In article , Andrew Gabriel
wrote:
Also, in the case of an extension cable, beware of max length
due to earth fault loop impedance. In the case of an extension
cable fused at 13A, that is 15m for 1.5 mm² and 25m for 2.5 mm².

Oh dear. Does that mean that the 30m extension lead that I made
for the electric lawn mower has significant electrical risks? Naturally
I used a properly sealed connector to "puddle-proof" the joint between
the cables (I can't remember the IP rating of the connector, but it was
suitable for regular immersion to a couple of metres, but not for
diving with. I'd have to cultivate an ROV technician to obtain higher
ratings. Which could be done.). The cost of a 30 or 50m reel of mains
flex at B+Q was considerably higher (as in, times several) than the
cost of 2 X 15m extension leads.
The risk is what? That in the event of a fault at the remote
socket, current travelling back down the earth line will raise the
potential of the remote end of the earth (Ohms Law), which leaves the
person at the remote end holding something live while standing in a
puddle?
90% of the time I remember to plug the extension lead into an
RCD through-plug before I take the lawn mower out of the cellar. Maybe
I'd better tie-wrap or gaffer-tape the extension lead and RCD together
to make it 100% (including when the wife/ daughter does the lawn while
I'm away).

--
Aidan
Aberdeen, Scotland
Written at Wed, 29 Nov 2006 08:07 GMT, but posted later.