DC and AC trench system

[Doug248]

I am working on a preliminary design for a solar facility in Pennsylvania, USA. The construction manager would like to utilize a single trench to route all AC and DC cables. Some issues have come up that may or may not be code related. I appreciate any suggestions or comments.

1. AC and DC will run in separate conduits within the trench. However, when the conduits enter a quazite handhole/junction box, does AC and DC need to have a physical barrier within that box? If so, is it typical to have a barrier down the center? Conduits come in/out on all sides.

2. As far as I can tell, there is no minimum separation required between AC and DC cables, according to the NEC. Is that correct?

3. The DC cables are running at +380V and -380V. I was told that this means the phase-to-phase voltage is exceeded if using 600V cable. This generally makes sense, but I think it would be fine using 600V cable. I was also told this violates the "low voltage directive", but I believe that only applies to European countries.

4. On another note, does anyone know of a good training program for solar facility design?

Again, thank you for your time.

 

[Twoskinsoneman]

I am working on a preliminary design for a solar facility in Pennsylvania, USA. The construction manager would like to utilize a single trench to route all AC and DC cables. Some issues have come up that may or may not be code related. I appreciate any suggestions or comments.

1. AC and DC will run in separate conduits within the trench. However, when the conduits enter a quazite handhole/junction box, does AC and DC need to have a physical barrier within that box? If so, is it typical to have a barrier down the center? Conduits come in/out on all sides.

2. As far as I can tell, there is no minimum separation required between AC and DC cables, according to the NEC. Is that correct?

3. The DC cables are running at +380V and -380V. I was told that this means the phase-to-phase voltage is exceeded if using 600V cable. This generally makes sense, but I think it would be fine using 600V cable. I was also told this violates the "low voltage directive", but I believe that only applies to European countries.

4. On another note, does anyone know of a good training program for solar facility design?

Again, thank you for your time.

You may have an easier time finding answers to these by using the search function. I know I have come across many threads that give opinions about AC + DC together.

IMO the search function on this site is VERY WEAK but if you suffer through it you'll find them.

 

[don_resqcapt19]

In general AC and DC can be mixed but there may be something in Article 690 that says otherwise. I have not studied that Article.
As far as the voltage, 110.4 would prohibit the use of 600 volt rated conductors on a 760 volt system.

 

[raider1]

Take a look at 300.3(C)(1)

Chris

 

[don_resqcapt19]

Take a look at 300.3(C)(1)
Chris

Buy you also have to look at Article 690 as the rules in there may modify any Chapter 1 though 4 rule. I am not saying there is a rule there, as I have not really looked at the article, but when dealing with installations covered by Chapters 5, 6, and 7 you always have to check there for any modifications.

 

[raider1]

Buy you also have to look at Article 690 as the rules in there may modify any Chapter 1 though 4 rule. I am not saying there is a rule there, as I have not really looked at the article, but when dealing with installations covered by Chapters 5, 6, and 7 you always have to check there for any modifications.

Agreed, I missed the solar part when I first read the original post.

Chris