Inverter source circuit taps in meter can.

[peterlarsen.suntec]

I started recently with a residential solar installation company in SC. SC implements NEC 2014 July 1st 2016. We are installing mostly large systems for resi (10Kw to 20Kw). Most of our interconnections have been supply side taps in the meter can using self piercing taps on the load side feeders. Result...fail, fail, fail again. Both the utility and inspectors have been failing us. So our design team came up with a solution supposedly accepted by the inspectors and the utility. Here's the solution...Have the utility pull the fuses at the transformer, modify the terminals in the can with bolt on double lugs on the line side and tie in the inverter source circuit. Sounded sketchy to me, I never heard of such a thing. Its such a waste of time waiting for the service interruption and I felt there are better solutions. I called an engineer that I know from the same utility in NC. He said no, that won't be acceptable. He stated " if you are going to tie into the meter can you must use the UL Listed accessory for that make of can. Such as Milbank K4977-int. Another engineer from a co-op said NEVER!
I reached out to some of my associates doing taps for other companies. One, let's call her the Tap Queen, said never ever tie into the meter can. She said pull the meter (get approval to cut the tab) run new line side feeders through a new 12×12×8 and make your tap there. She said "no one can argue with that as long as you observe the 10' rule for taps.
Another, let's call him the Tap King said, " Just tap your supply feeders in the MDP using self piercing taps. "We are doing it on all of our installs regardless of size, Its quicker!" Is this solution a violation of NEC 312.8.

Also I read an article on 705.12(D)(2) "Junction box blog" and I can't see where any options are acceptable without "primary source OCP" there is no way to calculate the ampacity of the portion of the supply feeders on the load side of the inverter output connection according to 705.12(D)(2)(1)(a). Do we use the transformer fuse rating?

Thanks for your input.



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[ggunn]

I started recently with a residential solar installation company in SC. SC implements NEC 2014 July 1st 2016. We are installing mostly large systems for resi (10Kw to 20Kw). Most of our interconnections have been supply side taps in the meter can using self piercing taps on the load side feeders. Result...fail, fail, fail again. Both the utility and inspectors have been failing us. So our design team came up with a solution supposedly accepted by the inspectors and the utility. Here's the solution...Have the utility pull the fuses at the transformer, modify the terminals in the can with bolt on double lugs on the line side and tie in the inverter source circuit. Sounded sketchy to me, I never heard of such a thing. Its such a waste of time waiting for the service interruption and I felt there are better solutions. I called an engineer that I know from the same utility in NC. He said no, that won't be acceptable. He stated " if you are going to tie into the meter can you must use the UL Listed accessory for that make of can. Such as Milbank K4977-int. Another engineer from a co-op said NEVER!
I reached out to some of my associates doing taps for other companies. One, let's call her the Tap Queen, said never ever tie into the meter can. She said pull the meter (get approval to cut the tab) run new line side feeders through a new 12×12×8 and make your tap there. She said "no one can argue with that as long as you observe the 10' rule for taps.
Another, let's call him the Tap King said, " Just tap your supply feeders in the MDP using self piercing taps. "We are doing it on all of our installs regardless of size, Its quicker!" Is this solution a violation of NEC 312.8.

Also I read an article on 705.12(D)(2) "Junction box blog" and I can't see where any options are acceptable without "primary source OCP" there is no way to calculate the ampacity of the portion of the supply feeders on the load side of the inverter output connection according to 705.12(D)(2)(1)(a). Do we use the transformer fuse rating?

Thanks for your input.

FWIW, we install supply side connected PV with IPC's in the MDP on the supply side of the main breaker all the time in every AHJ's territory in which we operate, save one - San Antonio, where they do not allow it.

 

[peterlarsen.suntec]

FWIW, we install supply side connected PV with IPC's in the MDP on the supply side of the main breaker all the time in every AHJ's territory in which we operate, save one - San Antonio, where they do not allow it.

My friend the "Tap King" never had any issues either, still the question remains which 705.12 option do we reference. We are treating our PV Disco as a service entrance for bonding and grounding. But there is no OCP on the primary source that I can tell, is the meter itself considered OCP or do we use the utility fuse rating.

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[ggunn]

My friend the "Tap King" never had any issues either, still the question remains which 705.12 option do we reference. We are treating our PV Disco as a service entrance for bonding and grounding. But there is no OCP on the primary source that I can tell, is the meter itself considered OCP or do we use the utility fuse rating.

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Meters are not OCPD's. Whenever we encounter a MLO (main lug only) MDP (main distribution panel), that is, a MDP without a main breaker in a residential service, we install one. Commercial services are a bit different.

 

[peterlarsen.suntec]

Meters are not OCPD's. Whenever we encounter a MLO (main lug only) MDP (main distribution panel), that is, a MDP without a main breaker in a residential service, we install one. Commercial services are a bit different.

There is no OCPD between the meter and the main. The MDP has 200 amp main breaker and buss. I get all the methods concerning back feeding breakers in the panel. Including, 120% rule, changing out buss bars, de-rateing the main. Still the question remains, how do I verify the 10 foot rule calculations without primary source OCPD. Our designers want taps everywhere to handle various situations with a one size fits all SOP, even on interconnections where we could back feed a breaker In the main. I'm not sold on that practice mostly because of this issue. But I can be convinced if I only had a code or exception to reference. I can't find one. Maybe I'm reading it wrong.

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[ggunn]

There is no OCPD between the meter and the main. The MDP has 200 amp main breaker and buss. I get all the methods concerning back feeding breakers in the panel. Including, 120% rule, changing out buss bars, de-rateing the main. Still the question remains, how do I verify the 10 foot rule calculations without primary source OCPD. Our designers want taps everywhere to handle various situations with a one size fits all SOP, even on interconnections where we could back feed a breaker In the main. I'm not sold on that practice mostly because of this issue. But I can be convinced if I only had a code or exception to reference. I can't find one. Maybe I'm reading it wrong.

Here's the thing - a supply side inverter interconnection is not a tap, and the governing code is is 705.31. Note that the word "tap" does not appear anywhere in the article and it says if it's over 10' from the point of interconnection to the OCPD you must use current limiters at the POI. No 25' rules, etc.

 

[ggunn]

There is no OCPD between the meter and the main. The MDP has 200 amp main breaker and buss. I get all the methods concerning back feeding breakers in the panel. Including, 120% rule, changing out buss bars, de-rateing the main. Still the question remains, how do I verify the 10 foot rule calculations without primary source OCPD. Our designers want taps everywhere to handle various situations with a one size fits all SOP, even on interconnections where we could back feed a breaker In the main.

I am not sure what you are asking; no OCPD between the meter and the MDP is normal. Connecting outside the MDP main breaker is what makes it a supply side connection, and in such a connection there is no OCPD between the POI and the transformer feeding the service. Again, totally normal. I have landed my interconnection directly on the output busbars of a transformer; if the service is CT metered and the CT's are on the transformer busbars right where they enter the wiring cabinet, you can do that and still be on the customer side of the meter. Some AHJ's will approve it.

And like I said in my other response, don't try to use the tap rules; it's not a tap.

It is not possible to establish a SOP concerning supply side connections, at least not in central Texas. CPS (San Antonio) wants it grounded completely differently from every other AHJ in the state and they will not allow IPC connections or supply side connections inside the MDP.

 

[peterlarsen.suntec]

I see, I've been thinking tap. Agreed one size does not fit all. I've been overthinking it. Once line drawings are submitted to the utility it is difficult to make changes and can hold up the PTO. We can pass an inspection, then the utility disapprove the connection, then we have to start over with our design, resubmit the line drawing to the utility change the connection method then fail the inspection and we go to the bottom of the list. It's just a little frustrating.
We will get it straight. I've got a 19KW coming up. I'll be asking the inspector and utility engineer to review our connection (I will suggest a connection on the feeders in the MDP) before we submit our drawings and see what they say.


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[peterlarsen.suntec]

Thanks ggunn, until last year in the Carolinas we didn't do many residential systems over 10Kwdc The utilities, and regulating commissions had burdensome requirements for interconnecting systems over 10Kw. South Carolina passed and implemented its new net metering laws and Distributed Energy Resource Program and utilities are offering amazing incentives to participate. This has created a huge surge in residential installations, for now anyway. As a solar guy, my hope is to do it right, to avoid issues down the line for the public and the industry. Thanks for your help.

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[jaggedben]

Ask all the relevant people what they allow when there are multiple service disconnect enclosures.

These questions highlight why the code needs to clarify the status of line-side conductors. But there's no reason for the relevant authorities to reject any listed method for splicing them. I can't imagine why anyone would reject something like the Millbank accessory.

 

[ggunn]

I see, I've been thinking tap. Agreed one size does not fit all. I've been overthinking it. Once line drawings are submitted to the utility it is difficult to make changes and can hold up the PTO. We can pass an inspection, then the utility disapprove the connection, then we have to start over with our design, resubmit the line drawing to the utility change the connection method then fail the inspection and we go to the bottom of the list. It's just a little frustrating.
We will get it straight. I've got a 19KW coming up. I'll be asking the inspector and utility engineer to review our connection (I will suggest a connection on the feeders in the MDP) before we submit our drawings and see what they say.

Ask your AHJ for a preconstruction meeting if you are at all unsure of what they will and will not approve.

 

[pv_n00b]

This is getting to be a common question on supply side interconnections.

1) Ask what the AHJ and utility want, in the end you have to make them happy and the utility can care less about the NEC.
2) The NFPA has been less than clear about whether the supply side interconnection should be installed as a 10' tap or as a new service entrance. Reading into a lot of guidance outside of the NEC that the NFPA and CMP4 has put out it seems they are leaning towards it being the same as a 10' tap. I and many others feel it's safer to treat it as a service entrance. Both seem to be allowed since neither is required or disallowed. So basically it's up to you and your AHJ how you do it.

In all the PV systems I have been involved in I have found that utilities are very touchy about letting anyone into any area of the system that is theirs, and that includes the meter can. They seem to think that everyone is just waiting for a chance to steal electricity.

Has anyone ever used the exception in 705.31 to use limiters on a supply side interconnection?

 

[pv_n00b]

Also for fun, when the question was submitted to the NFPA in 2013 for guidance here was the response:

Q:

I and the PV industry need some further guidance on how we should be handling the "feeder" circuit for the Supply Side (of the service disconnect) Connection of a Photovoltaic Power system as allowed by 705.12(A), and 230.82(6). It is not clear also why 230.2(5) mentions additional "services" for parallel power production systems, which seems to indicate that a utility interactive PV system could be considered being connected by a service.

A:

Section 230.2(A)(5) retained the “parallel power production systems” as a special condition for an additional service from the 1984 NEC 230-2 exception No. 2. Based on the definition of a service at that time being an “electric supply system” the substantiation which stated “The addition to Exception No. 2 is necessary to permit a solar photovoltaic, wind or other electric power production source to be installed in addition to a (utility) service in a building or other structure” made sense as an additional “electric supply system.” However, once the service was redefined and specified as only being supplied by a utility other solar photovoltaic, wind or other electric power production sources no longer fit the description and more specifically the service cannot “supply” them as 230.2(A) permits.

A service can only be supplied by the serving utility. If electric energy is supplied by other than the serving utility, the supplied conductors and equipment are considered feeders, not a service. See the definition of service in Article 100. The understanding of other electric supply systems being considered a service changed when the definition of service changed during the A98 code cycle. ROC A98 Comment 1-199 Log # 2472 on Proposal 1-132 was accepted and specified that the term “serving utility” not an “electric supply system” be the language used to define a service.



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This indicates that in 2013 the NFPA considered supply side interconnections of PV systems to be feeders and not services. The addition of 705.31 strengthens this determination. It still looks like a service entrance to me so that's how I design them since there is always some load on the circuit even if just the inverter sleep load.

 

[peterlarsen.suntec]

Thanks pv_n00b, I'm learning.

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[iwire]

Here's the thing - a supply side inverter interconnection is not a tap,

I agree.