On Mon, 19 Jan 2004 15:08:13 -0000, "Christian McArdle"
wrote:

The which? book doesn't make this clear and actualy says not to
connect the houseshed cable earth wire to the shed csu, connect the
shed csu to an earth rod, but what would you do with the houseshed
earth?

It seems that some people isolate the cable earth at the shed,

As per the regs then?

whilst others
connect it to the earthing terminal. Obviously, there is always a connection
to the earth rod.

From the fixed wiring in the shed.

I can see advantages to both. Using the cable introduces a second earth to
the system, in case one earth fails.

Kind of true, actually entirely true, however the regs don't allow you
to do this.

However, using the cable could result
in current flowing from the house to the shed under earth fault conditions.

However, I suspect any such flow would be shortlived and limited in current,
preventing the small earth SWA earth overheating. Also, the supplier's earth
is probably much better anyway.

That is assuming there is a suppliers earth and it is all correctly
connected to the installation.

In any case, there should be an RCD in the shed covering the entire
installation.

I personally favour an RCD at the house to cover the cable also in the
event of a spde related incident or similar!

The "best" solution is a time delayed 100mA RCD with 30mA RCBO
for sockets and 6A MCB for lights. However, unless you are using dangerous
machinery in the shed, this is overkill and you could get away with a 30mA
"whole shed" installation.

As you say, a prebuilt 'garage unit' with 30mA RCD, 16A and 6A MCB in
one pvc enclosure would be the cheapest solution.

The difference is (apart from being around 40
quid cheaper) that when you chop the power cord, the lights go out (which
isn't a good idea if you are holding a still rotating dangerous piece of
machinery!)




SJW
A.C.S. Ltd.