Service Side Tap Rules and PV Interconnection

[pvgreeze]

Hello all...I have an unusual predicament that I've run into a couple of times for a couple of perspective projects.

I've run into a number of meter enclosures that feed two separate service disconnects, and the two sets of parallel conductors are tapped within the meter enclosure, so the only available points of interconnection exist outside of the meter enclosure. In one particular instance, there are two separate 200A circuits (3/0 Cu) coming out of the meter enclosure, and we want to interconnect a 225A PV circuit on the line side.

I'm trying to think of different interconnection solutions aside from 1) upgrading one of the existing 200A circuits to 225A and connecting on the line side of the MCB or 2) downsizing the AC output of the system.

Is it possible to intercept one of the two 200A circuits and interconnect via taps? Sorry if this is a stupid solution, but I can't think of many other options. My thought process was to replace one of the 3/0 feeders leaving the meter enclosure with a 4/0 meter between the load side of the meter and the PV interconnection (we have utility access inside of the meter enclosure). Below the meter, we will install our taps with the existing 3/0 (200A) circuit and our incoming 4/0 (225A). In essence, there will be 4/0 between the meter and the tap, 4/0 between the tap and the PV disconnect (fused for 225A), and 3/0 between the tap and the existing 200A MCB. This scenario seems acceptable under 240.21(B)(2) with the exception of the conductor between the meter and tap not being a 'feeder' but rather a 'service' conductor.

Does any of this sound reasonable? I apologize if what I am describing is is a very rudimentary question or a completely code violation filled way to interconnect. I've attached a sketch to help illustrate what I'm describing. I'm just trying to figure out the best way to interconnect a solar system that is sized off of a single utility meter that has multiple services tapped out of the meter enclosure, and I'm still learning the basics of the solar world. Thanks, -pvgreeze


PS - I read thru that other feeder tap thread, but that seems concerned with load side interconnection, not line side.

 

[wwhitney]

A little more background information would help: what version of the NEC is applicable, what is the voltage (just for reference), and what is the sum of the maximum continuous currents of all the inverters (call that I_inv)?

Note that for the 2020 NEC (and perhaps earlier versions), 705.11(A) does not require the service conductors to have an ampacity of 125% of I_inv, but just 100% of I_inv. That is distinct from feeders, where you have to use 125% of I_inv unless you use a 100% rated breaker, and you have to use 125% of I_inv for all load side busbar and feeder computations. Of course, you do have to install a service disconnect (in effect) for the PV supply side connection, so the sizing requires a little thought about where the 125% requirement starts.

Cheers, Wayne

 

[pvgreeze]

This is in NJ, so it falls under the 2017 NEC, so that provision doesn't actually exist in the 2017 NEC haha. Voltage is 240/120V, 1Ph, 3W.

We're looking at three Solaredge SE11400H-US inverters and one SE5000H-US inverter, so a total I_inv of 163.5A...125% puts us at 204.4A. If that is the case with the 2020 NEC, then this won't be the first time 2020 has had a very useful clause that 2017 lacks! Wish NJ would just adopt it already.

 

[pv_n00b]

I don't see any reason this would not be acceptable. NEC 240 tap rules don't apply since these are not protected feeders, there is no upstream OCPD until you get to the utility protection. So best to size the conductors based on the service conductor sizing rules in 230.