I intend wiring up a remote garage so it will have a TT earth.What is the
best way of protecting the exposed part of the earth rod and the cable clamp
from the elements outside?Could I drill a hole through the garage base and
hammer the rod into the foundations so the top is inside?I don't have and
specialised test equipment, how do I know for sure I have a good earth
except by deliberately causing an earth fault to check the RCD?
Borrow an earth loop impedence tester. Connect earth to the rod and live to
your supply (before the RCD, or with the RCD shorted out). Press Test. You
need a much better earth than that required to simply trip the RCD. The
tester will attempt to draw up to 20A and measure the voltage drop.
Technically, you can get away with higher impedences without breaking the
rules, but 200 ohms is a recommended maximum to allow some margin. You
should be aiming for much less that this, unless you have some sort of
problems with soil or rocks.
"Mark Atherton" wrote in message
og40>. With a 30 mA RCD the earth electrode resistance must be less than
1600 ohms (500 ohms with a 100 mA RCD) but, as Christian says, the OSG
recommends a figure of under 200 ohms to give a large margin of safety in
case of drying out or freezing of the soil.
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