I'm looking a project where the owner has a switchboard lineup of |Dist-A|CT-Cab-A|Main-A|Tie|Main-B|CT-Cab-B|Dist-B|
Dist-A is rated at 3000A while all other bus sections, main breakers, and tie breakers are 4000A.
The switchboard already has a load side PV connection tapped into CT-Cab-A that has an output current of 758A. This was installed in 2014 under 2011 NEC so it appears to be code, I haven't confirmed the size of the overcurrent protection but it would have to be 800A for it to be code since back then the two breakers could add up to 120% of the bus rating.
The client is looking to add (2) 350kw generators that would parallel before getting to the switchboard. These generators together would be roughly 1052A.
Based on the NEC 2017 Article 705, we will need to relocate the PV Connection as it currently would not meet the bus rating considering it is not at the opposite end of the bus. I was planning on tapping the bus past the 3000A Dist. Section to a new switchboard that would tie in the PV and Generators. This would allow us to use the 120% value of the 4000A bus. However, we will need to dial down the long term trip setting of the 4000A main circuit breaker based on the following.
(758A+1052A)*1.25 = 2263A.
4800A allowance - 2263A = 2537A.
We would need to set the breaker to the next available trip setting of 0.6 or 2,400A to make it work. This also means if the PV and or Generators are down the building will need to be able to run on it's own through the Main Circuit Breaker with only 2,400A worth of capacity. I'll need to verify what load has been seen through the switchboard meter to figure out if 2,400A will be enough.
Are there any other work arounds that I'm not seeing here? Any input or critique is welcomed and appreciated.
Dist-A is rated at 3000A while all other bus sections, main breakers, and tie breakers are 4000A.
The switchboard already has a load side PV connection tapped into CT-Cab-A that has an output current of 758A. This was installed in 2014 under 2011 NEC so it appears to be code, I haven't confirmed the size of the overcurrent protection but it would have to be 800A for it to be code since back then the two breakers could add up to 120% of the bus rating.
The client is looking to add (2) 350kw generators that would parallel before getting to the switchboard. These generators together would be roughly 1052A.
Based on the NEC 2017 Article 705, we will need to relocate the PV Connection as it currently would not meet the bus rating considering it is not at the opposite end of the bus. I was planning on tapping the bus past the 3000A Dist. Section to a new switchboard that would tie in the PV and Generators. This would allow us to use the 120% value of the 4000A bus. However, we will need to dial down the long term trip setting of the 4000A main circuit breaker based on the following.
(758A+1052A)*1.25 = 2263A.
4800A allowance - 2263A = 2537A.
We would need to set the breaker to the next available trip setting of 0.6 or 2,400A to make it work. This also means if the PV and or Generators are down the building will need to be able to run on it's own through the Main Circuit Breaker with only 2,400A worth of capacity. I'll need to verify what load has been seen through the switchboard meter to figure out if 2,400A will be enough.
Are there any other work arounds that I'm not seeing here? Any input or critique is welcomed and appreciated.