Cameron Hall Power was: [tech] morwong

[Simon Fryer]

Bingle

> A while ago Grahame Bowland tapped:

> On Tue, Sep 19, 2000 at 04:50:01PM +0800, David Cake wrote:
> I had a talk with a university electrician a couple of weeks back. He blamed 
> the RCD - apparently there must be a device somewhere with a few milliamps 
> of earth leakage current causing the thing to trip occasionally.

This is no real suprise. Actually, there is an imbalance between the currents
in the active and neutral conductors. As most of our hardware is computer
equipment there shoudl not be any large problems with this apart from the
following - which I am not too sure of the physics about:
* The air conditioner and coke machine. Inductive motors are bad for this 
kind of thing. 
* Current draw characteristics through a bridge rectifier. Although even in
this case current should be even in both active and neutrals but I am not
totally sure of the diode model I am using is appropriate for this situation. 
* Earth leakage etc through the ethernet cable shield?

This poses the problem - does the extension leads from upstairs cause any 
trips? Would the power conditioner in the UCC cause a sufficient difference
in current load characteristics to solve the second problem above for this
circuit?

> He suggested we find the device but offered no help on how to do so.

Take your pick. There are two ways I can think of at the moment. 

1) Brute force - Unplug XXX price of equipment and see what happens.
This is a problem because we don't have continuous tripping of a certain
device as far as I know.

2) Get a clamp on current measurer device. One that will measure well
below 30mA. Clamp it on the Active and Neutral (But not earth) and work out
which appliences are leaky and to what extent. You may find that a number of
appliances are leaky and the sum of several is causing the problem. 

These are my suggestions. 

See Ya
Simon

-- 
------------------------------------------------------------------------
"Well, an engineer is not concerned with the truth; that is left to 
philosophers and theologians: the prime concern of an engineer is 
the utility of the final product."  
Lectures on the Electrical Properties of Materials, L.Solymar, D.Walsh