Point of Interconnection - Solar

[inforaj]

Hello everyone,

Yesterday, I visited the site and noticed that the utility company had installed a new CT cabinet with a meter and the service disconnect switch in the same cabinet in the button. Additionally, the customer has installed a tapping box to connect the solar system. The maximum size of the breaker is 1200A, 480V. In this setup, the solar system is connected to the load side rather than the line side.

It appears that utilities are now installing new meter cabinets that include the service disconnect switch and the CT cabinet with a meter. This is the first time I've observed this setup at two sites.

My question is: How can we install the solar system on the line side rather than the load side to maximize the system size?

Looking forward to your insights and thoughts.

TP = Tapping box
CT= Utility CT with meter cabinets
SD=Service disconnect switch
XFMR = Utility transformer.

 

[ggunn]

The short answer is that if you cannot connect to the service conductors between the utility CTs and the service disconnect, you cannot install a supply side connected PV system unless you build a new separately metered service. Some utilities will let you land a tap in their CT can, but in my experience most will not. Good luck.

 

[jaggedben]

You can use the full 1200A rating of the feeder* as long as you have additional 1200A overcurrent protection for the load downstream. See 705.12(A) [2023 NEC reference]. If you were hoping to have a system with greater output, see ggunn's response; the service conductors, CT cabinet, and transformer would also have to be higher rated.

*meaning you could have 960A inverter output, 960A×125%=1200A

 

[ggunn]

You can use the full 1200A rating of the feeder* as long as you have additional 1200A overcurrent protection for the load downstream.

Good luck with that as well; with most of the services of this size I have seen, if there is OCP at the service disconnect the switchgear is MLO.

 

[jaggedben]

Good luck with that as well; with most of the services of this size I have seen, if there is OCP at the service disconnect the switchgear is MLO.

I didn't say it would be cheap.

 

[pv_n00b]

If you can tap into the bus at the top of the service disconnect section of the cabinet you are good for a supply side interconnection. It can be tight in this kind of arraignment, not much room between the service disconnect and the sealed CT cabinet.

 

[Hv&Lv]

Hello everyone,

Yesterday, I visited the site and noticed that the utility company had installed a new CT cabinet with a meter and the service disconnect switch in the same cabinet in the button. Additionally, the customer has installed a tapping box to connect the solar system. The maximum size of the breaker is 1200A, 480V. In this setup, the solar system is connected to the load side rather than the line side.

It appears that utilities are now installing new meter cabinets that include the service disconnect switch and the CT cabinet with a meter. This is the first time I've observed this setup at two sites.

My question is: How can we install the solar system on the line side rather than the load side to maximize the system size?

Looking forward to your insights and thoughts.

TP = Tapping box
CT= Utility CT with meter cabinets
SD=Service disconnect switch
XFMR = Utility transformer.

Agree with others here. You can't

We won’t allow line side taps.

 

[ggunn]

Agree with others here. You can't

We won’t allow line side taps.

In most jurisdictions you can have line side PV interconnections; in designing commercial and residential PV systems for more than 15 years I have only run across a few places where there was a blanket prohibition of line side PV interconnections. If the utility metering CTs and service disconnect are in the same enclosure, however, the POCO may not allow a PV interconnection inside it even if it would be mechanically and electrically possible.

 

[jaggedben]

Agree with others here. You can't

We won’t allow line side taps.

What about services with multiple disconnects?

 

[Elect117]

Did the utility install that or did they approve for the customer to install that gear?

I have never heard of a utility installing service equipment themselves. Rather they approve switchgear based on certain metering specifications and such.

 

[electrofelon]

What about services with multiple disconnects?

Right, and pretty sure we have ranted about this before, but a "tap" for a 230.40 ex #2 install is ok but a "tap" that has PV on it is not ok? Did these utilities score a deal on one way energy taps or something ?

 

[Hv&Lv]

What about services with multiple disconnects?

Anything AFTER the metering is up to the electrician/designer.
In a CT can, as long as it's after the metering do whatever you want.
But taps before the metering is a no no with us

 

[electrofelon]

Anything AFTER the metering is up to the electrician/designer.
In a CT can, as long as it's after the metering do whatever you want.
But taps before the metering is a no no with us

No one really does that anyway, and thats not what a "line side tap " is in electrician/PV jargon (unless of course it is specifically required to have the PV on its own meter due to regulations such as "buy all sell all" schemes)

 

[ggunn]

No one really does that anyway, and thats not what a "line side tap " is in electrician/PV jargon (unless of course it is specifically required to have the PV on its own meter due to regulations such as "buy all sell all" schemes)

There is a jurisdiction near Austin where all PV interconnections must be on a separate meter connected ahead of the customer's meter, and Austin Energy is buy all sell all through a PV meter on the load side of the revenue meter for residential PV whether it is a line side or load side connection. As far as what makes a line side connection, whether it is on the line side or the load side of a customer's meter makes no difference to the system design.

 

[Hv&Lv]

No one really does that anyway, and thats not what a "line side tap " is in electrician/PV jargon (unless of course it is specifically required to have the PV on its own meter due to regulations such as "buy all sell all" schemes)

You would be amazed at home many people ask us if they can tap ahead of the meter. Especially homeowners and small solar companies.

And I don’t understand why they ask. When they export they are paying for what they are producing because it's on the wrong side of the meter. We don’t net meter, but we do bill by TOU, and a different rate for export.
I have at least two to three conversations a year regarding this very thing. Some of these solar companies popping up really have no clue of how to interconnect.

 

[ggunn]

You would be amazed at home many people ask us if they can tap ahead of the meter. Especially homeowners and small solar companies.

And I don’t understand why they ask. When they export they are paying for what they are producing because it's on the wrong side of the meter. We don’t net meter, but we do bill by TOU, and a different rate for export.
I have at least two to three conversations a year regarding this very thing. Some of these solar companies popping up really have no clue of how to interconnect.

There are different ways to interconnect, and the rules for doing so vary from jurisdiction to jurisdiction. There is a POCO near here where connecting on the utility side of the revenue meter is the only way to do it.

 

[Hv&Lv]

There are different ways to interconnect, and the rules for doing so vary from jurisdiction to jurisdiction. There is a POCO near here where connecting on the utility side of the revenue meter is the only way to do it.

Ok. Maybe I’m not thinking this through here..
This type of connection puts all the export on the utility side of the meter. Any power needed through the meter for loads is charged for.. so, connecting on the utility side of the meter sends the export power back through the meter as import power.


How does the utility keep up with export? And I know many IOUs net meter.

 

[electrofelon]

Ok. Maybe I’m not thinking this through here..
This type of connection puts all the export on the utility side of the meter. Any power needed through the meter for loads is charged for.. so, connecting on the utility side of the meter sends the export power back through the meter as import power.


How does the utility keep up with export? And I know many IOUs net meter.

I had the same thought, having a PV meter and then connecting to the load side of the utility meter seems kind of strange, not sure how that works

 

[electrofelon]

Trying to think about it but getting a "server busy, please try again later" message from my brain

 

[Hv&Lv]

I had the same thought, having a PV meter and then connecting to the load side of the utility meter seems kind of strange, not sure how that works

We used to do that a few years back. We had a "buy all export" meter and another house meter that was import only. We realized we were ripping the consumer off (in a way)..
The customer has the right to offset their energy bill with their own solar.
It's like you have a heat pump and you add a wood stove... you get the benefit of those savings in heat.

That's why we went with one kV2c TOU meter.
It reads any direction, any time, with different rates for import at what time, and a totally different rate for export at peak vs export off peak.