Proper Way for Panel High Side "tap" for PV system?

[live4soccer7]

I have designed a larger residential PV system and have come up to a hurdle that I'm not quite sure how to tackle. The system outputs about 190A @240v at peak production. For 125% rating of that it would come out to a panel needing to be rated at: 237.5A. This automatically puts me into the 400A panels. The panel closest to the original PUD meter is a 200A panel, so I can not simply backfeed this panel as it is not rated high enough.

My solution is to use a load center after the inverters to "combined" the 3 inverters where each inverter will have an 80A breaker (sized based on inverter documentation). Then to go into the 200A panel and tapping "top side" or above the 200A breaker. There aren't lugs or anything like that in the 200A panel on the topside that I could utilize. What would be an NEC appropriate way of going about this?

This is kind of one of the last pieces to my puzzle, at least for now. Any input would be extremely helpful.

 

[jaggedben]

I don't think you can connect that system to a 200A service, if that's what you're describing. So the utility may need to upgrade the service. So that's problem #1. Even if the NEC allows it the utility may not. Have you applied for interconnection yet?

To advise on how to do a proper supply side connection we'd probably need more pictures or description. You can't always do it: for example on a factory meter main you usually can't.

 

[live4soccer7]

@jaggedben

A CLASS 200 meter is spec'd for 200A continuous so it isn't subjected to the 125% rule itself, from my understanding. I spoke with one of the representatives at the utility company and he was 100% ok with the system running through the meter. The utility company has approved the system. We have upgraded the onsite transformer as well.

I quickly drew a diagram, but there isn't an option to upload pictures, only to provide a link to a photo.

The PV AC power would only enter the breaker box for means to connect to the upstream feeder from the meter to the panel since the utility company will not allow me to tap into the load side lines within the meter box/can. The PV AC power would not be back fed through the bus or breakers. I was looking at the insulated polaris style taps for this and the "wire tap" would run 24' horizontally and be directly connected into a fused disconnect at the end of that 24'.

 

[jaggedben]

The cleanest way would be a separate meter socket and a junction box where you Polaris the the home panel feeder together with the solar output. If that isn't clear then get an experienced electrician to help you. I've done supply side connections where I tapped the conductors in the main panel on the supply side, but I usually didn't like it much. Especially at 200A, it may not be feasible. Again, if the existing panel is a meter/main combo you'll probably have to replace it.

 

[Hv&Lv]

I’m going to assume this is an UG service and the POCO already has 4/0 minimum feeding this meter?
What size transformer did you upgrade to?

 

[live4soccer7]

@Hv&Lv
It is a UG service and I am unable to see the wire size feeding the meter itself since there is a tamper proof lock on the meter can. I do know they looked at this when approving the system, so I would assume this as well.

@jaggedben
This is precisely what I'm attempting to do, however doing it within the main panel. It is not a combo meter, but they (meter base and main panel) are back to back on a wall of a detached garage.

I do believe the meter can itself is a 400A/class320 with a class 200 meter plugged into it.

 

[jaggedben]

What size is the wire between the meter and exisiting panel? (What is the existing panel rating, just to get a feeling?) I think that wire needs to be rated above 237.5A.

If you can get a double entry Polaris style block that is a couple wire sizes bigger than the service conductors, you can strip them and pass them through one side of the connector uncut. It makes it a lot cleaner. With a newer panel with adequate space it can be clean. With older panels that weren't made with enough space it's a dicier proposition. Nothing like struggling to stuff conductors back into a tight panel knowing that they don't have any overcurrent protection.

 

[live4soccer7]

The wire between the existing meter and the panel is 2/0, so I think I would upgrade that to 4/0. That should be pretty trivial though since they units are back to back. The existing panel is rated for 200A (225BUS w 200A main).

I think someone requested a couple pictures. Thank you to whoever enabled the ability for me to add photos. There's plenty of room in the panel, in my opinion.

 

[synchro]

705.11(C)(1) says the conductor length from the taps on the service conductors to the overcurrent device has to be within 10 feet.

 

[wwhitney]

So in the diagram, meter to splice would be 3/0 Cu (200A ampacity >190A continuous PV supply, protected by calculation only), from splice to existing 200A breaker could be 2/0 Cu (175A ampacity, 83% rule, protected by 200A main breaker), and from splice to PV disconnect would need to be 250 kcmil Cu (255A ampacity > 125% * 190A continuous PV supply, protected by say 250A fuses). Unless you are able to use a 100% rated 200A disconnect, then you could use 3/0 Cu from the splice to the PV disconnect.

Is that the correct minimum sizing for 75C Cu conductors?

Cheers, Wayne

 

[live4soccer7]

This is what I have found in the book relating to the "Service Conductor Tap", wire sizing aside for the moment.

705.31 Location of Overcurrent Protection. Overcurrent
protection for electric power production source conductors,
connected to the supply side of the service disconnecting
means in accordance with 705.12(A), shall be located
within 3m (10ft) of the point where the electric power
production source conductors are connected to the service.

Informational Note: This overcurrent protection protects
against short-circuit current supplied from the primary
source(s) of electricity.

Exception: Where the overcurrent protection for the power
production source is located more than 3 m (10 ft) from the
point off connection for the electric power production
source to the service, cable limiters or current-limited circuit breakers for each ungrounded conductor shall be installed at the point where the electric power production
conductors are connected to the service.


705.12 Point of Connection. The output of an interconnected electric power source shall be connected as specified
in 705.I2(A), (B), (C), or (D).
(A) Supply Side. An electric power production source shall
be permitted to be connected to the supply side of the service
disconnecting means as permitted in 230.82(6). The sum of
the ratings of all overcurrent devices connected to power production sources shall not exceed the rating of the service.

 

[electrofelon]

.

I do believe the meter can itself is a 400A/class320 with a class 200 meter plugged into it.

Yes they can. But hold on, are you saying your meter is actually a class 320? Why not just put double lugs in it then if it doesn't already? That is how I often make line side connections, replace the meter socket with a class 320 as it is typically the neatest and cleanest way to make the connection.

 

[live4soccer7]

@electrofelon
The meter itself is a class200, but the meter base is a class 320 (400A). I have asked two separate times and they do not want me in the meter can, period. It is the best option in my opinion as well. I do know that there is already likely double lugs in it, but they are being utilized because this meter base feeds my house as well (2 additional panels) that are about 100' away (underground).

It's quite frustrating not being able to do anything in the meter base.

Right now, I'm looking at having to put the disconnect just on the other side of the wall (offset and outside/exterior) from the panel and then trying to get into the panel through the wall. This would put me at less than 10ft.

 

[electrofelon]

).

It's quite frustrating not being able to do anything in the meter base.

.

Yeah. For future reference, maybe call your supply side connections a 230.40 exception 2 or 3 install. I usually do this then just hit a main breaker panel board which is also my combiner, and everything just gets connected load side, with the same advantages of a supply side because you use the sum of all breakers excluding the main rule. Not sure if this is what they are thinking in your case, but some power companies for some reason call a line side connection a "tap" and don't allow it in their meter base.

 

[live4soccer7]

Yeah. For future reference, maybe call your supply side connections a 230.40 exception 2 or 3 install. I usually do this then just hit a main breaker panel board which is also my combiner, and everything just gets connected load side, with the same advantages of a supply side because you use the sum of all breakers excluding the main rule. Not sure if this is what they are thinking in your case, but some power companies for some reason call a line side connection a "tap" and don't allow it in their meter base.

Thanks! I planned on getting a breaker panel/load center where I could add 3x 80A breakers for the inverters and combine them there.

Inverters --> Load Center to combine inverter AC outputs --> Production Meter --> Disconnect --> Service Conductor "Tap"