In article <kqshgm$427$
1...@dont-email.me>,
Without an RCD, the earth fault loop impedance can be an issue.
PAT test guidelines for extension leads with 13A fuse:
1.25mm² 12m max length
1.5mm² 15m max length
2.5mm² 25m max length (won't fit in most 13A plugs though)
They mustn't be daisy-chained to longer lengths.
By fitting a lower current fuse, you could in theory increase
the cable length proportionally. The RCD removes the concern over
earth fault loop impedance, but you may in theory end up with a
short on the cable which takes long enough to blow the fuse that
the cable gets damaged.
I have a dedicated outdoor socket circuit, and that's on a 10mA
RCBO in the consumer unit. After a couple of accidents, I had to
replace the hedge cutter flex anyway, and so I used 3-core, but
the earth is not connected at the hedge cutter end. However,
having it in the cable seemed to me like a good thing, as it
increases the chance of an earth fault if the cable is cut (thereby
tripping the RCD), and reduces the chance of the earth fault going
through me whilst I'm balanced at the top of a ladder. I have
managed to cut through the lawnmower cable without blowing a fuse
or the RCD (probably too quick), leaving a live cable-end in the
garden. I suspect that if I had the earth in the cable too like
I do on the hedge cutter, that might have tripped the RCD.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]