vw55
Member
- Location
- California
I have a project I'm reviewing that serves 22 residential units and 4 retail units. The main switchboard is 120/24V 3ph 4w, rated 1200A. Phase C is noted as the high leg or red leg of the system.
The current residential calculated load, based on NEC 220 is 112.86 kVA and is fed by a 600A, 120/240V, 1ph, 3W sub-section of the main switchboard with a 600/2 breaker connected across phases A & B. Each of the residential units has a 125A load center installed, fed by a 100/2 tenant disconnect and meter.
The house distribution (elevator, pump equipment, etc.) is consists of a 400A, 120/240V 3ph, 4w sub-section of the main switchboard with a 300/3 breaker. It's calculated load, based on NEC 220 is 76.0 kVA.
Two retail spaces are fed from the main switchboard with a 100/3 circuit breaker and a third retail space is fed from the main switchboard with a 125/3 circuit breaker. Their combined calculated load, based on NEC 220 is 43.5 kVA.
The fourth retail space is tapped at the utility source and fed from the main switchboard with a 400/3 circuit breaker. It's calculated load, based on NEC 220 is 42.375 kVA.
The owner wants to add air conditioning to the residential units, connecting to each unit's metered sub-panel. The mechanical engineer has suggested two types of HVAC systems, a VRF system which will add 356.3 kVA and a split system which will add 283.632 kVA to the system. Either system will require the 600A residential distribution to be replaced.
I need to determine if the 1200A main switchboard is sufficient for this added load or will it need to be replaced as well?
Since there isn't a totalizing meter on the switchboard, I'm left to calculating the equivalent load at the utility point of connection. I've seen red leg calculations before, but am not familiar enough with them to understand the conversion of the three phase load to single phase and use of the multiplying factors depending on the line current ratios. Is there a step-by-step reference available that someone can recommend? Any help would be truly appreciated.
The current residential calculated load, based on NEC 220 is 112.86 kVA and is fed by a 600A, 120/240V, 1ph, 3W sub-section of the main switchboard with a 600/2 breaker connected across phases A & B. Each of the residential units has a 125A load center installed, fed by a 100/2 tenant disconnect and meter.
The house distribution (elevator, pump equipment, etc.) is consists of a 400A, 120/240V 3ph, 4w sub-section of the main switchboard with a 300/3 breaker. It's calculated load, based on NEC 220 is 76.0 kVA.
Two retail spaces are fed from the main switchboard with a 100/3 circuit breaker and a third retail space is fed from the main switchboard with a 125/3 circuit breaker. Their combined calculated load, based on NEC 220 is 43.5 kVA.
The fourth retail space is tapped at the utility source and fed from the main switchboard with a 400/3 circuit breaker. It's calculated load, based on NEC 220 is 42.375 kVA.
The owner wants to add air conditioning to the residential units, connecting to each unit's metered sub-panel. The mechanical engineer has suggested two types of HVAC systems, a VRF system which will add 356.3 kVA and a split system which will add 283.632 kVA to the system. Either system will require the 600A residential distribution to be replaced.
I need to determine if the 1200A main switchboard is sufficient for this added load or will it need to be replaced as well?
Since there isn't a totalizing meter on the switchboard, I'm left to calculating the equivalent load at the utility point of connection. I've seen red leg calculations before, but am not familiar enough with them to understand the conversion of the three phase load to single phase and use of the multiplying factors depending on the line current ratios. Is there a step-by-step reference available that someone can recommend? Any help would be truly appreciated.