Residential Service/ Solar

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Michael Duffy

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Location
Redding, California
BACKGROUND INFO:
Utility enters the property from overhead pole transformer. The service the runs underground in 2 inch PVC containing three 4/0 aluminum conductors approximately 315 feet. I calculate 5% voltage drop (not the point of the question because it is existing). Conductors terminated into 200 amp residential meter combination panel. The house is using around 11K KWH/yr.

MORE BACKGROUND INFO:
Customer purchased 19.8 KW solar system to connect to this residential service.

QUESTION:
The breaker that ties the solar into the main panel is a 2 pole 125 amps. This would greatly exceed the 200 amp bus withing that main panel. To comply, the panel requires a 385 amp buss (400). Upgrading the service to 400 amp would incur a huge cost of replacement of the underground from the utility pole to the existing 200 amp meter combination panel. I suggested to install a 400 amp meter combination panel and de-rate the main breaker to 200 amps, leaving the existing underground as it is. Am I creating a violation ANYWHERE? I am asking for permission, not forgiveness. :)
 
Michael Duffy said:
BACKGROUND INFO:
Utility enters the property from overhead pole transformer. The service the runs underground in 2 inch PVC containing three 4/0 aluminum conductors approximately 315 feet. I calculate 5% voltage drop (not the point of the question because it is existing). Conductors terminated into 200 amp residential meter combination panel. The house is using around 11K KWH/yr.

MORE BACKGROUND INFO:
Customer purchased 19.8 KW solar system to connect to this residential service.

QUESTION:
The breaker that ties the solar into the main panel is a 2 pole 125 amps. This would greatly exceed the 200 amp bus withing that main panel. To comply, the panel requires a 385 amp buss (400). Upgrading the service to 400 amp would incur a huge cost of replacement of the underground from the utility pole to the existing 200 amp meter combination panel. I suggested to install a 400 amp meter combination panel and de-rate the main breaker to 200 amps, leaving the existing underground as it is. Am I creating a violation ANYWHERE? I am asking for permission, not forgiveness. :)
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Why not just interconnect on the line side of the MDP OCPD and call it good? But yes, you can beef up the bus of the MDP and leave the main breaker as is to fit the 120% rule. A line side tap would probably be cheaper, though.
 
Michael Duffy said:
Great points, however, I am guessing my suggesting is easier to get approval through local building inspectors. I really appreciate your reply. You have helped me greatly. Thank you.
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You are welcome. We do what you are suggesting (increase the bus rating while leaving the main breaker the same in order to fit more PV in the MDP) pretty often. We had one inspector drag his feet a bit when he first saw it but he came around.
 
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