Burried earth terminated directly Into earth bar

Post Reply
Dan L
Posts: 158
Joined: Tue May 19, 2020 10:00 pm
Answers: 0
Has thanked: 4 times
Been thanked: 3 times

Burried earth terminated directly Into earth bar

Post by Dan L »

It's not un common for 25mm burried earth to be terminated directly to earth bar ( no MEC)

Personally I feel in the situation where the distance from where the earth bar is to where the 25mm burried earth enters ground is approx 6m is un reasonable to expect an a MEC and an accessible testing point just for the sake of rules as common sense should prevail in this situation

However with this way of thinking where would the cut off point be for example if you had 25mm earth electrode terminated direct to earth bar then a 40m run before going underground would this still be OK with no accessible testng point? In this situation though not as likely for cost and practical reasons but not impossible I would think that you would want an accessible testing point close to where the 25mm earth enters ground.

but technically is this situation is the 40m run all the horizontal electrode or is the above MEC and burried the electrode as Iv heard some electricians say?
AlecK
Posts: 912
Joined: Thu Apr 16, 2020 11:24 am
Answers: 5
Has thanked: 2 times
Been thanked: 351 times

Re: Burried earth terminated directly Into earth bar

Post by AlecK »

The rules require a number of parts that, together, make up the installations earthing system.
These parts are listed in 5.3.1; and the only one that's in any way optional is (f) (equiotential bonding conductors).
Details of requirements for each of these part5s are in the following clauses;:
earthing conductor material / type [5.3.2]; earthing conductor size [5.3.3] (including MEC 5.3.3.2); main earthing terminal / bar [5.3.4]; the MEN connection[ 5.3.5]; and the earth electrode [5.3.6].
The MEC is not an optional extra .

The electrode can be in any form listed on Table 5.2; one of which is bare copper cable.
Between the electrode and the main earth bar is MEC, which must be insulated.
If we choose to provide the MEC using an extension of the bare copper cable used as electrode, the MEC part must be insulated.
This configuration may make sense where the required size of MEC is at least 25 mm2, or where the MEC is very short. Otherwise costs will dictate not wasting money on over-sized MEC.

The only requirement that changes when adopting this configuration is that if there's no possibility of disconnection the connection between these two parts, we don't need a "do not disconnect" label.
An accessible test point is a requirement regardless of what form the electrode and / or MEC take.
As is recording the location of the electrode 'connection' / test point at the switchboard.

Taking your example of a 6 m run of cable between earth bar & entry of electrode to ground; that's a 6 m MEC.
There's nothing hard about providing it; it's 6m less you have to strip the insulation off (or for cable bought bare 5 lengths of G/Y sleeving).
And there's not much trouble providing the accessible test point either.

And why would you not want to, when one of the required tests [8.3.5.2] is from this point to the earth bar?
Are you suggesting that this test can be omitted, not just for a new installation being commissioned; but for the entire life of the installation?
Most buildings have a minimum life of 50 years (required by Building Code); and in 50 years there's very likely to be occasions when faults need to be identified and corrected. That requires testing, including testing of the MEC.
Even in a new installation, there's the chance some wally may have cut the MEC between the time you install it and when the installation is livened.
So in my view there's nothing "common sense" about not providing an accessible test point; regardless of how long or short the MEC may be.
Dan L
Posts: 158
Joined: Tue May 19, 2020 10:00 pm
Answers: 0
Has thanked: 4 times
Been thanked: 3 times

Re: Burried earth terminated directly Into earth bar

Post by Dan L »

I was more thinking in that situation as the length from earth bar to ground was short that the earth bar connection would also be the test point as such but yes in that case the test would be omitted.

What you say makes sense. So if it is one 25mm cable from earth bar to ground then the above ground must be insulated and is the mec, the below ground obviously bare, no main earth conductor do not disconnect needed as continuous and no chance of disconnection but a testing point required as close as practical to where the cable enters ground.

Thanks for your answer understood and appreciated.
Post Reply