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Thread: load calculation for a store

  1. #1
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    load calculation for a store

    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.

  2. #2
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    work your way through article 220 and use the sections that would apply to your situation.

    Roger
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  3. #3
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    Check annex D in the back of the nec. I believe there are examples there
    They say I shot a man named Gray and took his wife to Italy
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  4. #4
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    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.

  5. #5
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    Quote Originally Posted by Dennis Alwon View Post
    Check annex D in the back of the nec. I believe there are examples there
    Another vote for referring to annex D.
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

  6. #6
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    Quote Originally Posted by ActionDave View Post
    Another vote for referring to annex D.
    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.

  7. #7
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    Quote Originally Posted by Stevenfyeager View Post
    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.
    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.

  8. #8
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    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.

  9. #9
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    Quote Originally Posted by Stevenfyeager View Post
    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.
    Since this is existing see 220.87.

    Roger
    Moderator

  10. #10
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    Quote Originally Posted by Stevenfyeager View Post
    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.
    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.
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

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