electrical earthing!!!?

Question

can anyone explain in very simple terms, what the difference is between extraneous bonding & equipotential bonding?? & why we do it

regards

Answer 1

an extraneous conductive part is not part of of an electrical system but some thing which could become live under a fault condition, such as copper pipes, boilers or air ducting. so exteraeneous bonding would be the bonding of these parts bach to the consumer unit. usially 10mm earthing (green and yellow) cable.

equipotential bonding it when everything is bonged together to the same potential, ie two pipes to two taps have to be cross bonded in case a fault occures in one pipe and you touched both pipes at the same time, if not bonded the current will flow from one tap to the other through YOU!!

in a domestic situation, everything inside the house should be inside the equipotential zone, this is why sockets have to be on an RCD in case you plug something into it which will be used outside this zone( lawnmower etc).

hope this helps, if not post again.

Answer 2

Their seems to be some confusion on the site concerning bonding in
domestic premisis, here it is in a nutshell.
Main bonding with green/yellow 10mm square (See table 54H of BS 7671
The IEE Regulations) from main earth terminal either in the board or
from the supplied main earth terminal link.
Connect to incoming gas supply on hard pipes (not lead) within 600mm of
the meter and before any tee.
Connect to incoming water supply on hard pipes (not lead) on the
consumers side of the stop valve and across the meter if one is fitted.
A similar connection must be made to any other incoming services such
as oil pipes.
The connection to the pipes must be made using a bonding clamp
complying to BS 951 with a label attached SAFETY ELECTRICAL CONNECTION
DO NOT REMOVE.
You may loop from one service to another with the bonding lead, but if
you do this you must not cut the lead, just strip off the insulation
and wrap it around the screw on the clamp. Clean the pipes and ensure
tight connections. Get it tested by a qualified electrician.

Supplimentary bonding with 4.0 mm square green/yellow to hard pipes
using BS 951 clamps and labels, connect to earth at the nearest socket
outlet, immersion heater switch, shower switch or fused connection
unit. DO NOT RUN IT BACK TO THE CONSUMER UNIT.
If you need more advive get a copy of the On Site Guide (ISBN 0 8526
987 2) around £17 and read it ALL, don't ignore the bits you don't
understand. they know better than you do.


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