Electric shocks operating RCDs

[JohnW2]

There are two main situations in which an RCD may operate (in correctly-wired installations). Firstly (known mainly by electricians), when a N-E fault (or ‘leak’) occurs in the installation or equipment/appliances, particularly if an OPD does not operate because the fault current/leak is too small – either because it is a ‘small leak’, or because EFLI is too high (as in pure TT installations). This is common - we have all seen, and/or heard of, that happening all the time – sometimes ‘appropriately’ and sometimes as a ‘nuisance’ phenomenon.

The other situation, much more discussed (and probably the only function of RCDs known to many of the general public), is when someone receives an electric shock involving a current of >30mA flowing through their body from L to earth – i.e. the situation in which an RCD has the potential to directly ‘save lives’. Has anyone got any clue as to how common this occurrence is? (I suspect extremely rare) Proper statistics would be extremely difficult to collect, but I wonder if anyone has tried. Anecdotally, I have never suffered an electric shock which has caused an RCD to operate, and nor have I heard of anyone in my family/ social/ work circles having experienced this.

What is the experience of others? Has anyone here ever experienced a shock which caused a 30mA RCD to operate, or heard of this happening to anyone? Does anyone know of any attempts that have been made to collect statistics about this?

Kind Regards, John

 

[EFLImpudence]

I don't think there is any difference in the number of annual fatalities before or after RCD use - therefore ...

 

[JohnW2]

I don't think there is any difference in the number of annual fatalities before or after RCD use - therefore ...

Indeed - and, of course, some of those fatalities will always be ones which could not have been prevented by an RCD, anyway. An obvious problem is that the numbers are so small - even if RCDs prevented all the fatalities which they were theoretically capable of preventing (i.e. those due to N-E currents flowing through people), the difference in overall fatality numbers might not be easy to notice. ...and, of course, there will always be those shocks >30mA which didn't result in death, even without an RCD.

Kind Regards, John

 

[OwainDIYer]

I don't think there is any difference in the number of annual fatalities before or after RCD use - therefore ...

Actually there may be an increase in fatalities, caused by people falling down stairs or finding it harder to escape when the RCD has tripped in a fire.

Fires and stair falls are both more common than electrocution.

I've had electric shocks where the RCD has not tripped.

[/u]

 

[JohnW2]

Actually there may be an increase in fatalities, caused by people falling down stairs or finding it harder to escape when the RCD has tripped in a fire.

Indeed so (albeit 314 of current regs makes some attempt to reduce that risk), but data/statistics about that would be effectively impossible to find, since the official cause of death would almost certainly mention nothing about electricity at all.

Fires and stair falls are both more common than electrocution.

Surprising though it is (at least, to me), deaths due to almost anything appear to be more common than those due to electrocution - including things like falling out of bed, choking on food etc.

I've had electric shocks where the RCD has not tripped.

I think I must be getting wiser or more cautious (or just plain lucky!) as I age, since it's many years since I last had a significant shock - but I've certainly never tripped an RCD (with current flowing through my body)! When I think about some of the things I got up to in my youth (long before anyone had even dreamed of an RCD), I rather shudder

Kind Regards, John

 

[ericmark]

I have tripped mine when installing a water supply for the fridge. I had two hacksaw blades and was cutting two lines down the wall to hide the pipe in. But the strappers between the two way switches went horizontal and I cut through them.

Enough to throw me to the floor and make me feel unwell. But mainly pride hurt as I had not tested for horizontal cables.

But in the main the RCD stops shocks by tripping the power before we touch it. Leakage when wet bread put in toaster has tripped the power before any one has received a shock.

Working in radio equipment my son has tripped the RCD he would not admit he caused the trip.

As a child I put my fingers up the socket where a bulb should be and got a large belt and also trying to repair a spool to spool tape recorder got a large belt walked to plug and unplugged before fainting. I survived both so in consideration of that the shock I got when cutting through wires may not have been any worse without an RCD as within 40 ms I had removed the hacksaw blade.

As to darkness I have a emergency light above stair well and in garage so if there is a power failure I can see to exit and to reset the power. Likely I would not have fitted these if it were not for the RCD. So indirectly the RCD has made egress safer.

The 314.1 Every installation shall be divided into circuits, as necessary, to:

(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

Leaves me with questions on how any other item other than lights can be supplied from the same RCD and comply? I know sockets up with lights down means that with standard lamps you don't lose all lights but that assumes you use standard lamps.

To me unless like myself you have emergency lights to put sockets and lights on the same RCD is breaking the rules. Yet I see it again and again.

What I personally think is the risk assessment should be made as part of the installation certificate detailing what effect loss of power will have.

But to state with lighting failure street lights give enough light for egress is all well and good until heavy curtains are fitted. Same as writing JB below on floor boards before the laminate flooring is laid.

So I will ask my own question. Should all houses have emergency lighting?

 

[JM2]

Q. Are there any regular (consumer) RCDs or RCBOs than have a rated detection of <30mA ?

Whilst they could be liable to more nuisence tripping at least on an RCBO would show the circuit - and possibley isolate before a main/section RCD could trip (saving everything else).

 

[JohnW2]

Q. Are there any regular (consumer) RCDs or RCBOs than have a rated detection of <30mA ?

There are certainly ones available down to at least 10mA (maybe even lower), but I'm not sure whether one could classify them as "regular (consumer)".

Whilst they could be liable to more nuisence tripping at least on an RCBO would show the circuit - and possibley isolate before a main/section RCD could trip (saving everything else).

There are so many appliances and gadgets around these days that result in (very small, but finite) live-earth leakage that 10 mA RCDs or RCBOs would probably simply not be practical in many households. Of course, the presence of those 'leaky appliances/gadgets' means that a 30 mA RCD or RCBO will often trip in response to a 'new leak' (through a person or whatever) appreciably less than 30 mA.

Kind Regards, John

 

[JohnW2]

I have tripped mine when installing a water supply for the fridge. I had two hacksaw blades and was cutting two lines down the wall to hide the pipe in. But the strappers between the two way switches went horizontal and I cut through them.

Fair enough, but how sure are you that the tripping was due to >30mA passing through your body, rather than (at least partially) through the hacksaw blades to CPCs? Most of us will have experienced, or at least known of, RCDs tripping because of tools or conductors 'touching the wrong things' (notably N-E shorts!), but that's nothing to do with current flowing through a human body.

But in the main the RCD stops shocks by tripping the power before we touch it. Leakage when wet bread put in toaster has tripped the power before any one has received a shock.

Indeed, that the first 'RCD function'I referred to. However, my interest is in knowing how often RCDs have tripped as a result of currents through human bodies.

Leaves me with questions on how any other item other than lights can be supplied from the same RCD and comply? I know sockets up with lights down means that with standard lamps you don't lose all lights but that assumes you use standard lamps.

In the average-sized house, a hall or landing light is enough to enable one to navigate around the house. If they are on different RCDs and one has up/down two-way switching for both hall and landing lights, one always ought to be able to get a bit of light (providing there is still power, and only one of the RCDs has operated ).

So I will ask my own question. Should all houses have emergency lighting?

See above.

Kind Regards, John

 

[Adam_151]

Q. Are there any regular (consumer) RCDs or RCBOs than have a rated detection of <30mA ?

When we built the home workshop at my dad's house, I fitted two socket radials, one protected at 30mA for general use, and one protected at 10mA for separate sockets intended to be used for equipment under going repair.

That was a a hager Rcbo fitted within a domestic con/unit (although the 10ma was actually from their commercial range, its compatible with the domestic range)

 

[WabbitPoo]

As to darkness I have a emergency light above stair well and in garage so if there is a power failure I can see to exit and to reset the power.

I could do with such an item in my workshop. Is this the sort of thing?

 

[OwainDIYer]

yes, and especially useful in a workshop as in a power cut the lights can go out but power tools still spin down.

 

[plugwash]

I've had a shock off the mains which tripped a RCD when I was young and foolish and couldn't be bothered unplugging my amplifier before replacing the output fuses (the amplifier in question would probablly be regarded nowadays as class 0 though the case may have actually been earthed by virtue of other equipment it was connected to) so it can certainly happen that a person getting shocked trips a RCD.

But I suspect hardly anyone reports non-fatal shocks so probablly noone really knows how RCDs affect the mortality rate of electric shocks.

 

[ban-all-sheds]

I could do with such an item in my workshop. Is this the sort of thing?

Fine for a workshop.

For anybody who would like emergency lights on landing/stairs/hall, note that any fluorescent light with its own ballast can be converted to an emergency one if you want.

 

[JohnW2]

I've had a shock off the mains which tripped a RCD when I was young and foolish ... so it can certainly happen that a person getting shocked trips a RCD.

Thanks. No-one is doubting that it not only can, but will, happen if the RCD is functioning satisfactorily and >30 mA passes through a person to earth. My interest was in how often people have heard of it actually happening, since I personally hadn't.

But I suspect hardly anyone reports non-fatal shocks so probablly noone really knows how RCDs affect the mortality rate of electric shocks.

Indeed, as I said it would be very difficult to get data. As you say, 'reporting' just doesn't happen (reporting to whom, anyway?!), so one could only attempt to get data by undertaking surveys. However, as for the effect of RCDs on mortality, as EFLI said, the introduction of RCDs did not seem to result in any particularly noticable reduction in the total number of deaths due to electrocution, which gives us some handle on the situation.

I think that electric shocks are still relatively 'common', but deaths due to electrocution in the home struggle to get over about 20 per year. Since that was true even before RCDs, it is apparent that the great majority of shocks are non-fatal even without RCDs - which is therefore quite a hard an act for RCDs to follow.

Death by electrocution obviously isn't the only issue. Physical injuries (due to falls etc.) consequent on receiving an electric shock can be serious, life-changing or even fatal, but almost certainly would not get recorded as being related to electricity. Lasting significant physical damage following a severe shock (usually due to external and/or internal thermal effects {'burns'}) obviously does occasionally happen, but is very rare. Of course, if one gets up to HV voltages or above, then those goalposts move.

Kind Regards, John