[RE-wrenches] DC conduit with AC secondary?

[Daniel Young]

Having DC and AC in the same trench (but in separate conduits) is acceptable in the NEC, the conduit itself is all the separation required by the NEC. 

 

That being said, I would also not worry about twisting DC wires or ensuring any special distance between conduits based on concerns of electro-magnetic noise between conductors. If you are talking about a system with a third party arc fault detection/interruption system (like AFCI combiners, not a string inverter with built in AFCI). I have not run into it yet, but I have heard that the third party AFCI combiners are known to nuisance trip due to noise in the wires (mostly from the inverter is what I’ve been told). So anything you can reasonably do to prevent more noise in the DC side of things, why not do it. I would not go so far as to try to twist a set of 3/0 copper conductors in a 200’ conduit pull though J I’d rather just bump my conduits up one trade size across the board to push my wires farther apart. Since EMF’s decay in strength by the square of the distance (2x the distance equals ¼ the emf) just upping the PVC conduit sizes makes it simple to significantly reduce any potential emf.

 

All the above is moot though if we’re talking small wire/currents. 

 

Generally most people don’t think about separating AC and DC conduits in a trench, and I have not yet heard of an instance where it has caused a problem. I over think most things, just to sit back and bring myself back to planet earth where I say “ Put AC and DC in separate conduits, try to keep them separate in the trench if you can do so easily, then bury it and walk away”. 

 

With Regards,

 

Daniel Young, 

NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Benn Kilburn
Sent: Wednesday, October 07, 2015 11:22 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] DC conduit with AC secondary?

 

Adam,
My Canadian Electrical Code requires "separation" between conductors of different "systems".  I believe the NEC is the same/similar.  
You may notice a flimsy (yet stiff) paper(?) barrier between the AC and DC wiring areas in some AC/DC inverter disconnect enclosures.... assume this is sufficient as the inverter (should be) certified as such.
In a raceway or "gutter" box, i've been given the ok from electrical inspectors to bundle and keep the AC and DC wire bundles separate from each other.
In a trench, since you are running separate conduits, that could be sufficient, otherwise the separation could easily be a layer of dirt or perhaps a pressure treated plank.

Good Luck.




Benn Kilburn 

Partner, CSA Certified Solar Photovoltaic Systems Electrician, SkyFire Energy Inc

6706 – 82 Ave NW | Edmonton, AB | T6B 0E7

M: 780-906-7807 P: 780-474-8992 | F: 888-405-5843 |  <http://www.skyfireenergy.com/> www.skyfireenergy.com

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On Mon, Oct 5, 2015 at 8:45 AM, AE Solar <autonomousenergies at gmail.com> wrote:

Wrenchers,

Anyone know of code violations associated with running DC conduit in the same trench as conduit for AC secondary? Is that allowed? Bad practice even if allowed?Thanks

Adam




Adam Katzman
Autonomous Energies
4872 State Route 9G 
Germantown NY, 12526
www.autonomousenergies.com
(518) 567-1468 <tel:%28518%29%20567-1468> 


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