Do we have to follow 2017 NEC 240.21(B)(2) for the supply side connection per 705.31?

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Frank6172

Member
Location
Maryland
Occupation
Engineer
Hi all,

Any help will be greatly appreciated! Here is the scenario:

We interconnected our solar system through a supply side connection made at the utility service entrance conductors of a 1200A MSP with 1200 MCB. The conductor run from the fused PV system AC disconnect(OCPD) to the point of interconnection is 14' so we plan to use the cable limiters per the Exception of 705.31 to work around the 10' rule. However, the inspector is saying we need to comply with the 25' tap rule per 240.21(B)(2) which will result in increasing our conductor size to not less than 1/3 of the rating of MCB. In my understanding, 240.21 is for the tap conductors that receive their supply, not for conductors that backfeed the utility. Also, I believe supply side connection has the different definition to "tap" so 240.21 does not really apply to the supply side connection for solar photovoltaic. Am I right? Has anyone encountered this situation during the inspection?

Thanks!
 
Your AHJ is treating the interconnection conductors as feeders and not as the service entrance conductors they are. NEC 240.21 is not applicable to service entrance conducers since there is no customer owned OCPD upstream.
 
Frank6172 said:
Hi all,

Any help will be greatly appreciated! Here is the scenario:

We interconnected our solar system through a supply side connection made at the utility service entrance conductors of a 1200A MSP with 1200 MCB. The conductor run from the fused PV system AC disconnect(OCPD) to the point of interconnection is 14' so we plan to use the cable limiters per the Exception of 705.31 to work around the 10' rule. However, the inspector is saying we need to comply with the 25' tap rule per 240.21(B)(2) which will result in increasing our conductor size to not less than 1/3 of the rating of MCB. In my understanding, 240.21 is for the tap conductors that receive their supply, not for conductors that backfeed the utility. Also, I believe supply side connection has the different definition to "tap" so 240.21 does not really apply to the supply side connection for solar photovoltaic. Am I right? Has anyone encountered this situation during the inspection?

Thanks!
Click to expand...
240.21(B) specifically applies to taps of feeders, not service conductors. pv_n00b beat me by about 2 seconds. :D
 
Are you still on the 2017 code? I thought that rule about cable limiters was removed in 2020.

Treating supply side connections according to rules for services is a lot clearer in 2020 and 2023 than it was in 2017. That said, under 2017 one argument against having to follow 240.21 is that the rules for this are in 705 and chapter 7 modifies chapter 2. Also, your conductors don't strictly meet 240's definition of tap conductors if there is no overcurrent protection ahead of them.
 
pv_n00b said:
Your AHJ is treating the interconnection conductors as feeders and not as the service entrance conductors they are. NEC 240.21 is not applicable to service entrance conducers since there is no customer owned OCPD upstream.
Click to expand...
Thanks very much!
 
jaggedben said:
Are you still on the 2017 code? I thought that rule about cable limiters was removed in 2020.

Treating supply side connections according to rules for services is a lot clearer in 2020 and 2023 than it was in 2017. That said, under 2017 one argument against having to follow 240.21 is that the rules for this are in 705 and chapter 7 modifies chapter 2. Also, your conductors don't strictly meet 240's definition of tap conductors if there is no overcurrent protection ahead of them.
Click to expand...
Yes. We are still on 2017 code. I found out 2020 and 2023 are much more clear on this matter but the AHJ does not allow us to use them in advance. Thanks for your insight!
 
jaggedben said:
Are you still on the 2017 code? I thought that rule about cable limiters was removed in 2020.
Click to expand...
The cable limiter language was removed from the 2023 NEC due to a fight with the CMP that covers Art. 230. In 2023 the supply side interconnection points back to 230. In 2026 it looks like the language will substantially return to what it was before 2023 since the CMPs seem to have buried the hatchet, although I don't know who they buried it in. ;) The return of cable limiters in 2026 includes the requirement that they will only be allowed under engineering supervision.
 
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