X5 RCD Test ?

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I still do not seem to be able to find out the correct reason for carrying out the X5 test on RCDs . I do the three tests each time but have no idea why we do the fast test . ?:|

Is it just to prove it will trip quickly when a high fault current occurs , or what ?

Deke

 
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Thanks Batts, I'm looking at 415.1.1 and it confirms my belief that the 17th suffers from an overdose of gobblededook, or perhaps I'm past it . I'm reading the words but they 'aint making sense. I'll try the OSG. I do not understand the last sentance .

 
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Strictly speaking the x5 RCD test is only required where your max Zs values cannot be met..

e.g. TT installations..

nowt to do with 17th ed... the "old money" reg was 412-06-02 (ii)

If all of your max Zs values are met then the MCB will do its disconnection job OK.. & no need for x5 RCD test..

BUT Pepe's like NICEIC still like you to do x5 ALL of the time anyway! :|

its all down to those levels & duration of shock currents to prevent death!

and where RCD is used as "Additional Protection" due to probability MCB cannot operate fast enough under live - earth fault!

they say 20ma - 30ma can impair breathing ,,

50ma & above can cause ventricular fibrillation (whoever she is?) and Death! :(

5x30ma...

ensure fault current @ 150ma or greater cuts off in 40ms MAX!! ;)

 
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For information:

ventricular fibrillation is a rapid fluttering of the heart muscle that shows as a trace on an ECG but isn't able to pump blood around the body. The person would have no pulse.

They shock patients in hospitals with a defibrillator to STOP the heart, with the hope that all the muscle cells will re-co-ordinate and start with a normal heart rhythm.

 
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For information:ventricular fibrillation is a rapid fluttering of the heart muscle that shows as a trace on an ECG but isn't able to pump blood around the body. The person would have no pulse.

They shock patients in hospitals with a defibrillator to STOP the heart, with the hope that all the muscle cells will re-co-ordinate and start with a normal heart rhythm.
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PC Electrics

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The relevant BS that RCDs are built to perform against requires that at 5x they trip in <40ms. Therefore we are testing the RCD to ensure it meets this performance spec.

I've had a few recently that failed at 5x (especially Crabtree RCBOs) which makes me wonder if the manufacturers do a 100% EOL performance test (or use an SPC method) or just rely on us to do their testing for them? I personally believe the BS should insist on 100% EOL testing, given the increased reliance on RCDs now.

 

Battersby

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Strictly speaking the x5 RCD test is only required where your max Zs values cannot be met..e.g. TT installations..

nowt to do with 17th ed... the "old money" reg was 412-06-02 (ii)

If all of your max Zs values are met then the MCB will do its disconnection job OK.. & no need for x5 RCD test..

BUT Pepe's like NICEIC still like you to do x5 ALL of the time anyway! :|

its all down to those levels & duration of shock currents to prevent death!

and where RCD is used as "Additional Protection" due to probability MCB cannot operate fast enough under live - earth fault!
Dude, you're getting well confused.

RCDs may be used to assist disconnection for earth faults where disconnection times cannot be met by overcurrent devices.

As minimum earth fault currents will be of the order of 1A+ a 100 or 300mA RCD will do this job perfectly well.

But, RCDs of 30mA or less are used as additional protection against electric shock (formerly referred to as 'supplementary protection against direct contact'). And these are required, by the regulations, to disconnect within 40ms at 5xResidual current rating. That's why they are tested at this level - nothing to do with NICEIC and nothing to do with disconnecting earth fault currents (see definition).

These are two distinct uses of RCDs that every spark should understand.

Hope that helps. :)

 
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I still do not understand why it has to be X5 . Where does X5 come from , why not X3 or X8 . If an RCD trips at ,say 29mA ,30mA or 31mA leakage to earth is there a danger that it may not trip at all at a greater leakage current or the coils cannot handle a greater current . And if it did not trip at 150mA or didn't do it in 40ms what would be the reason ?

Deke

 
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