BigWallop wrote:

"Adrian Simpson" wrote in message
...

I'm having a bit of "fun" with my electrical system at home, and would
appreciate any advice.

The system has a RCD between the meter and the consumer unit (not sure
why, it was there when I moved in, but it has proved useful). The earth
is a spike in the ground at the back of the house.

Thursday night just as I turned the shower on, the RCD tripped out. So
I found a torch and reset the trip in the dark. I tried the shower
again, and off went the power again. I concluded that the shower had
died (it is 10-12 years old, so that seemed a fair conclusion).

This evening (Saturday), I was busy cooking my evening meal (on an
electric hob), and after about 10 minutes, off goes the power. Having
been moving the wiring for the boiler earlier in the day, I wondered if
I had got something wrong on that, so I turned off the RCD for that on
the consumer unit, put the power back on, and went back to cooking. 5
minutes or so later (certainly not straight away), off goes the power
again. I turned off the hob (which is 15 months old, so should have
some life in it yet), reset the trip, then tried the other two rings,
and within a minute or so, off goes the power again. The good news is
that by now the spuds are done, so at least I can get something to eat.

Having eaten the spuds, and thought about it, I consulted my tame
electrician (Dad). One thought that crossed my mind was that after a
long dry summer, the earth spike could be making a bad contact (*), so
whilst it was a long shot, it was worth a try. So I slowly poured some
salty water round the spike, allowing it to soak in. I then tried the
hob again for 20 minutes or so, and this time it was fine.

(*) memories of tales of old phone systems not working until a bucket of
water was tipped over the earth lead.

So, is it a coincidence that watering the earth spike has got things
working ?. Is there anything else I should do (getting it looked at
professionally will be arranged next week) ?.


TIA

Adrian



You could try putting another metre length on the earth spike to take it
further in to the ground. :-))

One thing I've noticed on new installation I'm visiting, is that the RCD's
which are fitted in the mains supply like yours, are only rated at 30mA
imbalance fault signal. This is really not adequate for a whole house
supply. This, to me, is erring on the "to safe to be properly functional"
side of things and is now causing a lot of nuisance breaks in whole house
supplies that are being installed these days.



Hear Hear!

I replaced my 30mA with a 100mA and haven't had a nuisance trip since.

By all ,means protect sockets or outsode rings witha sperate 30mA, but
teh amount of leakage off electronic equipment is enough to regurarly
trip 30mA IME.


A split load consumer unit seems to be a better design for a whole house
supply system and this is the road I'd advise you to take, if not already
installed, in your property. The split load CU separates low Wattage loads
like lighting and ventilation fans etc. from heavier loads like heating
circuits and larger domestic appliances fitted to other ring circuits
throughout the house. The heavier loads are controlled by an RCD with
individual MCB's to each circuit and depending on the load you may be
putting on the supply, can be rated up to 100mA fault signal before a trip
is activated. The lighter loads are controlled through a standard double
pole mains switch. This is safer because it leaves the lighting on so
you're not stumbling around in the dark to find torches and things, and if
the it is the lighting that has tripped off, then you can still plug in a
table to see your way around.

I still think designers of these electrical installations are not
considering that many people are actually drawing a lot more power from the
supply than they think and they are not allowing for heavier heating
elements in showers and washing and cooking appliances, and the fact that a
lot more dwellings can have more than one of each of these items installed
today.

The only place I now err on the side of "better safe than sorry" is in the
earthing continuity I install. If I can't get below 2 ohm impedance to
earth on any of my installations, then I feel that I have failed to provide
an adequate safety measure, even though an allowance of 10 ohms or below is
required to pass current testing approval.

These are just my thoughts on things. So. End of ramble. :-)