procedure and format for load calculations

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DCjr

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Colleagues,
Thank You for the opportunity to ask for some suggestions.
What is a good procedure and format for making load calculations on a 3phase 120/208 breaker panel. Their seems to be a few of ways of doing this. A recent example is a small retail shop adding a caf?. They have 120V and 208V single and three phase circuits. I understand the adjustment factors and the code requirements. I am a little hazy about getting the formula right for the 3 phase connected loads, and doing it in an efficient way that will in the end help generate the demand load, balanced breaker schedule and load on neutral. I can get there, but it takes a long time and my notes look like Einstein?s chalk board.
DCjr
 
Thanks Ron, that would take care of the existing circuits but to add a sub panel with more circuits brings me to my larger question of how to organize the information efficiently. Like right now I'm making a list of circuits for each load type. Then taking the wattage of each circuit and splitting it up on each bus according to its voltage and phase. Then balancing it out, then totaling the columns, then taking the largest of the three*3. then the total/208*1.732. Then multiply the demand factor, then add up all the demand loads for the various types. Then go back and and make a breaker schedule
integrating everything. Must be an easer way.
 
Hi DCjr. Your asking design questions that are best suited for detailed load calculations, not "hang a meter on it for a month or see if the Utility Bill shows a demand". The demand factors will change from year to year as new tenants move in and out.

The easiest way to obtain these values and organize them in a report is with Dolphins Software's Volts, http://www.dolphins-software.com.
 
Snorks,
Thank you, I see the software can be downloaded for a trial which I will do, however I am still hoping for some suggestions on my old school pencil paper and excel spread sheet method.
DCjr
 
So far so good

So far so good

DCjr said:
. . . Then go back and and make a breaker schedule
integrating everything. Must be an easer way.
Click to expand...

It sounds like you have a pretty good method so far, it won't get much easier than steps like those. I would definately do it in a spreadsheet, which takes even longer to set up, but will save time on changes.

Ron is right about the demand meter for the existing loads, especially if they have been there for a few years as Snorks hinted at. Or you can list all the existing loads and receptacles.

Be sure to allow at least the sq ft va for lighting, plus any track lights / ft, plus a sign circuit / pedestrian entrance, plus the show window va / ft. These won't show up on the demand if not being used . . .

Of course you can use diversity for the some of the kitchen loads, probably 65% in this case.

Welcome to the forum.
 
Volta, Thanks for your response.
Do you think the I=Watts/1.732x208V. is correct regardless if the wattage comes from a 120V. circuit or a 208?.
DCjr
 
Look in the back of your NEC. The examples will show you how to set up the load calculation along with the reference section in case you have something a little different.
Get it on a spreadsheet and you wont have to start from scratch next time you have to do one.
 
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