Bonding of services

[Zorro]

I recommend you read Guidance Note 8 Earthing & Bonding

 

[Jimmy Boy]

Right bit of a wake up call..
Definitions BS7671
Extraneous Conductive Part..
A conductive part liable to produce potential,generally Earth potential,and NOT forming part of the electrical installation .

Now how to test for this ? I know how to Biff over to you official forum troll LMFAO
J

 

[WayneL]

I recommend you read Guidance Note 8 Earthing & Bonding

That is good advice and it is a good read.........it certainly 'puts to bed' some of the myths and rumours.

Which reminds me, I need to get a new copy now that it's out.

 

[ferg]

@ J GIT!! nice looking dog BTW

 

[Zorro]

I recommend reading GN8 Earthing & Bonding

 

[Jimmy Boy]

This is a extraneous test...it's in GN8 ...
FFS learn !

DETERMINING IF A PART IS EXTRANEOUS OR JUST A PIECE OF METAL
A test should be made using an Insulation Resistance Tester set on MΩ, supplying 500 Volts.
Test procedure:
Connect one test lead to the metal part and the other lead to a known earth. (MET)


If the resistance value is 0.022MΩ (22000Ω) or greater, no supplementary bonding conductor is required.
If it is less than 0.022MΩ, supplementary bonding should be carried out.


From the Ohm’s law:


I = V / R;


I = 500V / 22000Ω = 0.023Amp


This shows that if the fault was on a single phase 230Volt supply the current that would flow between the conductive parts would of course be only 0.0115Amp (11.5 mA).


This current is unlikely to give a fatal shock.


Guidance Notes GN8 and GN5 state:
" If extraneous metalwork is above 22KΩ then it need not besupplementary bonded.

 

[Zorro]

Yes use Ohms law Villa Is Rubbish

 

[Jimmy Boy]

Yes use Ohms law Villa Is Rubbish

On drugs lol
J

 

[Zorro]

I never take drugs lol just don't like Aston Villa FC

 

[Jimmy Boy]

i never take drugs lol just don't like aston villa fc

avfc...yuk

j

 

[WayneL]

This is a extraneous test...it's in GN8 ...
FFS learn !

DETERMINING IF A PART IS EXTRANEOUS OR JUST A PIECE OF METAL
A test should be made using an Insulation Resistance Tester set on MΩ, supplying 500 Volts.
Test procedure:
Connect one test lead to the metal part and the other lead to a known earth. (MET)


If the resistance value is 0.022MΩ (22000Ω) or greater, no supplementary bonding conductor is required.
If it is less than 0.022MΩ, supplementary bonding should be carried out.


From the Ohm’s law:


I = V / R;


I = 500V / 22000Ω = 0.023Amp


This shows that if the fault was on a single phase 230Volt supply the current that would flow between the conductive parts would of course be only 0.0115Amp (11.5 mA).


This current is unlikely to give a fatal shock.


Guidance Notes GN8 and GN5 state:
" If extraneous metalwork is above 22KΩ then it need not besupplementary bonded.

Nearly right.

 

[Jimmy Boy]

Nearly right.

Dependi on the 'let go' ?
J

 

[WayneL]

Dependi on the 'let go' ?
J

Yeh - and you forgot the bit about the resistance of the human body.

The equation is actually:

Rcp> (Uo/Ib) - Ztl


where,
Rcp is the resistance between the conductive part and the MET in ohms.

Uo is the nominal voltage to Earth in volts .

Ib is the value of current through the body in amperes that should not be exceeded.

Ztl is the impedance of the human body in ohms. The value suggested is 1000 ohms where Uo is 230 V (50 Hz), under dry or wet conditions.

Taking Ib as 10 mA and Ztl as 1000 ohms (as suggested above where the disconnection times in the installation are 0.4 s or less and Uo is 230 V), the limiting value of Rcp is given by:

Rcp > (230/0.01) - 1000

Rcp > 22,000 ohms

So, if RCP of metal part is > 22,000 ohms, then no main bonding required.


We all discussed it in some depth here:

http://www.electriciansforums.net/e...ns/16558-extraneous-yes-no.html#ixzz2Bg5wiQgp

 

[shagbite]

I've just recently read somewhere about the conductivity of water being poor and that the object of bonding is to bond the pipework that is extraneous.
I'm doing something rare here and sticking my neck out waiting for a potential barrage

ultra pure water is a very poor conductor. it has been de-ionized to such an extent that it can be used as an insulator. you can get water with resistances upto 18 megohms. you have to store it carefully though, any contact with air will introduce ions back into the water. it is also a very strong solvent when kept in such a distilled state.

 

[Jimmy Boy]

Your quite right Wayne I was of course just working on the recognised 10ma 'let go' figure based on a Ztl of 1000 ohms under dry conditions for a Uo of of 230v
J