240v from Sink

[adrian.groves]

Just to let you know that the sparky found a damaged cable where when testing one end, the neutral and earth where connected and the other end of the cable was dead. He is also going to come back and "improve" the earthing.

Thanks to everyone and in particular for suggesting I disconnect the wires inside the consumer unit as I got up one morning to find my nearest and dearest had switched the breaker back on!

 

[securespark]

Has he made the circuit safe now?

 

[John D v2.0]

Glad you found out what the problem is, I hope the cable is easy to fix without too much disruption! I guess the live was going through an appliance to the neutral then earth conductor then sink without having an onward path. I'm still surprised the rcd didn't trip though.
Lost neutral and earth with both shorted together is a really unlucky and dangerous fault!

 

[Taylortwocities]

I would have your electrician test the RCD using a proper tester to ensure it trips within the specified limits. It is not unknown for an RCD to be faulty.

 

[EFLImpudence]

If the RCD were faulty and should have worked but didn't, wouldn't the people who received the shocks be in a poorer state of health - i.e. no longer with us?

 

[JohnW2]

If the RCD were faulty and should have worked but didn't, wouldn't the people who received the shocks be in a poorer state of health - i.e. no longer with us?

If the RCD "should have worked" (i.e. if the 'shock current were at least 30mA), those who suffered shocks might have died, but there's no guarantee of that - don't forget that 30mA is deemed to be the shock current at/below which very few people should die - which means that most people would not die with shock currents a bit above that.

However, there are umpteen variables and uncertainties associated with electric shocks and their consequences. The fact that there is a high pd between two things does not necessarily mean that a high shock current will flow through someone touching them both - since the current depends upon such factors as the dryness of the skin and the quality of contact between skin and conductive parts. Hence, the presence of a high pd and the fact that people experienced shocks does not guarantee that anyone received a shock whose current was such that an RCD "should have worked".

In other words, we just don't know.

Kind Regards, John

 

[John D v2.0]

30ma can easily kill someone, and a lot more can flow in the time before the RCD trips anyway. In terms of bs7671 the RCD is more to protect the circuit than directly to protect end users directly.

 

[EFLImpudence]

Oh no. 30mA (Edit - or less) RCDs are for personal protection.

 

[EFLImpudence]

If the RCD "should have worked" (i.e. if the 'shock current were at least 30mA), those who suffered shocks might have died, but there's no guarantee of that - don't forget that 30mA is deemed to be the shock current at/below which very few people should die - which means that most people would not die with shock currents a bit above that.

However, there are umpteen variables and uncertainties associated with electric shocks and their consequences. The fact that there is a high pd between two things does not necessarily mean that a high shock current will flow through someone touching them both - since the current depends upon such factors as the dryness of the skin and the quality of contact between skin and conductive parts. Hence, the presence of a high pd and the fact that people experienced shocks does not guarantee that anyone received a shock whose current was such that an RCD "should have worked".

In other words, we just don't know.

I think that's what I meant.

Conversely:
If someone were electrocuted and an RCD had not tripped then it may be suspected that it is faulty.

 

[JohnW2]

30ma can easily kill someone, and a lot more can flow in the time before the RCD trips anyway.

Sure, 30mA can kill and, as you say, an RCD does nothing to limit the current during the brief period before an RCD responds to a residual current above its In - so that very high currents can flow for that very brief period. However, duration is as important as current magnitude in terms of lethality, so an RCD does a lot to protect life, even if the current flowing before it operates is very much greater than 30mA. In any event, the point is that 30mA is deemed to be the current below which 'protection' (of persons) is not 'considered necessary.

In terms of bs7671 the RCD is more to protect the circuit than directly to protect end users directly.

I don't really agree with that, in a TN installation (TT is obviously different). In a TN installation, the circuit is protected by ADS (EEBADS if you wish). If one (or BS7671) regarded the primary purpose of an RCD as being as a 'backup' for that primary protection (of the circuit), then one would only need to require the RCD to have an In of 'a few amps', not 30mA. [Edit] ...as EFLI was writing whilst I was writing the above, "30mA (or less)" RCDs are specifically for protection of persons.

Kind Regards, John

 

[JohnW2]

I think that's what I meant.

Fair enough - although that's not what I read your words to mean!

Conversely: If someone were electrocuted and an RCD had not tripped then it may be suspected that it is faulty.

One could certainly 'suspect' - but, again, there is no certainty. There is no guarantee that limiting the duration of a shock current (in the worst case, to just the maximum duration allowed by the RCD Standard) will inevitably prevent death, particularly if the current is very much higher than 30mA for however long it is allowed to flow.

Kind Regards, John

 

[EFLImpudence]

I thought some were doubtful that RCDs had saved anyone - or more than a very few.

 

[JohnW2]

I thought some were doubtful that RCDs had saved anyone - or more than a very few.

I suppose you are talking at least partially of me!

There certainly is not scope for RCDs to save 'more than a very few'. With the number of UK domestic electrocutions only about a couple of dozen a year, the circumstances of a good few of which mean that an RCD could/would not have helped, there obviously is no possibility that RCDs (or anything else) could save more than a small handful of lives per year.

If someone's life may have been 'saved' by an RCD, they would have to have experienced a shock which caused an RCD to operate - but, even then, we would not know whether or not they would have survived in the absence of the RCD. What you are probably referring to is my observation that, despite having often asked, in different places (including this forum), I think that I have only heard of one case of a person suffering a shock which caused an RCD to operate (and surviving!).

I have also been known to suggest that if the vast amount of money which has been spent on buying (countless millions of) RCDs and having them fitted over the past few decades had, instead, been spent on some other risk reduction (e.g. in relation to road safety), I'd be very surprised if more lives could not have been saved than the RCDs ever have saved (or ever could save)!

Kind Regards, John

 

[bernardgreen]

My recollections are that RCDs save lives by reducing the number of dangerous, potentailly fatal, situations by tripping before a person comes in contact with a Live item.

It is said ( by fire protection officer ) that RCDs reduce the number of fires ignited by electrical faults ( Live to Earth via a resistive short that heats up will trip the RCD before ignition temeperature is reached )

 

[John D v2.0]

Sorry my point was inaccurate and muddled, what I should have said is an RCD doesn't make things safe, the circuit is supposed to be safe from basic protection and then disconnection time from short circuits as they were before RCDs became common place.
In my mind the RCD would more often detect faults not of negligible impudence, which was a big gap in the previous editions of the regs, but clearly in the less likely case of direct contact, the consequences would be worse without an RCD.
I think more RCD trips have been from circuit faults than current flowing through a person, but maybe more lives were saved by the latter!

After all that we still don't understand why the OP's RCD didn't trip