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Further Earth Bonding questions



Well the 1974 act was a good start, as up to that time the safety of employees wasn't a particular concern of employers as my dad found out one day when he went to adjust the height of a circular saw blade, and discovered the hard way that it didn't have the expected guard blade protecting its underside.
He said afterwards that he didn't feel a thing at the moment it happened it was the shock of seeing four fingers missing that caused him to keel over.....

Humm.... Well the earth had come off at the distribution board and the whole house was wired with this lead sheathed cable. So presuming that the lead sheathing was all bonded together then there would have been quite a lot of Capactive leakage from the live to earth, as one could assume that at some stage the un-earthed lead casing would be connected to another earth in the house, via lets say something like an immersion heater or similar appliance, so I reckon that their would have been sufficient Capactive and an unknown amount of resistive leakage sufficient to trip the RCD.
There was quite enough current there to prevent me from doing anything about it, and FWIW I have very dry skin and my hands were very dry on that day, so I reckon that a trip would have been taken out.
--
Tony Sayer



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Thought the time taken for the RCD to trip made this rather unlikely?
--
*Why is the man who invests all your money called a broker?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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The RCD won't *ever* trip if you put your finger across live and neutral, it dosn't trip on that sort of fault.
--
Chris Green

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*Not strictly true, if you know how an RCD actually works. There will still be "some" leakage current through your body that does not go back via the neutral return so if that exceeds the RCD trip current, quite likely, then out she goes!.....
--
Tony Sayer


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Standing on a ladder on a wooden (probably) floor the leakage through your body to earth will be virtually non-existent. You'll probably have shoes with rubber/plastic soles as well.
--
Chris Green

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Don't you believe it!. Well if you do, then grab the mains in one hand and note the results.
Usual disclaimer don't they this at home unless by doing so you'll help the gene pool along.......
--
Tony Sayer


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Have *you* actually done it? I've hung on to the output of a Van de Graaf generator while simply standing on a piece of perspex and charged myself up to hundreds of thousands of volts if not millions - not a tingle, until someone walks to close to you.
In reality in the house you have to be touching something metallic or standing on a wet (probably concrete) floor to get a shock. In ordinary shoes on a carpet you will feel *nothing* if you touch live mains with one finger (and, yes, I have done it occasionally when working on something live). Mostly one gets a shock because *both* hands are touching something conductive (and that's the worst for you too as the electricity runs across your chest).
In workplaces where live working on benches is commonplace significant shock prevention is provided by a vinyl floor covering and training people to use only one hand.
--
Chris Green

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No...
AC v DC ?...

I refer you to the above..

So have I..

Yes, I have had first hand/s experience of that:(

Good idea...
--
Tony Sayer


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"tony sayer" wrote | >> >The RCD won't *ever* trip if you put your finger across live and | >> >neutral, it dosn't trip on that sort of fault. | >> *Not strictly true, if you know how an RCD actually works. There | >> will still be "some" leakage current through your body that does | >> not go back via the neutral return so if that exceeds the RCD | >> trip current, quite likely, then out she goes!..... | >Standing on a ladder on a wooden (probably) floor the leakage | >through your body to earth will be virtually non-existent. | >You'll probably have shoes with rubber/plastic soles as well. | Don't you believe it!. Well if you do, then grab the mains in one | hand and note the results.
I have done exactly this in the past, standing on rubber-backed carpet tiles on a dry suspended timber floor. I vibrated gently at 50Hz and the RCD did not trip. This was not a glancing touch as I was holding the L wire intending to put it into a replacement socket faceplate.[1]
| Usual disclaimer don't they this at home unless by doing so you'll | help the gene pool along.......
Glad I can do my bit for the gene pool without being forced into the messy business of procreation :-)
Owain
[1] I pulled out the fuse and checked the first socket. Dead. Checked the second socket. Dead. How the f'k was I supposed to guess the third socket in the lounge was on the garage circuit (garage being on opposite side of house, as well).
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stirlingcity.co.uk> writes

Course some people conduct better then others;!....

Theres a howler there somewhere....

On three occasions over the years I've seen someone take apparently dead wires in their hands and mutter "I suppose this *is* dead"?. Touch them together, and you'll soon find out SEZ I:)
On each occasion there was a flash and loud bang!, very loud in the first instance as it was a three phase supply.
Last time was in the belfry of Ely Cathedral where once had been a mobile phone base station. The 'err "short circuit" took out most of the lights as well as disrupting a service.
A bit of positive spin helped lots,
"ere look arch-bish-whatever guv" "just imagine if that little lot had gone up by accident at night eh?"
"wouldn't have any where to pray now would yer?"
Seemed to earn a lot of brownie points:)
--
Tony Sayer


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"tony sayer" wrote | >| Usual disclaimer don't they this at home unless by doing so | >| you'll help the gene pool along....... | >Glad I can do my bit for the gene pool without being forced | >into the messy business of procreation :-) | Theres a howler there somewhere....
I am doing my best to avoid producing little howlers and continue to enjoy a good night's sleep, no vomit in the carpets, and no need to buy a people-carrier.
| Last time was in the belfry of Ely Cathedral where once had been a | mobile phone base station. The 'err "short circuit" took out most | of the lights as well as disrupting a service.
What's really fun is when there's no-one in the church office on a Sunday and an incoming phone call rings round all the extensions before ending up at the one hidden under the pulpit.
| A bit of positive spin helped lots, | "ere look arch-bish-whatever guv" "just imagine if that little lot had | gone up by accident at night eh?" | "wouldn't have any where to pray now would yer?"
"You wouldn't get any better if Jesus himeself was here, he was a chippie not a sparkie."
Owain
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Seen on a roadside pulpit:-
Jesus was a carpenter. Come and join us.
--
*Nothing is foolproof to a sufficiently talented fool.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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tony sayer wrote:

In typical dry indoor conditions you will feel nothing, as Chris rightly says. I've often demonstrated this to people, sometimes to their great surprise. It provokes thought.
Don't try it outdoors though while standing on an aluminium ladder with its feet in damp soil...
And don't try it if the frequency of the supply is a few orders of magnitude higher than 50 Hz or you'll discover the meanings of "earthed via a reactance" and "skin effect" at the same time.
--
Andy

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Depending on how moist your skin is. Mines very dry, scaly lizard like according to the missus, whilst hers is rather wet most of the time and No, she does have a dishwasher.....

No...
Yes and working with RF a lot of the time this is a good way to test if an aerial is radiating;)

--
Tony Sayer


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You miss the point. You'd have to bridge line and neutral within the trip time of the RCD. That's what I was querying.
I'm not, of course, saying they are perfect. But perhaps better than nothing?
--
*When the going gets tough, the tough take a coffee break *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Not if it's the N you touch first - there'd be naff-all current passing through you given the negligible potential between N and local earth, together with the much higher resistance which you present as a path to earth/transformer-return as compared to the copper path it's got. Then when you make contact with L (other side of the finger - possible finger-cooking but little likelihood of death; other hand - definite risk of fatality, hence the habit inculcated into generations of sparkies of working with one hand at a time) you become an attractive path for L-to-N current; and by far the greater part of the flow through you will be on the L-to-N path, which doesn't do anything to trip the RCD, rather than the L-to-E-via-shoes/clothes/whatever which the RCD is sensitive to.

Definitely better than nothing, but not a cure-all, and a possible source of a "risk compensation" effect - "oh, it's OK to work live on the electrics, I have a whole-house RCD"...
Stefek
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