"tony sayer" wrote in message
...
In article , G&M
writes

"Rick Hughes" wrote in message
...

"tony sayer" wrote in message
I'd much prefer everything to be on a 30 ma RCD after all a 100 ma
ones
not going to be much fun to try to trip through your body


Agree on life protection, and the 30mA RCD wil provide protection to
the
AC
outlets, Radial and Ring Final circuits.

The Best Practise oft talked about is not to have lighting on a 30mA
trip
duwe to nusisance tripping, many on this group for example have
advocated
no
protection for light circuits.

I stuggle with this. When a light blows here it takes out the circuit
trip
but has never to my knowledge tripped our 30mA RCD. Is there something
system dependent here ?



There are some misconceptions about what an RCD actually does, well
modern ones.

An RCD (Residual current device) is designed to trip when there is a
current UNBALANCE between what is coming IN and what is going OUT on the
circuit it is protecting.

Now under normal operating conditions it matters not how much current is
flowing through the device, provided that its within its ratings like 64
amps for example.

Agreeed 100%, but it's the leaqkage that causes the nusianace trips I would
assume.


instance a cooker element develops some leakage between the element
casing then some current will flow to earth and if that current is
greater than the tripping unbalance current then off the trip will go.

So my question on whether to protect a cooker is a valid one?


Sometimes you may experience this as the element will only do this when
it gets hot and then the insulation will breakdown and the trip current
will be exceeded!.

Another "*******" problem comes if there is a short betwixt the neutral
line and the earth line in the wiring somewhere.



I had such a fault on a previous house .... trip would operate once a week
or so .... after hours and hours of fun, eventually could re-create it as
soon as I put a high current on the ring (toaster & kettle) eventually found
that SWMBO after loosening a socket for painting some months previous - had
crushed a neutral wire under the socket plate screw ...

If I didn't have an RCD on the cct ..... when would I have found the fault
? when it burst into flames ?

Rick