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Posted By Topic: MEC is foundation steel

Oct 30 2019 17:22

Ive been to a couple of jobs this week where the MEC appears to be connected to the foundation mesh steel. Was this common at a time? Both installations do not include an accesible test point. How do i test the MEC or confirm it is <0.5 Ohm?

Oct 30 2019 19:39

You're still allowed to do this has table 5.2 that says the allowable earth electrodes but there is an exception to this above the table at the end of

"Exception: Conductive reinforcement of—
(a) concrete foundations embedded directly in the soil; or
(b) concrete foundations of a building or floor slab in contact with the
ground and not impeded by a continuous insulating barrier,
may be used in lieu of an electrode specified in Table 5.2"

However if there it still must comply with which one of the conditions is "be accessible for visual inspection and for the purposes of testing; and
1 Where necessary, access by means of an underground pit with its cover
accessible above ground is considered acceptable, provided adequate
space is available for the connection of test leads and the pit is suitably
identified as to its purpose.
2 Where the reinforcing steel is used as the earth electrode, this testing
condition is deemed to be satisfied by the provision of a test point on the
main earthing electrode."

Oct 31 2019 15:35

So if it doesn't include a test point then i imagine it's technically impossible to issue an ESC (in my case) because you can't satisfy the requirements of "verification", namely verification of earth continuity and resistance from 3017. In saying that, can i just expose part of the MEC (6.0mm conduit wire) that appears to go into the ground and that becomes the accessible test point?

Oct 31 2019 17:10

The connection must be accessible.

You said that the MEC "appears to go into the ground"...

I think you need to do further investigation. Start digging.

Nov 04 2019 07:56

Lifting the main earth connection lug from the earth bar of the main switchboard earth bar is also a means to test the earth electrode contect to the mass of earth where is no exposed earth lead connection point (e.g. earth connection plate).

It was also common to use a ferrous connection plate on the surface of the concrete to provide a test point for the earth electrode buried in the concrete slab which does not have plastic sheeting between the concrte slab and the mass of earth.

Nov 04 2019 09:39

you appear to be confusing two different tests.
You're talking about testing the effectiveness of the electrode's connection to mass of earth. Spometimes necessary, but not a required test for installation work.

DougP is referring to a specific requirement for access to the MEC / electrode junction, for purposes of testing continuity of the MEC. Which IS a required test; and also needs to be done periodically when fault-finding.

True we don't have to put a "do not disconnect" label on this point if the connection method precludes disconnection (eg cadweld); but in ALL cases the point MUST be accessible for testing.