CT Cabinet Interconnection

Carultch

Senior Member
Location
Massachusetts
for the purpose of this discussion, that’s all I care about
Plenty of systems are interconnected between the meter and main disconnect, on hot-sequence metered services. The NEC would treat this as a supply-side interconnection. I could see the OP's question being applicable to both supply-side behind-the-meter, and systems with a new stand-alone service (built in context of existing service equipment on the same property).
 

Carultch

Senior Member
Location
Massachusetts
So I ask you the same thing I ask gunny: why can I land " normal" conductors there but not PV conductors? What is the difference?
I could understand a utility having a different standard, depending on the mechanics of how you make the tap for the supply-side interconnection. I'd call it a tap regardless of what termination product is used, because it is a "not-yet-protected conductor" that will land on an OCPD as soon as it can. Others may disagree with the word "tap".

320A meter sockets may have a second terminal per phase. CT cabinets may come with factory lugs that give you 3 terminals per phase, or possibly more. This means there's a chance of having an otherwise-unused lug in this enclosure, which would appear to be the perfect spot for interconnecting PV.

Perhaps a utility would allow a solution in their cabinet like one described above, but not allow a solution using separately-installed tap connectors (e.g. Polaris blocks, insulation piercers, etc). It would mean one sole manufacturer of all terminals inside the unit, all sold under the same product listing, and the risk of terminal failure would be no different than it would be in any application. But the alternative would introduce a third-party connector, which the utility could be unwilling to risk.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I could understand a utility having a different standard, depending on the mechanics of how you make the tap for the supply-side interconnection. I'd call it a tap regardless of what termination product is used, because it is a "not-yet-protected conductor" that will land on an OCPD as soon as it can. Others may disagree with the word "tap".

320A meter sockets may have a second terminal per phase. CT cabinets may come with factory lugs that give you 3 terminals per phase, or possibly more. This means there's a chance of having an otherwise-unused lug in this enclosure, which would appear to be the perfect spot for interconnecting PV.

Perhaps a utility would allow a solution in their cabinet like one described above, but not allow a solution using separately-installed tap connectors (e.g. Polaris blocks, insulation piercers, etc). It would mean one sole manufacturer of all terminals inside the unit, all sold under the same product listing, and the risk of terminal failure would be no different than it would be in any application. But the alternative would introduce a third-party connector, which the utility could be unwilling to risk.
320A meter sockets like you are describing we do all the time with solar. It is ahead of the meter.
i think you and I are on two different lines of thinking here.
we do line side taps.

What we do not do is like the OP or someone else said was do these taps on the H2 side of the CT.
Thats all I’m referring to in this discussion.
 

Carultch

Senior Member
Location
Massachusetts
320A meter sockets like you are describing we do all the time with solar. It is ahead of the meter.
i think you and I are on two different lines of thinking here.
we do line side taps.

What we do not do is like the OP or someone else said was do these taps on the H2 side of the CT.
Thats all I’m referring to in this discussion.
It likely is jurisdiction / utility / policy specific, and that might be why you and I are thinking differently.

I've seen plenty of line side taps on the H2 side of the CT, but rarely allowed inside the utility's meter socket or CT cabinet. Usually it has to be accomplished in a separate enclosure, or in the same enclosure as the main disconnect. It helps when the main disconnect has a spare terminal not used for the service conductors.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
... my apologies to the OP if he considers the discussion between gunny and I as off topic. I have made a connection in a CT cabinet before. There are no issues other than utility rules.
Perhaps you think I am disagreeing with you. I'm not. The utility rules are not for electrical issues, they are for jurisdictional issues. The AHJ's I deal with do not allow PV connections in their metering equipment, whether it be a CT can or an in-line meter socket. They want a sharp line of demarcation between what is their equipment and what isn't.
 
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Perhaps you think I am disagreeing with you. I'm not. The utility rules are not for electrical issues, they are for jurisdictional issues. The AHJ's I deal with do not allow PV connections in their metering equipment, whether it be a CT can or an in-line meter socket. They want a sharp line of demarcation between what is their equipment and what isn't.
If they do not allow ANY customer connections in their equipment, which I think would mean the service point is downstream, then that would make sense. But if they allow multiple sets to come off for installations falling under 230.40 ex 2 or 3, BUT NOT 5, then I still say that doesn't make any sense.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
If they do not allow ANY customer connections in their equipment, which I think would mean the service point is downstream, then that would make sense. But if they allow multiple sets to come off for installations falling under 230.40 ex 2 or 3, BUT NOT 5, then I still say that doesn't make any sense.
It doesn't have to make sense electrically or per the NEC, it's just their rule. Like I have said many times before (paraphrasing Tennyson), it is not ours to reason why, it is ours but to do what they say or fail the inspection. I have questioned it a few times but I was talking to the wall. They want only their service conductors to enter and leave their monitoring equipment, and I can (sort of) understand it. Everything in the can and ahead of it is theirs and theirs alone, and everything behind it is the customer's problem. One AHJ we deal with is an exception; they require all PV interconnections to be ahead of their meter, but they still won't allow PV connections inside their equipment.

BTW, AHJ owned meter/CT cans are usually sealed with a tag, and in most cases if we cut their tag without their supervision, they get very upset.
 
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Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
BTW, AHJ owned meter/CT cans are usually sealed with a tag, and in most cases if we cut their tag without their supervision, they get very upset.
we have actually disconnected before because a seal was removed excessively. We required an inspection and explained to the inspector why we required it.
after a couple of weeks, (it took that long to please the inspector) we returned and placed a padlock on the meterbase.
 

jaggedben

Senior Member
At the risk of repeating myself....
The OP asked a simple question about whether a CT meter functions differently than other types with respect to energy flow. The answer to that question is that it makes no difference whether the meter is a CT setup or a self-contained type. It makes no difference to any of these utility policies either, as far as I've seen in my career. He did not specifically ask about connecting to utility owned equipment, and mentioned a possible load side connection as well as supply side.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
At the risk of repeating myself....
The OP asked a simple question about whether a CT meter functions differently than other types with respect to energy flow. The answer to that question is that it makes no difference whether the meter is a CT setup or a self-contained type. It makes no difference to any of these utility policies either, as far as I've seen in my career. He did not specifically ask about connecting to utility owned equipment, and mentioned a possible load side connection as well as supply side.
Well, like always, his question was answered early on and then we go off on tangents. Same as it ever was. :D
 
It doesn't have to make sense electrically or per the NEC, it's just their rule. Like I have said many times before (paraphrasing Tennyson), it is not ours to reason why, it is ours but to do what they say or fail the inspection. I have questioned it a few times but I was talking to the wall. They want only their service conductors to enter and leave their monitoring equipment, and I can (sort of) understand it. Everything in the can and ahead of it is theirs and theirs alone, and everything behind it is the customer's problem. One AHJ we deal with is an exception; they require all PV interconnections to be ahead of their meter, but they still won't allow PV connections inside their equipment.

BTW, AHJ owned meter/CT cans are usually sealed with a tag, and in most cases if we cut their tag without their supervision, they get very upset.

So, an academic question: how do you differentiate between a service utilizing multiple sets of SE conductors and multiple disconnects (230.40 ex 2) with a load side PV interconnection, and a supply side interconnection? Does simply having some non PV loads mixed in the the set serving the PV make it the former? In theory it is just semantics and that is why I dont like the whole concept of supply side PV connections. I Think it would be simpler if everything just fell under 230.40. ex 2. as a load side (with a few other tweaks here and there). In practice, probably these anti supply side connection utilities would judge by the sequence of installation. That is, if a building already had a 230.40 ex 2 service one could utilize my loophole, but if they were adding it for a PV system, it would be called a supply side PV.
 
At the risk of repeating myself....
The OP asked a simple question about whether a CT meter functions differently than other types with respect to energy flow. The answer to that question is that it makes no difference whether the meter is a CT setup or a self-contained type. It makes no difference to any of these utility policies either, as far as I've seen in my career. He did not specifically ask about connecting to utility owned equipment, and mentioned a possible load side connection as well as supply side.
I dont think what I brought up is irrelevant to the OP. 😇.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
So, an academic question: how do you differentiate between a service utilizing multiple sets of SE conductors and multiple disconnects (230.40 ex 2) with a load side PV interconnection, and a supply side interconnection? Does simply having some non PV loads mixed in the the set serving the PV make it the former? In theory it is just semantics and that is why I dont like the whole concept of supply side PV connections. I Think it would be simpler if everything just fell under 230.40. ex 2. as a load side (with a few other tweaks here and there). In practice, probably these anti supply side connection utilities would judge by the sequence of installation. That is, if a building already had a 230.40 ex 2 service one could utilize my loophole, but if they were adding it for a PV system, it would be called a supply side PV.
That's really a different discussion. What we have been discussing so far is utilities not allowing supply side connections inside their metering equipment. If behind the meter the conductors go into a gutter where several service disconnects are split out, there isn't a problem with adding a PV supply side interconnection in that gutter; most if not all the AHJs I deal with allow that. Of course there is nothing electrically different between doing that and tapping the conductors in the POCO's CT enclosure, but the AHJs I deal with will not allow taps in their CT/meter cans. As I have said, their rule is for jurisdictional reasons, not electrical concerns.

Outlawing supply side interconnections across the board would be a major blow to the PV industry and would serve no purpose in the safety or reliability of PV systems.
 

jaggedben

Senior Member
So, an academic question: how do you differentiate between a service utilizing multiple sets of SE conductors and multiple disconnects (230.40 ex 2) with a load side PV interconnection, and a supply side interconnection? Does simply having some non PV loads mixed in the the set serving the PV make it the former? In theory it is just semantics and that is why I dont like the whole concept of supply side PV connections. I Think it would be simpler if everything just fell under 230.40. ex 2. as a load side (with a few other tweaks here and there). In practice, probably these anti supply side connection utilities would judge by the sequence of installation. That is, if a building already had a 230.40 ex 2 service one could utilize my loophole, but if they were adding it for a PV system, it would be called a supply side PV.
The difference is whether the PV is allowed to be the 7th handle, and whether you are required (or conversly, not allowed) to bring only a neutral and MBJ to the disconnect to bond it and the EGC.
 
Outlawing supply side interconnections across the board would be a major blow to the PV industry and would serve no purpose in the safety or reliability of PV systems.
The difference is whether the PV is allowed to be the 7th handle, and whether you are required (or conversly, not allowed) to bring only a neutral and MBJ to the disconnect to bond it and the EGC.
Note that although my proposal would eliminate supply side connections, nothing would really change as you could still do the same thing using 230.40 exception #2. It just makes more sense as you get rid of the concept of a "normal" and "non normal" service disconnect and all the problems that go with that. 230.71 and 230.72 would still cover number and grouping so with a small tweak there you could still have a 230.40 exception #2 disconnect serving PV by ungrouped and not count as one of the 6 if desired.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Note that although my proposal would eliminate supply side connections, nothing would really change as you could still do the same thing using 230.40 exception #2. It just makes more sense as you get rid of the concept of a "normal" and "non normal" service disconnect and all the problems that go with that. 230.71 and 230.72 would still cover number and grouping so with a small tweak there you could still have a 230.40 exception #2 disconnect serving PV by ungrouped and not count as one of the 6 if desired.
I don't have a code book with me, but if PV connects before the service OCPD, it's a supply side connection, and without the ability to do that it would be much harder if not impossible to interconnect some systems. As it is now, a supply side connection on a residential service in most of Texas is easy peasy and does not require a shutdown.
 
I don't have a code book with me, but if PV connects before the service OCPD, it's a supply side connection, and without the ability to do that it would be much harder if not impossible to interconnect some systems. As it is now, a supply side connection on a residential service in most of Texas is easy peasy and does not require a shutdown.
I think perhaps you are not "seeing" it. Say you are making a line side tap for a PV interconnection. Lets say you place the PV disconnect next to the existing service disconnect(s). If I come along and claim that it is NOT a supply side PV connection, but instead you added an additional set of service conductors per 230.40 exception #2, and now have multiple service disconnects per 230.71, who is right? I contend there is no purpose for 230.40 exception #5, 230.82(6), and 705.12(A) and all it causes is lots of confusion (grounding, silly poco rules that say its a "tap", normal/not normal service disconnects, etc). I am open to hearing of any flaws or unintended consequences in my plan.
 

jaggedben

Senior Member
Note that although my proposal would eliminate supply side connections, nothing would really change as you could still do the same thing using 230.40 exception #2. It just makes more sense as you get rid of the concept of a "normal" and "non normal" service disconnect and all the problems that go with that. 230.71 and 230.72 would still cover number and grouping so with a small tweak there you could still have a 230.40 exception #2 disconnect serving PV by ungrouped and not count as one of the 6 if desired.
While I acknowledge that you're being perfectly logical and knowledgeable, I don't trust AHJs to be the same, and that's why I'd oppose your proposal. :cool: These days in my area most AHJ's are probably more familiar with 705.12(A) than with 230.40. (Yes, believe it.) Moreover one major AHJ actually has modified their local code to prohibit multiple service disconnects. So notwithstanding you're being technically correct, eliminating 705.12(A) or pairing it down would be in effect outlawing the method as ggunn states it. At the very least it could only work if replaced with a long informational note explaining why eliminating the section does not mean it was eliminated. :p
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I think perhaps you are not "seeing" it. Say you are making a line side tap for a PV interconnection. Lets say you place the PV disconnect next to the existing service disconnect(s). If I come along and claim that it is NOT a supply side PV connection, but instead you added an additional set of service conductors per 230.40 exception #2, and now have multiple service disconnects per 230.71, who is right? I contend there is no purpose for 230.40 exception #5, 230.82(6), and 705.12(A) and all it causes is lots of confusion (grounding, silly poco rules that say its a "tap", normal/not normal service disconnects, etc). I am open to hearing of any flaws or unintended consequences in my plan.
If a PV system pushes energy onto unprotected conductors ahead of the first OCPD, even if there are several of them, it is a supply side interconnection; I don't care what you call it. I agree that whether or not it is considered a separate service can generate some confusion for AHJs as to the way grounded and grounding conductors are treated, and I wish the NEC would address it directly rather than forcing them to depend on nomenclature and the second order interpretation of articles to decide which way we need to install PV systems in their jurisdictions.
 
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