1000v DC PV Disconnects

[BackCountry]

I’ve seen a few topics on 1000v DC disconnects, but none that mentioned this product quite yet.

Siemens makes a 1000v DC disconnect, single circuit (see line diagram). Looks like a standard 3 pole AC disconnect, and they route the positive conductor through all three poles to get the rating.

It’s a big unit for a single circuit.

I have a ground mount with four arrays, 9 strings, and while the stamped drawing does not show a DC disconnect leaving each ground mounted array — I sure would like to have disconnecting means. It doesn’t look like that’s going to be possible though, at $1000/each and no lead time from two suppliers.

Of course there’s a DC disconnect at the SMA TriPower inverter, just not physically exiting the array itself.

I suppose we’ll just have to transition into conduit in a 3R box. Which brings up the which wire to use in conduit question — I guess we’ll have to use PV wire the whole way.

 

[jaggedben]

Did you have a question?

 

[jaggedben]

You may be interested to go here and choose 1000V from the voltage dropdown.

Enclosed DC Disconnect Switch | Industrial Control Direct

IMO Enclosed DC Switch (IP65),16A IEC 800VDC / UL 600 VDC, 2 Pole,Grey Body With Lockable Black Rotary in OFF position, UL508.

www.industrialcontroldirect.com

They are built to European standards but are basically the same DC switches you find in most inverters.

EDIT: Sorry, I see they are only 600V for UL standards. Your AHJ may or may not be willing to accommodate this. I've only used this line of products up to 600V.

 

[Carultch]

Siemens makes a 1000v DC disconnect, single circuit (see line diagram). Looks like a standard 3 pole AC disconnect, and they route the positive conductor through all three poles to get the rating.

It’s a big unit for a single circuit.

The problem is, that you are no longer allowed to use a disconnect on only one polarity per the NEC, unless you have the very rare case of a solidly grounded system, or a pre-2017 version of the NEC applies. Most (if not all) inverters built in the current century, will either be functionally-grounded or ungrounded, and therefore will require you to disconnect both polarities. If you can use pole #1 and pole #2 on the positive, while using pole #3 on the negative, and the manufacturer approves that use, you could use that disconnect. Your diagram did not come through, so I can't make that call.

It used to be the case that you'd have one polarity grounded through a GFCI device, and you'd only require a disconnect switch on the ungrounded polarity. Now, even if you have that kind of system, the NEC requires breaking both polarities, since that is now called functionally-grounded, as opposed to solidly grounded. It is much more common today, that your inverter is set up with both polarities floating at equal and opposite voltages to ground, which always has required disconnecting both polarities. The SMA Sunny Tripower inverters are an example of an inverter with both polarities floating.

 

[ggunn]

The problem is, that you are no longer allowed to use a disconnect on only one polarity per the NEC, unless you have the very rare case of a solidly grounded system, or a pre-2017 version of the NEC applies. Most (if not all) inverters built in the current century, will either be functionally-grounded or ungrounded, and therefore will require you to disconnect both polarities. If you can use pole #1 and pole #2 on the positive, while using pole #3 on the negative, and the manufacturer approves that use, you could use that disconnect. Your diagram did not come through, so I can't make that call.

It used to be the case that you'd have one polarity grounded through a GFCI device, and you'd only require a disconnect switch on the ungrounded polarity. Now, even if you have that kind of system, the NEC requires breaking both polarities, since that is now called functionally-grounded, as opposed to solidly grounded. It is much more common today, that your inverter is set up with both polarities floating at equal and opposite voltages to ground, which always has required disconnecting both polarities. The SMA Sunny Tripower inverters are an example of an inverter with both polarities floating.

I assume you are referring to 690.13(E), but it is not clear to me that it is applicable to PV DC conductors. For example, 690.13(C) is the six handle rule, but if a PV system has more than six strings there would be more than six DC disconnect handles. 690.13 is about PV system disconnecting means; it doesn't look to me like it is referring to DC disconnecting means within the PV system.

What you are saying also looks a bit strange to me in light of the DC OCP change where it used to be that we had to fuse both the positive and negative DC conductors but now one or the other is sufficient (690.9(C)). If a fuse blows on a positive DC conductor the negative is still connected; why would the code specify both conductors for a disco but only one for an OCPD?

 

[ggunn]

Another thing: 690.13(E) says "...shall simultaneously disconnect the PV system conductors...from all conductors of other wiring systems." The DC conductors of a PV system are not connected to any conductors of other wiring systems for a disco to disconnect them from.

Is it another part of the code that you are talking about?

 

[BackCountry]

Did you have a question?

I sure do! What do I do? I forgot the question mark I haven’t done a ground mount at 1000v strings yet without a supplied combiner.

 

[BackCountry]

The problem is, that you are no longer allowed to use a disconnect on only one polarity per the NEC, unless you have the very rare case of a solidly grounded system, or a pre-2017 version of the NEC applies. Most (if not all) inverters built in the current century, will either be functionally-grounded or ungrounded, and therefore will require you to disconnect both polarities. If you can use pole #1 and pole #2 on the positive, while using pole #3 on the negative, and the manufacturer approves that use, you could use that disconnect. Your diagram did not come through, so I can't make that call.

It used to be the case that you'd have one polarity grounded through a GFCI device, and you'd only require a disconnect switch on the ungrounded polarity. Now, even if you have that kind of system, the NEC requires breaking both polarities, since that is now called functionally-grounded, as opposed to solidly grounded. It is much more common today, that your inverter is set up with both polarities floating at equal and opposite voltages to ground, which always has required disconnecting both polarities. The SMA Sunny Tripower inverters are an example of an inverter with both polarities floating.

Thanks for breaking that down for me. Most of the time when we’re doing a ground mount we’re in single phase territory, strings less than 600V, and I try to locate the inverter at the array to avoid any disconnect issues.

In this case we have four separate arrays, 9 strings, with the inverter on a panel board apart from the arrays.

The SLD and approved plan don’t show a disconnect at each array, the challenge I’m running into is… it’s 1000v strings, so I have to use PV wire the whole way (including in conduit underground) since THWN is a no go due to voltage.

A TriPower requires amphenol PV connectors, so we can’t land the wire in a terminal block. My thought so far is to hit a 3R box at each array, use a 1000v listed wire connector, and then pull to the inverter and stub out of another 3R box with a cable gland.

I just don’t like not having a disconnect at each array.

 

[BackCountry]

The problem is, that you are no longer allowed to use a disconnect on only one polarity per the NEC, unless you have the very rare case of a solidly grounded system, or a pre-2017 version of the NEC applies. Most (if not all) inverters built in the current century, will either be functionally-grounded or ungrounded, and therefore will require you to disconnect both polarities. If you can use pole #1 and pole #2 on the positive, while using pole #3 on the negative, and the manufacturer approves that use, you could use that disconnect. Your diagram did not come through, so I can't make that call.

It used to be the case that you'd have one polarity grounded through a GFCI device, and you'd only require a disconnect switch on the ungrounded polarity. Now, even if you have that kind of system, the NEC requires breaking both polarities, since that is now called functionally-grounded, as opposed to solidly grounded. It is much more common today, that your inverter is set up with both polarities floating at equal and opposite voltages to ground, which always has required disconnecting both polarities. The SMA Sunny Tripower inverters are an example of an inverter with both polarities floating.

Let’s see if that diagram came through.

 

[BackCountry]

You may be interested to go here and choose 1000V from the voltage dropdown.

Enclosed DC Disconnect Switch | Industrial Control Direct

IMO Enclosed DC Switch (IP65),16A IEC 800VDC / UL 600 VDC, 2 Pole,Grey Body With Lockable Black Rotary in OFF position, UL508.

www.industrialcontroldirect.com

They are built to European standards but are basically the same DC switches you find in most inverters.

EDIT: Sorry, I see they are only 600V for UL standards. Your AHJ may or may not be willing to accommodate this. I've only used this line of products up to 600V.

I wish I could make that work.

I’ve got 2-3 strings at each array. This is new territory for me with strings at 1000v.

With a combiner box it’s easy since it includes the disconnect. See array layout.

 

[ggunn]

Thanks for breaking that down for me.

I think he may be mistaken about having to break both the + and - conductors with a DC disconnect.

 

[jaggedben]

I think he may be mistaken about having to break both the + and - conductors with a DC disconnect.

If it's just considered an isolating device, I think you are correct.

 

[BackCountry]

If it's just considered an isolating device, I think you are correct.

I was thinking the same thing — at the inverter it clearly does that, but for a non fused safety switch, I didn’t think so.

I can’t find a single manufacturer of a non fused safety switch that goes above 600v except for that Siemens unit that routes the + conductor through three separate disconnect poles (essentially a 3 pole disconnect).

 

[electrofelon]

.

The SLD and approved plan don’t show a disconnect at each array, the challenge I’m running into is… it’s 1000v strings, so I have to use PV wire the whole way (including in conduit underground) since THWN is a no go due to voltage.

.

So I'm not clear on what the challenge is. If it's been approved with no discos than don't install discos. What is the challenge with using PV wire?

If you don't want to go with 1kv strings, have you looked at just going 600? Probably not a huge difference unless it's a large system.

 

[BackCountry]

So I'm not clear on what the challenge is. If it's been approved with no discos than don't install discos. What is the challenge with using PV wire?

If you don't want to go with 1kv strings, have you looked at just going 600? Probably not a huge difference unless it's a large system.

It’s more habit — I’ve always tried to install a disco exiting each array if I have multiple arrays so we can isolate them. It’s a 63kw system not huge but about 300 feet from the inverter at the furthest point.

PV wire — just bigger and requires larger conduit. This is my first time doing a ground mount at 1000v, rooftop is a lot easier it’s just a home run to the inverter and call it a day. With multiple ground mount arrays I have to transition from racking to underground and back to the inverter, and no terminals to land — has to be an amphenol connector at the inverter.

I may he over thinking it, I’m just trying to pre game all of where I would normally splice and convert to THWN and I’m realizing most of my traditional moves aren’t an option at 1000v.

 

[electrofelon]

It’s more habit — I’ve always tried to install a disco exiting each array if I have multiple arrays so we can isolate them. It’s a 63kw system not huge but about 300 feet from the inverter at the furthest point.

PV wire — just bigger and requires larger conduit. This is my first time doing a ground mount at 1000v, rooftop is a lot easier it’s just a home run to the inverter and call it a day. With multiple ground mount arrays I have to transition from racking to underground and back to the inverter, and no terminals to land — has to be an amphenol connector at the inverter.

I may he over thinking it, I’m just trying to pre game all of where I would normally splice and convert to THWN and I’m realizing most of my traditional moves aren’t an option at 1000v.

I think you are over thinking it a bit. I've done (well helped on, didn't do it all myself!) about 4 multi megawatt ground mounts and it's all 1kv with no discos at array sections. 1kv PV wire run either thru the array or underground (or a combination) all the way to the inverters.

 

[Carultch]

Another thing: 690.13(E) says "...shall simultaneously disconnect the PV system conductors...from all conductors of other wiring systems." The DC conductors of a PV system are not connected to any conductors of other wiring systems for a disco to disconnect them from.

Is it another part of the code that you are talking about?

Yes, 690.15 in 2017 and later editions, specifies to disconnect all conductors that are not solidly grounded. Whether it is the intentionally ungrounded conductor, or whether both conductors float for a transformerless inverter, or whether it is GFCI-OCPD-grounded as in the case in most inverters with a grounded polarity, it counts as a conductor that is "not solidly grounded".

My understanding of why there is a double standard on the 2017 & later requirements between OCPD's and disconnecting means, is that a disconnecting means on all conductors that either are ungrounded, or could become ungrounded during a fault, allows for serviceability. There is no guarantee that a fuse on each polarity would both blow from the same fault anyway, so it is redundant to have double the OCPD's.

 

[ggunn]

Yes, 690.15 in 2017 and later editions, specifies to disconnect all conductors that are not solidly grounded. Whether it is the intentionally ungrounded conductor, or whether both conductors float for a transformerless inverter, or whether it is GFCI-OCPD-grounded as in the case in most inverters with a grounded polarity, it counts as a conductor that is "not solidly grounded".

My understanding of why there is a double standard on the 2017 & later requirements between OCPD's and disconnecting means, is that a disconnecting means on all conductors that either are ungrounded, or could become ungrounded during a fault, allows for serviceability. There is no guarantee that a fuse on each polarity would both blow from the same fault anyway, so it is redundant to have double the OCPD's.

I don't think that 690.15(E) applies; see post #6. The DC conductors do not connect to the conductors of any other wiring systems, so no disco can be in a position to separate them. The article, IMO, is referring to L2 and L2 for single phase PV systems and phases A, B, and C for three phase PV systems, as opposed to a neutral if which is solidly grounded if it is there.

 

[ggunn]

...as opposed to a neutral which is solidly grounded if it is there.

 

[BackCountry]

I think you are over thinking it a bit. I've done (well helped on, didn't do it all myself!) about 4 multi megawatt ground mounts and it's all 1kv with no discos at array sections. 1kv PV wire run either thru the array or underground (or a combination) all the way to the inverters.

That’s good for me to hear. I probably am over thinking it.

Once we expand in scale, we want things to conform (so we’re comfortable) and that’s probably unrealistic