AC/DC in the same conduit [RE-wrenches]

[Nick Lucchese]

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Thanks John, Jeff, Dan and Jay,
  Yes, to what degree that this may be a problem sounds like is still 
somewhat of a mystery and probably won't be a problem from what you 
all have shared. Unfortunately the customer's mind will most likely 
not be at ease unless I can prove that it surely won't be a problem 
for him. The MX-60 is at the end of the line so hopefully there won't 
be any PWM noise on the AC line. If the wire is re-pulled at least 
the twisted Tri-Metric wire and Mate cable can be placed in the 
conduit alongside the DC solar wires where the undersized #6 AC wires 
are now. Luckily they did wire the battery/inverter cables alone 
although they only hooked up one set and stole/took the other set 
home to hide so the customer would not know they were left over 
-similar to the Tri-Metric and GFP/2 that was pushed aside in the 
"parts left over" area.

  I would still like to hear more on the fundamental electrical 
engineering issues as Jeff stated if anyone has anything to add. 
Thanks again for all the responses,

Nick A Lucchese



>
>From an electrical engineering standpoint, well... it all depends. 
>The one thing that you NEVER want to do, if at all possible, is to 
>run high impedance DC SENSE or metering lines in the same conduit as 
>120VAC, definitely not without properly terminated shielding.
>
>In the case of DC power lines running along side of AC power lines, 
>the impedances of both the AC and DC lines tend to be low in 
>comparison to sense circuits, so a given amount of interference 
>energy will not induce anywhere near the amount of actual voltage on 
>the other line, as it would in a high impedance metering circuit.
>
>That doesn't mean that you're home free, though.  A "DC" solar 
>array/charge circuit still probably uses high frequency PWM circuits 
>to regulate charge, and those pulsing currents can induce small 
>potentials on the AC lines.  Shouldn't be a problem unless it 
>interferes with the sense circuits on the output of the inverter, or 
>on the input circuits of an intelligent appliance.  I've never heard 
>any such cases, but I could see where pulsed PWM noise from a charge 
>controller could interfere (in theory) with the sense circuitry 
>associated with an inverter's search function, or with other 
>inverter output metering circuits.  The inverter manus would have to 
>comment further as if there's any real possibility of that.
>
>Running battery/inverter cables in the same conduit as AC lines 
>could be a real mess.  There's a lot of high-energy current pulsing 
>occurring on the DC lines when the inverter is powering loads, much 
>higher than a typical solar charge circuit.  I wouldn't want that 
>combination to occur in any circumstance, not that I could imagine 
>that ever happening.
>
>
>Conversely, AC noise, coupled onto the DC lines, could mess with the 
>sense circuits on a charge controller, but I would expect that those 
>sense circuits would be pretty heavily filtered in all but the 
>lowest end products, since there's no reason not to.
>
>Just my $0.02 for what it's worth,
>
>John Raynes
>RE Solar
>Torrey, UT
>
>
>At 08:56 AM 6/21/2005 -0700, you wrote:
>>Hey Nick and Jay and all,
>>
>>Yes there is a provision in the code "if part of the same system" 
>>but beware.  Not only can you run into interpretation issues by 
>>inspectors there is a very real possibility of induced currents and 
>>noise.  I'm not an expert on it but from my experience with high 
>>voltages and amperages in electric vehicles, DC current can cause 
>>some serious induction currents.  So you may get away with it on a 
>>code level but the physics of the matter should really be checked 
>>out!  At the amperages you are talking about with your PV system - 
>>they may not be a problem - but it would be nice to quantify that.
>>
>>Anyone out there with a fundamental electrical engineering head 
>>better than mine know the really issues, here?
>>
>>Best,
>>
>>Jeff C.
>
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