AC discos needed per NEC?

[david]

The micro string circuits should be combined at the detached garage and then run a feeder back to your AC combiner at the house. I would look to 225.30(A)(5) for allowing the additional feeder to the garage, (assuming it already has a power to the garage). Also follow 225.31, 225.32, 225.33, 225.34...and also label the 225.31 disconnect as the 690.12 Rapid Shutdown for the PV system on the detached garage. Then you need a grounding electrode system.

Transfer equipment? Why? The interconnection is just a simple load side connection through a breaker in the MDP like we build every day; it's just that the PV is on one building and the interconnection is on the other. The conductors from the PV do not interact with whatever power the garage has except that they are both tied to the same service.

I may not have stated it very well, but my comment wasn't directed at your PV array at the garage. i do not think the PV array falls under the scope of article 705 for the garage at all. Your system does not enter the garage. Do you agree that article 690 applies to the garage array. and Article 705 applies to the interconnection at the dwelling?

The micro string circuits should be combined at the detached garage and then run a feeder back to your AC combiner at the house.

My thought was that would be one way of doing it based on article 690

I would look to 225.30(A)(5) for allowing the additional feeder to the garage, (assuming it already has a power to the garage).

225.30 Number of Supplies.
(4) Optional standby systems
(5) Parallel power production systems

My though was if your feeder is not supplying in Parallel with the primary source feeder at the garage how does 225.30 (A) (5) provide a permissive path for a second feeder to a garage?

However 225.30 (4) a permissive rule would imply a transfer switch.

Article 690 would also provide allowance for a PV system Source supplying a garage but that would not be a feeder from a primary source correct?

 

[ggunn]

However 225.30 (4) a permissive rule would imply a transfer switch.

The only times I have had to deal with a transfer switch when doing solar was when a generator was involved. In a straight grid tied system (no batteries) the PV must be kept isolated from the generator to avoid backfeeding the genny. Sometimes the customer experiences a little heartburn over this when he finds out that his PV system won't be running when he is powered up by the generator instead of the grid, but a PV system that would keep running under those conditions is so much more expensive that usually it isn't worth it.

 

[david]

The only times I have had to deal with a transfer switch when doing solar was when a generator was involved. In a straight grid tied system (no batteries) the PV must be kept isolated from the generator to avoid backfeeding the genny. Sometimes the customer experiences a little heartburn over this when he finds out that his PV system won't be running when he is powered up by the generator instead of the grid, but a PV system that would keep running under those conditions is so much more expensive that usually it isn't worth it.

From my limited amount of experience with PV sources, I would think if you wanted to supply loads common to the primary source feeder and the PV source and for whatever reason did not want to interconnect the two sources, a transfer switch may be a pathway to do that.

 

[jaggedben]

I think it is a very gray area to claim you are running two primary source feeders to a building and claim one is a different animal.

Again, see 225.30(A)(5). It's not gray. Nobody is claiming they are a different animal but you are allowed to run a second feeder for this purpose.

In my way of thinking it would be correct to run the inverter output circuit to the main building unless you want to define a feeder connection point at the garage a load side connection

A connection to a feeder at the garage is a permitted load side connection, that is correct. Load side and supply side are defined in 705.12 as referring to the service. Whether there are multiple buildings on the premises is irrelevant to the concept of load-side or supply-side connection.

 

[jaggedben]

I may not have stated it very well, but my comment wasn't directed at your PV array at the garage. i do not think the PV array falls under the scope of article 705 for the garage at all. Your system does not enter the garage.

:blink: ??? Article 705 applies to all parts of premises covered by the NEC.

Do you agree that article 690 applies to the garage array. and Article 705 applies to the interconnection at the dwelling?

No, that really makes no sense. Both articles are applicable to the aspects of the installation they cover. And since this is a micro-inverter system, article 705 comes into play in the AC circuitry on the array. Your statement only makes a bit of sense if your meaning is that 690 applies primarily to the DC side and 705 applies only to the AC side.

225.30 Number of Supplies.
(4) Optional standby systems
(5) Parallel power production systems

My though was if your feeder is not supplying in Parallel with the primary source feeder at the garage how does 225.30 (A) (5) provide a permissive path for a second feeder to a garage?

His feeder is supplying in parallel with the primary source feeder, no matter where it's connected. That is what utility interactive inverters do.

Article 690 would also provide allowance for a PV system Source supplying a garage but that would not be a feeder from a primary source correct?

Please stop and listen to this: There is no boundary on what the PV system supplies. It does not 'supply the garage'. Stop talking about what it supplies. The PV system theoretically supplies the entire grid; it effectively reduces the load on all other generators connected to the grid, without meaningful distinction between them. When you say "a PV system Source supplying a garage" you are making a nonsense statement in the context of this discussion. For your statement to make any kind of sense, you'd have to be talking about an off-grid system that is not connected to the grid, which is not what this thread is about.

 

[jaggedben]

I would feel much better about both papers if they did not totally confuse voltage drop as a function of position in the string with end voltage drop as a function of number of modules in the string.
Worse, there is a fair chance that some of the calculated numbers are incorrect as a result.

Beware thread drift...

I'm curious about your statement although I haven't taken the time to figure out exactly what your concern is, let alone check their math.

I think the purpose of the paper is to get installers to consider the worst case for a string of a certain length. The Vdrop at, say, position 7, will be different for any given number of additional inverters in the string, but the worst case will always be the end of the string. If the graphs in the white paper show the worst case for end of a string of a certain number, the that's what the installer needs to know. If they've confused the presentation and math enough that it doesn't show that, then I agree with you.

It certainly is a confusing vrise calculation when the amount of current changes at 16 locations along the wire. :happyyes:

 

[ggunn]

From my limited amount of experience with PV sources, I would think if you wanted to supply loads common to the primary source feeder and the PV source and for whatever reason did not want to interconnect the two sources, a transfer switch may be a pathway to do that.

In a word, no. You cannot supply power to loads with grid tied PV which are not are not also connected to the grid. If the PV inverter cannot "see" the grid, it shuts down.

 

[david]

In a word, no. You cannot supply power to loads with grid tied PV which are not are not also connected to the grid. If the PV inverter cannot "see" the grid, it shuts down.

You guys can stop thinking i don't understand this concept

547.9 Electrical Supply to Building(s) or Structure(s) from a Distribution Point.
A distribution point shall be permitted to supply any building or structure located on the same premises. The overhead electrical supply shall comply with 547.9(A) and (B), or with 547.9(C). The underground electrical supply shall comply with 547.9(C) and (D).

(E) Identification. Where a site is supplied by more than one service with any two services located a distance of 150 m (500 ft) or less apart, as measured in a straight line, a permanent plaque or directory shall be installed at each of these distribution points denoting the location of each of the other distribution points and the buildings or structures served by each.

 

[david]

Only added to consider a comment on Intent
“The intent of 230.2(A) is that a disruption of the main building service should not disconnect fire pump equipment, emergency systems, legally required standby systems, optional standby systems, or parallel power production systems.”

225.30
I agree that a second feeder is allowed to a garage to distribute loads through a parallel power production systems at that garage to loads associated with the garage. I’m not sure you are allowed to send a second feeder to a garage under the alleged reason of supplying the garage, when the feeder does not supply loads at the garage.

I am just not with you on this yet. i may very well change my mind and see it as you guys do.

I do not see a code restriction that states the added ( for solar) distribution is restricted from suppying primary source loads.

a solution that complies with both concepts would eliminate the existing feeder and define the added panel in the garage primary source distribution. Pull the branch circuits from that feeder after eliminating
the duel (original)supply.

215.5 Diagrams of Feeders.
If required by the authority having jurisdiction, a diagram showing feeder details shall be provided prior to the installation of the feeders. Such a diagram shall show the area in square feet of the building or other structure supplied by each feeder, the total calculated load before applying demand factors, the demand factors used, the calculated load after applying demand factors, and the size and type of conductors to be used.

 

[ggunn]

You guys can stop thinking i don't understand this concept.

If you stop talking about GT solar working on the other side of an open transfer switch from the utility service or about GT solar supplying specific loads, we will.

 

[GoldDigger]

You guys can stop thinking i don't understand this concept

OK, then I will simply summarize the simplest answer to what I think is your basic question:

If you are talking about supplying a particular piece of equipment either from service #1 or service #2 without interconnecting the two services, then in that case a transfer switch is exactly what you need.
This situation does not change in the least whether you do or do not have a GT inverter connected to one of those services.

If you are talking about supplying a particular piece of equipment from one feeder or another off the same service without causing a parallel conductor violation, then a transfer switch is needed. Again, whether or not a GTI is connected to one of the feeders has no affect on the situation at all.

 

[david]

If you stop talking about GT solar working on the other side of an open transfer switch from the utility service or about GT solar supplying specific loads, we will.

If you stop talking about GT solar supplying specific loads, we will.

I think you guys are very solar strong in your thinking and I’m not saying it is a bad thing.

i'm not talking about the GT solar designated to specific loads i'm talking about a feeder distribution from a service to a load.
225.30 Number of Supplies. to
• each additional building or structure ( distribution of load from the service to a detached structure) (other building)
• (A) Special Conditions. (Not every day normal conditions)
• (5)Parallel power production systems i(t’s still a supply ( feeder) from the service to supply distribution of load at the additional building or separate structure0

215.5 Diagrams of Feeders.
Mr./ Miss authority it meets the definition of feeder and it allows my Parallel production system (GT inverter) to see the utility source. Yes but is it a second supply to the garage? No. Than how is that feeder given permission under 225.30?

225.30 does not say you can connect a feeder between two points for a specific purpose
it states you can supply a separate building or structures loads from the service under the conditions addressed in 225.30

From my very strong electrical non solar back ground I say you have to get past the specific allowance in 225.30 Number of supplies not feeders.

you state the permission to connect a feeder between a dwelling and a garage is 225.30(D)

I do not see where, I do see however the permission to supply the garage from the dwelling service is given and limited in that section

 

[ggunn]

I think you guys are very solar strong in your thinking and I’m not saying it is a bad thing.

i'm not talking about the GT solar designated to specific loads i'm talking about a feeder distribution from a service to a load.
225.30 Number of Supplies. to
• each additional building or structure ( distribution of load from the service to a detached structure) (other building)
• (A) Special Conditions. (Not every day normal conditions)
• (5)Parallel power production systems i(t’s still a supply ( feeder) from the service to supply distribution of load at the additional building or separate structure0

215.5 Diagrams of Feeders.
Mr./ Miss authority it meets the definition of feeder and it allows my Parallel production system (GT inverter) to see the utility source. Yes but is it a second supply to the garage? No. Than how is that feeder given permission under 225.30?

225.30 does not say you can connect a feeder between two points for a specific purpose
it states you can supply a separate building or structures loads from the service under the conditions addressed in 225.30

From my very strong electrical non solar back ground I say you have to get past the specific allowance in 225.30 Number of supplies not feeders.

you state the permission to connect a feeder between a dwelling and a garage is 225.30(D)

I do not see where, I do see however the permission to supply the garage from the dwelling service is given and limited in that section

OK, from your very strong non solar electrical background, do you think I need a disco at the garage on the conductors carrying the PV output from the garage to the interconnection point at the house? That's my only question; from my very strong solar background I am solid on the rest of the design.

No offense intended, but all I need is a yes or no, although for this particular project it's moot. I put in a disco because it's better to have and not need than to need and not have.

 

[gadfly56]

I think you guys are very solar strong in your thinking and I’m not saying it is a bad thing.

i'm not talking about the GT solar designated to specific loads i'm talking about a feeder distribution from a service to a load.
225.30 Number of Supplies. to
• each additional building or structure ( distribution of load from the service to a detached structure) (other building)
• (A) Special Conditions. (Not every day normal conditions)
• (5)Parallel power production systems i(t’s still a supply ( feeder) from the service to supply distribution of load at the additional building or separate structure0

215.5 Diagrams of Feeders.
Mr./ Miss authority it meets the definition of feeder and it allows my Parallel production system (GT inverter) to see the utility source. Yes but is it a second supply to the garage? No. Than how is that feeder given permission under 225.30?

225.30 does not say you can connect a feeder between two points for a specific purpose
it states you can supply a separate building or structures loads from the service under the conditions addressed in 225.30

From my very strong electrical non solar back ground I say you have to get past the specific allowance in 225.30 Number of supplies not feeders.

you state the permission to connect a feeder between a dwelling and a garage is 225.30(D)

I do not see where, I do see however the permission to supply the garage from the dwelling service is given and limited in that section

I could be wrong, but I think you're getting unnecessarily hung up on the garage. Suppose the array was not attached to any structure and the wiring ran back to the house as described. Disco, or no disco?

 

[jaggedben]

225.30
I agree that a second feeder is allowed to a garage to distribute loads through a parallel power production systems at that garage to loads associated with the garage. I’m not sure you are allowed to send a second feeder to a garage under the alleged reason of supplying the garage, when the feeder does not supply loads at the garage.

I am just not with you on this yet. i may very well change my mind and see it as you guys do.

i'm not talking about the GT solar designated to specific loads i'm talking about a feeder distribution from a service to a load.

When 225.30(A)(5) says "Parallel power production systems" that is clearly not a load!

215.5 Diagrams of Feeders.
Mr./ Miss authority it meets the definition of feeder and it allows my Parallel production system (GT inverter) to see the utility source. Yes but is it a second supply to the garage? Yes!

Fixed that for you.

225.30 does not say you can connect a feeder between two points for a specific purpose

:huh: Really? What does it say then?