[Year 12 IPM] RE: ipm Digest, Vol 13, Issue 59

[Muscat, Laurie J]

----- Original Message -----
From: <kgration at myrtlefordsc.vic.edu.au>
To: <ipm at edulists.com.au>
Sent: Monday, March 27, 2006 8:14 PM
Subject: [Year 12 IPM] OT: Computer Room Power Issue - I'm desperate!!!


Hi there folks,

Thought I'd pick your brains and send out a general query to you all about
the following rather difficult and painful situation:

Over Christmas we had two new computer rooms cabled with both data and power
outlets by Nilsen (a reputable company).

Upon completion of the project, it was found that one of the rooms is fine
but the other one has a major issue on the power side of things.

The two rooms are provided with power from two separate switchboards (the
one that is working fine is from the main switch, the problematic one from a
sub-switch connected to this main). This sub-switch has numerous other
problem-free circuits running from.

Both rooms have Acer PCs (different models in both rooms) and three combo
RCD (safety switch)/circuit-breakers providing power to them. The
problematic room has Veriton 5500's (16), Veriton 5100's (3) and the
remainder are Veriton 5600G's (2) = total 0fr 21 PCs. i.e. 7 PCs are
connected to each circuit-breaker (not a particularly huge number).

The problem that we are having basically is that one or more of the
circuit-breakers keeps tripping whilst classes are using this room. It
doesn't seem to happen when the PCs are on but not in use and has not been
affecting the same circuit-breaker every time (i.e. not consistent and very
unpredictable).

Nilsen's wiring has been checked by our local electrician and by an
electrical inspector and has been found to be fine.

So far (with our trusty local electrician) we have tried the following to no
avail:
- upgrading the circuit-breakers from 16 to 20 amps
- installing three RCDs (safety switches) in place of the three
circuit-breakers and one RCD (that was in the original installation)
- manually tested turning on and off various combinations of computers
connected to each of the three RCDs etc.
- tested the RCDs (all are OK and within the expected limits)
- had an Acer tech out (no real help at all)
- megad (I assume that's how you spell it!) the circuit (nothing obviously
wrong)
- directly swapping the full complement of computers over between the two
rooms (nothing unusual happened)
- balancing the phases across the three RCDs (i.e. three phase power)

Based on what we have observed so far it would appear that the cummulative
total of the current leakage across the power supplies is the most likely
cause of the problem . . . it is proving whether this is the case or not
that is currently a real problem!

Has anyone experienced difficulties anything remotely like this? How did you
resolve the problem? Has anyone else had power issues specifically with
Veriton 5500's? Any ideas/suggestions are not too ridiculous at the moment
as we are in a real bind and are fast running out of things to try!

If you could email responses directly to me rather than to the list that'd
be fine and would spare others from having to read this already sizeable
story again!

Cheers,

Kim

---
Kim Gration
ICT Manager
Myrtleford Secondary College
http://www.myrtlefordsc.vic.edu.au
******************************************************************

G'day Kim.

My 1st guess, could be a neutral problem.

1. Have Powercor checked Neutral at the pole? (BTW: is it a MEN system or direct earthing?)
2. "It doesn't seem to happen when the PCs are on but not in use and has not been
affecting the same circuit-breaker every time"...so do you mean the PC's are not on and you get tripping?? What about weekends if all PC's are turned off? Is there any sort of loading in supply area that is peculiar in cycling (like a nearby metal fabricator that uses frequency controlled welders? What Ham Radio operators? Get Powercor on the job!!!)
3. If you've swapped PC's around, I reckon it's not the PC's themselves. So, yes, an earth leakage problem (ie. a cabling problem that manifests itself over time, like very common chaffed twin isulated cable whilst pulling through metal celing supports/tray etc. (very common with the "new" style (well.. it's 8 or so years old..)V75/90 TPS cable) . 

I am very suprised the combo units (RCD/MCB) did not fix the problem.

Cheers.

Laurie Muscat.

Bellarine Secondary College.
Drysdale Campus.

Mug Graduate Teacher. :-)
REC & ACA Registered Cabler.
muscat.laurie.j at edumail.vic.gov.au





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