Type of OCPD & disconnect for line side tap

[SolarAlternativesDesign]

I've read some suggestions that a service rated fused disconnect be used at a line side tap. One person suggested breakers. Is there a section in the code that specifies what type of OCPD and disconnect should be used? Are there operational or safety reasons for using a service rated fused disconnect instead of breakers? 2011 NEC 705.12(D) seems to be the article that addresses the connection and it doesn't specify which type.

 

[Carultch]

I've read some suggestions that a service rated fused disconnect be used at a line side tap. One person suggested breakers. Is there a section in the code that specifies what type of OCPD and disconnect should be used? Are there operational or safety reasons for using a service rated fused disconnect instead of breakers? 2011 NEC 705.12(D) seems to be the article that addresses the connection and it doesn't specify which type.

I think "service rated" just means that the device is capable of bonding the neutral and ground within the unit, using factory standard hardware.

I have wondered for years whether or not you are supposed to bond ground and neutral at such a disconnect, as it is a bit of a gray area on whether or not it qualifies as a "service disconnect". And I know that the bonding of ground and neutral is problematic, if you simply do it out of ignorance at every possible opportunity.

 

[ggunn]

I think "service rated" just means that the device is capable of bonding the neutral and ground within the unit, using factory standard hardware.

I have wondered for years whether or not you are supposed to bond ground and neutral at such a disconnect, as it is a bit of a gray area on whether or not it qualifies as a "service disconnect". And I know that the bonding of ground and neutral is problematic, if you simply do it out of ignorance at every possible opportunity.

All this depends on what the AHJ wants. San Antonio wants me to bond the neutral to ground in the disco, break the ground back to the service, drive a new ground rod at the disco, and bond the two ground rods. Austin just wants an EGC pulled through back to the service. Both AHJ's want a bladed fused disco, not a breaker.

If your AHJ has posted example electrical drawings, it helps a lot.

 

[Carultch]

All this depends on what the AHJ wants. San Antonio wants me to bond the neutral to ground in the disco, break the ground back to the service, drive a new ground rod at the disco, and bond the two ground rods. Austin just wants an EGC pulled through back to the service. Both AHJ's want a bladed fused disco, not a breaker.

If your AHJ has posted example electrical drawings, it helps a lot.

In the event that you don't know whether or not your AHJ will want a neutral-to-ground bond at a PV system supply-side tap disconnect, is it a good idea to do it anyway out of ignorance? Or can it be wrong, if you do it when not needed in this kind of situation?

 

[jaggedben]

We've had some knock-down drag out arguments in this forum about the meaning of the code with regards to whether a supply-side connection disconnect is necessarily a service disconnect. And as ggunn's statement shows, AHJs don't agree either. So the first rule is, ask your AHJ.

With that said, my attitude is that any equipment connected with no OCPD between it and the utility presents exactly the same dangers as a service disconnect and must be suitable for use as service equipment. However, this doesn't mean you have to use a fused disconnect instead of a circuit breaker enclosure. There are plenty of circuit breaker enclosures out there that are suitable for use as service equipment. The AHJ requirements that ggunn mentions would frustrate the hell out of me if I had to deal with that regularly.

 

[SolarAlternativesDesign]

All this depends on what the AHJ wants. San Antonio wants me to bond the neutral to ground in the disco, break the ground back to the service, drive a new ground rod at the disco, and bond the two ground rods. Austin just wants an EGC pulled through back to the service. Both AHJ's want a bladed fused disco, not a breaker.

If your AHJ has posted example electrical drawings, it helps a lot.

Do they provide reasoning for why they want fused disconnect instead of breaker? Apparently out AHJ is OK with either so we may get to pick the best method. We have a 62.5A inverter output and we think a subpanel with 80A breakers would be simple and adequate.

 

[jaggedben]

Some utilities want a visible break disconnect, but the NEC does not require that. I believe in Austin the utility and AHJ may be one-and-the-same, so that may explain that. (ggunn will correct me if I'm wrong, I'm sure. )

The NEC does require the disconnecting means to be lockable in the open position. (705.22) That might cause some AHJs to favor disconnects which usually have a clear place for a lock on the handle. On the other hand, I think it's fairly open to interpretation if, say, you have a subpanel containing only PV breakers, and it has a cover that can be locked closed, as most panelboards do. (I also think that if, say, the DC disconnect is lockable and disables the system, the AC disconnect should not be required to be lockable. Frankly, I'm just thankful that most AHJs just ignore this one line in the code.)

Also any of this logic applies equally to supply-side or load side connections, so if an AHJ only applies it to supply-side connections there's not much point in trying to understand the reasoning. The one time I had to deal with this I could not get a straight answer out of the AHJ, and I think it was just a matter of 'that's the way I've always seen it done.'

 

[ggunn]

Some utilities want a visible break disconnect, but the NEC does not require that. I believe in Austin the utility and AHJ may be one-and-the-same, so that may explain that. (ggunn will correct me if I'm wrong, I'm sure. )

You are correct, sir; Austin Energy is a municipally owned utility.

The AHJ's I mostly deal with (Austin Energy, CPS - San Antonio, Pedernales Co-op, and ONCOR) all require an AC disco with a visible break, i.e., bladed discos and not enclosed breakers, for PV system disconnecting means whether they be line or load side interconnections. I got into a discussion with the AE inspector and his boss over this issue a couple of years ago but they stood fast on this requirement.

 

[wwhitney]

The AHJ's I mostly deal with (Austin Energy, CPS - San Antonio, Pedernales Co-op, and ONCOR) all require an AC disco with a visible break, i.e., bladed discos and not enclosed breakers, for PV system disconnecting means whether they be line or load side interconnections.

OK, I gotta ask. What is their logic on requiring that for a PV disconnect when it is not required for a usual service disconnect?

Cheers, Wayne

 

[Carultch]

OK, I gotta ask. What is their logic on requiring that for a PV disconnect when it is not required for a usual service disconnect?

Cheers, Wayne

It's a very common utility requirement for any distributed generation system to require an outside-mounted visible open AC disconnect. It is a "belt and suspenders" way of being able to make sure that the on-site generation doesn't backfeed if they are doing maintenance in the area, even though the UL inverter standards require that the inverter not backfeed a de-energized grid already. I don't think they've ever used one for this purpose, but they require it anyway.

This is most challenging when you are trying to put it on a building where the architect doesn't want any equipment on the outside. Or when you have a system at the very top of a building, with a perfect spot in an upstairs subpanel. But no, you have to route the conductors all the way down to the ground level.

 

[ggunn]

OK, I gotta ask. What is their logic on requiring that for a PV disconnect when it is not required for a usual service disconnect?

Cheers, Wayne

I'm not sure. It is, as Carultch says, a very common requirement placed on PV systems by AHJ's. If you look at AHJ interconnection agreements you will see a lot of word for word duplication of language; there is obviously a lot of copy and paste going on. It could be at least partly that it is just the way everyone is doing it because everyone is doing it that way.

But no matter; I has a customer whose exterior wall near the MDP was very limited and who wanted to install an enclosed breaker instead of a bladed disco. I went to the inspector and his boss, but I lost that one.

 

[Carultch]

I'm not sure. It is, as Carultch says, a very common requirement placed on PV systems by AHJ's. If you look at AHJ interconnection agreements you will see a lot of word for word duplication of language; there is obviously a lot of copy and paste going on. It could be at least partly that it is just the way everyone is doing it because everyone is doing it that way.

But no matter; I has a customer whose exterior wall near the MDP was very limited and who wanted to install an enclosed breaker instead of a bladed disco. I went to the inspector and his boss, but I lost that one.

I actually said utility, rather than AHJ. But they sort of are like an AHJ, in that they do control some parts of the way your system is built.

As I understand, anything the actual AHJ requires, has to be based on a specific NEC requirement.

 

[ggunn]

I actually said utility, rather than AHJ. But they sort of are like an AHJ, in that they do control some parts of the way your system is built.

As I understand, anything the actual AHJ requires, has to be based on a specific NEC requirement.

As noted above, here in Austin they are pretty much one and the same.

The AHJ can require anything they want whether it is required by the NEC or not. Example: color coding of conductors.

 

[SolarAlternativesDesign]

The NEC does require the disconnecting means to be lockable in the open position. (705.22) That might cause some AHJs to favor disconnects which usually have a clear place for a lock on the handle. On the other hand, I think it's fairly open to interpretation if, say, you have a subpanel containing only PV breakers, and it has a cover that can be locked closed, as most panelboards do. (I also think that if, say, the DC disconnect is lockable and disables the system, the AC disconnect should not be required to be lockable. Frankly, I'm just thankful that most AHJs just ignore this one line in the code.)

Also any of this logic applies equally to supply-side or load side connections, so if an AHJ only applies it to supply-side connections there's not much point in trying to understand the reasoning. The one time I had to deal with this I could not get a straight answer out of the AHJ, and I think it was just a matter of 'that's the way I've always seen it done.'

How about a circuit breaker lockout to meet 705.22?

 

[SolarAlternativesDesign]

Home Power article

Home Power article

Here's a good article by Brian Mehalic in Home Power.
http://www.homepower.com/articles/s...g-supply-side-connection-article-705/page/0/1
However, it still isn't definitive on whether breakers can be used instead of a fused disconnect.

 

[ggunn]

How about a circuit breaker lockout to meet 705.22?

As we have said, some AHJ's won't go for it.

 

[Zee]

This is most challenging when you are trying to put it on a building where the architect doesn't want any equipment on the outside. Or when you have a system at the very top of a building, with a perfect spot in an upstairs subpanel. But no, you have to route the conductors all the way down to the ground level.

...or an out building (barn, detached in-law unit, garage etc) with the solar panels on it and the MSP is on the main building.

As an alternative,
You may be able to re-route the sub-panel feeder wire (the sub-panel with the solar breaker in it) from the MSP into a new visible blade, lockable AC Disco that you mount adjacent to the MSP.
Label it "Solar AC Disconnect." or whatever the local lingo is.

 

[electrofelon]

Some utilities want a visible break disconnect, but the NEC does not require that.

Yeah pretty much all utilities around here want that. Note that (here at least) we could still use a circuit breaker for our "PV line side tap disconnect", but would need the safety switch somewhere on the exterior fot the utility. Gunn, would this work in the jurisdiction you were referring to, or must the "first disconnect" be fused?

 

[ggunn]

Yeah pretty much all utilities around here want that. Note that (here at least) we could still use a circuit breaker for our "PV line side tap disconnect", but would need the safety switch somewhere on the exterior fot the utility. Gunn, would this work in the jurisdiction you were referring to, or must the "first disconnect" be fused?

I have not run that particular scenario past the AHJ's I deal with, but I'm pretty sure it would not fly. San Antonio and Austin both have published sample interconnection circuits, and with very few exceptions their position is "do it like the drawing". As I described in another thread, there are significant differences in the line side interconnection drawings between the two AHJ's, but what they have in common is a fused, bladed, visible break, lockable AC disco within 10' of the connection.

 

[jaggedben]

So basically their rule is 'do it like the drawing because we are not smart enough to read the code and determine with our own minds if it meets code.' I'm glad I'm not dealing with that. :slaphead:

So what do you do when you have a meter main combo with slots for multiple service disconnecting breakers? Or do those not exist in your area?