Earthing ?

[Richard3009]

All extraneous-conductive parts of the location are effectively connected to the protective equipotential bonding according to regulation 411.3.1.2 (Previously termed main equipotential bonding).


Whats this in english and how is it physically achieved

 

[electricAl]

Excerpted from ` a room containing a bath or shower` me thinks...

Extraneous conductive parts are those that don`t make up part of the electrical system (those are exposed conductive) but which may introduce an earth potential into the location.
So this would basically be any accessible, metallic (or otherwise conductive) part that was connected to earth that could provide a path for a fault current to flow from a live part, to earth (particular danger there to persons) If you`re unsure if a part is extraneous or not, you can confirm with a particular test.

All such parts need to be effectively bonded to the MET thru` the main equipotential conductors or otherwise, supplementary bonds may also be required between the location`s exposed AND extraneous parts - in effect, bonding all parts to the same potential (hence the term `equipotential`)

in bit of a rushso hope makess sense

 

[Richard3009]

clear as mud, are they saying all exposed metal parts of a bathroom need connecting via a cable to the main earth bar somehow? lets assume RCD of correct type is used to meet the requrement to remove the need for suplementary earthing what extra earthing do you need????? and how is it done physically

 

[electricAl]

clear as mud, are they saying all exposed metal parts of a bathroom need connecting via a cable to the main earth bar somehow? lets assume RCD of correct type is used to meet the requrement to remove the need for suplementary earthing what extra earthing do you need????? and how is it done physically

Okay. For the relaxation of supplementary bonding to be permissible, certain criteria have to be met.

i.e. all ccts in the location (supplying the bathroom/shower room etc) must be 30mA RCD protected, & meet disconnection times.
Also, any extraneous conductive parts of the location must be effectively connected to the MET.
I`ve highlighted the operative word there.
It is not a requirement for this to be done directly - it can (& more often, will) be achieved indirectly via the extraneous part`s remote connection to the main bonding conductor(s) & hence to the MET.
This connection must be proven to be effective/adaquate - no greater than 50 mOhms.

If these three pre-requisites are achieved then no supplementary bonding between the extraneous & exposed conductive parts need be provided.

Hope that`s clear enough for you. It`s all there in the On-Site, p69.

Al

 

[saveloy]

clear as mud, are they saying all exposed metal parts of a bathroom need connecting via a cable to the main earth bar somehow? lets assume RCD of correct type is used to meet the requrement to remove the need for suplementary earthing what extra earthing do you need????? and how is it done physically

Yes if supplementary bonding is required then all ECP have to be linked.

It all depends upon the resistance between the extraneous conductive part and the MET as well as the requirements mentioned by Electric AL as to whether you can omit supplementary bonding.

If the resistance between the MET and the ECP is 1666 ohms or less AND all circuits are RCD protected AND dissconnection times can be met, then supplementary bonding can be ommited.

Any metalwork in a bathroom that has a resistance when measured to MET greater than 22K ohms this will not be classed as an ECP and does not have to be bonded.

This applies when all plumbing that is copper/ conductive. If you have plastic pipes supplying taps rads etc then supplementary bonding can be ommitted.l

 

[Richard3009]

How you measuring resistance back to the MET, with a long test lead with a known resistance, or are you using a cpc from a local circuit for your path back to the MET.

 

[saveloy]

How you measuring resistance back to the MET, with a long test lead with a known resistance, or are you using a cpc from a local circuit for your path back to the MET.

Use a long test lead with a known resistance.