Re: Clean power for Audio and AV

Christopher Jahn wrote:
Clive Mitchell <bigclive1@xxxxxxxxxxxx> wrote in
news:VRCMo6J4El3DFwdP@xxxxxxxxxxxx:

In message
<1138638446.654472.200820@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Thomas Paterson <t_p_paterson@xxxxxxxxxxx> writes 
What level of separation do I need to ask the engineers for on
the sound and AV power supplies for our event space.  Is it
true clean power with a separate transformer, or do I need
simply separate earth connections?

You can go too far with "clean power" particularly when
technically clueless consultants are involved. Even if you do
have a special earth run for the AV system it will instantly
be defeated when you do something trivial like place a piece
of earthed metal equipment in contact with a part of the
buildings metalwork. Think about the amount of metal cased
gear like infra red units that clamp on structural steel. 

The easiest (non anal) definition of a clean supply is one
that is basically a dedicated cable to the main incoming
supply to the building. Since the heavier equipment tends to
be fed from dedicated switch-fuses in the distribution room,
it tends to effectively have it's own clean supply anyway.

I'd say just get dedicated distribution boards mounted locally
to the lighting system, sound system and control booth. That
way you won't get much interference from the rest of the
buildings loads.

Does the OB feed need to be clean power? Again, if so, how
clean? 
They tend to have their own high current feed from the
distribution room anyway, so they are inherently "clean".


Something like this:

            MAIN FEED
    	   /      |        \
LX PANEL   SOUND PANEL   HOUSE PANEL (EVERYTHING ELSE)






The other thing is to have extremely good electrical grounding system in place. Do not allow them to use the conduit as a safety ground path. (although the conduit should be grounded). NEC does not allow you to have a separate electrical safety ground. Having a superior ground system in place, and nice fat ground conductors to all your distribution panels will serve you well.
Having the dimmers on a separately derived system will help you tame the power factor beast, but it may be a bit overkill for your venue.

  --Dale
.

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