can panel schedules be used to determine the service

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hi. a space in the building is used for a new restaurant. an electrical room for this space has an existing 400a,120-208v, 3ph, 4w service. total building service is 2,800a.

guided by article 220.88 nec 2011, i put together all restaurant equipment including dishwashers, coffee makers, toasters, refrigerators, freezers, refrigration racks, ventilation equipment, air conditioning equipment, computers, projectors, loundry, compactor, lighting, outlets. it came out to be 279.6kw. using table 220.88 and
201-325kw option i reduced it to 239.8kw, which comes out to be 666a and thus the service to be 800a.

i am trying to get a calculated value of the current that the rms clamp would read on each phase should the restaurant is operating at full load.

can the sum of panel schedules loads and loads from equipment on separate swithces be used as grounds for the service for this new restaurant.

an electrical room can accomodate the upgrade to 600a by putting 600a ct and 600a switch, not 800a. for 800a we need additional room.


thank you, igor
 
alternate method to determining service

alternate method to determining service

hi. i needed the calculted current to determine if the service could be 600a instead of 800a.

so, the answer is no, i cannot use this method to base my service on? am i understanding you right?

thanks, igor
 

kwired

Electron manager
Location
NE Nebraska
Try your calculations not using the optional method in 220 part IV. Use whichever calculation results in lower value if it gets below 600. Double check that you have correct values in either calculation.

Remember if you are trying hard to find a way to get it under 600, there must be significant enough load that making it 800 is worth serious consideration anyway.

Maybe looking for different type of 800 amp gear that will fit where you need it is a better solution than trying to shave the load calculations? Example may be I-line panel in place of a 800 amp fused disconnect - you can fit the main and distribution branches all in a tighter space than with separate enclosures for each. 600 and 800 amp I line panel are both going to be approximately same size - just will have different bus.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
If the service is 800 amps now but they only have 3- 200 amp mains feeding the building then you can be pretty sure the 800 amp service is not needed if nothing is added. However a load calculation is the way to go.
 

kwired

Electron manager
Location
NE Nebraska
If the service is 800 amps now but they only have 3- 200 amp mains feeding the building then you can be pretty sure the 800 amp service is not needed if nothing is added. However a load calculation is the way to go.
My understanding is this is a space in a building with a 400 amp feed to it. All the occupant has for limitations is border walls but can do most anything within that space. If the 400 amp feed is not enough something will need to be done about that.

Hint for OP: making that feed 480 volts instead of 208 could be an effective way to increase capacity if that is an option.
 
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