Load Calc.

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sparky76

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Hey Guys, long time reader. first time poster, looking to take advantage of the wealth of knowledge available here. I need a 2nd or 3rd or 4th opinion on a load calc. for an addtion to an existing office building. Service is 120/208V, 3 phase. 1684 sq ft including addition, 1-30A 3 phase condenser. They are adding appliances in the kitchen- 2 ovens @ 4000W each, 1-micro @ 1100W, 1 micro @ 1200W and hard wired coffee brewer @ 4000W (120/240).

They are adding a 3 phase UPS later w/ a 56Amp draw which I would like to factor in seperately. I gotta have this to them tomorrow and comm. load calcs are definitely not my strength. Thanks smart people.
 
You have two choices, for determining whether an existing building has capacity for adding load. One is to perform a load calculation. But to do that, you need to know everything in the building that draws current. I have to ask whether your list includes everything.

If you can?t put together a list of everything in the building, then you need to determine how much power is being drawn by the existing stuff. One way is to look at utility bills over the last year. But that is only worthwhile, if the utility bills actually show maximum demand (in units of KVA) each month. The other way is to install meters at key locations, and measure peak demand in 15 minute increments for a year.

What more can you tell us about this building?

Have you made an attempt to do a calculation yourself yet? If so, what have you determined so far?
 
Much more information is needed to perform a load calculation as Charlie mentioned. Light load, heat load, equipment loads, etc. There are no shortcuts...
 
more info

more info

In that suite there are no high draw items currently. just computers and typical office equipment. When I put my clamp meter on the feeders w/ just general lighting and receptacle load i got about 10-11 amps / phase. The kitchen appliances are something that will be added.
 
sparky76 said:
When I put my clamp meter on the feeders w/ just general lighting and receptacle load i got about 10-11 amps / phase.
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Well, that's a start. It can give you a degree of confidence, regarding whether there is capacity to add more load. But it's not enough to work with. You need to measure peak demand, in units of KVA, with a metering system that can store information every 15 minutes for a month.

Take a look at 220.87. If you don't have the time to go through one of the two options it gives you, then you will have to make a list of each and every load. No general statements like "computers and typical office equipment" will get the job done. You can count the receptacles, rather than counting the computers plugged into receptacles. But you must make a complete list.

haskindm is right. There are no shortcuts.
 
I really am more interested in the new load- The new addition to building (196 sq ft, 17-26W recessed cans, 2-100W incandescent, 2-21W undercab fluorecent, 1-sm appliance circ, 19- duplex recepts, 1- vending machine)

New load in kitchen: 2 ovens @ 4000W each, 1-micro @ 1100W, 1 micro @ 1200W and hard wired coffee brewer @ 4000W (120/240) and one new small appl circ. The existing kitchen is already on a seperate subpanel which is full and the new appliances and addition will be added to the supanel which has the existing load for 1250 sq ft of general office space.
 
Rather than counting individual receptacles I can use 220.14 K (1) which allows 1VA/sq ft and 220.12 for lighting which allows 3.5 VA/sq ft. Is that correct?
 
I know that our POCO does not include max monthly usage in kVA for residential customers and I doubt that it does for commercial ones either.
 
sparky76 said:
Rather than counting individual receptacles I can use 220.14 K (1) which allows 1VA/sq ft and 220.12 for lighting which allows 3.5 VA/sq ft. Is that correct?
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I think not. Let?s start by recognizing that the NEC provides only the minimum requirements for a safe installation. Nothing prohibits the owner from asking for more. So if you are working on a brand new building, you can use those figures to get the minimum required ratings for the service and feeders.

But that does not tell you whether the owner had the original installer double or triple the amount of receptacles and lights. If you are working with an existing building, you have to deal with what is actually there. You can look to see what is really installed, add all that up, add in the new stuff, and determine whether the added load would push the load on any panel over the panel?s rating. If you don?t want to do that, and if the utility does not give demand information, and if you don?t have time to do a 30 day load study, then there is no remaining code-compliant way for you to complete this project.

Please don?t expect us to condone the notion of, ?I don?t have time to do it per the code, so I?ll just do the best I can.? You might be able to get some type of reprieve from your AHJ. I have seen an AHJ give a provisional approval to proceed with a project, on the condition that a 30 day load study be performed, and on the condition that the designer come back after the 30 days (and before final approval of the installation) to prove that the building really did have enough spare capacity to handle the additional load.
 
i should add that the existing subpanel has already been upgraded from 100A to 200A and that we are simply trying to determine what the load will be. The kitchen appliance additions were only decided on by the building owner after the subpanel upgrade was done for the addition of square footage and the new UPS.
 
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