Solar plant power cabling installation NEC compliance

[rgrichener]

1. We would like to receive a professional review for our design for a new solar plant that is under construction in California.

2. We have developed an engineering package , installation drawings that include the 48 VAC and communication feed to ~ 4000 heliostats , when no vehicles shall be driving and operators are not supposed to trip on the cables , we would like your opinion regarding compliance with NEC article 356.12 for LNFC conduit system .

3. The cable design includes a 22 gage and 10 gage cables , wrapped in a prefabricated cabling system in LNFC conduit , with plug connectors on each end for low labor cost installation, our design is to lay down the cables on the ground, we are dealing with ~ 120,000 ft of cables .

4. According what we see from the code, if we show that the cables are not subjected to a physical damage , we are in compliance to NEC code , we just need to verify that the cable and connectors are UL listed .

5. Therefore , we need a second written evaluation and approval that our design complies with the NEC code , we shall send our design after NDA and commercial approval .

6. As an option, we might ask you to support you in the presentation of our design with the final client.

 

[don_resqcapt19]

If people can walk on it, it is subject to physical damage, in my opinion. Also what about 356.30?

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Hi :

Thanks for the comment, the point is that the O&M of the solar field eliminates any viehecle driving in the area , the operator has a routh for maintenance , and the cables are installed in pre-determined locations , where there is no reason to be submjected the physical damage .

The only potential for [hysical damage is a violation of the procedures , this can be reflected for any other cable, valve or component in the plant that can not be designed for violation of instructions.

Considering the large area with no access , is there other cost efective conduit that could fully satisfy the NEC 356 or 250 articles , with prefabricated optional production for cable with two sided plugs?
Thanks,
Ricardo

 

[don_resqcapt19]

The term physical damage is very subjective and not defined in the code. As a result of the lack of definition, you may get many different answers from various AHJs. In general my view is that if you can see it, it is subject to physical damage.
As far as making cables out of the LFNC, not sure that is a permitted use of that raceway, unless you make it an Article 604 wiring system. Either way, you can't just lay it on the ground as the the code rules require it to be secured, not just supported.

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Hi Don:
Thanks for the proffesional answer .

The problem we have is that the NEC code does not cover our case of a remote and confined solar field , they have just closed the window for comments to the NFPA that might assist us for code update .

The term of reaceways usually refer to operational areas : plants and facilities that require day to day operation and could be subjected to operators or machinery potential damage unless secured by underground or aboveground support system, our case is different and might require "out of the box" approach to understand the case and the reasoning for engineering solution .
We are operating exactly the same facility in the middle east for 1.5 years with HDPE Conduit which is not allowed by the NEC , therefore , we have searched a cost effective and appropriate solution , LNFC seems to be one, other recommendations are welcome for prefabricated cables with two sided plug manufacturing thousends of units .

 

[don_resqcapt19]

The problem with an "out of the box" solution is with the Authority Having Jurisdiction (AHJ), and is compounded if you are planning installations in multiple jurisdictions. If this is a single installation, you could work directly with the AHJ for approval prior to installation. If you have multiple installations, you need to find a solution that works under the terms of the NEC, and even then you may have issues as some areas adopt the NEC with amendments that can be more or less stringient than is the NEC itself.
I think that many would accept your idea that the LFNC is not subject to damage, but I don't think too many would waive 356.30 that requires the conduit to be secured every 3'.
I still think that if you have the LFNC complete with conductors and plugs, you are looking at a manufactured wiring system as found in Article 604. It does add a few requirements and keeps all of the Article 356 requirements.

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Hi Don :

Thanks, would you recommend in considering FMC or EMT as potential solutions to a mass production cables connectors solution for solar application?.

This refers to your latter comments regarding article 604 , the support cost for the cables is small and we could accomodate this .

 

[don_resqcapt19]

Ricardo,
Under the 2008 code FMC is out as it is not permitted in wet locations and I am assuming this would be an outside installation subject to rain.
As far as Article 604, the only reason I mention it, is because I think that is the only way you can put plug type connectors on the LFNC.
As long as the AHJ says your installation is not subject to physical damage, laying it on the ground would provide the support, but the code rule in 356.30 requires it to be secured every 3'. Not sure how you would do that with the cables on the ground.

 

[Pierre C Belarge]

Hi Don:
Thanks for the proffesional answer .

The problem we have is that the NEC code does not cover our case of a remote and confined solar field , they have just closed the window for comments to the NFPA that might assist us for code update .

The term of reaceways usually refer to operational areas : plants and facilities that require day to day operation and could be subjected to operators or machinery potential damage unless secured by underground or aboveground support system, our case is different and might require "out of the box" approach to understand the case and the reasoning for engineering solution .
We are operating exactly the same facility in the middle east for 1.5 years with HDPE Conduit which is not allowed by the NEC , therefore , we have searched a cost effective and appropriate solution , LNFC seems to be one, other recommendations are welcome for prefabricated cables with two sided plug manufacturing thousends of units .

The NEC does cover this scenario, see the definition of Premises Wiring (System), located in Article 100.

I am not sure the wiring method you have chosen will be compliant. What is the rating of the cables you intend to install inside the LNFC? Is it possible to string the cables along the structures and either go overhead (above head height), or possible undergrade across access areas?

 

[wireguru]

seems like this prefab cabling system would be pretty costly. I would explore the option of burying HDPE conduit where needed and using tray cable for your power and control circuits.

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Hi Don and Pierre :
The code of cource includs every type of electrical installation, the intention of NEC that is missing our case reflects to the fact that this is a unique application by the project definition : remote unmanned facility , when there are thousends of electrical units that require power and communication control , outdoor ,daily cycling , with cost driven solution .
I wish power (and not only communication) could have been wireless ...
As it seems , we might need to change the concept of 10 gage and 22 gage power and communication transfer method with LNFC conduit, to be underground - direct burial with HDPE conduit or other , or aboveground with some physical protection (unistrat , concrete precast or other) , this is unfortunet and might be critical for projects commerciallity in the US , but this is the US code at the moment.
The length of cabling in these facilities are from 100,000 ft in pilot plant, up to 1,000,000 ft and more in commercial projects , the cost is clear .
If there are any recommendations- this shall be appriciated , next week we are meeting the AHJ and see the verdict .

 

[petersonra]

Is this generating plant considered an electric utility?

90.2 Scope.
(B) Not Covered. This Code does not cover the following:

(5) Installations under the exclusive control of an electric
utility where such installations

c. Are on property owned or leased by the electric
utility for the purpose of communications, metering,
generation, control, transformation, transmission, or
distribution of electric energy.

You could also go for the special permission angle, but it is a dicey thing that might be approved one place and not somewhere else.

I think your best bet is TC and cable trays, or UF cable in a trench. Laying it on the ground seems to be asking for trouble.

You might consider putting some kind of metal grid over top of the cables to protect them while they are laying on the ground to eliminate the issue of being protected from damage.

I am also not overjoyed with the idea of making up the cables with some kind of connectors. It just seems like you would have thousands of extra places where you could get a failure.

 

[petersonra]

As long as the AHJ says your installation is not subject to physical damage, laying it on the ground would provide the support, but the code rule in 356.30 requires it to be secured every 3'. Not sure how you would do that with the cables on the ground.

Go to Walmart and buy a bunch of tent pegs and stake the thing.

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Bob :

This is a high pressure steam production plant , no electrical power generation.

Regarding connectors - is there any other solution for connecting 4000 mirrors that shall reduce costs of hardware and labor ?, this is one of the unique requirements of this application ,

Fixng to the ground is indeed easy and cheap , trenching or aboveground supporting in low cost solution is the great challange in the solar energy market .

Thanks for the possitive responses to all.

Ricardo

 

[jghrist]

The steam isn't being produced to generate electricity??

I would worry about rodents damaging cables that are laid on the ground with no protection.

 

[petersonra]

2. We have developed an engineering package , installation drawings that include the 48 VAC and communication feed to ~ 4000 heliostats , when no vehicles shall be driving and operators are not supposed to trip on the cables , we would like your opinion regarding compliance with NEC article 356.12 for LNFC conduit system .

3. The cable design includes a 22 gage and 10 gage cables , wrapped in a prefabricated cabling system in LNFC conduit , with plug connectors on each end for low labor cost installation, our design is to lay down the cables on the ground, we are dealing with ~ 120,000 ft of cables .

I am guessing the 10 gauge cable is for the 48VAC power and the 22 gauge is for comms?

I'd be inclined to get rid of the comm line and go wireless.

I'd also be inclined to run 600V/3 phase cables past all the units and tap off to a small xfmr to get the 48VAC. You could also power the comms channel off that feed as well.

That avaoids the connectors altogether.

 

[rgrichener]

Solar field power feeding concept NEC compliance opinion

Solar field power feeding concept NEC compliance opinion

Hi Bob :

We need at this stage to have redundant systems for communication since we are dealing with 4000 systems operation with safety implications , once the wireless solution could be agreed as reliable solution , this shall be the only solution , currentely we need to hard wire also for communication , but this is not the main issue as could be clearly seen.

Regarding voltage level, we planned to feed the users with 480 VAC , but from safety reasons and technical reasons , we prefer to conduct the transformation 480 to 48 in local cabinets and not per user to reduce costs ,the connectors are only for the physical connection for plug instead of terminal box that requires high skilled team .
The best solution could have been a prefabricated cabling system , when a rigid counduit as PVC schedule 80 , suitable for aboveground installation that could be installed during the prefab stage , connectors installation and sealing , this would be low investment , low labor and compatible to NEC for phisical protection - does somebody know a company than can produce this type of solution ? , other solution under investigation is a prefab of the cable with HDPE conduit for direct burial and connectors , recieving the 4000 sections of the aboveground solution or PVC sch 80 aboveground solution should result with the most economical solution , the question is the availability of this solution and if the AHJ shall approve this?

Thanks, Ricardo

 

[petersonra]

Hi Bob :

We need at this stage to have redundant systems for communication since we are dealing with 4000 systems operation with safety implications , once the wireless solution could be agreed as reliable solution , this shall be the only solution , currentely we need to hard wire also for communication , but this is not the main issue as could be clearly seen.

IMHO, it is likely that the wireless solution is more reliable than one dependent on connectors, and run in plastic tubing laying on the ground just waiting for lightning strikes. I am less then thrilled with using a communications channel for safety interlocks, unless it is designed for that.

Regarding voltage level, we planned to feed the users with 480 VAC , but from safety reasons and technical reasons , we prefer to conduct the transformation 480 to 48 in local cabinets and not per user to reduce costs ,the connectors are only for the physical connection for plug instead of terminal box that requires high skilled team .

I don't know how much 48VAC you need at each device but you may find that buying 4000 small transformers in lieu of running a lot of wire is pretty cost effective. I am not sure just who you think is going to connect up the thing. I'd be willing to bet it won't be some dufous off the street. In any case if it is just a matter of hooking up a few terminals, that does not require a great deal of skill, probably less than the skill required to troubleshoot 4000 connectors that are bound to have a few failures here and there.

The best solution could have been a prefabricated cabling system , when a rigid counduit as PVC schedule 80 , suitable for aboveground installation that could be installed during the prefab stage , connectors installation and sealing , this would be low investment , low labor and compatible to NEC for phisical protection - does somebody know a company than can produce this type of solution ?

I don't think there is a NEC compatible system that uses connectors. If the issue is to reduce the labor, I might see prefabricated cables and using push on disconnect style terminals, that could be put inside waterproof junction boxes.

, other solution under investigation is a prefab of the cable with HDPE conduit for direct burial and connectors , recieving the 4000 sections of the aboveground solution or PVC sch 80 aboveground solution should result with the most economical solution , the question is the availability of this solution and if the AHJ shall approve this?

Thanks, Ricardo

I am not sure you can get past the connector issue. The AHJ is likely going to see it as a splice and that has to be put in a box in most cases.