Regarding the earth.
So, you take the cable from the house csu to the shed and do you
connect the earth to the shed csu or direct to the earthing rod.
The which? book doesn't make this clear and actualy says not to
connect the house>shed cable earth wire to the shed csu, connect the
shed csu to an earth rod, but what would you do with the house>shed
It's probably obvious to you all but not to me.
FIGHT BACK AGAINST SPAM!
The cable you use as the supply should be connected at both ends regardless.
The only thing you need then is to connect the earth bar in the consumer
unit to an earth rod in the ground local to the shed. The requirement is
not to rely on the length of cable your using as the supply as the main
earthing point of the shed, because if this breaks down in any way it is not
supplying a proper earth point to the shed.
How deep should I go, I heard 2m but that seems a lot for 2 or 3 double
sockets and 1 or 2 lights.
Also what, in your opinion, supply cable mm2 size should I use 4 or 6mm2?
Should a 4mm2 use 30/32A and 6mm2 use 40A. Plus what earth cable to rod
should i use?
If you go with a 6mm csa' SWA cable with a 40amps breaker in the house, then
you can literally fit and forget it, because it is heavy enough to take any
sort of load you put on, within reason of course, and the difference in the
price between 2core X 4mm and 2core X 6mm isn't that much for a more safety
conscious supply that is going to last for many, many years.
The earthing cable between the CU and the rod should be taken in 16mm which
is the heaviest needed by any installation and introduces the least
impedance (resistance) to any fault current. This 16mm cable combined with
a 2mtr length of copper pipe hammered into the ground, and a proper earthing
strap wrapped around it, is going to give you a very safe supply which will
keep its integrity through many a large fault condition if it needs to.
What you want from a local earthing point is that the impedance is as low as
possible between the consumer unit and the ground. So taking 2mtrs of
copper into the ground is about the right amount to keep good contact
between rod and ground in almost all conditions.
The consumer unit should also have an RCD main switch fitted which will drop
the supply at the slightest hint of a local fault in the outbuilding without
causing nuisance tripping back at the house.
2m is likely to be excessive. The recommendations say at least 450mm but
more if it is likely to be heavily dug over - say 800mm.
Normal practice is to bury the cable - back fill 150mm or so, and then
lay a warning tape, then backfill the rest. That way if someone does get
carried away recreating their very own air raid shelter in the future
they should reach the tape before they get chance to damage the cable.
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