Re: shielding low voltage wire, running low voltage wires aside 12-2 romex

["Robert L Bass" <RobertLBass@xxxxxxxxxxx>]

"John M Lauck" wrote:
>
> So considering interference with 120V electric wires, is it caused
> by the electric current in general or is it caused when there's a
> problem with the electric wiring?

There are two separate issues.  Code, which prohibits running low
voltage cables too close to parallel high voltage wires, is mainly
concerned with life safety.  In the event the two get shorted
together your low voltage hardware could become energized with lethal
voltages.  For the same reason combo boxes like the ones you mention
below come with an insulating separator to keep the two apart.

Performance can be affected adversely when data cables run close and
parallel to high voltage cables due to inductance -- the same thing
that makes transformers work.

> If you go to home depot they sell electric/data combo  boxes with a
> little sheet of plastic to separate the wires.  I haven't bought
> any of these, but I can't see how or why that could qualify for
> "code".

The plastic insert keeps the low voltage components and cables
separated from 110/220VAC and, as long as the box bears the
appropriate UL label it will comply with US electrical codes.
Because there's such a small length of wire inside the box, induction
isn't a problem there either.

There's one point I failed to address earlier.  You asked about
wrapping the part of the cable near the high voltage runs.  That
won't really be effective.  To keep garbage out of your data cable,
the shield would usually need to run the length of the cable and be
grounded at one end.  If you can keep the major part of data cable
runs at least a foot away from parallel 110VAC you'll be OK though.

--

Regards,
Robert L Bass

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