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Too Modest
Coby
61 Posts
Question
If it can be demonstrated to the scientific community/press/public at large that "the RCD will trip or nary a tingle will be felt", then CBE's, MBE's, Knighthoods or perhaps a Nobel prize will be sure to follow!

This is surely the biggest step forward in Electrical safety since the invention of fuse wire!

In these bleak times the British public needs to hear good news like this.
27 Replies
Simon Barker
806 Posts
Given that 30mA is enough to kill you, I think "nary a tingle" is wishful thinking.  The standard European 30mA RCD is only intended to be quick enough to break the power before you're dead.

The Americans seem to prefer a 10mA RCD on high-risk radial circuits.  But they would keep nuisance tripping on UK ring finals that cover half a house.
Coby:
If it can be demonstrated to the scientific community/press/public at large that "the RCD will trip or nary a tingle will be felt", then CBE's, MBE's, Knighthoods or perhaps a Nobel prize will be sure to follow!
In these bleak times the British public needs to hear good news like this.

I maybe wrong but wasn't much of the 1930's 30mA RCD dertermination achieved in Germany experimenting on hospital patients?
But then what inspired the Nobel prize?
Legh

Roger Bryant
278 Posts
A few years ago on an electrical safety training course we were allowed to pass a 50 Hz current between a metal tube gripped in our hand and a moist sponge clamp around our wrist on the same side. The current was applied by turning a knob, if you turned the knob the current increased, if you stopped turning the current dropped to zero. 
Most people stopped at 4-5mA a few got to 6mA. It hurt at those current levels.
When I had my electrical body tests I asked the technician how much current was passing through my body. He said to me it wasn't the voltage, it was the current and the instruments were reading 18mA. Mind you it was being delivered at a pulse and not continuous .
When in situations like this its a bit like having your teeth drilled without anaesthetic, I know, You remember absoluetely everything.
Legh
I have had a cardioversion (under general anaesthetic) using external paddles. Apparently, from Google, they do not talk about Volts or Amps, but Joules. Generally between 50-360 J.
Clive
 
The tests were EMG and NCV which basically measured what was happening with my nervous system to various extremities. watching my thumbs twitch for instanst.
It became rather sore after about 5 minutes.
Legh
Coby
61 Posts
Simon Barker:
Given that 30mA is enough to kill you, I think "nary a tingle" is wishful thinking.  The standard European 30mA RCD is only intended to be quick enough to break the power before you're dead.

 

How is a standard European 30mA RCD intended to be quick enough to break the power before you're dead?

Simon Barker
806 Posts
Coby:
Simon Barker:
Given that 30mA is enough to kill you, I think "nary a tingle" is wishful thinking.  The standard European 30mA RCD is only intended to be quick enough to break the power before you're dead.

 

How is a standard European 30mA RCD intended to be quick enough to break the power before you're dead?

By tripping in a maximum of 300ms at 30mA, and quicker if the current is higher.

The biggest worry with electrocution is the heart.  But the clever thing about the heart is that it will automatically restart itself after a brief zap.  That's how hospital defibrillators work - they are rebooting the heart.  So long as the heart hasn't suffered from any permanent damage, you should survive.

Coby
61 Posts
 

By tripping in a maximum of 300ms at 30mA, and quicker if the current is higher.

 

It is a well documented fact that as little as 2mA is enough to be fatal, if the duration of the shock is long enough.

mapj1
2851 Posts
Not as well documented that it isn't, unless you are considering shocks of 70-80 year duration, when I agree most will have died, but not specifically  from electrocution.
If you restrain yourself to considering external shocks, those applied through the skin, and ignore shocks during surgery and from deeply penetrating electrodes, as not being typical of domestic shocks, the following curves apply to humans and low frequency AC. The kink between half  a second and perhaps 0.2 of a second relates to the period of a human heart beat. Shocks that are of short duration c.f. a heartbeat are  can be higher magnitude without effect than those that span a heartbeat or more. although this refers to IEC 60479, that in turn is based on the works of Dalziel and others in the 20th century.
iec shock curves
Coby
61 Posts
Demonstrate and claim your Nobel prize then.
Simon Barker
806 Posts
Coby:
Demonstrate and claim your Nobel prize then.

Nobel prize for what?  Showing that a product that has been in use for decades actually does what it is supposed to do isn't going to win you any prizes.

mapj1
2851 Posts
As I have mentioned before, I have received two shocks in my life I would class as 'near fatal'.
One disconnected by prompt action of a friend, the other by an RCD.
The first at school, from a flex with a live plug (instead of the more conventional live socket ! ) that was part of the theatre lighting lit. For the several seconds before I was disconnected by the prompt thinking of a school friend with me at the time, I was unable to breath, and apparently I was making a strange growling noise. Afterwards I was shaking for a good half hour, and missed the afternoon's lessons. The burns to the palms of my hands from the entry and exit of the current (the other hand was holding a well earthed fitting at the time to complete the circuit) took ~ 2 weeks to heal. This circuit had no RCD.

The second was when re-locating the wiring to an immersion heater that ran through the loft of a friends house. - The wiring ran through the loft, and knowing the whole house was RCD wired I carefully cut through the 2.5 mm T & E strand by strand to avoid an earth-neutral trip.
I was happy in the illusion that I had isolated the correct circuit at the board.
Only this was the wrong wire - a socket drop from the main ring ran in nearly the same place as the immersion heater, and in the dimness of the loft I had not realised. Once again good contact, this time with tools to sweaty hands, the no-let-go grip, and the same pain and shakes, but only for long enough to think
"Oh *&%%$ I've had it this time",
and then at about that point the RCD cut the current off.
Still the shakes and dizzy feeling, but no burns, and I needed no help to get myself down from the loft after a minute or two of deep breathing.
I was able to go back and re-connect the mis-cut cable, and solve the original problem, later in the same day.It is possible some of the shock was live-neutral, rather than all live-earth but clearly there was still enough to fire the trip - fortunately the place had a simple TT feed, all tripped at 30mA.

Yes a 30mA RCD can save you from more serious injury, and no, if the shock is hand to hand, the sensation is very far from painless, but it is at least as good as a friend sprinting across the stage and pulling a big switch for you, and that fact it is probably faster reduces the burns !
I'd recommend them
regards Mike .
Coby
61 Posts
412-06-01 A residual current device shall not be used as the sole means of protection against direct contact.

Explain please.
Andy Millar
1750 Posts
Hey, I've just had a brilliant idea, how about if we put some non-conductive material around live conductors, we could call it something like "insulation", as a primary protection, and then in case that fails put some sort of secondary protection in such as an RCD?

I'll wait for the Nobel prize to arrive in the post...
Rob Eagle
126 Posts
Only 2 shocks in you life Mike?  I've lost count, it would top one hundred I guess.  The worse was from the final anode of a colour TV (discharge only), it felt like someone had whacked me around the head with a railway sleeper! 
Many many shocks developing mains powered devices in my early days as an electronic designer and earlier from the Christmas tree lights every year as a child.
I remember once, at Christmas, with all the adults still sitting at the table, I used to like making sparks with my 12V train transformer, this day I decided to wire a bit of flex to a 13A plug, plug it in then touch live and neutral together - now that was quite a spark and sent the heeby jeebies down me.
In school we had collective shocks from both Van de Graff and Wimshurst machines, all part of the curriculum in those day!  I made myself an electrophorus which made nice sparks when charged with polystyrene but when I tried to charge it off the static off the TV screen it sent me flying across the room!
Ahh, the good old days eh.
Coby
61 Posts
Andy Millar:
Hey, I've just had a brilliant idea, how about if we put some non-conductive material around live conductors, we could call it something like "insulation", as a primary protection, and then in case that fails put some sort of secondary protection in such as an RCD?

I'll wait for the Nobel prize to arrive in the post...

In which case; when your 'primary protection' fails, you are therefore reliant on 'a residual current device being used as the sole means of protection against direct contact'...that doesn't work!

I think you'll find that primary and secondary 'protection' is provided by 'two layers' of insulation.

Coby
61 Posts
Rob Eagle:
Only 2 shocks in you life Mike?  I've lost count, it would top one hundred I guess.  The worse was from the final anode of a colour TV (discharge only), it felt like someone had whacked me around the head with a railway sleeper! 
Many many shocks developing mains powered devices in my early days as an electronic designer and earlier from the Christmas tree lights every year as a child.
I remember once, at Christmas, with all the adults still sitting at the table, I used to like making sparks with my 12V train transformer, this day I decided to wire a bit of flex to a 13A plug, plug it in then touch live and neutral together - now that was quite a spark and sent the heeby jeebies down me.
In school we had collective shocks from both Van de Graff and Wimshurst machines, all part of the curriculum in those day!  I made myself an electrophorus which made nice sparks when charged with polystyrene but when I tried to charge it off the static off the TV screen it sent me flying across the room!
Ahh, the good old days eh.

All of this and you still refuse to test your RCD by touching a line conductor?

Simon Barker
806 Posts
Coby:
Andy Millar:
Hey, I've just had a brilliant idea, how about if we put some non-conductive material around live conductors, we could call it something like "insulation", as a primary protection, and then in case that fails put some sort of secondary protection in such as an RCD?

I'll wait for the Nobel prize to arrive in the post...

In which case; when your 'primary protection' fails, you are therefore reliant on 'a residual current device being used as the sole means of protection against direct contact'...that doesn't work!

I think you'll find that primary and secondary 'protection' is provided by 'two layers' of insulation.

Only if you're using double insulation.  Class I appliances may contain single insulated wires.  And there's always "reinforced" insulation, to confuse matters.

And the pedants will argue that most electrical cable doesn't have two laters of insulation - it's "insulated and sheathed" - even though the sheath is made of the same stuff af the insulation.

" And the pedants will argue that most electrical cable doesn't have two laters of insulation - it's "insulated and sheathed" - even though the sheath is made of the same stuff af the insulation. "
Nothing pedant about clarity and precision. What is the pupose of insulating something twice?  Surely, two layers of insulation becomes either a form of reinforced insulation or as stated insulated and sheathed regardless of insulating material.
Legh.....🤔
mapj1
2851 Posts
Rob Eagle:
Only 2 shocks in you life Mike?  I've lost count, it would top one hundred I guess.
 

Well, no, like you,  rather more than 2 shocks, just those 2 that I consider near fatal as opposed to just a warning nip and a few choice phrases uttered .  Not sure how many probably not 100, but  a few per decade.

Oddly not during intentional live working (of which I have done rather more than would probably be approved, such as odd light switch swaps with the lights on and so forth.)

Quite a few back EMF tingles from 28V relays and things, car ignition, oh  and the odd electric fence while camping, and back indoors dropping one TV tube having scuffed the EHT sucker point. That was very memorable from an instant of panic, but luckily it landed intact ,and worked ok after a re-focus.

Not so many mains shocks, though I have been bitten by a hot water tank external thermostat where the bimetallic element is exposed when it is not on the tank and it is the part of the moving live contact... nasty design that one, and wet  cables outdoors.
I'm sure many of us are the same.
Mike.

Helios
115 Posts
The RCD is undoubtably one of the real biggest saftey improvements the electrical buisness has come up with , but sensative to every tingles , I dont think will work , in part because at the moment the national grid , is living with the reality of 40% (at times) of electricty generation comming from arrays of turbines that may vary output , and this causes /can cause variations in quality of supply , and the thought of main RCDs tripping out on voltage variations strikes me as being a lot more common if you have the wrong sort of sensativty in RCDs , certainly into the future of electricty generation at the moment.
Simon Barker
806 Posts
Helios:
The RCD is undoubtably one of the real biggest saftey improvements the electrical buisness has come up with , but sensative to every tingles , I dont think will work , in part because at the moment the national grid , is living with the reality of 40% (at times) of electricty generation comming from arrays of turbines that may vary output , and this causes /can cause variations in quality of supply , and the thought of main RCDs tripping out on voltage variations strikes me as being a lot more common if you have the wrong sort of sensativty in RCDs , certainly into the future of electricty generation at the moment.

Why would an RCD trip on a voltage variation?  There's nothing in them that measures the voltage.

Coby
61 Posts
Coby:
412-06-01 A residual current device shall not be used as the sole means of protection against direct contact.

Explain please.

An RCD used in conjunction with an 'earthed wrist strap' could be effectively used as "protection against direct contact".

Coby
61 Posts
mapj1:
Not as well documented that it isn't, unless you are considering shocks of 70-80 year duration, when I agree most will have died, but not specifically  from electrocution.
If you restrain yourself to considering external shocks, those applied through the skin, and ignore shocks during surgery and from deeply penetrating electrodes, as not being typical of domestic shocks, the following curves apply to humans and low frequency AC. The kink between half  a second and perhaps 0.2 of a second relates to the period of a human heart beat. Shocks that are of short duration c.f. a heartbeat are  can be higher magnitude without effect than those that span a heartbeat or more. although this refers to IEC 60479, that in turn is based on the works of Dalziel and others in the 20th century.
iec shock curves

The 'Supply Voltage' is missing from the graph above!

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