load calculation for a store

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Stevenfyeager

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United States, Indiana
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electrical contractor
I've never done a load calculation for a store. This a tire store/shop. I've gone through and collected name plate ratings of equipment, like there are nine lifts, (20 amps/ 208v), tire balancers, etc. Any suggestions? Thank you ! I have only done residential load calc.s.
 
work your way through article 220 and use the sections that would apply to your situation.

Roger
 
180 VA per duplex rec, general lighting loads, mostly motor loads, hot water, heating air conditioning, what ever else you might have in a tire repair shop.
 
ActionDave said:
Another vote for referring to annex D.
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Thank you. I can't find a similar example. My customer's store is a tire store which has more power tools than a average retail store. Do you have any suggestions for a 7300 sq ft store with 9 (20 amp/ 208v) lifts, 2 compressors (each 20 amp 208v), 40 amp AC.208, 4 balancers 20 amp, 208v. I counted 30 4 plex receptacles, 2 gas furnaces. I used 180 VA per receptacle, and multiple of 3 VA per square ft. The store has a 225 amp 240v panel and a 100 amp 208 panel.
i have to do some work there and would like to see if they are maxed out or not. There must be some multipliers for the machines? They are not all on at once. Thank you.
 
Stevenfyeager said:
Thank you. I can't find a similar example. My customer's store is a tire store which has more power tools than a average retail store. Do you have any suggestions for a 7300 sq ft store with 9 (20 amp/ 208v) lifts, 2 compressors (each 20 amp 208v), 40 amp AC.208, 4 balancers 20 amp, 208v. I counted 30 4 plex receptacles, 2 gas furnaces. I used 180 VA per receptacle, and multiple of 3 VA per square ft. The store has a 225 amp 240v panel and a 100 amp 208 panel.
i have to do some work there and would like to see if they are maxed out or not. There must be some multipliers for the machines? They are not all on at once. Thank you.
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NEC won't be of real use to get real demand data on some of that equipment

Sure the air compressors you can probably assume could possibly run nearly continuously at times. But the lifts - you run them for 10-30 seconds and they may not run again for an hour - several hours in many instances, you possibly have maybe two going at same time on rare occasion but probably never more then two at a time, still only 10-30 seconds at a time. Similar for the tire balancing machines. They spin tire for testing for a few seconds at a time but most of the time just sit there idle only drawing very limited power to run the display. Break room probably has much more overall demand then the lifts or balancing machines. I'd probably only count one lift and one balancing machine if I thought I had to include them at all.
 
Sounds like you've already done most of the legwork by getting nameplate data of the large equipment.

You can simply add up the VA of each piece of equipment to determine your load there. The NEC does not dictate the application of demand factors, you need to use best judgement there depending on its use. However, an appliance is generally considered to be a continuous load where a motor can be classified as intermittent or continuous.

Receptacle count is straight forward per NEC. 100% for the first 10KVA, 50% of the rest with each receptacle rated for 180VA.

Lighting you can get from square footage using 1-3VA per sq. ft. I would take a look at your local energy conservation code which will tell you the maximum lighting power densities allowed per type of space. You can get a better idea of what Watt per sq. ft you would need that way.

If reasonable, you can get historical demand data from the utility which will tell you exactly what you are looking for.
 
Stevenfyeager said:
Thank you. I can't find a similar example. My customer's store is a tire store which has more power tools than a average retail store. Do you have any suggestions for a 7300 sq ft store with 9 (20 amp/ 208v) lifts, 2 compressors (each 20 amp 208v), 40 amp AC.208, 4 balancers 20 amp, 208v. I counted 30 4 plex receptacles, 2 gas furnaces. I used 180 VA per receptacle, and multiple of 3 VA per square ft. The store has a 225 amp 240v panel and a 100 amp 208 panel.
i have to do some work there and would like to see if they are maxed out or not. There must be some multipliers for the machines? They are not all on at once. Thank you.
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Since this is existing see 220.87.

Roger
 
Stevenfyeager said:
Thank you. I can't find a similar example. My customer's store is a tire store which has more power tools than a average retail store. Do you have any suggestions for a 7300 sq ft store with 9 (20 amp/ 208v) lifts, 2 compressors (each 20 amp 208v), 40 amp AC.208, 4 balancers 20 amp, 208v. I counted 30 4 plex receptacles, 2 gas furnaces. I used 180 VA per receptacle, and multiple of 3 VA per square ft. The store has a 225 amp 240v panel and a 100 amp 208 panel.
i have to do some work there and would like to see if they are maxed out or not. There must be some multipliers for the machines? They are not all on at once. Thank you.
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Rodger and kwired answered your question. Just for kicks you should put your ampmeter on the main feed just to see. I would doubt it would ever read more than 80A.
 
jeremy.zinkofsky said:
Sounds like you've already done most of the legwork by getting nameplate data of the large equipment.

You can simply add up the VA of each piece of equipment to determine your load there. The NEC does not dictate the application of demand factors, you need to use best judgement there depending on its use. However, an appliance is generally considered to be a continuous load where a motor can be classified as intermittent or continuous.

Receptacle count is straight forward per NEC. 100% for the first 10KVA, 50% of the rest with each receptacle rated for 180VA.

Lighting you can get from square footage using 1-3VA per sq. ft. I would take a look at your local energy conservation code which will tell you the maximum lighting power densities allowed per type of space. You can get a better idea of what Watt per sq. ft you would need that way.

If reasonable, you can get historical demand data from the utility which will tell you exactly what you are looking for.
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I called the utility, they said they can not give me KW hrs only $. $1200 per month on a 12 month average. They said I would need to contact the owner for KW r usage. I hate to bother the workers, manager, son of the owner, etc.,they are always so busy with customers
 
Are you just trying to do a quick and dirty load calc or something you need to present to an inspector?

We have a Fluke logger we install on services, etc for 30 days for things like this. If you have time to wait, this is the option I like best, assuming I can't get the info I need from the utility company.
 
220 for commercial is very conservative because it doesn't offer any significant demand factors like there is for residential. You can't arbitrarily say that you think only one lift runs at any given time on average.

Your best bet to get any real sense of the load is per NEC 220.87 get it from their bills or put a meter on it for 30 days as mentioned in the previous posts.
 
ron said:
You can't arbitrarily say that you think only one lift runs at any given time on average.
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No but reality and duty cycle of those is in a place you can still sort of forget they even exist to some extent. OP could probably have 5 run at same time and still never have a problem overloading anything, they just don't run long enough to be a problem. I haven't seen one that doesn't require operator to be standing there holding switch to raise it. That also means that is one less person available at that time to operate some other machine.

I bet if you put all nine that OP has on a 60 amp feeder you never trip the feeder, maybe even if you intentionally ran all 9 at once. It might draw more then 60 amps, but they can't run more then maybe 20-30 seconds max - they have reached their travel limit by then.
 
ron said:
Agreed, but nowhere in 220 does it let you forgive any of those loads in a calculation.

That's why he is better off using the bill or meter method
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I know. If you are in a place that wants plans review then you have more of a problem. If no plans review - a typical EI will seldom question load calculations on service or most feeders unless something seems pretty obviously wrong.
 
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