I am afraid that your question is not entirely clear. The word "Incomer" does
not really define whether we are talk about a feed from a system transformer
on a major switchboard, or a cable connected to a ring main unit in a local
The purpose of Earthing Switches is to enable one to securely and safely
earth a cable or transformer so that work can be carried out on it. You
mention 11 kV, so the system is presumably based on UK practice, in which
case the Earthing Switches will probably be fault making. The equipment
makers label should enable you to confirm which standard is applicable to the
If you are referring to a major switchboard the arrangements for
circuit-breakers in such a switchboard have changed significantly with time.
Thirty years ago UK circuit-breakers would use oil for fault interruption,
and be withdrawable. Then earthing was achieved either by :-
(a) Fitting an earthing device on to the isolating contacts of the
(b) Moving the circuit-breaker carriage to an alternative earthing
position and earthing through the circuit-breaker
(c) Fitting a special earthing switch in place of the withdrawn
Since this time fixed circuit-breakers have been introduced using
Vacuum and SF6 technology, and with this has come a number of different ways
of providing the necessary earthing facilities.
The answer to understanding what has been provided is to carefully study the
The incomer I mean is, "a cable connected to a ring main unit in a
local substation". Within a single board, we have an incomer, and 3
feeders. For every each feeder, they come with an integral earth
switch, which is in place with vacuum circuit breaker.
The manufactures suggest having a earth switch at incomer side is not
necessary and redundant. I am not sure whether it is true. Please
Thank you very much.
In this situation it is up to you the operator to decide whether the switch
is neccessary or not. The question is basically can you safely earth up the
incoming cable to work on it at both ends ? If it is a radial system with no
present or future possibilities of backfeeds, or if you are happy to havethe
complete substation dead while you work on the cable, then maybe you can
managewithout the earth switch, but I would argue that you should know how
you would safely repair a fault in the incoming cable or cablebox.
I would have thought the supply authority would have insisted on a means
of earthing the cable, for the safety of their own employees, and they
would come in and ensure it was properly locked in place.
---< On Line using an Acorn StrongArm RiscPC >---
Same here :-)
From is valid but subject to change without notice if it gets spammed.
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