SERVICE LOAD CALCULATIONS

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EXCEL12

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I,m looking at a engineers plan on a retail center. For the Service load Calculations he uses the following:
Lighting Load 3.5 VA/sq.ft
Receptacle Load 2 VA/ sq.ft.
Hvac Load 12va/sq.ft.
Tenant Signage Future 1200 VA/Tenant
Show Window Receptacle (future) 200 VA/Lin. Ft.
Miscellaneous Load 18VA/Sq.ft.

Per NEC 220 where is he getting his VA calculations other then Lighting?
 
EXCEL12 said:
yes, I'm just curious how he justifies his calculations.
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He's probably basing it on his firm's experience with actual load calcs. IMO, plan review should reject it... but I've heard of instances where such has been "approved".
 
Why reject?

Why reject?

Smart $ said:
He's probably basing it on his firm's experience with actual load calcs. IMO, plan review should reject it... but I've heard of instances where such has been "approved".
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Why should plan review reject it? If it is a new retail center as the poster suggests, how would you estimate the loads to size the service for the building? The NEC gives minimum lighting loads (3 watts per sq. ft.) they are above that, 200 VA per lin. ft. of show window (check), and an estimate of other loads (check). Retail centers usually limit tenants on a watts per square foot based on the design parameters. I don't see why it would be rejected by plan review? Once the tenant finishes their infill plans, then actual loads must be verified to the now existing service size provided and any updating must be done at that time if necessary.
 
ronmath said:
Why should plan review reject it? If it is a new retail center as the poster suggests, how would you estimate the loads to size the service for the building? The NEC gives minimum lighting loads (3 watts per sq. ft.) they are above that, 200 VA per lin. ft. of show window (check), and an estimate of other loads (check). Retail centers usually limit tenants on a watts per square foot based on the design parameters. I don't see why it would be rejected by plan review? Once the tenant finishes their infill plans, then actual loads must be verified to the now existing service size provided and any updating must be done at that time if necessary.
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So you believe it is impossible to do an estimate using the NEC-prescribed calculation method?

(To clarify, my question is rhetorical.)
 
Smart $ said:
So you believe it is impossible to do an estimate using the NEC-prescribed calculation method?

(To clarify, my question is rhetorical.)
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Why do you think they are not estimating the service size per the NEC? In the scenario of a new retail center with the tenant infills yet to be decided assumptions must be made for unknown items. It seems the designer has made reasonable estimations of loads prior to knowing actual designed/installed loads. They may be cold dark shells or warm dark shells and you do not know the loads to do the calculations per 220, so some assumptions must be made as to type of possible tenants and loads that may be encountered. The loads will still have to be calculated per 220 once the tenant/tenants move in and actual loads are known. They have included the known code dictated items such as a sign circuit, lighting and show window and estimated the remainder. How would you size a service with unknown tenants and loads otherwise?? I do not claim to be all knowing, but if you know a better more code compliant way of doing this, please share...
 
ronmath said:
Why do you think they are not estimating the service size per the NEC? In the scenario of a new retail center with the tenant infills yet to be decided assumptions must be made for unknown items. It seems the designer has made reasonable estimations of loads prior to knowing actual designed/installed loads. They may be cold dark shells or warm dark shells and you do not know the loads to do the calculations per 220, so some assumptions must be made as to type of possible tenants and loads that may be encountered. The loads will still have to be calculated per 220 once the tenant/tenants move in and actual loads are known. They have included the known code dictated items such as a sign circuit, lighting and show window and estimated the remainder. How would you size a service with unknown tenants and loads otherwise?? I do not claim to be all knowing, but if you know a better more code compliant way of doing this, please share...
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If you know enough to convert your experience to kVA per sqft., then you have enough experience to assign an assumed load. Technically, that's all you are doing anyway. 200.14(A) does not exclude such an assumed load... and you don't have to state it as xxx kVA per sqft. A note regarding assumed loads is sufficient.
 
Smart $ said:
If you know enough to convert your experience to kVA per sqft., then you have enough experience to assign an assumed load. Technically, that's all you are doing anyway. 200.14(A) does not exclude such an assumed load... and you don't have to state it as xxx kVA per sqft. A note regarding assumed loads is sufficient.
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I'm not sure why we are disagreeing then and why you state it should be rejected? x KVA per sqft. equals assumed load. I would state that these types of buildings are often in flux as to square footage of Tenants and sizes of buildings where a xxx KVA per sqft. might be more helpful in the long run, especially when writing tenant leases and tenant criteria.
 
ronmath said:
I'm not sure why we are disagreeing then and why you state it should be rejected? x KVA per sqft. equals assumed load. I would state that these types of buildings are often in flux as to square footage of Tenants and sizes of buildings where a xxx KVA per sqft. might be more helpful in the long run, especially when writing tenant leases and tenant criteria.
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Justify it however you want, but plan review is about Code compliance, not design. If I were involved with plan review, I'd reject any calculation that does not take the form of what is prescribed in Article 220.
 
I have done service calculations in this format many times. It has never been rejected, nor (I believe) should it. It is not in conflict with 220. For example, 220 tells us how to account for HVAC loads. On a design/bid/build project, for which a complete mechanical, plumbing, and electrical design is issued for bids, and those same design drawings are used by the successful bidder for obtaining the permits, the calculation has to be complete. That is, all the M & P equipment is described in some table that accounts for the electrical load of each item. The service load calculation is the sum of all those loads, with any applicable demand factors included.

But for a design/build project, the drawings are often submitted for permit before the mechanical contractor has finalized the equipment list. NEC 220 it doesn't give us guidance for those projects for which the HVAC equipment has not yet been selected. Using a VA/SF estimate that is based on past experience is, IMO, a reasonable approach.
 
Smart $ said:
Justify it however you want, but plan review is about Code compliance, not design. If I were involved with plan review, I'd reject any calculation that does not take the form of what is prescribed in Article 220.
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Now that I get your point of contention and why you would reject the loads, I guess I would agree that the actual service calculation given to the city for review should be in concise compliant totals and not require math to be done to reach those totals. In criteria or information to an electrician however, (which I believe this is) it makes much more sense to state how you arrived at those numbers so it can be broken out on a Tenant by Tenant basis. I've also run into many inspectors that want to know how the numbers were arrived at and calculated so they too can feel comfortable with the assumptions. Once again, not sure we are really disagreeing, was just trying to point out to the OP that while all the numbers are not prescribed by the NEC, that does not make them invalid and non code compliant and if given in the correct form, should be accepted by the AHJ.
 
charlie b said:
... Using a VA/SF estimate that is based on past experience is, IMO, a reasonable approach.
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ronmath said:
Now that I get your point of contention and why you would reject the loads, I guess I would agree that the actual service calculation given to the city for review should be in concise compliant totals and not require math to be done to reach those totals. ...
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It's all about using the correct format. Has nothing to do with how you arrived at your numbers, though noting assumed loads is being professionally responsible IMO.
 
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