Have I got this right?

[dook]

Hi guys and gals,

Another potentially stupid question from me but I need a bit of clarification. (Still Learning).

Am I right in saying that if you were to touch a live conductor only whilst standing on the floor you would not receive a shock. (You would not be creating a circuit for the current to flow).

...... and is this the principle behind equipotential bonding. Example, I'm in the bathroom and I touch a pipe which has become live under fault conditions. If I touch the pipe only I will not get a shock even though it is at 230v. If I then touch a non-bonded pipe at the same time I would get a shock as I would then be completing the circuit.

Sorry for the basic question but any comments would be appreciated.

 

[derek preece]

To the best of my knowledge, electrical shocks happen when there is a potential difference and a complete circuit for the current to flow. If for example the cold water tap became live due to a fault and the hot water tap introduced earth (i.e. zero volts) then there would be potential difference between the hot and cold tap and if you touched them both at the same time you would get a nasty shock. If they were linked by equipotential bonding then there would be no p.d. so you would only get a shock if earth potential was introduced through something else you were in contact with (the fault conditions that would give rise to this situation would not last for long, 0.4 seconds max, if you had adequate automatic disconnection of supply in place like suitable circuit breakers/RCDs, bonding etc).
In answer to your question, I think you are right, as long as the surface you are standing on does not also allow current to flow.

 

[Rageth]

I'd say you'd still get a belt. Depends if your grounded really. So I guess you could work on a rubber mat or a Faraday cage Think of birds sitting on a pylon. They are only touching the 'live' phases and nothing else. Where as if your standing on the floor there will be some grounded contact.

Yes you would get a shock by completing the circuit in your example if the non bonded pipe was grounded. Which chances are it would be.

 

[Deleted member 9648]

Hi guys and gals,

Another potentially stupid question from me but I need a bit of clarification. (Still Learning).

Am I right in saying that if you were to touch a live conductor only whilst standing on the floor you would not receive a shock. (You would not be creating a circuit for the current to flow).Pretty much it yes,as long as the floor was dry and insulated....best not try it though

...... and is this the principle behind equipotential bonding. Example, I'm in the bathroom and I touch a pipe which has become live under fault conditions. If I touch the pipe only I will not get a shock even though it is at 230v. If I then touch a non-bonded pipe at the same time I would get a shock as I would then be completing the circuit.Pipes dont become live under fault conditions,this is a very common misunderstanding,and this is not the reason bonding is carried out. Earthed metal work which is part of the electrical installation,(a conductive part),is likely to have a voltage relative to earth for the duration of a fault,a metallic pipe is usually at or near earth potential by virtue of being phisically connected to earth by the incoming service.Anyone touching the conductive part while the fault is in progress(such as the case of a kettle),and also in contact with a pipe may thus recieve a serious shock because the pipe is connected to the general mass of earth. This is the reason for bonding,connecting conductive parts of the installation to incoming metallic services liable to introduce an earth potential means there can be no potential difference between the two and the shock risk during fault conditions is reduced.
It is important to see and understand the difference between 'conductive parts'and 'extraneous conductive parts' as defined in bs 7671..............

Sorry for the basic question but any comments would be appreciated.

...................

 

[dook]

but what if the fault was the pipe?

 

[malcolmsanford]

but what if the fault was the pipe?

Not sure where you going with this, in which way can a pipe be a fault

 

[telectrix]

Not sure where you going with this, in which way can a pipe be a fault

was wondering that myself. think what he's on about is should a live conductor, due say to damaged insulation contact a metal pipe. the answer is that as the pipe is earthed, the resulting fault current will cause the protective device to operate.

 

[accordfire]

Hi guys and gals,

Another potentially stupid question from me but I need a bit of clarification. (Still Learning).

Am I right in saying that if you were to touch a live conductor only whilst standing on the floor you would not receive a shock. (You would not be creating a circuit for the current to flow).

...... and is this the principle behind equipotential bonding. Example, I'm in the bathroom and I touch a pipe which has become live under fault conditions. If I touch the pipe only I will not get a shock even though it is at 230v. If I then touch a non-bonded pipe at the same time I would get a shock as I would then be completing the circuit.

Sorry for the basic question but any comments would be appreciated.

The definition of equipotential is "at the same potential at every point".

The idea behind equipotential bonding is that by connecting exposed and extraneous metal work to earth, current has a low resistance path to earth - or in simpler terms that the exposed metal work cannot store a charge beyond the level that exists in the circuit at a given time.

Depending on the nature of the fault, it may be that you touching the metal may complete a lower resistance circuit than the bonding, for at least part of the potential in the circuit.

The very best you can say is that equipotential bonding, therefore, REDUCES the risk of shock, as if you are standing on the ground, you are still connected to earth yourself in some way. It may be slightly different if you were floating in free air, however.