PV Supply side connection

[dwils1980]

I have an older meter main combo style service that is getting a PV system tied to it. This older meter main has a bussed connection on the load side of the meter going to the customer side of the equipment where you have 4 total slots. There is a 100amp breaker installed on the bus feeding the main panel leaving two slots open which will be used for a PV OCPD. To me this would qualify as a supply side connection, but article 705.11 only talks about sizing the PV system based on the size of service conductors. If the rating of the service equipment is 125 amps and the service conductors are 1/0 CU or larger that means I could potentially install a PV system sized larger than the max rating for the service bus. Any thoughts on this? Is there an article in the NEC that I’m missing that would prevent an installation like this?

 

[jaggedben]

The bus bars are also service conductors. 'Conductors' is not defined in the NEC so you use the dictionary definition. The busbars conduct electricity for the circuit on the line side of the service disconnect so they meet the definition of service conductors.

 

[dwils1980]

The bus bars are also service conductors. 'Conductors' is not defined in the NEC so you use the dictionary definition. The busbars conduct electricity for the circuit on the line side of the service disconnect so they meet the definition of service conductors.

I get that, but in the case i stated above do you size your PV system to the service conductor rating or the service bus bar rating as they are different? Obviously best practice would lean towards the most restrictive of the two but as far as code enforcement goes I don’t see anything that would push you one way or the other.

 

[jaggedben]

If I recall correctly the code simply says 'rating of the service' which would be the weakest link in the chain, i.e. the busbar. I think any other interpretation, no matter what the letter of the code says, would be in bad faith.

 

[Carultch]

If I recall correctly the code simply says 'rating of the service' which would be the weakest link in the chain, i.e. the busbar. I think any other interpretation, no matter what the letter of the code says, would be in bad faith.

If service conductors were sized with the 83% rule, does that impact the upper limit of PV that can be interconnected?

For example, given 2/0Cu on a 200A service, does this limit you to 200A, or does it limit you to 175A? My guess is that it limits you to the ampacity of the service conductors as if they were in a feeder, which would be 175A in this example.

 

[shortcircuit2]

If service conductors were sized with the 83% rule, does that impact the upper limit of PV that can be interconnected?

For example, given 2/0Cu on a 200A service, does this limit you to 200A, or does it limit you to 175A? My guess is that it limits you to the ampacity of the service conductors as if they were in a feeder, which would be 175A in this example.

How about the meter sockets are generally rated 160amp continuous for 200 and 320amp for the 400 socket.

 

[dwils1980]

If I recall correctly the code simply says 'rating of the service' which would be the weakest link in the chain, i.e. the busbar. I think any other interpretation, no matter what the letter of the code says, would be in bad faith.

705.11(A) does not mention a service rating but it states service conductors

 

[wwhitney]

If service conductors were sized with the 83% rule, does that impact the upper limit of PV that can be interconnected?

No, it shouldn't. Because of the 125% factor in the supply side connection rules, the continuous current carried will be at most 80% of the service rating. Which is less than 83%, and ampacity is a continuous rating. So no problem.

The 2020 NEC actually get this correct for a supply side connection, it no longer refers to "rating of the service," and it doesn't include the 125% factor:

705.122(A) The sum of the power source continuous current output ratings on a service, other than those controlled in accordance with 705.13, shall not exceed the ampacity of the service conductors.

So that would let you connect power source output breakers (which have the 125% factor) exceeding the ampacity of the service conductors.

Cheers, Wayne

 

[wwhitney]

705.11(A) does not mention a service rating but it states service conductors

Right, it's the ampacity of the service conductors, but that includes the busbars in your meter main. So even though the ampacity of your wire-type service conductors may be 150A, the ampacity of your busbar-type service conductors is 125A, and so the 125A ampacity controls.

Cheers, Wayne