On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so obviously
by fitting another one it would go down 8 feet. In the end I couldn't
get the last foot down so I sawed it off leaving 7 feet in the ground.
The reading was now 212 ohms - with the house earth disconnected again.
Better, but still not good enough - and I can't think why it remains so
high. Anyway, I then reconnected the house earth and got a reading of 59
ohms. I think I'll leave it at that - especially as it's improved the
ELI throughout the property!

Still baffled about the high reading though.