Utility Requiring Line-Side & Load-Side Disconnect

[pvgreeze]

Hello all, I'm going back and forth with a utility on a design I am working on. The proposed system is to be interconnected on the secondary bushings on an existing pad mounted transformer and is participating in a community solar program, so it is not a typical line side/load side interconnection.

The utility is requiring a "utility disconnect" upstream of the CT cabinet, which is obviously understandable, but then they are requiring a second disconnect immediately downstream of the CT cabinet. I originally proposed a fused DS line side of the CT cabinet and a MLO panel on the load side, which to me was something you would see on a typical new service. I read the utility literature and could not find specific requirements for a singular disconnect on the load side of the CT cabinet. When I inquired, the utility reviewer cited "IEEE/NEC Standards." The reviewer provided no specific code or citation. I initially argued that the line side DS upstream of the CT cabinet could serve as the single disconnecting means as required by 690.13 and 705.22, neither of which states where the switch needs to be sequenced other than that it needs to be between the PV system and the POI.

Am I missing something in 690 or 705? The state is under the 2017 NEC for what its worth. I quickly flipped through both articles (and IEEE 1547) and did not see any mention of the need for a second disconnect. All inverters have dedicated CBs for what its worth per 690.15.

Thanks in advance for any feedback.

 

[jaggedben]

You are not missing anything. There is nothing in 690 or 705 about CT cabinets. The NEC does not give a --- whether you have metering or where it is.

What was their precise objection to your proposal? You didn't say.

 

[pvgreeze]

You are not missing anything. There is nothing in 690 or 705 about CT cabinets. The NEC does not give a f--- whether you have metering or where it is.

What was their precise objection to your proposal? You didn't say.

They didn't have a precise objection, other than that it is "required by IEEE/NEC standard," which (as you stated and I stated initially) it is not. I've attached the screenshot that the reviewer shared with me. I shared specific codes from NEC 690.13, but they did not cite anything specific back other than this screenshot.

This is PEPCO/MD, and I couldn't find whatever document the reviewer is sharing with me when I first designed this.

Seems like the utility is just deciding they want a second DS for no reason.

 

[jaggedben]

My interpretation would be that the "IEEE/NEC" required disconnect is your service disconnect and that the PEPCO required disconnect is a 'meter disconnect' such as is referred to in 230.82(3). (If this different than what they would require for a non-generation service of the same voltage/phases/amps, I'd consider that discriminatory. If anyone cares.) So the meter disconnect does not need to be fused or follow any particular NEC rules other than general suitability (Article 110), although it likely needs to be PEPCO approved. But then it is also not your service disconnect

An MLO panel on the load side of the CT cabinet would likely be non-compliant as a service disconnect under the 2020 or 2023 NEC (see new language in 230.71(B).) A main breaker panel, or anything else that the AHJ approves of as a service disconnecting means, should be okay and I would push back against the utility having any say about it if the AHJ approves of it. If it is worth your time, that is.

 

[pvgreeze]

I appreciate the thoughtfulness of the reply. I think where I'm hung up is that cold-sequenced equipment is extremely common in commercial systems, as I'm sure you know. I've done reviews & designs before in non-PEPCO territory where the service entrance is a switchboard with a MCB > CT Compartment > Distribution Section, but maybe it is different because a cold-sequenced switchboard is listed for that? And I'm quite sure I've come across designs & configurations in other jurisdictions where it is as I've described, with an external DS and a CT cabinet to an MLO panelboard for traditional (non-generation) loads.

The only other thing that the reviewer shared was the following diagram (attached). I also checked the PEPCO Service Guide and attached the only mention of the a CT line side "isolating" switch. I understand what you're saying about DS > CT > MLO being questionable per typical NEC requirements, but, in my interpretation, that line side DS is the "service disconnect" and wouldn't subjugate the MLO to the six disconnect rule. You can see on the PEPCO diagram they even call that line side DS the "service switch," again, per cold-sequence metering requirements.

All this to say, I do think the utility is being "discriminatory" in terms of requiring this for interconnected generation vs traditional loads. I'll see what the developer wants to do, but, regardless, I appreciate your thoughtfulness and responses!

 

[jim dungar]

IEEE and NEC are two separate entities. Whenever I see boilerplate stuff, like IEEE/NEC, I know I am dealing with non-technical people. In these cases rational discussion is not worth the effort, your life will be easier if you just give them what they want.
I agree with jaggedben, they are probably using the latest NEC, put one of those new 'meter disconnects' on the line side and your fused DS on the load side.

 

[don_resqcapt19]

Around here the disconnect on the line side would have a utility lock in the on position. While in most cases, a lock does not prevent the disconnect from being readily accessible, it does here because the people that need the ready access, other than utility personnel, do not have the key and do not have ready access.

 

[don_resqcapt19]

The "IEEE" reference may be to the NESC as that is published by the IEEE, but if that is the case, it should say NESC.

 

[pvgreeze]

The "IEEE" reference may be to the NESC as that is published by the IEEE, but if that is the case, it should say NESC.

I think the reviewer was just throwing around jargon to be honest. I'm hoping throwing an MCB in the switchboard will make the reviewer happy, albeit at the cost of several tens of thousands of more dollars.

 

[electrofelon]

. I've done reviews & designs before in non-PEPCO territory where the service entrance is a switchboard with a MCB > CT Compartment > Distribution Section, but maybe it is different because a cold-sequenced switchboard is listed for that? And I'm quite sure I've come across designs & configurations in other jurisdictions where it is as I've described, with an external DS and a CT cabinet to an MLO panelboard for traditional (non-generation) loads.

FWIW I have never had, nor do I recall ever hearing of a cold sequenced CT cabinet or metering section (or the requirement for a "meter disconnect" ahead of one).

 

[ggunn]

I have many times run into an AHJ requiring that there be, in some situations, a disconnect on both sides of PV metering equipment. One in particular may require three disconnects on the AC side of a PV system if certain conditions apply. It has also been my experience that when this happens there is virtually no chance of arguing them out of it.

 

[pvgreeze]

I have many times run into an AHJ requiring that there be, in some situations, a disconnect on both sides of PV metering equipment. One in particular may require three disconnects on the AC side of a PV system if certain conditions apply. It has also been my experience that when this happens there is virtually no chance of arguing them out of it.

In your experience, have they required literal disconnect switches in the both sides instances? We have room for a line side DS and CT cabinet, but I'm hoping that the utility will be fine with an MCB on the load side because there isn't enough physical room for a second disconnect switch.

 

[pvgreeze]

FWIW I have never had, nor do I recall ever hearing of a cold sequenced CT cabinet or metering section (or the requirement for a "meter disconnect" ahead of one).

They are pretty common in NJ & MD, where I have most of my work. It is definitely a newer utility requirement, because older commercial/industrial buildings will have traditional "hot sequence" metering whereas newer apartments/warehouses/etc. would have a singular switchboard with a MCB > CT Cabinet > Distribution Section in that order. They are the bane of my existence for typical BTM systems because we immediately get saddled with the 120% load-side rule (unless we want to use relays). I think it is usually 400A & 480/277V and above its mandantory around here, maybe a slightly larger service size...feels like it changes with each utility, along with literally every other requirement......

 

[ggunn]

In your experience, have they required literal disconnect switches in the both sides instances? We have room for a line side DS and CT cabinet, but I'm hoping that the utility will be fine with an MCB on the load side because there isn't enough physical room for a second disconnect switch.

For residential systems I have encountered situations where one of the disconnects could be an enclosed breaker if two were required, but I don't remember doing that for any commercial systems. In all cases the disconnect closest to the point of interconnection has been required to be a bladed disco. Of course, every AHJ has its own rules, so when in doubt I always ask when there isn't a formal design review before permitting.

 

[Carultch]

Hello all, I'm going back and forth with a utility on a design I am working on. The proposed system is to be interconnected on the secondary bushings on an existing pad mounted transformer and is participating in a community solar program, so it is not a typical line side/load side interconnection.

The utility is requiring a "utility disconnect" upstream of the CT cabinet, which is obviously understandable, but then they are requiring a second disconnect immediately downstream of the CT cabinet. I originally proposed a fused DS line side of the CT cabinet and a MLO panel on the load side, which to me was something you would see on a typical new service. I read the utility literature and could not find specific requirements for a singular disconnect on the load side of the CT cabinet. When I inquired, the utility reviewer cited "IEEE/NEC Standards." The reviewer provided no specific code or citation. I initially argued that the line side DS upstream of the CT cabinet could serve as the single disconnecting means as required by 690.13 and 705.22, neither of which states where the switch needs to be sequenced other than that it needs to be between the PV system and the POI.

Am I missing something in 690 or 705? The state is under the 2017 NEC for what its worth. I quickly flipped through both articles (and IEEE 1547) and did not see any mention of the need for a second disconnect. All inverters have dedicated CBs for what its worth per 690.15.

Thanks in advance for any feedback.

This stack of disconnects on both sides of a meter is purely a utility & incentive program rule, and not an NEC rule. National Grid in MA, in particular, requires this on 277/480V systems. This is for an incentive program meter, that has quasi-utility ownership.

As far as the NEC is concerned, how you install a meter that is purely customer-owned with no involvement of the utility, you have a lot more flexibility of how you can do it, and you can do it with a lot less equipment.

 

[pvgreeze]

This stack of disconnects on both sides of a meter is purely a utility & incentive program rule, and not an NEC rule. National Grid in MA, in particular, requires this on 277/480V systems. This is for an incentive program meter, that has quasi-utility ownership.

As far as the NEC is concerned, how you install a meter that is purely customer-owned with no involvement of the utility, you have a lot more flexibility of how you can do it, and you can do it with a lot less equipment.

I figured as much...I think the most frustrating part is that, when I asked for the utility manual/guide that spelled out the need for both, I was just met with "its the standard." I read through as much utility provided literature I could find readily accessible online and the only time I heard of both discos being needed was from the reviewer. The screenshot I shared above was all I was given, and I could not find that anywhere online. Just annoying when utilities have obscure & innane rules and obfuscate access to their resources & requirements.

 

[ggunn]

I figured as much...I think the most frustrating part is that, when I asked for the utility manual/guide that spelled out the need for both, I was just met with "its the standard." I read through as much utility provided literature I could find readily accessible online and the only time I heard of both discos being needed was from the reviewer. The screenshot I shared above was all I was given, and I could not find that anywhere online. Just annoying when utilities have obscure & innane rules and obfuscate access to their resources & requirements.

The two largest AHJs I routinely deal with are Austin Energy and CPS in San Antonio. AE has an interconnection guide that includes sample one line drawings for all AC voltage line and load side interconnections that show when one or two disconnects is/are required. CPS is a little more obtuse about it, but I was able to discern their rules from an email exchange with their main commercial PV plan reviewer. Both utilities require a PV meter.