On 20/11/2018 02:10, Fredxx wrote:
On 19/11/2018 17:22, John Rumm wrote:
On 19/11/2018 11:34, Fredxx wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
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?Â*Â* By all means use the new
stake in
parallel.Â* 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 wonder? Does the house earth benefit from other earth sources
such as copper/lead water pipes, or did you test the house earth
rod on it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are
plastic so I am assuming that there are no parallel paths to earth
and that the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential
bonding wires at the main earthing terminal while doing the test if
needs be for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

http://wiki.diyfaq.org.uk/index.php/...ode_resistance




OOI, is there any reason I can't use the neutral incomer as an
alternative to "Supplier's main earthing terminal"?

I would not fancy it ;-) Remember neutral is a "live" wire - it could
be several volts[1] away from local earth, and can supply reasonably
significant current in some circumstances.

Several is less than 24V. I am aware that neutral is now considered
'live' so best to take care.

If there is a small residual voltage on the neutral, swapping the
transformer phase and taking the average of two measurements would
help but should be a fraction of 24V.

[1] Or possibly more depending on the load being applied to it locally
(by yours and neighbouring properties), and distance from the
substation etc.

Which should be taken into account if averaging in-phase power and
reverse phase currents.

The resistance ought to be a fraction of the local earth-spike
resistance. Either way it gives a worst case scenario of true live
conductor to local earth resistance and prospective earth fault current.

Or am I wrong?

No, you will get a reading...

All in all though it seems like more hassle than using a bit of pipe
stuck in the ground though!


--
Cheers,

John.

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