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Topic Title: Zs (loop) testing 10mA rcd controlled circuits
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Created On: 30 July 2010 07:00 PM
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 30 July 2010 07:00 PM
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dbullard

Posts: 1166
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Hi all,

Getting through the test and report at a large school, now i have a question how can you loop test a circuit controllled by a 10mA rcd.

I can test the operation with my RCD tester but need verify also a max zs for the circuit.

Any help greatly appreciated as i cant see a way around this one as all loop testers i know of only allow a 15mA test for the purposes of loop testing on 30mA controlled circuits.


Cheers Daren

-------------------------
..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 30 July 2010 07:18 PM
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intrinsic4225B

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Measure (R1+R2) and then add to an impedance measurement taken at the distribution board?
 30 July 2010 07:26 PM
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dbullard

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Cheers, trying avoid R1+R2 tests as no circuits are identifiable due to the amount of circuits in the board Federal boards and they are rammed, been doing R2 wanderlead measurments but if i have to then ..... bugger.

Sorry forgot to add part of the contract all tests on 100% of socket outlets ......................... where accesible


Cheers again

Daren

-------------------------
..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 30 July 2010 07:37 PM
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intrinsic4225B

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Daren,

There are two main approaches to loop testing with a reduced risk of operating an RCD in circuit - one (as you have already mentioned) is to use a test current which is less than the minimum operating current of the RCD.

The other is to inject DC onto the circuit which saturates the magnetic core of the RCD and which should prevent it detecting the out of balance condition created by the loop test current.

If you can find a test instument using the second approach, you may be lucky - however this approach does not always work with certain types of RCD, such as those with internal electronic amplifiers.
 30 July 2010 07:58 PM
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mrcornbeef

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Can You not link out RCD is it located local in class room with mcb behind , obviously you would have to make sure no one using sockets etc, may be a problem if rcbo in board still possible to temporary feed circuit from another mcb on same phase, Just a thought
 30 July 2010 08:23 PM
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flashtestdummy

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Originally posted by: dbullard

Cheers, trying avoid R1+R2 tests as no circuits are identifiable due to the amount of circuits in the board Federal boards and they are rammed, been doing R2 wanderlead measurments but if i have to then ..... bugger.



Sorry forgot to add part of the contract all tests on 100% of socket outlets ......................... where accesible


What do you mean they arent identifiable? Take your R1+R2 and calculate Zs as per GN3

Sort of the same situaction as 2 & 4amp MCB's & 88's





 30 July 2010 08:33 PM
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dbullard

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Originally posted by: flashtestdummy

Originally posted by: dbullard



Cheers, trying avoid R1+R2 tests as no circuits are identifiable due to the amount of circuits in the board Federal boards and they are rammed, been doing R2 wanderlead measurments but if i have to then ..... bugger.







Sorry forgot to add part of the contract all tests on 100% of socket outlets ......................... where accesible




What do you mean they arent identifiable? Take your R1+R2 and calculate Zs as per GN3



Sort of the same situaction as 2 & 4amp MCB's & 88's




Well if i say no circuit diagramme's No labeling, all singles no ledgable means of ID as all old twin insulated singles, Now after having a long talk with the site manager it transpires that the previous test 5 years ago was halted for the same reason........ most of these boards are 30 + years old and have "dicked " with all this time, class rooms moved etc etc etc.

I think im doing ok so far on this one on my todd.

Just this one has put a spanner in the works, i have 36 of these beauties to test and im looking for a quick easy solution, im not like the previous mob and put lim after lim on the test sheets before riding of into the sunset, for my peice of mind i like to find as many circuits as possible.

When i did a site walk around visit looking at all the boards they looked like 30mA rcd's now after removing the dust and crap i can see and from a loop test they are 10 mA

Would like get past this hicup before quoting for the remedials of which a budget is already set.

Regards

Daren

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..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 30 July 2010 09:55 PM
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deleted_2_tony30

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well if the last contractor didnt just do the minimum and used ferrules that would have helped?

tony
 30 July 2010 10:24 PM
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dbullard

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Very true, the whole scholl has been rewired at sometime in its life as the original parts are from the 50's and alterations made since / switch gear changes etc etc

regards

Daren

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..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 31 July 2010 06:19 AM
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Jobbo

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I know its not practical, but from one of the sockets the in ring, perfom the tests as if at the distribution board (note this is the extent and limitations)

Please note unless you have previous test results, continuity of the ring final circuits and polarity must be performed
 31 July 2010 09:29 AM
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dg66

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I suggest a read of GN3s recommendations on what is required on an installation with no DB charts or information regarding circuit designation,otherwise how can you issue a satisfactory report.Also without knowing exactly what you're testing how can you comply with
reg 621.3?

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Dave(not Cockburn)
 31 July 2010 11:53 AM
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ant1uk

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Originally posted by: dg66

I suggest a read of GN3s recommendations on what is required on an installation with no DB charts or information regarding circuit designation,otherwise how can you issue a satisfactory report.Also without knowing exactly what you're testing how can you comply with

reg 621.3?


exactly! how can anyone expect to sign a satisfactory report without even doing any testing. what are they going to put in the extent and limitations? the whole installation?

Without even reading GN3 I can remember it says something along the lines of saying around 10% of testing is required if you have the previous completed test reports and a higher percentage is required depending on the number of faults found.

When there is no previous paperwork I test the whole installation to put my mind at rest.

It don't matter how long it takes to test the job it needs doing! and doing properly!

How does anyone that lies on test reports sleep at night? Do they really know how serious this is?

edit: grammer
 31 July 2010 11:58 AM
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perspicacious

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Perhaps if this time, an "unsatisfactory" was recorded, some funds to do the job properly may be found......

Regards

BOD
 31 July 2010 12:10 PM
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ant1uk

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we give an honest report and the client replies 'well the last guy did it ok for us' which in the clients eyes is trying to make us look bad.

If the installationis dangerious I tell the client the other guy came on a horse and left behind dangerious defects which need action straight away.

I know some clients/employers try to pressure us. but at the end of the day its not their signiture. So use your own judgement and don't allow them to pressure you.
 31 July 2010 03:05 PM
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kj scott

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As it appears that there are inadequate records; you should not be quoting inspection and test of this type of installation; without an initial survey.
If you are able to identify the socket outlets and their protective devices; R1+R2 should be achievable. However this installation does not have adequate circuit identification; so record it as a deviation. The Zs and R1+R2 can then be established whilst carrying out the remedial works.
For future projects quote to survey first.

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http://www.niceic.biz
 31 July 2010 08:18 PM
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dbullard

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Thats why im doing the very best i can .... im testing 100% of found socket supplied circuits and keeping a log and diagramme with me of the circuits found.

As i said im on my own and have done well so far, only unable to locate or find 4 circuits so far and one was labelled as unknown circuit ??? on a recent unlabelled board change.

Oh well


Many thanks

Daren

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..... Dont pee in my pocket and tell me its raining ......


www.quest-electrical-sw.co.uk
 01 August 2010 12:24 AM
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sparkingchip

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I have been known to label a couple of circuits as " unknown circuit ", but only because I had stupid clients who would not allow me free access to the property to test and inspect correctly, there is only so far you can go with stupid clients.

My first thought if faced with a distribution board full of 10mA RCBO's would be to test at 30mA or more at various points in the installation and see what trips then label accordingly, I have a fuse finder but have not used it for some months it's OK but not perfect, otherwise turning off breakers and waving a non-contact tester about or plugging in a plugtop tester seems to be the norm, whilst attaching various colours of insulation tape to fittings to identify what goes where.

Being the one to label the boards correctly when no one else has bothered goes against the grain, I hope you get the Brownie points you deserve if you do it.

Andy
 01 August 2010 08:32 AM
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dg66

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Another alternative is to isolate any unknown circuits and see who moans about the power being off,whilst it may make you unpopular you will at least be able to find these unknown circuits.

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Regards

Dave(not Cockburn)
 01 August 2010 03:20 PM
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John Peckham

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"Another alternative is to isolate any unknown circuits and see who moans about the power being off,whilst it may make you unpopular you will at least be able to find these unknown circuits"

Not a good idea DG66 as you may be switching off a critical alarm or a circuit that feeds such things as a trace heater to prevent a pipe freezing in winter. You will only find out when a disaster happens.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 01 August 2010 05:02 PM
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dg66

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JP all the things you have pointed out could easily be checked,and power restored if need be.

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Regards

Dave(not Cockburn)
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