified the building wiring was being safe, or maybe because our data is from demand meters that do some averaging, but just an interesting fact that we find at our utility and lots of my counterparts around the country will say the same thing.
 
Again I'm very new here but: Here in Florida as a qualfier (master electrician/contractor) I sign my own plans! I do so many times.
Provided its 800 amp 3 phase max anyways!.
 
I use something similar to the attached Spreadsheet to calculate my service size when working on pre-construction budgets at the conceptual stage.

I also use 15,000 SF per Electrical room when working on a budget.

I could not get the Excel file to attach so if you want a copy of it PM me and I will forward it to you.

-Ed
 
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