PV Trenching & Conduit

[Gold Country Russ]

I have been agonizing about trenching for a single 9-panel string of west facing vertical bifacial panels. My problem is very thin soil and lots of shale and rock. I finally realized that using IMC (threaded steel conduit) allows shallow 6" depth trenches instead of the required 18" for PVC plus the metal conduit also functions in place of a ground wire. This would allow up to 6ea #10 THHN wires in a single 1/2" conduit. In my first case it would be a single 3.6KW PV 348VDC #10-2 wire circuit and a 20A 120VAC #10-2 wire circuit for a utility receptacle circuit & yard flood light. So much simpler!

 

[Hedges]

Some comments about OK to mix AC and DC of same system. But not separate system like flood lights.

DC Source Circuits and AC in same raceway

690.4(B) says that PV Source or Output circuits shall not be installed in the same raceway, etc.........of other systems. My question is this: I have an installer with a ground mount system. It has 2 separate racks, separated by approx 20 ft. He only installed (1) conduit between the racks and...

forums.mikeholt.com

Multiple conduits would fix that.

1/2"? Go larger, 3/4" or 1".
Don't believe conduit fill tables. Go larger.

I don't want rusty steel threaded connections as safety ground, I want copper wire.
Although may be code compliant.

 

[Gold Country Russ]

@Hedges IMO, 100+feet of galvanized & threaded steel conduit is itself a very significant ground, especially when connected to 10ea. 3'-imbedded 50+Lb. steel posts. I found a better place for the utility power and flood light so no AC. Will use 1/2" IMC, 2-#10 THHN, and leave a pull cord for another potential PV circuit.

 

[TheViper]

You couldnt have 6 #10's in a 1/2 conduit, as that violates the conduit fill amount. (Its dang near 100% full. ) You'd have to go with 1" for 6 #10's.

 

[BerndL]

I would hate to have anything buried that shallow tbh. 6" is well below my "check before you dig" threshold for casually banging in spades and posts.

But yeah, I'm in a similar situation with shallow topsoil over gravel and rock. Hand-trenching is a bloody pain, but iirc 18" was the minimum for what I was running, so it had to be done.

 

[PreppenWolf]

As a person who's dug a few ditches and learned a few slivers of wisdom, put pipe in 50-100% larger diameter than what you need. Put in 2-3 of those pipes in any trench you dig, because 5 years from now technology changes, expansions/upgrades happen and you'll wish you weren't now digging the same ditch again.

 

[DPC]

put pipe in 50-100% larger diameter than what you need

That goes for everything.

Just makes your life simpler when when you have to pull wires into starters disconnect from splitters ect.
And change always happens, and suddenly your making things bigger