Service will be 120/240 volt single phase and will feed one commercial occupancy, a bar, and two apartment units, each with 100 amps metered separately. Can I use a 200 amp service? Or do I need a 320 amp service? What if I install 60 amp services for each apartment? Will that allow me to use a 200 amp service. The total load is about 140 amps.
What size service?
- Thread starter mlnk
- Start date
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kwired
Electron manager
- Location
- NE Nebraska
If you have a common service conductor supplying all three service disconnecting means and the total load calculation is only 140 amps, technically you can get by with that common conductor being a 140 amp conductor. You still need conductor sized in accordance with overcurrent protection at each individual disconnecting means though.
So lets say you decided to put three 150 amp mains in (for whatever reason) you could have a code compliant install if you had a three gang meter socket with at least 140 amp conductor supplying it, and then had 150 amp conductor to each 150 amp main. Seems strange but code allows it.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Without going into all the permutations of how you could do it...
- The code doesn't generally require the service to be rated greater than the calculated load. So you could put this all on a single 200A service disconnect, as far as I know.
- If you have separate service disconnects for the different occupancies, the code arguably requires the apartments (dwellings) to each have 100A rated disconnecting means. The other two occupancies could be 60A. See 230.79.
- Oddly, if there are multiple service disconnecting means, the service conductors don't have to be rated for the sum of the overcurrent devices, only for the calculated load. So conceivably you could have 4 main breakers whose total rating together is 320A, and service conductors rated 140A. See 230.90 Exception 3. But if there is a single disconnect that's not true. If you have a single 200A main breaker then the service conductors must be rated 200A (or at any rate more than 175A per 240.4(B)).
- The code doesn't generally require the service to be rated greater than the calculated load. So you could put this all on a single 200A service disconnect, as far as I know.
- If you have separate service disconnects for the different occupancies, the code arguably requires the apartments (dwellings) to each have 100A rated disconnecting means. The other two occupancies could be 60A. See 230.79.
- Oddly, if there are multiple service disconnecting means, the service conductors don't have to be rated for the sum of the overcurrent devices, only for the calculated load. So conceivably you could have 4 main breakers whose total rating together is 320A, and service conductors rated 140A. See 230.90 Exception 3. But if there is a single disconnect that's not true. If you have a single 200A main breaker then the service conductors must be rated 200A (or at any rate more than 175A per 240.4(B)).
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
140 amps load calc sounds low to me.
My load calculations are:
1. residential dwelling unit 1230 SF = 68 amps per NEC 220-83
2. small dwelling unit 270 SF = 26 amps
3. commercial bar 1780 SF = 86 amps all equipment @ 100% FLA
total calculated load: 180 amps ( it is not 140 amps as mentioned above)
Use 200 amp 120/240 single phase service
with three 3/0 copper conductors in 2 " rigid conduit service riser
can not use 2/0 copper because on unit is commercial.
Does this look OK?
1. residential dwelling unit 1230 SF = 68 amps per NEC 220-83
2. small dwelling unit 270 SF = 26 amps
3. commercial bar 1780 SF = 86 amps all equipment @ 100% FLA
total calculated load: 180 amps ( it is not 140 amps as mentioned above)
Use 200 amp 120/240 single phase service
with three 3/0 copper conductors in 2 " rigid conduit service riser
can not use 2/0 copper because on unit is commercial.
Does this look OK?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If your calcs are correct then this looks fine. You have hvac and water heaters in there also
kwired
Electron manager
- Location
- NE Nebraska
More technically you can't use 2/0 copper because it isn't supplying a single family dwelling or an individual dwelling unit of two family or multifamily dwelling units.
If this were three dwellings being supplied with same load calc, you still can't use it for any common supply conductors but can use 310.15(B)(7) for feeders to individual dwelling units.
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