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Posted By Topic: Old switchboard/No earth stake

sausages
Mar 17 2020 06:31

Hi Guys.

I was working on an old switcboard the other day and noticed it had no earth terminal installed, all the earths were connected together using a bolt inside the board. There was no earth stake visible at the property, so I presumed the property was getting its earth via the waterpipes. I could not tell which cable this was inside the switchboard, but there were a couple of bare, uninsulated cables connected to the 'earth bolt'. I presume one of these was some form of earth connection. The EFLI reading at this bolt was 0.55 ohms.
Does this board require a new 6mm main earth and earth stake installing?
   

AlecK
Mar 17 2020 09:19

Not necessarily.

What's required [ESR 73A(1)(e)(iv)] is that whoever wants to connect anything to the installation must check that there is a "main earthing system" (as defined).

So the three components that comprise a "MES" (ie electrode, MEC, & MEN) must be identified, and shown to be connected together.

If there's no MES there's still no obligation to upgrade - but we can't connect anything. Including a simple replacement fitting.

I believe you are correct in presuming that this installation was once earthed to a water pipe as electrode. and if that's still intact, and the pipe is still oin electrical contact with mass of earth, then ESR 113 says it can continue in service.
But if the installation's MES is no longer compliant with originals requirements; then same ESR 113 says the installation is not permitted to continue in service.

And arguably there's a need to notify Worksafe & owner under ESR 19. There's certainly at least a moral obligation to notify the owner; since it can't be regarded as being electrically safe (even if not considered an immediate danger) and ESR 15 makes allowing it to be used an offence.

That done; comes the question of what must be done to allow the installation to continue in, or be put back into, service. ESR 59 (3) provides three paths; but clearly the best one would be to install a new MES compliant with "3000", rather than simply re-instate to original condition (if that's even possible).

   

Cookies
Mar 17 2020 14:07

Just wondered if that EFLI test has been completed with the MEN link still in?, with the power off have you tested between the earth mass and neutral without the link? Or checked the voltage between the incoming main and your earth mass?, Appreciate you can have parallel paths but it should indicate whether there actually is an earth connection especially when not visible at all.

I find it very awkward when faced with the same issue as fixing one issue almost certainly will lead to another i.e. sleeving, upgrade of earth/neutral bars, inspection etc it can be a difficult thing to pass on to a customer for adding a PowerPoint or something with the cost spiralling out of control.


   

AlecK
Mar 17 2020 14:55

agreed once you start actually doing things, compliant completion can rapidly get expensive.
The idea being to recognise that risk BEFORE starting, when all you have to do is warn them that continued use is an offence.

Seems to me very likely that the requirement was imposed as a cheap (for Govt) way of checking on older installations; no inspection regime to be administered & paid for. They just made it our problem instead.

Good point about the EFLI test validity. The result is more likely due to a decent main N than to whatever MES there may be. Really the only option is to search for the electrode in all likely places, ensure it has continuity to mass of earth, then test continuity back to swbd. Could also test effectiveness of electrode as per "3017"; but as there's no pass / fail criterion the value of the test is questionable. The requirement is just that a MES exists.

Many older installations didn't have a removable link; just had a single busbar for both N & E; with (typically) MEC being connected to same terminal as main N. In fact often soldered into common lug with it, and sometimes also with all the PECs as well. Which makes it hard to conduct a valid test without doing something that then needs to be reconnected.