OCPD between Production Meter and Line Tap

[RickwithSisuSolar]

Hi I am in the midst of applying for Utility incentives for a solar install. I am planning on connecting a 11.5kW DC system with a line tap just above the home's main breaker. Further down this line will be a production meter and utility AC disconnect (fused). The utility says that there must be a OCPD (fuse, MCB, or fused disconnect, immediately after the interconnection. They also say that the utility AC disconnect must be in between the PV system and the production meter. I'm a bit confused because I thought that a single fused AC disconnect would suffice for the line tap's OCPD, even if there is a production meter between the OCPD and the line tap. Below is a picture of my original plan and the utility's words.


UTILITY'S WORDS:
3.7 - Note - Protective device shall be provided immediately after the main service meter. There must be protection in the form of a breaker or fuse or fused AC disconnect between the DER and utility located immediately after the main service meter.

3.21.2 - For installations that require a Production Meter, the Utility AC Disconnect shall be located between the DER and production meter. Ensure this is satisfied when addressing 3.18. In this design, a single device cannot simultaneously satisfy 3.7 and 3.21.2. There needs to a be a Utility AC Disconnect in appropriate location AND a protective device in appropriate location. Note that if there are two or more AC disconnects, only one should be distinguished as Utility.

I have a gut feeling that I'm missing something. But maybe not.

Whats the most effective way to put an OCPD between the production meter and the line tap? A second AC fused disconnect? (changing the first to a non-fused one)

 

[Designer101]

since its a line side tap( supply side Per NEC), The tap is between main breaker and Utility meter. if there is no extra ac disconnect between utility meter and Production meter then power company has to shut off the whole power from their side to service the production meter. for that reason they wanted extra AC disconnect between line side tap and Production meter.
The other ac disconnect between Inverter and Production meter is some what redundant as when one disconnect is off towards line side tap the inverter will go off automatically as there will be no grid current But utility wants them and we cannot do anything about that. My be they just wanted to be extra safe for the line worker so as to turn off both inverter power and grid power.

 

[jaggedben]

I agree that the fused disco should be the first device after the tap. I see no need for a second disconnect, but their rule seems to be stated clearly enough. Probably give them what they want if you don't want to waste your time?

God knows how they come up with these requirements. To me it should go: service -> disconnect w OCPD -> meter -> inverter. There is no sensible need for an additional disconnect in all cases. But the people who make the rules don't always understand the systems very well.

 

[jaggedben]

Maybe they want to be able to disconnect the system but still have their meter report data when powered from the utility side. Not sure why they'd care so much about it, but their request would make sense that way.

 

[Another C10]

seems to me in California the solar tech lands their metered PV source through a 30-40 amp 2 pole breaker right on the breaker bus creating a nice disconnect and over load protection.

 

[jaggedben]

seems to me in California the solar tech lands their metered PV source through a 30-40 amp 2 pole breaker right on the breaker bus creating a nice disconnect and over load protection.

That doesn't work with a 60A solar breaker and a 200A busbar/breaker. Read article 705. Also it's basically irrelevant to the question.

 

[ggunn]

That doesn't work with a 60A solar breaker and a 200A busbar/breaker. Read article 705. Also it's basically irrelevant to the question.

It would if the solar breaker were on the line side of the main breaker. Also, it would work on the load side if the 200A panel were to be built with a 225A bus, which some are.

 

[jaggedben]

It would if the solar breaker were on the line side of the main breaker. Also, it would work on the load side if the 200A panel were to be built with a 225A bus, which some are.

Right. The OP shows your first suggestion.

 

[Another C10]

That doesn't work with a 60A solar breaker and a 200A busbar/breaker. Read article 705. Also it's basically irrelevant to the question.

I tend to be irrelevant so I suppose were good.

 

[Another C10]

For anyone that cares to respond, I'm curious .. what is the advantage of tapping into the load side of the grid meter, is it to assure a credit of providing solar power to the grid of neighboring loads or is its purpose to eliminate breaker space within the 1 persons distribution panel, or both.

The only down side I could imagine from tapping into the upside of the distribution main is that ones solar array could easily be maxed from outside grid loads during a power outage possibly not leaving much for the resident to utilize.

Meaning lets say 55 Amps from outside loads of a outed grid is consuming your array, and you decide to add your own 20 Amps of load, wouldn't your solar main trip.

Whereas if the array went through ones distribution panel they could shut off their utility main during a grid outage and have their 60A PV source.

 

[ggunn]

For anyone that cares to respond, I'm curious .. what is the advantage of tapping into the load side of the grid meter, is it to assure a credit of providing solar power to the grid of neighboring loads or is its purpose to eliminate breaker space within the 1 persons distribution panel, or both.

The only down side I could imagine from tapping into the upside of the distribution main is that ones solar array could easily be maxed from outside grid loads during a power outage possibly not leaving much for the resident to utilize.

Meaning lets say 55 Amps from outside loads of a outed grid is consuming your array, and you decide to add your own 20 Amps of load, wouldn't your solar main trip.

Whereas if the array went through ones distribution panel they could shut off their utility main during a grid outage and have their 60A PV source.

I am not sure what you are asking. The reason for line side PV connections is to eliminate the need to comply with 705.12(B), which is the code that protects the busbars of a main distribution panel from an overload. The available current on the line side of the MDP OCPD is already essentially infinite, so injecting the current from a PV system on the line side doesn't make any appreciable difference.

Grid tied PV systems are current sources which are limited by the maximum output capacity of the inverter(s); that means that the current through a PV system OCPD is determined by the output of the system, not the demand from loads. You cannot trip a PV system OCPD by adding load.

Grid tied PV without batteries shuts off when the grid goes down, so it doesn't make any difference which side of the main OCPD it is connected to. Grid tied PV systems with batteries can power a home during an outage, but they must be equipped with lockout devices which disconnect a customer's service when the grid is down so that the PV system does not try to energize the external grid.

 

[solarken]

Hi I am in the midst of applying for Utility incentives for a solar install. I am planning on connecting a 11.5kW DC system with a line tap just above the home's main breaker. Further down this line will be a production meter and utility AC disconnect (fused). The utility says that there must be a OCPD (fuse, MCB, or fused disconnect, immediately after the interconnection. They also say that the utility AC disconnect must be in between the PV system and the production meter. I'm a bit confused because I thought that a single fused AC disconnect would suffice for the line tap's OCPD, even if there is a production meter between the OCPD and the line tap. Below is a picture of my original plan and the utility's words.
View attachment 2559665

UTILITY'S WORDS:
3.7 - Note - Protective device shall be provided immediately after the main service meter. There must be protection in the form of a breaker or fuse or fused AC disconnect between the DER and utility located immediately after the main service meter.

3.21.2 - For installations that require a Production Meter, the Utility AC Disconnect shall be located between the DER and production meter. Ensure this is satisfied when addressing 3.18. In this design, a single device cannot simultaneously satisfy 3.7 and 3.21.2. There needs to a be a Utility AC Disconnect in appropriate location AND a protective device in appropriate location. Note that if there are two or more AC disconnects, only one should be distinguished as Utility.

I have a gut feeling that I'm missing something. But maybe not.

Whats the most effective way to put an OCPD between the production meter and the line tap? A second AC fused disconnect? (changing the first to a non-fused one)

I agree with JaggedBen, should be Service > Disconnect > Meter > PV System. Not sure what meter you are installing, but you are connecting to a service with lots more short circuit current than it may be able to handle, even if the disconnect fuses blew. Why would you want the meter on the unprotected/live side of the fused disconnect? If it ever needed to be serviced, being able to shut off the disconnect to do so would be much safer. As for why the extra disconnect, all utilities in Ohio require that disconnect to be outside accessible and lockable, so they can shut the PV system off if needed by their techs. I know it is redundant and that pulling the meter would also shut down the grid tied inverter, but they probably do not want to have to worry about understanding how every PV system they come cross works in that regard and hving the disconnect there gives them that security of knowing it is safe. I would just move the meter to other side of disconnect, and be done with it. Or,forget that meter and see if the inverter you are installing supports production monitoring using CT's, Like SolarEdge Energy Hub, or buy a compatible meter like Watnode or other that uses CT's.

 

[b_electric]

I don't understand the precedent of any utility's need to service a production meter...

The production CT's are applied to the tapped conductors down stream from the tap terminations, and nominal aux power for the meter is tapped from the PV AC disco.

You drop the PV, you inherently drop the production meter with it.

A consumption meter in this instance is understandable because it monitors the same thing the utility meter does.

A production meter solely dedicated to production is completely isolated from the main service and is moot to any utility work or servicing, so I'm thoroughly confused by this entire thread.

What am I missing here?

 

[jaggedben]

...

You drop the PV, you inherently drop the production meter with it.
...

Right.

My two theories would be...
1) They don't understand that.
2) They for some reason think they want to be able drop the PV without dropping the meter.

Or maybe even...
3) that's not even their requirement, but the person enforcing it was confused

 

[PWDickerson]

We used to have a state production incentive, and so we would install a production meter on every system. For residential supply-side connected systems, the utility required: Service Tap - Production Meter - Fused Disconnect (lockable, visible break knife switch type) - Inverter. I think one of their net metering folks told me they didn't want a switch between the utility and meter so they could always communicate with the meter. For 480V systems or systems over 25 kW, they wanted it the other way around.