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Posted By Topic: Verify main earthing system

ShaneR
Oct 05 2017 11:00

It is my understanding that before any PEW is done a few tests must be undertaken.

One of these tests is "Verify main earthing system" ESR 2010 73A 1.(e)(iv)

I'm looking for practical solutions to comply with this requirement.

The references I found to comply are:

AS/NZS 3000:2007 8.2.2 (f)
AS/NZS 3000:2007 8.3.5
AS/NZS 3017:2007 3.1
AS/NZS 3017:2007 Figure 3.1

I'm assuming to comply you would need to find main earth tag/label. Visually check compliance to 8.2.2 (f) then do a test as per figure Figure 3.1 (disconnected the MEC at the bar)?

or is there an easier solution?



http://www.legislation.govt.nz/regulation/public/2010/0036/latest/DLM5344613.html
   

mowgli
Oct 05 2017 17:04

Don't make life harder than it had to be. 73A actually says we must: "if the supply is from a MEN system, verify that there is a main earthing system."

It doesn't say compliance with 3000 or require any testing other than to prove that "there is" a main earthing system.

You could simply sight all the parts and note their arrangement is consistent with an earthing system.

If you can't sight the peg then isolate the board, remove the MEN link and do two mains polarity tests - one to the earth bar and one to an independent earth. If the MEC is in effective connection with earth then you should get similar results.

73A requires the polarity check anyway so this really isn't that much extra work.


   

zl2aj
Oct 06 2017 08:25

Agree with most of above however I get nervous around testing for a main earthing system unless I am able to identify an earthing conductor as the main earthing conductor. Testing all the earths for connection to the dirt can result in false positives.

If I cant see the main earth (and the MEC attached), and am unable to identify the MEC to test, my answer is there is no main earth and its time the installation had one. Maybe a bit over the top but I'd rather be safe than sorry.
   

AlecK
Oct 06 2017 08:35

Until some poor bugger has been the test case, we can't be sure what a court would make of it. And then it will probably depend largely on how well each lawyer was briefed.
Meanwhile we each have to decide for ourselves what is required.
I'd suggest the minimum would be identifying the three fittings that combine to make a "main earthing system"; and the maximum would be testing MEC continuity of MEC as per "3017".
Remembering that some installations have "earth stakes" other than the one for earthing the electrical system, so just sighting a bit of pipe with a wire on it wouldn't be enough.
On the other hand always worth a look in the ceiling space, as many MEC connections used to be made to water pipe at the header tank for the HWC

   

ShaneR
Oct 06 2017 09:46

Thanks guys for the practical advice

I suspect 90% of electricians don't even bother with the minimum
   

zl2aj
Oct 06 2017 14:11

Would a main earth attached to a Hot Water pipe count as a main earth? Or is it considered a bond? (taking care not to apply todays rules and definitions to yesterdays work).

Agree re other comments ALl - yes other non main earth electrodes exist and labels havent been around long enough for us to rely on them. Agree also checking the MEN (I have found an installation without one in the past).
   

pluto
Oct 06 2017 15:01

zl2aj Oct 06 2017 14:11
Your comment
Would a main earth attached to a Hot Water pipe count as a main earth? Or is it considered a bond? (taking care not to apply todays rules and definitions to yesterdays work).

My comment
Under the 1935 regulations there was a main earth lead as we know it today. But then it reached the switchboard enclsoure or location all final subcircuit were then twisted together and all joined together by a number of methods, soldering. line taps. etc.

It was NOT until 1961 regulations that the main serth lead was maintained separated in its own lug on the neutral bar stud.
All final subcircuit earths were then terminated nn the earth busbar and then joined by a removal link on all switchbaords.

Later in 2003, the main earth lug was re-located to the earth bar stud, with all final sub circuit on the earth busbar. It was at that time that the links between neutral and earth on distribution switchboard busbars was removed from the regulations.