frflaspo
Member
- Location
- Fayette, Missouri
- Occupation
- General Contractor
I am working on a multi-unit apartment building, containing 8 individual units on the second floor above a commercial retail space (the lower level is completely independent, and has it's own electric service). Each unit will be approximately 450-500 sq feet, with individual mini-split heat/air, hot water heater, stove, & refrigerator. Utility service is supplied by the local municipality. I believe I have my demand load calculations complete, but I was looking for someone to verify them. These are based on the standard calculation under the NEC Article 220:
Each apartment is approximately 450 sq ft (450 * 3vA = 1350vA), plus the presumed two small appliances (3000vA). Additionally, each will have its own mini-split A/C & heat system (15A x 240v = 3600vA). Each unit will also have its own stove range (40A x 240v = 9600vA). Water heaters will be 30gal tanks, 3.8 kW (3800vA). I am not including any washer/dryers, which will be in a communal area on a separate panel, which already has its own service line (as will hallway and exit lights).
As I understand the calculation, for the general load, the first 3000vA gets calculated at 100%, with the remaining 1350vA at 35% (3000 + 473). The A/C unit and range are at 100% (3600vA + 9600vA) and the water heater at 75% (3800 x .75 = 2850vA). That brings me to 19,523vA per unit (3000+473+3600+9600+2850). As I see it, that will allow me to run each unit on it’s own individual 100 amp panel.
Multiplied by 8 units, that's 156,184vA demand. The formula I have is Demand=vA/(240 x 1.732) for single phase service, which give me a 376 amp demand. In order to keep it at 80% usage, a minimum of 500 amp service would be required (which is significantly lower than I was imagining, so I may have gotten lost in the numbers).
If those numbers are correct, then my next question is about 3-phase power. I only want single phase service in the apartments, but there is currently 3-phase power coming to the building. It appears to be coming in on 3/0 copper stranded wire. Can that line provide 500 amp service? Would I need to convert the power over to a single phase system?
I am also looking at several different residential meter stacks, and it appears that Eaton makes several 4-gang units that take three-phase in, and then single phase out at 125 A. If that eliminates the requirements for a transformer, then I think I could use that to feed at least one of the meter gangs.
I would appreciate any thoughts, suggestions or recommendations...
Each apartment is approximately 450 sq ft (450 * 3vA = 1350vA), plus the presumed two small appliances (3000vA). Additionally, each will have its own mini-split A/C & heat system (15A x 240v = 3600vA). Each unit will also have its own stove range (40A x 240v = 9600vA). Water heaters will be 30gal tanks, 3.8 kW (3800vA). I am not including any washer/dryers, which will be in a communal area on a separate panel, which already has its own service line (as will hallway and exit lights).
As I understand the calculation, for the general load, the first 3000vA gets calculated at 100%, with the remaining 1350vA at 35% (3000 + 473). The A/C unit and range are at 100% (3600vA + 9600vA) and the water heater at 75% (3800 x .75 = 2850vA). That brings me to 19,523vA per unit (3000+473+3600+9600+2850). As I see it, that will allow me to run each unit on it’s own individual 100 amp panel.
Multiplied by 8 units, that's 156,184vA demand. The formula I have is Demand=vA/(240 x 1.732) for single phase service, which give me a 376 amp demand. In order to keep it at 80% usage, a minimum of 500 amp service would be required (which is significantly lower than I was imagining, so I may have gotten lost in the numbers).
If those numbers are correct, then my next question is about 3-phase power. I only want single phase service in the apartments, but there is currently 3-phase power coming to the building. It appears to be coming in on 3/0 copper stranded wire. Can that line provide 500 amp service? Would I need to convert the power over to a single phase system?
I am also looking at several different residential meter stacks, and it appears that Eaton makes several 4-gang units that take three-phase in, and then single phase out at 125 A. If that eliminates the requirements for a transformer, then I think I could use that to feed at least one of the meter gangs.
I would appreciate any thoughts, suggestions or recommendations...