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

[Ray Walters]

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Just a quick note:

THe MX-60 will still be sending a Pulsed signal back down the line to the 
array as it modulates the array current. I've heard C-40 modulation at the 
solar panels 200 ft away. ALso while not recommended, I've run Trimetric 
meter wire in conduit with AC wires without a problem, the twisted pairs 
cancelled any noise.

Ray



>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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