to earth or not to earth.

[Deleted member 26818]

whats that got with a discussion????

I'm wondering if I know you.

 

[pushrod]

As spin says I would think that an rcd would operate without a cpc but that it might involve a limited electric shock.

Also aren't there various installations that are earth free zones, particularly scientific experimental areas and certain medical areas? Electrical separation can remove the earth. IT systems don't have earths(?). Lighting circuits for many years were allowed without a cpc and we have masses of equipment that is double insulated and is just supplied with 2 core - we don't panic that there in no earth to it.

We all live in a BS7671 regulated world and have probably got to where we are by being to able to recite it. I am more than happy having earths/cpcs and think it makes things safer but i would think there are alternatives. (tin hat on )

 

[IQ Electrical]

There are various earth-free situations but the op asked specifically about a domestic situation which would be virtually impossible to maintain as 'earth-free'.

 

[pushrod]

There are various earth-free situations but the op asked specifically about a domestic situation which would be virtually impossible to maintain as 'earth-free'.

It certainly would demand a new emphasis in building technique.

 

[Deleted member 26818]

The Regulations are always changing.
New technologies, all sorts of reasons.
There may well come a time when CPCs are deemed to be no longer neccassary.
The ECS's current guidance for lighting circuits indicates that the lack of of a CPC is acceptable and that the provision of RCD protection and the use of class II fittings and accessories offers the same degree of safety as would be provided by a CPC.

 

[dekachad]

when you say a domestic situation is impossible to maintain as earth-free because........... then i ask why because, and you come back with no answer. its like a "because i say so" or "because the regs say so" answer. if you came back and said because this or that would happen in a given situation and without an earth " we are all dooooomed" etc then i would say thanks, take note, advise everyone i know with no earth to get one put in, plus be able to tell all the sparkies i have asked before, the definitive answer. Everybody's happy.

 

[Paul.M]

is it time now for an actual test involving a live body, an RCD and 230v, sod the theory, let's go and grab some live cables, show the videos on youtube or you've been framed. last one to fibrillate is a cissy.

Can I be the one holding onto the circuit protected by a cpc, rcd and mcb because I'll be the one going to the pub afterwards and not the morgue.

I am qualified but not much experience as its not my main vocation. Its a question I have pondered way before I qualified as I have seen many houses with no earth, abroad obviously.

Qualified, debatable. Not much experience, correct. Not my main vocation, that's what all bad plumbers say.

 

[IQ Electrical]

Dekachad, you need to understand that I don't know how much you don't know!

Normally if I say it's virtually impossible to ensure an earth-free situation in a domestic scenario, I expect people to at least visualise a domestic scenario ie. The incoming services with 'earthy' potential, the vast majority of class 1 appliances, power tools etc. used on 'true earth' surely I don't need to ramble on?

I believe I made these points for you way back in this thread?

 

[IQ Electrical]

You keep saying oh it's reg's and college talk but it's actually electrical theory and it has no reliance on BS 7671 or any City & Guilds course.

 

[terminator]

dekachad -

It can be a hard concept to grasp, and an equally hard subject to explain clearly on a BB, but once the penny drops you will be converted forever. I have heard this same argument many times, especially in college classes.

I would go so far as to say if you cannot grasp/understand it, you are not qualified to work safely on electrical installations. There are lots of good books on the subject - good bedtime readingl

 

[Adam W]

You get a shock when current flows through you because it's trying to get back to the transformer via the general mass of earth.
If the transformer wasn't earthed you wouldn't get a shock because the electric would have nowhere to flow (Kirchoff's law), which is how a shaver socket works.
However if the transformer wasn't earthed the voltage would "run away" and you would get an unacceptably high (400 or 500v) flowing which would mess up all the electrical equipment.
Alternatively ALL of the equipment could be class 2 which doesn't require an earth.

Sorry if someone already mentioned that, to be Frank I couldn't be bothered trawling through the last 7 pages.

 

[Engineer54]

What your never going to get through to the OP is that whether he understand earthing systems or not, whether he understands the function of RCD devices or not. Neither an earthing system or a 30mA RCD device are fool proof. He thinks they ARE!! Alas many consider 30mA as a safe value, and it generally is, but in certain situations it can't protect you. In those situations 10mA can kill you just as surely as a 30mA.

RCDs are nowhere near being capable of total reliance at this time, which is why they are classified as being Additional protection, only a fool would rely on them for sole protection against earth faults . Others here have pointed out electrical theory to the OP only to be totally ignored, and the same question asked yet again.... Just as well he isn't in the industry, he wouldn't listen to anyone if he was... a danger to himself and more importantly to others around him....

 

[amberleaf]

Some light Reading “ Dekached “

The Regulations is full of Information about Earthing . Scenario : My Lighting is Class 11 . No Eathing . must run a Separate Earth ??
Why a Light must have a Earth !!!!!!!! Taking for the Regulation’s BS-7671:2008

In the UK : 1965/6 ? the Rules changed for Earths & since that time Earths have needed to be Provided . ( “ Earthing “ )

As far as getting an Earth from Somewhere else it ” Sates the Earth Wire must Run along the Same Route as the Live Supply ”

Now we hit the Regulations . 2008 . ( 542.1.8. ) p/126
Where a number of Installation have separate Earthing Arrangements . any Protective Conductors Common to Any of these Installation(s) shall either be Capable of carrying the Maximum Fault Current likely to flow through them or be Earthed within One Installation “ Only “ & Insulated from the Earthing arrangements of any Other Installation . in the latter Circumstances . if the Protective Conductor form part of a Cable . the Protective Conductor shall be Earthed “ Only “ in the Installation containing the Associated Protective Device .

Regulations . 2008 . ( 543.2.8. ) p/131
An Exposed Conductive Part of Equipment shall ” Not “ be Used to form a Protective Conductor for Other Equipment except as provided by Regulation’s 543.2.2. – 543.2.4. & 543.2.5.

Circuit Arrangements .Regulations . 2008 . ( 521.8. / 1. ) p/98
Each part of a Circuit shall be Arranged such that the Conductors are ” Not “ Distributed over different multicore Cables . Conduits . Ducting Systems . Trunking Systems or Tray or Ladder Systems

 

[vitoboy]

wow
i think this is a great thread...
im not a geek (im not) but this is really geting down to it...
i hear you all on the regs...
i hear you all on the rcds arent 100% reliable

but the guy just wanted the total...... if the rcd is good.....if you dont put both fingers in the live and neutral...
i think the answer is no... no need for cpc..if the rcd is good(if)
but with is just safer....not because of shocks to people but because of faulty appliance ect..
i dont think he is about to install that way...other wise he couldnt write this thread.

or am i all wrong....help moderators...

ta
vito

 

[MarkieSparkie]

Lets go right back to first principles to explain earthing and see if this helps you dekachad.

What is earthing:
The whole of the world may be considered as a vast conductor which is at reference (zero) potential. In the UK we refer to this as 'earth' whilst in the USA it is called 'ground'. People are usually more or less in contact with earth, so if other parts which are open to touch become charged at a different voltage from earth a shock hazard exists . The process of earthing is to connect all these parts which could become charged to the general mass of earth, to provide a path for fault currents and to hold the parts as close as possible to earth potential. In simple theory this will prevent a potential difference between earth and earthed parts, as well as permitting the flow of fault current which will cause the operation of the protective systems.
The standard method of tying the electrical supply system to earth is to make a direct connection between the two. This is usually carried out at the supply transformer, where the neutral conductor (often the star point of a three-phase supply) is connected to earth using an earth electrode or the metal sheath and armouring of a buried cable. Lightning conductor systems must be bonded to the installation earth with a conductor no larger in cross-sectional area than that of the earthing conductor.
The advantages of earthing:
The practice of earthing is widespread, but not all countries in the world use it.
There is certainly a high cost involved, so there must be some advantages. In fact there are two. They are:
1. The whole electrical system is tied to the potential of the general mass of earth and cannot 'float' at another potential. For example, we can be fairly certain that the neutral of our supply is at, or near, zero volts (earth potential) and that
the phase conductors of our standard supply differ from earth by 230 volts in the UK.
2. By connecting earth to metalwork not intended to carry current (an extraneous conductive part or an exposed conductive part) by using a protective conductor, a path is provided for fault current which can be detected and, if necessary, broken.
The disadvantages of earthing:
The two important disadvantages are:
1. Cost: the provision of a complete system of protective conductors, earth electrodes, etc. is very expensive.
2. Possible safety hazard: It has been argued that complete isolation from earth will prevent shock due to indirect contact because there is no path for the shock current to return to the circuit if the supply earth connection is not made. This approach, however, ignores the presence of earth leakage resistance (due to imperfect insulation) and phase-to-earth capacitance (the insulation behaves as a dielectric). In many situations the combined impedance due to insulation resistance and earth capacitive reactance is low enough to allow a significant shock current .