Incoming Load Calculation for Non Dwelling Unit

[electricalintern]

The existing building has 3 tenants with a electrical service off 400AMP/208V/3 Phase.
Based on the landlord work letter, the tenants are asking for the following service
Tenant A: 400AMP/208V/3 Phase [General Store]
Tenant B: 400AMP/208V/3 Phase [Fast Food]
Tenant C: 200AMP/208V/3 Phase [Fast Food]

2 Tenants will be fast food and the other one is a general store. There will be gas at this location and not be fully electric.

Can I use Table 220.88 and keep the existing 400 AMP service for the General store?

=(400+200)*360 = 216kVA
.5(216) + 200 = 308kVA [Table 220.88]
308kVA/360 = 856 AMP

Should I ask the utility company to update the service to 1200AMP/208V/3 Phase

What is the best method to calculate the new service.

 

[JoeStillman]

We don't typically size a landlord service using the tenant's requested service sizes. If you don't have the actual connected loads for all the tenants (and we usually don't), we will size the landlord service for 20W/ft² retail and 30W/ft² restaurant. To be cautious, add in another 10W/ft² for the landlord's non-rental space like corridors, utility rooms, etc. kW and kVA are interchangeable, viewed at this level of accuracy.

So if I assume there is no landlord space, General store A gets 400A, 3Ø, 208 or 144 kVA. That service is big enough for a 7,200 ft² store. Fast food B wants a service big enough for a 4,800 ft² restaurant. And Fast food C wants a service big enough for a 2,400 ft² restaurant. Is this a 14,400 ft² building? If it's that size with the tenant proportions per my assumptions, a 1,000A service would not be unreasonable. But you can see that if the building is smaller, the sum of all the service sizes would be larger than the service you need for the building overall.

To sum it up, without actual connected loads, our service-size calculations are based on rules of thumb like these. You can't do an NEC calculation in reverse by looking at a service size; you can only do an NEC service size if you know the connected loads. When we consult for landlords, they often don't even have a tenant lined up yet, so we use our oija board, crystal ball, chicken entrails, and the thumb of the oldest guy in the office.

 

[electricalintern]

We don't typically size a landlord service using the tenant's requested service sizes. If you don't have the actual connected loads for all the tenants (and we usually don't), we will size the landlord service for 20W/ft² retail and 30W/ft² restaurant. To be cautious, add in another 10W/ft² for the landlord's non-rental space like corridors, utility rooms, etc. kW and kVA are interchangeable, viewed at this level of accuracy.

So if I assume there is no landlord space, General store A gets 400A, 3Ø, 208 or 144 kVA. That service is big enough for a 7,200 ft² store. Fast food B wants a service big enough for a 4,800 ft² restaurant. And Fast food C wants a service big enough for a 2,400 ft² restaurant. Is this a 14,400 ft² building? If it's that size with the tenant proportions per my assumptions, a 1,000A service would not be unreasonable. But you can see that if the building is smaller, the sum of all the service sizes would be larger than the service you need for the building overall.

To sum it up, without actual connected loads, our service-size calculations are based on rules of thumb like these. You can't do an NEC calculation in reverse by looking at a service size; you can only do an NEC service size if you know the connected loads. When we consult for landlords, they often don't even have a tenant lined up yet, so we use our oija board, crystal ball, chicken entrails, and the thumb of the oldest guy in the office.

Thank you for the helpful tip.

Can I ask how the rule of thumb work came to be 20W/ft² for retail and 30W/ft² for restaurant?
Is this only for stores with gas, what if it was all electric only?

 

[JoeStillman]

Thank you for the helpful tip.

Can I ask how the rule of thumb work came to be 20W/ft² for retail and 30W/ft² for restaurant?
Is this only for stores with gas, what if it was all electric only?

It's for all-electric with heat pumps. If you have more info about what will be on the gas service, you probably have enough info to do a real load calculation.

 

[JoeStillman]

The values are based on the experience of a client I once worked for who built shopping malls all over the country.

 

[electricalintern]

It's for all-electric with heat pumps. If you have more info about what will be on the gas service, you probably have enough info to do a real load calculation.

I wish I had more information about what loads are going to be connected. I just know the building is getting gas per the landlord work letter as well.