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Topic Title: Inspection and Test Exam Question
Topic Summary: Why do we push the test button on an Rcd last
Created On: 06 February 2013 12:47 PM
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 06 February 2013 12:47 PM
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keithredpath

Posts: 424
Joined: 30 March 2002

Why do we push the test button on a Rcd AFTER carrying out all the required tests.

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keithredpath
 06 February 2013 01:24 PM
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UKPN

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functional test?

Regards.
 06 February 2013 01:27 PM
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OMS

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1 - to ensure that it still works after we've been buggering about with it, and its terminations

2 - we want the test to be representative and include all the normal aspects such as friction, sticktionb blood muck and bullets that the device lives with normally and which exists in the mechanical components - so we test the device "cold" without first having "warmed up" the action by means of the test button

regards

OMS

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Failure is always an option
 06 February 2013 01:43 PM
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vesuvius

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Its testing the mechanical operation of the R.C.D.
 06 February 2013 02:53 PM
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rogersmith7671

Posts: 886
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Quote;
Why do we push the test button on a Rcd AFTER carrying out all the required tests.

I always do this, some RCD's get "stuck" after being left untested for a long period. if the RCD fails to open upon the normal test sequence i generally "fail" it. The owner of the RCD is often unaware that the test button needs to be activated periodically despite the proper notice advising them to do so.
All "lazy" RCD's need to be identified and if necessary replaced, after all they are added to electrical circuits to save lives in the event of danger. A useless RCD is precisely that.

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 06 February 2013 03:12 PM
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AJJewsbury

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Why do we push the test button on a Rcd AFTER carrying out all the required tests.

Most of the answers seem to be to a slightly different question: "why do we do the other tests first".

I could read the original question as: why do we bother pressing the test button at all when we've already just proved that the RCD is working by the "meter" tests.

I'd suggest it's simply to make sure that the test button itself works (together with its internal resistor) - i.e. we're testing not the RCD, but the householder's test facility.

- Andy.
 06 February 2013 03:54 PM
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OMS

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Well I suppose we could say beacuse that's what BS 7671 section 6 Reg 612.1 (para 4) tells us to do - 612.8.1 (a) and (b) prescribes the RCD testing for effectiveness and that appears before 612.13

So both types of test are mandared and the order is prescribed in BS 7671

The reasons for doing it that way are as described above or because BS7671 tells us to - depends on the question paper I guess

Regards

OMS

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Failure is always an option
 06 February 2013 04:13 PM
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daveparry1

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Its because you need to know how the rcd is going to work in normal conditions, ie in it's not recently activated state, by excercising it with the test button it will probably work much quicker than it normally would.
 06 February 2013 10:41 PM
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AncientMariner

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Originally posted by: OMS
1 - to ensure that it still works after we've been buggering about with it, and its terminations



Cheers!

Clive

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Clive S Carver GCGI IEng MIET
 07 February 2013 07:21 AM
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MrP

Posts: 843
Joined: 24 March 2006

My take on it
Your looking at the question the wrong way round
Why do we not press the button first
You have to satisfy the required induced current operates the device(mechanical device) and operates correctly by a fault and not by manually pressing the button, pressing the button may free the machismo if its stuck and not a true reflection of the required operating process.

MrP a tadge cool here at the mo
 07 February 2013 08:08 AM
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Legh

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@MrP....That seems to be reasonable. Why not simulate, as closely as possible, a fault condition as a first test by testing at 5 times for any device offering additional protection and 1 times for devices offering fault protection only.

If the owners were following the advice given on the packet, they would be doing this every quarter and 'lubrication' would be taking place as a matter of course.

This was suggested here by somebody a couple of years ago.

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

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"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 07 February 2013 09:46 AM
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OMS

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@MrP....That seems to be reasonable. Why not simulate, as closely as possible, a fault condition as a first test by testing at 5 times for any device offering additional protection and 1 times for devices offering fault protection only.


and what's wrong with a drummond test lamps applied L-E pray tell ? -

OMS

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Failure is always an option
 07 February 2013 12:36 PM
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Legh

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Originally posted by: OMS

@MrP....That seems to be reasonable. Why not simulate, as closely as possible, a fault condition as a first test by testing at 5 times for any device offering additional protection and 1 times for devices offering fault protection only.


and what's wrong with a drummond test lamps applied L-E pray tell ? -

OMS


and why not, indeed?......

Well.....

That would generate the first 20 - 60mA, and what would you put on the cert ?

Tested using a 'pigmy'

Hardly quantifiable...

Legh

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 07 February 2013 01:04 PM
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daveparry1

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It would trip so quicky you probably wouldn't even see the light come on Legh but as long as it tripped why worry? (agreed that's not much good if you're filling in a test sheet though!)

Dave.
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