CT Cabinet Interconnection

Caleb Bydone

Member
Location
Orem, UT
There is a home that I am going to be installing on, and I cannot for the life of me, figure out is this is possible...

The home has an existing CT cabinet which is connected to the main serivce panel. One thing that I'm wondering, if it's okay to actually backfeed via a supply-side connection, or even a load-side connection in these cases. The energy that is provided by the Solar system won't interfere with the existing CT rings, or if a new NET meter was installed, will it still monitor customer consumption vs production?
 

Carultch

Senior Member
Location
Massachusetts
The NEC would have no issue with it, but the utility likely wouldn't allow it (assuming it is a utility service meter's CT cabinet). By contrast, if the utility has nothing to do with the meter and its CT cabinet in question (which is uncommon), there would be no issue. Utilities typically want to control what happens inside meter sockets and CT cabinets, associated with service meters, and want to see only "service conductors in / service conductors out" within it. Some utilities might be more flexible, but most will not allow branching or tapping of customer circuits within the enclosure they seal.

If you were allowed to do this, it would be a supply-side interconnection, using either a vacant terminal on the load side of the CT cabinet, or a tap connector to intercept all load-side conductors of each phase. If a net meter is installed, it would still measure (consumption minus production), as long as you connect both circuits on the load side terminals.
 
I have ,mentioned this before, but one potential way to get around a silly utility requirement like "no line side taps/interconnections in the meter/CT cabinet" is bring out another set of conductors to feed another service disconnect per 230.40 Exception 2 and make a load side connection in it qualifying the bus under 705.12(D)(2)(3)(c). Its really the same thing, but use a panelboard grouped with the existing one to make it "look like" a typical 230.40 ex 2 install.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I have ,mentioned this before, but one potential way to get around a silly utility requirement like "no line side taps/interconnections in the meter/CT cabinet" ...
I don't think it's necessarily silly. Most utilities want a clear distinction between what is their responsibility and what is not. If you put a tap inside their CT can and something in the can fails it is less clear who needs to fix it, or more to the point, who pays for it.
 
I guess it depends on what exactly the "tap" is. But if it's a listed connector, why would it be any less reliable than the lugs in the meter or CT? Also it doesn't make any sense that a set of conductors for a supply side connection are "taps" but the conductors for a 230.40 exception #2 install are not.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I guess it depends on what exactly the "tap" is. But if it's a listed connector, why would it be any less reliable than the lugs in the meter or CT? Also it doesn't make any sense that a set of conductors for a supply side connection are "taps" but the conductors for a 230.40 exception #2 install are not.
I think it's not a matter of reliability but a clear delineation of who is responsible for what. That, and from the EC's point of view there is only one POCO, but from the POV of the POCO, there are many EC's, not all of whom necessarily know what they are doing.
 

jaggedben

Senior Member
In my opinion you guys are over complicating the answer to the OP's question.

Whether the site meter is a CT meter or not does not affect the basic questions of how a meter functions in relation to a solar system, nor how you connect. Moreover, I doubt you would often run into a utility that made any policy distinctions vis-a-vis where to connect that depended on the type of metering situation.

The most important difference is a safety one, i.e. whether you can pull the meter to safely de-energize conductors you might want to connect to.
 
I think it's not a matter of reliability but a clear delineation of who is responsible for what. That, and from the EC's point of view there is only one POCO, but from the POV of the POCO, there are many EC's, not all of whom necessarily know what they are doing.
I don't follow what you are saying. Why would " PV conductors" have different or vague responsibility criteria than "normal" conductors? Can you give an example?
 
My apologies to the OP for getting
In my opinion you guys are over complicating the answer to the OP's question.

Whether the site meter is a CT meter or not does not affect the basic questions of how a meter functions in relation to a solar system, nor how you connect. Moreover, I doubt you would often run into a utility that made any policy distinctions vis-a-vis where to connect that depended on the type of metering situation.

The most important difference is a safety one, i.e. whether you can pull the meter to safely de-energize conductors you might want to connect to.
And 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.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
In my opinion you guys are over complicating the answer to the OP's question.

Whether the site meter is a CT meter or not does not affect the basic questions of how a meter functions in relation to a solar system, nor how you connect. Moreover, I doubt you would often run into a utility that made any policy distinctions vis-a-vis where to connect that depended on the type of metering situation.

The most important difference is a safety one, i.e. whether you can pull the meter to safely de-energize conductors you might want to connect to.
You can’t pull a meter to disconnect the power in a CT cabinet. if you could it would be self contained.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
The NEC would have no issue with it, but the utility likely wouldn't allow it (assuming it is a utility service meter's CT cabinet). By contrast, if the utility has nothing to do with the meter and its CT cabinet in question (which is uncommon), there would be no issue. Utilities typically want to control what happens inside meter sockets and CT cabinets, associated with service meters, and want to see only "service conductors in / service conductors out" within it. Some utilities might be more flexible, but most will not allow branching or tapping of customer circuits within the enclosure they seal.

If you were allowed to do this, it would be a supply-side interconnection, using either a vacant terminal on the load side of the CT cabinet, or a tap connector to intercept all load-side conductors of each phase. If a net meter is installed, it would still measure (consumption minus production), as long as you connect both circuits on the load side terminals.
If it’s on the load side of the CT cabinet it wouldn’t be a supply side connection
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I have ,mentioned this before, but one potential way to get around a silly utility requirement like "no line side taps/interconnections in the meter/CT cabinet" is bring out another set of conductors to feed another service disconnect per 230.40 Exception 2 and make a load side connection in it qualifying the bus under 705.12(D)(2)(3)(c). Its really the same thing, but use a panelboard grouped with the existing one to make it "look like" a typical 230.40 ex 2 install.
It isn’t silly. ggunn has the reason. ”Ours” is separate from “yours”
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
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?
We don’t allow Net metering, and if you land them after the CTs where the terminal blocks are the back feed to the utility will go through the CT backwards and result in the meter going backwards, which results in net metering.
BUT! If the POCO has their meters set up like ours in a locked forward metering, any resulting backfeed will make the meter spin backwards BUT the meter will still record the energy pass through as forward energy.
this results in the customer actually paying our retail rate for energy he exported to the grid.
 
We don’t allow Net metering, and if you land them after the CTs where the terminal blocks are the back feed to the utility will go through the CT backwards and result in the meter going backwards, which results in net metering.
BUT! If the POCO has their meters set up like ours in a locked forward metering, any resulting backfeed will make the meter spin backwards BUT the meter will still record the energy pass through as forward energy.
this results in the customer actually paying our retail rate for energy he exported to the grid.
Ok, but that is due to a specific metering policy and arrangement where of course the interconnection has to physically be in a certain place. We/I am discussing a prohibition against supply side connections (also called line side taps), which in fact would seem to be preferred/required in areas that dont allow net metering.
 

jaggedben

Senior Member
We don’t allow Net metering, and if you land them after the CTs where the terminal blocks are the back feed to the utility will go through the CT backwards and result in the meter going backwards, which results in net metering.
BUT! If the POCO has their meters set up like ours in a locked forward metering, any resulting backfeed will make the meter spin backwards BUT the meter will still record the energy pass through as forward energy.
this results in the customer actually paying our retail rate for energy he exported to the grid.
So, for the record, the 'ours' vs 'yours' logic is not relevant in places that have net metering, right?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
So, for the record, the 'ours' vs 'yours' logic is not relevant in places that have net metering, right?
No, the ours vs yours arguments is very relevant. We stop at the terminations.
we have made line side terminations, but it has to be approved and liabilities spelled out.

electrofelon has a point. I may not have understood completely. I was reading about the termination block past the CT
 

Carultch

Senior Member
Location
Massachusetts
If it’s on the load side of the CT cabinet it wouldn’t be a supply side connection
Given hot sequence metering, it could still be a supply-side connection. It would be supply-side, in the sense that it is on the supply-side of the service disconnecting means. It would be load-side relative to the meter or metering CT's, as it would have to be if the system were operating behind-the-meter on the same service. The connection is happening between the meter and the main disconnect.

With cold-sequence metering, it is a logical consequence that you couldn't make a supply-side connection (i.e. supply-side of the service disconnect), without it being another service entirely. I.e. a stand-alone service dedicated to the PV, instead of offsetting on-site loads first in a behind-the-meter system. Unless a utility would allow two meters on the same service/account.
 
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