On 30/05/2015 16:59, Gareth Magennis wrote:


"Phil Allison" wrote in message
...

bud-- wrote:


As explained in the IEEE surge guide
(starting page 30) plug-in protectors work primarily by limiting the
voltage from each wire to the ground at the protector.

** Connecting MOVs to ground like that in a *plug-in device* is
prohibited on safety grounds under EU and similar regulations as
followed in most 230/240 V places - like Australia where I am.

MOVs either have or can develop after some use leakage currents well in
excess of the maximum permitted, which is only a milliamp or so for most
categories of appliances.

The only components that may be so connected are agency approved " Y
caps " with values like 4.7nF - while MOVs and " X caps" always go
across the line.



... Phil



Slightly OT but .....
In the UK you can buy "surge protected" multi outlet extensions like this:
http://www.amazon.co.uk/Sivitec-Swit...rge+protection


Problem is, these can't be tested with a typical PAT Tester, as they
fail the test every time, being as there is circuitry between live and
ground.



Gareth.






At least some testers measure the insulation resistance (between
live/neutral and earth) at either 500VDC or 250VDC. The 250V setting is
labelled "MOV". This document explains the testing process:
http://uk.megger.com/getmedia/a5f14a...AN_en_V01.pdf/

The note from Megger on testing these surge protectors above also seems
to imply that connecting MOVs between live and earth is a common
arrangement, however they show a gas discharge tube between the Earth
wire and the MOVs. It would be interesting to know if this is common and
if so, why and what are its ratings.

Other pages seem to suggest that at least in some cases/countries, MOVs
are connected directly from live to earth.
http://en.wikipedia.org/wiki/Power_s..._and_filtering
http://www.racktronics.com.au/gallery.php
http://badcaps.net/forum/showthread.php?p=10176

I'm not sure whether this is a good thing, unless you know for sure that
your earth connections are all present and correct, and your RCD/ELCB is
present and working. Whilst I would agree with Phil that a used MOV is
likely to be so leaky as to result in unacceptable current flowing from
live to earth, I'm not sure that many of the appliance standards would
catch this, unless the sequence of tests (during product approval not
PAT) would first damage and later test the leakage of the MOV.

Chris