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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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 01 August 2010 07:22 PM
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shaunbutler

Posts: 217
Joined: 25 July 2010

I take it when to test the circuit it trips using the test you have??
 04 August 2010 10:37 PM
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dbullard

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Cheers guy's

Well the saga continues, a large portion of the school has been shut down as a new DB is being fitted controlling some 65 circuits / db's etc so all the new supplies etc are down to the other contractor to label etc test etc.......

So all i can do is dead test theones not being changed altered etc etc, looks like they have 2 weeks + changing that lot which will mean that i will not have time to get back and test these as this was not mentioned in the original spec / contract along with the 1 or 2 missing boards that i have found on my travells.

What really gets my back up is the lack of labelling deceent installation methods etc etc etc, the list continues.

Anyway i decided to do all the dead tests on these rcd's zdb, r2 them and then calc it as i cant z's em.

Regards

Daren

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


www.quest-electrical-sw.co.uk
 04 August 2010 10:58 PM
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ebee

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I do sympathise you not being able to take a measurement of Zs with 10mA RCD as a sort of "confidence test" like we can do with 30mA RCDs all be it with D lok or a 15mA test current (not always as reliable as we might like to think but nevertheless an overcheck of Ze(Zdb) + R1 +R2) but what else can you reasonably do?


Not too long ago it was not uncommon for test gear manufactures to suggest temporaryy replacement of RCDs (or even shorting links) to enable such tests to be carried out and it was a common event by practising testers (including some NICE ones) OK you might shudder but it did happen - quite often.

Working live and the good old bang bang 240V test are not a too distant memory to many even today (I'm not suggesting it as a way of working but just pointing out what happend - and still does in the real world)

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 04 August 2010 11:41 PM
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alancapon

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Have you tried a tester that uses "D-Lok" ? It is possible that it will saturate the sensing coil in the same way as a 30mA device while the reading is being taken.

Regards,

Alan.
 05 August 2010 12:16 AM
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ant1uk

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I found this in my fluke instructions not sure if its any help?

Note
To do a Loop impedance test in a circuit with a 10 mA RCD, we recommend a trip time RCD test. Use a nominal test current of 10 mA and the factor x ½ for this test.
If the fault voltage is below 25 V or 50 V, dependent on the local requirement, the loop is good. To calculate the loop impedance, divide the fault voltage by 10 mA (Loop impedance = fault voltage x 100).
 05 August 2010 10:04 PM
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dbullard

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Originally posted by: ant1uk

I found this in my fluke instructions not sure if its any help?



Note

To do a Loop impedance test in a circuit with a 10 mA RCD, we recommend a trip time RCD test. Use a nominal test current of 10 mA and the factor x ½ for this test.

If the fault voltage is below 25 V or 50 V, dependent on the local requirement, the loop is good. To calculate the loop impedance, divide the fault voltage by 10 mA (Loop impedance = fault voltage x 100).



Ant, i have the facility to ramp test from 6ma to 10ma test on my trusty megger cbt3, just belts and braces really i like doing the full range of tests but may have to conceed defet on this one.

Many thanks folks.

Daren

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


www.quest-electrical-sw.co.uk
 05 August 2010 10:32 PM
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ant1uk

Posts: 2376
Joined: 22 June 2010

Unless you wanna bypass the RCD for testing? thats possible? I can't see that been a problem.
IET » Wiring and the regulations » Zs (loop) testing 10mA rcd controlled circuits

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