From: cullen@ac.dal.ca
Newsgroups: rec.audio.pro
Subject: Re: Power Dist. Point Current monitoring
Date: 6 Jan 93 23:54:43 -0400
Organization: Dalhousie University, Halifax, Nova Scotia, Canada

Please Note: This refers to wiring practice in the US/Canada on
60Hz 110/220V single phase and 110/208V three phase systems.
Any of the following may or may not be applicable in other areas
of the world.

This is gratuitious advice and I will not be held liable for
any damages that result from following it.

Scott Whittle writes:
> Lo net world.  Im in the process of building/desiging/putting together
> a central point AC power dist point for a small portable system.
> I planning on taking an 8 or 12 rack sp ATA and on one side feed in the
> juice from the connected mains and on the other side have the juice
> which feeds my equipment. In said box will be some contactors/ some

Contactors?

> filtering jobbies (probably a furman something or another) a fuse box
> and a control panel.  On the control panel will be various items such
> as a key switch to allow the turning on of main power, an emergency
> cut off switch, and some line condition monitors. One of the things I
> like to keep a lid on is the total current.  What I wish to know is the
> appropriate method of having contiuous current monitoring? Does someone
> make a toroid for "permanent" use? Ideally something which has a low voltage
> output preportional to the current draw (e.g. 0-5v : 0-30amps)
> Any ideas would be appreciated. thanks

First, a few questions. 
Are you attempting to institute a method of remote current monitoring?
Otherwise it is far far cheaper to just stick 2 (or 3 or 4) ammeter 
displays in the distro box, and even cheaper to just buy a clamp-on 
and use it on the tails.

Do you intend to condition _all_ audio power, or just processing/drive
/console?
If the latter, the conditioner would probably be better suited in the
main drive rack. 

I can't see the real need for a key switch or a kill switch. 
Any key lock switch that would handle that kind of current
(30+A, 1/3 Phase) is going to be some kind of solenoid type,
and therefore easily bypassed. The alternative is a box with 
holes for a padlock around the main switch/breaker, far cheaper,
and harder to bypass (and it usually locks the box, too).

As for a kil switch, if you need to cut the power, and you are 
using a remote current display, you aren't going to get to the box
before a breaker blows, and if you're there, you can just flip
the breaker yourself.

I would suggest what is common practice in Halifax.
Take a single phase two leg combo main switch/load center box,
assuming you can find one small enough for intended purposes,
and punch holesfor the branch circuits recepticles in the box.
Also punch a hole/holes in what would normally be the top of the
box for your line in, and mount either Camlok or Joy connectors, 
or some other tipe of high current plug in the end. I would advise not
to use Twist-lock for the line in, for the possibility of a crewmember 
getting confused.

If you can't find a small enough box, just bolt a load center to a
single breaker box, and use a very short piece of conduit to connect.

This type of distro is very small, and can fit in the cable trunk with
all your AC cable. It also doesn't cost very much at all.
  
If anyone is interested, I will post my idea of how a small to medium size
distro should be organized in detail.

						Mur
						Cullen@ac.dal.ca
						Cullen@ug.cs.dal.ca

Newsgroups: rec.audio