Do you think having a 2nd earthing source is good practice? My query was do
you feed house supply cable to earth rod or to the shed csu first and then
hook the earth rod into the shed csu.

"The "best" solution is a time delayed 100mA RCD with 30mA RCBO"

Isn't a RCBO a MCB and RCD combined? Which just plugs into the CSU (v.
expensive though). Is it possible to get different mA's for the RCBO?


It seems that some people isolate the cable earth at the shed, whilst
others
connect it to the earthing terminal. Obviously, there is always a
connection
to the earth rod.

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

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

Christian.