Article 705

[thepij]

We have two utility interactive inverters feeding step up transformer (208p/13.8kw s) then (due to distance) step down transformer then feeding load side of a circuit breaker inside a switchgear. The switchgear is feed on the line side (service entrance) by the utility. We would like to tap the 13.8kw feeder between the transformers to feed another load. Would 705(D)(1) not allow that? Or another requirement I am missing?

 

[thepij]

NFPA Response

NFPA Response

NFPA responded to the question stated above. The dedicated circuit breaker noted in 705.12(D)(1) is for each instance of a source interconnection - i.e. multiple PV systems, wind generation, etc. So my remaining question is there a code reference that would not allow a tap between the two transformers to feed another load (transformer feeding another building)?

 

[david]

where are the transformer located at?

 

[Dennis Alwon]

What code cycle are you under. Article 705.12(D)(1) in the 2014 says that that circuit must be dedicate

 

[david]

So my remaining question is there a code reference that would not allow a tap between the two transformers to feed another load (transformer feeding another building)?

Both buildings being served by normal utility power, How would you get the solar system to shut down when one of the buildings lost utility power? In my way of thinking your design is dangerous!!!

 

[jaggedben]

We have two utility interactive inverters feeding step up transformer (208p/13.8kw s) then (due to distance) step down transformer then feeding load side of a circuit breaker inside a switchgear. The switchgear is feed on the line side (service entrance) by the utility. We would like to tap the 13.8kw feeder between the transformers to feed another load. Would 705(D)(1) not allow that? Or another requirement I am missing?

You have not described the disconnecting means and overcurrent device(s) in detail. If the only disconnect and overcurrent device is at the switchgear, then tapping the feeder will make those devices no longer dedicated to the inverter source. If there is a disconnect and overcurrent device between the inverters and the place you intend to tap, or if you can install such, then you are okay.

There is also some ambiguity as to whether you would be allowed to put normal loads on the supply-side connection for the inverters. You are allowed up to six disconnects for the service for normal loads. If by chance the inverters are a seventh disconnect or some such, under the argument that they are not a 'service disconnect', then that could also cause you a problem.

Both buildings being served by normal utility power, How would you get the solar system to shut down when one of the buildings lost utility power? In my way of thinking your design is dangerous!!!

You are misunderstanding utility interactive inverters and the way they operate. If the feeder to the inverters is shut down the inverters will shut down. If someone wishes to de-energize one building or another, nothing changes for them.

 

[david]

You are misunderstanding utility interactive inverters and the way they operate. If the feeder to the inverters is shut down the inverters will shut down. If someone wishes to de-energize one building or another, nothing changes for them.

I don’t think I am misunderstanding how they work.

From the information given .

The solar is combined to feed a transformer to transformer to a dedicated breaker (load side) in the buildings service panel. He wants to tap the secondary of the first transformer and connect to another transformer and (load side ) breaker connection to a second building.

He gave no further information.

As stated if you lose utility power to one building the second building will back feed the building with power loss.
Since the inverter still has normal power from one of the buildings the solar will still be sent to the building with power loss

he did not actually say second building he said second load

 

[jaggedben]

As stated if you lose utility power to one building the second building will back feed the building with power loss.

No, it will not.

Since the inverter still has normal power from one of the buildings the solar will still be sent to the building with power loss

The inverter does not get 'normal power from one of the buildings'. That has no meaning. It either sees the utility power or it doesn't.

The inverter will only power circuits that are also connected to utility power. It will only export power if it sees the utility hooked up in parallel. If the utility power is disconnected from the inverter, the inverter will shut down. If either building loses utility power it will also lose power from the inverters, either because it is no longer connected to the inverters, or because the inverters have shut down.

 

[david]

No, it will not.



The inverter does not get 'normal power from one of the buildings'. That has no meaning. It either sees the utility power or it doesn't.

The inverter will only power circuits that are also connected to utility power. It will only export power if it sees the utility hooked up in parallel. If the utility power is disconnected from the inverter, the inverter will shut down. If either building loses utility power it will also lose power from the inverters, either because it is no longer connected to the inverters, or because the inverters have shut down.

We must not be looking at the information from the OP the same way

From solar to inverters a great distance from building one
From the inverters to step up transformer
From the step up transformer to a step down transformer at building #1
From the step down transformer to a load side connection to building #1 utility supplied service equipment.
He wants to tap the (feeder ) between transformers and duplicate the above.
As he states a second load.

If the second load is a second building and he plans on supplying it through a second step down transformer. To a building (load) that is as well utility supplied. Through a load side connection. How would a loss of utility supply to building # 2 shut down the inverters.

why wouldn't the inverters still see utility power from building #1?

 

[GoldDigger]

We must not be looking at the information from the OP the same way

From solar to inverters a great distance from building one
From the inverters to step up transformer
From the step up transformer to a step down transformer at building #1
From the step down transformer to a load side connection to building #1 utility supplied service equipment.
He wants to tap the (feeder ) between transformers and duplicate the above.
As he states a second load.

If the second load is a second building and he plans on supplying it through a second step down transformer. To a building (load) that is as well utility supplied. Through a load side connection. How would a loss of utility supply to building # 2 shut down the inverters.

why wouldn't the inverters still see utility power from building #1?

The key thing is that building 2 is not allowed to have any connection between its utility fed circuits and its single inverter fed circuit. If utility power is lost to building 2, the inverter circuit will still be powered, just as for any building supplied by two different sources, not in parallel with each other.

 

[david]

The key thing is that building 2 is not allowed to have any connection between its utility fed circuits and its single inverter fed circuit. If utility power is lost to building 2, the inverter circuit will still be powered, just as for any building supplied by two different sources, not in parallel with each other.

the only connection the OP described was a supply side connection to building one's utility supplied service equipment.

he indicated a secound tap to the stepped up voltage with indicates he will be continuing a distance to the secound load again stepping down the voltage. He gave no indication that the secound load does not have power supplied by the utility.

 

[jaggedben]

If the second load is a second building and he plans on supplying it through a second step down transformer. To a building (load) that is as well utility supplied.

He didn't say that. If that is the problem you see (one building supplied by two feeders), then yes there are some code issues pertaining to that and some potential dangers. But he neither said that, nor do such dangers have anything whatsoever to do with the inverters and whether they would shut down.

How would a loss of utility supply to building # 2 shut down the inverters.

If building #2 is supplied by the tapped feeder, then a loss of power (e.g. open circuit) anywhere on the line side of the tap will shut down both the building and the inverters.

why wouldn't the inverters still see utility power from building #1?

If the loss of power is on the load side of the tap heading towards building 2, then yes, the inverters would still see power (and export power) to building #1. But so what? It has no effect on building #2 whatsoever, and there is nothing dangerous that will happen at either building building because of that.

 

[GoldDigger]

the only connection the OP described was a supply side connection to building one's utility supplied service equipment.

he indicated a secound tap to the stepped up voltage with indicates he will be continuing a distance to the secound load again stepping down the voltage. He gave no indication that the secound load does not have power supplied by the utility.

Nor did he give any indication that the load is connected to both sources. I would have expected that to be unusual enough to mention. Especially as that load appears to be at a different voltage from the building 2 service voltage.
At least that is how I read it.

 

[david]

705. Point of Connection.
(D) Utility-Interactive Inverters.

Nor did he give any indication that the load is connected to both sources. I would have expected that to be unusual enough to mention.

The premise of his question is 705 and quoted in part from D “Where distribution equipment including switchboards and panelboards is fed simultaneously by a primary source(s) of electricity and one or more utility-interactive inverters,”

Until he says otherwise my assumption is both loads have simultaneous supply from both solar and utility. it could be possible the second load is only solar supplied but he hasn't said that.

Especially as that load appears to be at a different voltage from the building 2 service voltage.At least that is how I read it.

We have two utility interactive inverters feeding step up transformer (208p/13.8kw s) then (due to distance) step down transformer

I’m not seeing it that way I see the reason to step up the voltage is distance, my thought was he is stepping down the voltage the same as the normal utility voltage

He didn't say that. If that is the problem you see (one building supplied by two feeders), then yes there are some code issues pertaining to that and some potential dangers. But he neither said that, nor do such dangers have anything whatsoever to do with the inverters and whether they would shut down.

I am talking about both loads being supplied simultaneously by a primary source(s) and solar . he is tapping the feeder between where he stepped up output voltage from the inverters and the step down transformer to building one. He is taking the tap to a second step down transformer to supply a second load (building) that I think is simultaneously supplied by utility power.

Both buildings being served by normal utility power, How would you get the solar system to shut down when one of the buildings lost utility power? In my way of thinking your design is dangerous!!!

I never once said the power loss was from the solar supply. If both loads are utility power supplied and the inverter at the origin of the first step up transformer, will still see utility power if only one load is disconnected from utility power.

(due to distance) step down transformer then feeding load side of a circuit breaker inside a switchgear

He is talking about making load side connections, load side connections implies a utility power present at the load. If one of the simultaneously supplied loads has a loss of utility power the inverters will still see utility power from the other load

And as said it is possible the second load is only solar, though i did not read his post that way, I do not have the same concerns.

 

[david]

Could be wrong but this is how i see it.

 

[wwhitney]

Hi David,

Your diagram is a little small, so maybe I am missing something, but I don't see the problem. The grid-tied inverters are designed to shut down when they don't see grid voltage. So there is no way the inverters can feed a load _unless_ that load would already be getting grid power if the inverters weren't there. Barring inverter failure, the inverters can't ever power something that doesn't already have grid power.

Cheers, Wayne

 

[GoldDigger]

If a grid tie inverter associated with building one and a service associated with building two connect to the same load you have just made an illegal (and unwise) connection between service one and service two.
You cannot connect to a grid tie inverter without simultaneously connecting to its grid.
That says it all. Along with what Wayne said.

 

[ggunn]

Could be wrong but this is how i see it.

So, how is Load Two getting power? From your drawing it looks like power comes into Building One, goes out to a transformer, and comes into Load Two through another transformer with the PV tapped in between the transformers. If Load Two gets disconnected from the grid by a switch between it and that last transformer, the inverters still see the grid through Building One so there's no problem. If Building One loses power, so does Load Two and the inverters, so the inverters shut down and there's still no problem. There's no way for Load Two to get power if Building One is off line.

 

[GoldDigger]

So, how is Load Two getting power? From your drawing it looks like power comes into Building One, goes out to a transformer, and comes into Load Two through another transformer with the PV tapped in between the transformers. If Load Two gets disconnected from the grid by a switch between it and that last transformer, the inverters still see the grid through Building One so there's no problem. If Building One loses power, so does Load Two and the inverters, so the inverters shut down and there's still no problem. There's no way for Load Two to get power if Building One is off line.

But, and this may be an actual concern, there is a way for that load in Building Two to get power while the service to Building Two is off. It is not a second service, since it does not come directly from POCO without OCPD, but it is a second supply.

If there is no separate POCO connection to Building Two, then the interconnect is just a feeder, possibly through an SDS, although an unusually configured one, and there is again no problem.

 

[jaggedben]

Could be wrong but this is how i see it.

I don't know why you have building two labeled 'utility supplied' and what the red arrows would stand for. The red arrows represent nothing that the OP said.

As I understand it, the new loads building two would be supplied only by the feeder tap to the new transformer.

He is taking the tap to a second step down transformer to supply a second load (building) that I think is simultaneously supplied by utility power.

I don't know why you think the part in red. He didn't say that. Even if it were true, presumably the existing loads are completely separate from the new ones he wishes to supply. That would possibly entail some code violation (to have two feeders feeding an out-building), but it's not made more dangerous by the solar and has nothing to do with article 705.