Is it a PV Disconnect or a PV Service Disconnect?

[Smart $]

The problem with just calling it a "PV System Disconnect" is some may think the disconnect would not need important safety features such a grounded conductor connection to the disconnect switch...or a main bonding jumper. If it is not a AC supplied service then those are not required...right.

This is an area that takes a really good understanding of grounding. For now, I'm going to avoid direct comment and instead direct you to:
a) Information Notes No. 1 & 2 of 690.47(C),
b) 250.6, and
c) a general comment that bonding a grounded conductor at more than one point creates a path for objectionable current.

Any supply side connected PV System would still be subject to the 705.12...both supply side and load side.

So if you call the disconnect of contention a Service Disconnect, you have a load side connection and size the feeder to the 120% rule?

It is a Service. Inverters use power...data acquisition systems use power, all supplied to the premises wiring system by the serving utility. Without Service a Grid Tied PV system will not work.

If this power was not supplied directly through the PV System disconnect, it would be covered under 230.82(4), (5), (7), or (9).

 

[ggunn]

You may recall from the previous thread on this that I feel there is no question that you must bond the grounded conductor in this situation. I agree that "should" is not a strong enough word. To not bond could lead to catastrophic results in the right circumstances.
At the risk of offending others, I think most are to hung up on the code technicalities of whether this is a PV disco. or a service disco. rather than the electrical realities of this. That said, I think the NEC needs to address this.
+1 for John Wiles view.

I'm not sure I understand what you are saying. Say you have a PV system AC disco on a supply side tap right next to an MDP. The neutral and the EGC are bonded in the MDP. What catastrophe could result from not bonding the neutral to the EGC in the disconnect when they are tied together a few feet away and neither are interrupted by the disco? Tying them together in the disco would put current on the EGC between the disco and the MDP; don't we want to avoid that? Have I misinterpreted you?

 

[texie]

I'm not sure I understand what you are saying. Say you have a PV system AC disco on a supply side tap right next to an MDP. The neutral and the EGC are bonded in the MDP. What catastrophe could result from not bonding the neutral to the EGC in the disconnect when they are tied together a few feet away and neither are interrupted by the disco? Tying them together in the disco would put current on the EGC between the disco and the MDP; don't we want to avoid that? Have I misinterpreted you?

Well, suppose the installer chose to use a PVC nipple to the metallic PV disco. If a service conductor shorted to ground in that enclosure then the fault return path would be through the EGC on the load side back through the premises EGC's to the service. In my view this could be a big problem.
I'm not sure I follow why you would have an EGC from the MDP and the PV disco on the line side of a service.

 

[Smart $]

Well, suppose the installer chose to use a PVC nipple to the metallic PV disco. If a service conductor shorted to ground in that enclosure then the fault return path would be through the EGC on the load side back through the premises EGC's to the service. In my view this could be a big problem.
I'm not sure I follow why you would have an EGC from the MDP and the PV disco on the line side of a service.

Not an EGC but rather a bonding jumper. See 250.102... more specifically 250.102(C)

 

[texie]

Not an EGC but rather a bonding jumper. See 250.102... more specifically 250.102(C)

You're making my point. The enclosure must be bonded to the grounded conductor. There is no EGC on the line side.
And I might add that with no bond not only would the fault current flow on the load side EGC, the EGC would very likely be too small and the impedance would be greatly increased as the current would be no following the same path as the supply in a fault.

 

[Smart $]

You're making my point. The enclosure must be bonded to the grounded conductor. There is no EGC on the line side.
And I might add that with no bond not only would the fault current flow on the load side EGC, the EGC would very likely be too small and the impedance would be greatly increased as the current would be no following the same path as the supply in a fault.

As I said, BONDING JUMPER, not Main Bonding Jumper. The grounded conductor is not bonded in the PV System disconnect. That is handled by the Main Bonding Jumper(s) in the Service Disconnect(s).

Furthermore, when you follow the requirements for grounding the PV system, you end with either a combo EGC/GEC running through the PV System disconnect (which you can use to bond the enclosure), or you have a Bondiing Jumper from supply side and an EGC from the PV side. Refer to 690.47(C) including Informational Note No. 1 & 2.

 

[BillK-AZ]

Often the local utility will specify the wording to be used on the devices and drawings. As an example. Arizona Public Service (APS) has the attached requirements for a line side connection.

 

[texie]

As I said, BONDING JUMPER, not Main Bonding Jumper. The grounded conductor is not bonded in the PV System disconnect. That is handled by the Main Bonding Jumper(s) in the Service Disconnect(s).

Furthermore, when you follow the requirements for grounding the PV system, you end with either a combo EGC/GEC running through the PV System disconnect (which you can use to bond the enclosure), or you have a Bondiing Jumper from supply side and an EGC from the PV side. Refer to 690.47(C) including Informational Note No. 1 & 2.

Any disconnect attached directly to service conductors that are supplied from a grounded system has to comply with 250.24(C), plain and simple. Whether you call it a service disconnect or a PV disconnect is irrelevant .

 

[Smart $]

Any disconnect attached directly to service conductors that are supplied from a grounded system has to comply with 250.24(C), plain and simple. Whether you call it a service disconnect or a PV disconnect is irrelevant .

But that's what you are not getting...

The PV System disconnect is not a Service Disconnect when it is connected to the supply side of the Service.

 

[texie]

Often the local utility will specify the wording to be used on the devices and drawings. As an example. Arizona Public Service (APS) has the attached requirements for a line side connection.

Item #4 in the attachment makes my case. To do otherwise is simply unsafe.

 

[texie]

But that's what you are not getting...

The PV System disconnect is not a Service Disconnect when it is connected to the supply side of the Service.

I'm trying to tell you that it does not matter what you call it, it must comply with 250.24(C). To do otherwise is not safe.

 

[ggunn]

I'm trying to tell you that it does not matter what you call it, it must comply with 250.24(C). To do otherwise is not safe.

At the risk of appearing like I am looking for a fight (I'm really not)?

Say I have an AC disco from a PV inverter (480/277Y) right next to an MDP. The ungrounded conductors from the line side of the disco are landed on the line side terminals of the MDP main switch. There is an EGC passing through the disco from the inverters, bonded to its case, and tied to the ground bar in the MDP. There is a neutral coming from the inverters passing through the disco making no contact inside it and connected to the neutral bar of the MDP. The neutral bar and the ground bar of the MDP are bonded. How is this unsafe? How would it be more safe if the neutral and the ECG were bonded in the disco?

Or am I totally misconstruing what you are saying?

 

[texie]

At the risk of appearing like I am looking for a fight (I'm really not)?

Say I have an AC disco from a PV inverter (480/277Y) right next to an MDP. The ungrounded conductors from the line side of the disco are landed on the line side terminals of the MDP main switch. There is an EGC passing through the disco from the inverters, bonded to its case, and tied to the ground bar in the MDP. There is a neutral coming from the inverters passing through the disco making no contact inside it and connected to the neutral bar of the MDP. The neutral bar and the ground bar of the MDP are bonded. How is this unsafe? How would it be more safe if the neutral and the ECG were bonded in the disco?

Or am I totally misconstruing what you are saying?

No risk of a fight..just good technical discussion.

I guess I'm wondering if we are talking about a supply side connection why you are proposing to land the EGC and neutral from the invertor in the MDP. If you are doing a supply side connection you would connect the PV to the load side of a main breaker or fusible switch. The line side of this switch would connect ahead of the MDP directly to the service conductors at some compliant point.

I think it just hit me....in your example you are assuming this supply side tap is not in a separate enclosure! In others words the tap is done entirely within the existing MDP. If that is the case, I see your point, it is already in compliance with 250.24(C). I was thinking of the more typical situation where a separate MB or switch enclosure was installed and conductors run from that to a tap point ahead of the building main. I'm saying that this new MB or switch enclosure would have to comply with 250.24(C).

 

[ggunn]

No risk of a fight..just good technical discussion.

I guess I'm wondering if we are talking about a supply side connection why you are proposing to land the EGC and neutral from the invertor in the MDP. If you are doing a supply side connection you would connect the PV to the load side of a main breaker or fusible switch. The line side of this switch would connect ahead of the MDP directly to the service conductors at some compliant point.

I think it just hit me....in your example you are assuming this supply side tap is not in a separate enclosure! In others words the tap is done entirely within the existing MDP. If that is the case, I see your point, it is already in compliance with 250.24(C). I was thinking of the more typical situation where a separate MB or switch enclosure was installed and conductors run from that to a tap point ahead of the building main. I'm saying that this new MB or switch enclosure would have to comply with 250.24(C).

I agree, good discussion. For the sake of this discussion, what difference does it make, electrically speaking, if the tap is in the enclosure as the MDP or in a tap box between the service transformer and the MDP if the wiring pathway is the same, i.e., the EGC goes from the disco through the tap box (bonded to every enclosure, of course) and down to the ground block in the MDP, and the neutral is tapped along with the ungrounded conductors in the tap box? The neutral conductor is still solidly bonded to ground in the MDP and there is still solid continuity between neutral and ground no matter where you check them and no matter what the state of any of the switches.

 

[texie]

I agree, good discussion. For the sake of this discussion, what difference does it make, electrically speaking, if the tap is in the enclosure as the MDP or in a tap box between the service transformer and the MDP if the wiring pathway is the same, i.e., the EGC goes from the disco through the tap box (bonded to every enclosure, of course) and down to the ground block in the MDP, and the neutral is tapped along with the ungrounded conductors in the tap box? The neutral conductor is still solidly bonded to ground in the MDP and there is still solid continuity between neutral and ground no matter where you check them and no matter what the state of any of the switches.

I think I'm going to have to eat my words from my last post. I don't think what you are proposing is compliant.

First of all, the EGC you mention from the PV disco. through the tap box to the MDP ground bar does not comply. This would be akin to having 2 service disconnects while only one has the neutral bonded and the second disco does not have the neutral bonded but instead has an EGC run to the first disco. In your scenario, if there was a short to the enclosure of the PV disco of the conductor(s) from the supply side tap, the fault current supplied from the service would flow over an EGC to get to the service neutral in another panel.

250.24(C) requires neutral bonding at EACH disconnect that is connected to service conductors. In addition, unless the GES system is connected at a common point ahead of the original disconnect, the PV disconnect would also have to have a GEC from it to the GES.

 

[texie]

This might be of interest regarding neutral bonding for supply side PV connections: http://solarprofessional.com/articl...ec-section-70512-and-utility-interconnections

 

[Smart $]

This might be of interest regarding neutral bonding for supply side PV connections: http://solarprofessional.com/articl...ec-section-70512-and-utility-interconnections

Authored by Mike Holt...

Note he says should be bonded, not required to be bonded. Furthermore he does not show an EGC/GEC or Bonding Jumper and EGC... though the raceway appears to qualify as an EGC, and the GEC is depicted external to the raceway.

You'll also find elsewhere in that article, the PV System disconnect is not a Service Disconnect.

Here's a link to the EC&M article referenced in OP, also authored by Mike Holt...

http://ecmweb.com/code-basics/interconnected-electric-power-sources?page=2

FWIW, I am not taking sides regarding the Holt vs. Wiles camps. What I have posted on this matter is entirely my own interpretation.

 

[shortcircuit2]

Smart$...The way the code is written, the so called PV Disconnect is not subject to any of the important safety rules that Service Disconnects are cover by.

Question 1... Without Service requirements applied to the PV Disconnect in Mikes diagram, the PV Disconnect would not have to be located (grouped) next the Meter and MDP. There could be a supply side connection in a JB by the Meter (or in the Meter) with Service Entrance Conductors running into the building to the PV Disconnect at the opposite side of the building to a location of the inverter without Overcurrent protection until it lands at the PV Disconnect. This would be allowed now right?

Question 2... Without Service requirements applied to the PV Disconnect in Mikes Diagram, if the PV system didn't require a Grounded Conductor, one would not need to be installed? (And if the PV system did require a Grounded Conductor...705.95(B) says it only has to be sized to the equipment grounding conductor size.)

Question 3... Without Service requirements applied to the PV Disconnect in Mikes Diagram, a Grounding Electrode Conductor would not be required at the PV Disconnect right?

So now we could have a Supply Side Connection with say 100amp Service Entrance Conductors running through a building in PVC (or any allowed wiring method under 230.43) to a PV Disconnect without overcurrent protection near the point of tap...without a Grounded Conductor or Main Bonding Jumper...and without a large enough grounding path back to the point of supply.

I'm really trying to view your logic from a safety aspect, but I can't see it. I'm not trying to fight over this either...just like the constructive open dialog on the issue. This is what the forum is for.

 

[texie]

I should have mentioned in my last post that there is such a thing as making a supply side tap completely within the service equipment and compliance with 250.24(C) is assured. The document that Billz-AZ posted in post #27 even mentions this. The one I have seen is a SquareD meter/main combo with a 200 amp main and provision for an optional 50 main that can be used for a supply side tap.

 

[Smart $]

Smart$...The way the code is written, the so called PV Disconnect is not subject to any of the important safety rules that Service Disconnects are cover by.

Question 1... Without Service requirements applied to the PV Disconnect in Mikes diagram, the PV Disconnect would not have to be located (grouped) next the Meter and MDP. There could be a supply side connection in a JB by the Meter (or in the Meter) with Service Entrance Conductors running into the building to the PV Disconnect at the opposite side of the building to a location of the inverter without Overcurrent protection until it lands at the PV Disconnect. This would be allowed now right?

1) See 690.14(C) and 690.14(C)(1).

Question 2... Without Service requirements applied to the PV Disconnect in Mikes Diagram, if the PV system didn't require a Grounded Conductor, one would not need to be installed? (And if the PV system did require a Grounded Conductor...705.95(B) says it only has to be sized to the equipment grounding conductor size.)

2a) Correct.

2b) ...where used solely for instrumentation, voltage detection, or phase detection... which is to say it carries very little current. However, note it says equal to or larger. Sizing for current and ampacity prevail for conditions other than stated, such as with 120V inverters. This is no different than any other feeder conductor. Granted, a bit different than normal service conductors on the service side, but when bonding and grounding rules are followed, it is just as safe as you are wanting it to be... you're just not seeing it right now.

Question 3... Without Service requirements applied to the PV Disconnect in Mikes Diagram, a Grounding Electrode Conductor would not be required at the PV Disconnect right?

Correct. A GEC is not required. However, a supply-side bonding jumper is. See 250.96 and 250.102(C)

So now we could have a Supply Side Connection with say 100amp Service Entrance Conductors running through a building in PVC (or any allowed wiring method under 230.43) to a PV Disconnect without overcurrent protection near the point of tap...without a Grounded Conductor or Main Bonding Jumper...and without a large enough grounding path back to the point of supply.

Other than not having a main bonding jumper located in the disconnect, everything else is essentially the same as a Service Disconnect. The only difference is the main bonding jumper is located elsewhere. There is still a large enough grounding path back to the point of supply... both of them.

I'm really trying to view your logic from a safety aspect, but I can't see it. I'm not trying to fight over this either...just like the constructive open dialog on the issue. This is what the forum is for.

I do not take you dialog as wanting to fight about it. Just trying to help you see that it is safe.