ground a solar farm

[jjavier]

Hi

We have to ground one solar farm and we have a doubt. We have equipment (inverters, etc) that the conductor cables go form the equipment to the point of connection using pull boxes and underground pvc conduits. In the same trench we are going to install the ground ring. We need to connect the equipment to the ring, but the question is if need in each pvc conduit of the trench (form the manhole to the point of connection) the grounded conductor and equipament grounded conductor.
Sorry, It is hard to explain

 

[electrofelon]

Hi

We have to ground one solar farm and we have a doubt. We have equipment (inverters, etc) that the conductor cables go form the equipment to the point of connection using pull boxes and underground pvc conduits. In the same trench we are going to install the ground ring. We need to connect the equipment to the ring, but the question is if need in each pvc conduit of the trench (form the manhole to the point of connection) the grounded conductor and equipament grounded conductor.
Sorry, It is hard to explain

We really need more information. Specifically, we would need to know what type of equipment is on each separate structure, and the relative location of the various circuits and what type they are (feeder, inverter output, DC strings, etc). Then also we would need to know if the structure has elements that are considered grounding electrodes (i.e. driven pipes or beams).

 

[jjavier]

We really need more information. Specifically, we would need to know what type of equipment is on each separate structure, and the relative location of the various circuits and what type they are (feeder, inverter output, DC strings, etc). Then also we would need to know if the structure has elements that are considered grounding electrodes (i.e. driven pipes or beams).

Sorry, I try to explain me better. We have a rack system with metal piles inside the ground about 4-6 feets for the solar panels. Solar panels and rack system are connected to the ground ring. Also de Ac parts (inverters, ac combiners) are connected to the ring ground in the pull box. Our ground system is a bare copper cable inside the trench. The picture shows that our trench will have a bare copper cable and pvc conduits, with dc, communication and differents ac circuits (inverteres and combiner boxes)



Is it a better explanation?

 

[tom baker]

For the AC power conduit, you'll need an EGC (in the conduit). I can't comment on the PV DC power conduit as I don't know about that.

 

[jaggedben]

You need an equipment grounding conductor (EGC) run with both the DC and AC circuits. 300.3 The ground ring cannot be used as a ground fault return path.

 

[electrofelon]

It is still too unclear to me be be specific, but I will make some general comments (acknowledging that some of these have already been stated)

1. Basically every circuit - feeder, inverter output, DC string(s) should have an EGC routed with it. In the case of DC strings, your structure may be able to serve as part of the EGC.
2. If you have a feeder supplying a panelboard on a chunk of array structure, you will need a GE for that structure connected to the EGC bar in the panelboard.
3. For Array structures that are not supplied be a feeder, you may need a GE if the structure doesnt qualify. 690.47(D)

I think it is best to think of it this way: Dont think of it as 1 ground ring for everything, instead look at how many different structures you have, and what needs a local grounding electrode. For example, lets take a simpler system that has a service disconnect mounted on its own structure. Say this then supplied a house via a feeder, and then we have a pole mounted PV array which feeds an inverter in the house. So, we need a GES for the service pedestal/structure, a GES for the house, and a GES at the array (note this requirement may vary depending on which code cycle you are on). Note that the grounding electrode systems are bonded together by the EGC's, and you dont run an additional bonding conductor between them, nor "bond something back" to a different GES.

Maybe that helps. You could try asking a more specific question if it doesnt.

 

[electrofelon]

The bare ground wire in the trench, is that the ground ring? Where/how far does it go?

 

[PVfarmer]

Hi

We have to ground one solar farm and we have a doubt. We have equipment (inverters, etc) that the conductor cables go form the equipment to the point of connection using pull boxes and underground pvc conduits. In the same trench we are going to install the ground ring. We need to connect the equipment to the ring, but the question is if need in each pvc conduit of the trench (form the manhole to the point of connection) the grounded conductor and equipament grounded conductor.
Sorry, It is hard to explain

Ok- are you saying that the blue texted grounded conductor is the same thing as your ground ring *and* the "bare ground wire" which is green in your pic?

So if you are asking:
"should *both* EGCs (meaning DC and AC?) go to the point of connection INSTEAD of being connected to ground ring in pull box"...
Solar panels and rack system are connected to the ground ring. Also de Ac parts (inverters, ac combiners) are connected to the ring ground in the pull box.

I agree with the others- yes, for sure on the green part.

Wouldn't it be just one EGC (from inverter AC EGC connection) for non-isolated inverters, and two EGCs for isolated inverters?

Does this diagram describe your situation at all?

 

[jaggedben]

...
Wouldn't it be just one EGC (from inverter AC EGC connection) for non-isolated inverters, and two EGCs for isolated inverters?
...

For isolated inverters, the code allows the grounding electrode conductor (GEC) for the DC grounded conductor to be combined with the AC EGC. Whichever is the larger requirement applies for conductor size. For ungrounded systems (i.e. non-isolated inverters), the 2014 code allows the same conductor to be sized to AC EGC requirements. In the 2017 the code a single EGC is all that's required, period.

I should hasten to add that regardless, if you have two separate conduits with different circuits (AC, DC, whatever) you need an EGC in both, per each circuit.

 

[PVfarmer]

if you have two separate conduits with different circuits (AC, DC, whatever) you need an EGC in both, per each circuit.

Thanks! But, I'm a bit confused by that.
DC too?
How would that be possible here? If inputs A and B on the inverter are separate circuits in 2 conduits, you'd have to ground the combiner twice, which is not right.
(It's a combiner box with only 1 string on each side, so it isn't actually combining, just fusing as pictured.)

 

[jaggedben]

EGCs provide bonding, not grounding. Bonding is necessary for the ground fault detection on the DC and the overcurrent protection function on the AC. If you have two conduits running to two arrays, both of those arrays need to be bonded back to the combiner and/or inverter. While bonding everything to a ground ring might perform the same function, it's not an allowed method under the code. Simply put, the code requires EGCs to be run with the circuits. If nothing else, this is to avoid confusion about which wire provides the bonding. Someone not familiar with the installation would not be likely to assume that a ground ring was connected to everything.

 

[jjavier]

EGC in each pvc conduit

EGC in each pvc conduit

The bare ground wire in the trench, is that the ground ring? Where/how far does it go?

Thank you for answer.

We will have a ground ring in all our AC and DC trenches, from the dc part, inverters to the Point on connection (wye transformer). But my questions really is the follow one:

If our internal AC LV grid is wye grounded, do we need to lay-down a EGC and neutral conductor in each of our AC conduits? Cannot we use a 3P-4W and lay-down only the neutral wire?

In this case, we have some ciurcuits separated in the same trench, and we would like to know if we really have to use in each ac conduit a EGC cable with this system.

Regards.

 

[PVfarmer]

the Point on connection (wye transformer).

If our internal AC LV grid is wye grounded, do we need to lay-down a EGC and neutral conductor in each of our AC conduits? Cannot we use a 3P-4W and lay-down only the neutral wire?

ciurcuits separated in the same trench, and we would like to know if we really have to use in each ac conduit a EGC cable with this system.

Do not take my word as correct- but does anybody agree with me here?

When the point of connection is the panel on the right as pictured, you can only connect the neutral to EGC(s) in one place (solid green line).

The solid green line is where (and only where) the neutral of the wye is grounded.

You can't put a solid green line connection in the PV combiner panel, if you did N and G would be bonded twice, which is not allowed.

250.24(C)
Grounded Conductor Brought to Service Equipment.
Where an ac system operating at 1000 volts or less is
grounded at any point, the grounded conductor(s) shall be
routed with the ungrounded conductors to each service dis-
connecting means and shall be connected to each discon-
necting means grounded conductor(s) terminal or bus. A
main bonding jumper shall connect the grounded conduc-
tor(s) to each service disconnecting means enclosure. The
grounded conductor(s) shall be installed in accordance with
250.24(C)(l) through (C)(4)

 

[jaggedben]

Thank you for answer.

We will have a ground ring in all our AC and DC trenches, from the dc part, inverters to the Point on connection (wye transformer). But my questions really is the follow one:

If our internal AC LV grid is wye grounded, do we need to lay-down a EGC and neutral conductor in each of our AC conduits? Cannot we use a 3P-4W and lay-down only the neutral wire?

In this case, we have some ciurcuits separated in the same trench, and we would like to know if we really have to use in each ac conduit a EGC cable with this system.

Regards.

Yes, you have to run an EGC with each conduit, if your installation is governed by the NEC code.

Connecting everything to the ground ring would not inhibit the system function, and it may not be unsafe for a given condition, but it is not up to code.

 

[PVfarmer]

EGCs provide bonding, not grounding. Bonding is necessary for the ground fault detection on the DC and the overcurrent protection function on the AC. If you have two conduits running to two arrays, both of those arrays need to be bonded back to the combiner and/or inverter. While bonding everything to a ground ring might perform the same function, it's not an allowed method under the code. Simply put, the code requires EGCs to be run with the circuits. If nothing else, this is to avoid confusion about which wire provides the bonding. Someone not familiar with the installation would not be likely to assume that a ground ring was connected to everything.

Well...what does "leave the vicinity" mean, precisely?
If you have two conduits running from one array (which consists of four strings) to one combiner, and then one conduit from combiner to inverter?

Isn't leaving the combiner = to leaving the vicinity in the above case?
I thought you could bond all four strings back to the combiner with one conductor when they are next to each other, then use one conduit and continue that one EGC from combiner to inverter?

(F) All Conductors Together. Equipment grounding con-
ductors for the PV array and structure (where installed)
shall be contained within the same raceway or cable or
otherwise run with the PV array circuit conductors when
those circuit conductors leave the vicinity of the PY array.

 

[electrofelon]

Well...what does "leave the vicinity" mean, precisely?
If you have two conduits running from one array (which consists of four strings) to one combiner, and then one conduit from combiner to inverter?

Isn't leaving the combiner = to leaving the vicinity in the above case?
I thought you could bond all four strings back to the combiner with one conductor when they are next to each other, then use one conduit and continue that one EGC from combiner to inverter?

(F) All Conductors Together. Equipment grounding con-
ductors for the PV array and structure (where installed)
shall be contained within the same raceway or cable or
otherwise run with the PV array circuit conductors when
those circuit conductors leave the vicinity of the PY array.

I would say "vicinity" is up to the AHJ. I think there is also vagueness in what constitutes an "array". Would 2 sets of strings each feeding its own inverter but part of the same PV system be two arrays?

 

[electrofelon]

Thank you for answer.

We will have a ground ring in all our AC and DC trenches, from the dc part, inverters to the Point on connection (wye transformer). But my questions really is the follow one:

If our internal AC LV grid is wye grounded, do we need to lay-down a EGC and neutral conductor in each of our AC conduits? Cannot we use a 3P-4W and lay-down only the neutral wire?

In this case, we have some ciurcuits separated in the same trench, and we would like to know if we really have to use in each ac conduit a EGC cable with this system.

Regards.

(reiterating some of what has already been said) Generally ALL conductors of a circuit - including EGC's need to be run in the same raceway or cable. There are some exceptions for short lengths, DC while in the array, etc. I can see how it is tempting to use the ground ring as the EGC and skip the "extra" conductor, but it is not code compliant.

I have a few other comments, one which expands or modifies what I said before. I said to think of each structure as getting its own grounding electrode system. Now there is nothing that says you cant use 1 grounding electrode system for multiple structures, it is just usually not done because it often involves a lot of GEC. In your case with this ground ring (assuming it is one continuous ground ring) you would have 1 GES that everything grabs onto. Second comment: I do find some of these earthing arrangements in large ground mount PV systems to be quite comical. You often have hundreds to thousands of driven steel posts in the ground, yet you have some elaborate GES to get a "better ground". Recently I was working on a 1.3 MEG, cant remember how many hundred steel I-beams driven 10 feet in the ground. Then we have our GES which is "triad" of 10 foot rods, with some ridiculous size copper between them - oh and all cad welded just to be sure

 

[jaggedben]

Well...what does "leave the vicinity" mean, precisely?
...

I would say "vicinity" is up to the AHJ. I think there is also vagueness in what constitutes an "array". Would 2 sets of strings each feeding its own inverter but part of the same PV system be two arrays?

While there's some vagueness in the term 'array' the way people use it in the industry, there's a bit less vagueness in the code. It's a 'mechanically integrated assembly' of the components you'd expect.

My opinion: if you have two sets of modules that are sufficiently separated from each other that you need a raceway to support or protect the conductors between them, and there's no other mechanical integration, that's almost always gonna be two arrays. (That's especially true if the raceway is something like EMT, or PVC, or any flexible method, none of which can be counted on to hold anything together mechanically outside of themselves.) And if you have a raceway leaving one array to go to another, that's leaving the 'vicinity' and you need to have all conductors within that raceway.

...Second comment: I do find some of these earthing arrangements in large ground mount PV systems to be quite comical. You often have hundreds to thousands of driven steel posts in the ground, yet you have some elaborate GES to get a "better ground". Recently I was working on a 1.3 MEG, cant remember how many hundred steel I-beams driven 10 feet in the ground. Then we have our GES which is "triad" of 10 foot rods, with some ridiculous size copper between them - oh and all cad welded just to be sure

:thumbsup:

 

[PVfarmer]

Would 2 sets of strings each feeding its own inverter but part of the same PV system be two arrays?

While there's some vagueness in the term 'array' the way people use it in the industry, there's a bit less vagueness in the code. It's a 'mechanically integrated assembly' of the components you'd expect.

My opinion: if you have two sets of modules that are sufficiently separated from each other that you need a raceway to support or protect the conductors between them,

It sure is confusing.
How many strings are in "2 sets'?

I see a "set of modules" as a string, but the code seems to call a string a subarray.

I'm still confused- if code is calling an array one string, how can there be such a thing as a subarray?

Subarray. An electrical subset of a PV array.

 

[jaggedben]

A string is electrically integrated, not mechanically integrated. They are two completely different things and speaking generally there is no telling how they will relate. One could have multiple strings per array or multiple arrays per string. You have to look at the individual project.