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Posted By Topic: No earth bar in domestic switchboard

rarrar
Jul 03 2019 11:24

Today's job there's a cobweb of earth wires in behind the board and there's been a string of other people continue to hook into this over recent times. Legal to keep on smacking earth's onto this or not?
   

RacyJC
Jul 03 2019 11:56

Hey there,

How old is the installation? What is the main earth terminal? Check "3000" 5.3.1 and 5.3.4 and see if it complies but then the age of the installation also comes into play
   

DougP
Jul 03 2019 13:03

It's hard to imagine what you're looking at.

One of the ways it's commonly done in Australia, is to join all the PECs to the MEC about 400mm from the end. The section between where the PECs are connected and the end, then becomes the MEN link and the end of the MEC is joined to the N bar.

So as long as you have something resembling a MEN link, you can join onto the MEC for any new PECs.
   

AlecK
Jul 03 2019 16:36

That may have been common practice once, but it would be non-compliant now; in Oz or here [5.3.4].

The MEN isn't the last bit of the MEC, it's actually just the fact that the MEC is connected to the N-bar (as used to be required. If it's not on the n-bar, there will be 2 bars, N & E, and a separate MEN link between them.

But yes, PECs can be connected to the MEC.


However if you're adding a new circuit; you can't do the same for the N; it must go to its own terminal on the N-bar - and chances are that there won't be any spare terminals.

Eventually someone's going to have to fit a bar for the earths, and that means a new MEN link; and that requires inspection.
   

rarrar
Jul 03 2019 16:48

just a fifties house that's been added to again and again in a random matter....., he's had a lot of mates round and they all know better than me, one even writes the rules....
   

DougP
Jul 03 2019 19:16

Alec I'm unsure from what I described above, what doesn't comply with 5.3.4?

The MEC is in the MSB and connected to the PECs and other conductors at a "connection" point - it's not on a bar or terminal. The Aussies often solder these connections. Also from that connection point, there's a 6mm2 MEN link which connects to the neutral bar.

I think for simplicity, the MEC and MEN link are continuous and it's stripped back for the PECs etc to connect to it. They use solder, but I would probably use a line tap just to make it easier to add to. (You should see the mess their soldered "connection" gets into once there's 15-20 cables connected to it and soldered).

The Aussies are slowly coming around to using earth bars, but it's probably still around 50% of them would solder all the earths and MEN link together.
   

AlecK
Jul 04 2019 09:15

Sorry, need to correct that post.
Which will drag us well off rarrar's original issue.

Regardless / independent of the fact that we're allowed to connect PECs & EBCs to the MEC, 5.3.4 requires a main earthing terminal/connection or bar [5.3.4]. The MEC must be connected to this terminal,either directly of indirectly; as must all the other listed items. Obviously if they're connected to the MEC, then they're connected indirectly to the main earth terminal / bar.

What you describe doesn't fit that description in my view. Calling the assembly of PECs soldered / line-tapped to MEC over a short length a "terminal / connection or bar" is a stretch of the words, and I believe stretch too far. And unless it's accepted as fitting that description, it does not comply with the clause. I'll need to get into IEC definitions - as per ESR 4(3)- before I'll be willing to concede on my interpretation.

You also said that the last bit of MEC becomes the MEN. That's another matter that doesn't comply for many, but not all, installations in Oz. The MEN's CCC must be equal to the mains N; while the MEC is typically less. There are several Exceptions, one of which is where the mains has short circuit protection. All installations have this, but many in oz don't. Complicated by the fact that what is "consumer mains" varies State to State. In some areas the SC protection is on the house; in some there simply isn't any - which is why there are rules in the book for "unprotected consumer mains".

The new Figs 5.6 A, B, & C illustrate the variety; and while we technically don't have any "unprotected consumer mains" we do have many situations exactly like it. Anywhere with multiple installations fed from a common point (eg meterbox or main distribution enclosure) needs care. The only reason the incoming supply isn't "unprotected consumer mains" is because of the was NZ defines "Installation" & "Point of Supply"; resulting in the incoming supply being not "mains" but instead "works" (either network or private); and so not part of the installation, and so not subject to rules of "3000".
But while the definition of the components may have changed, the fault current to be carried hasn't.

Back the rarrar's old house; there are a lot still around that were done that way back in the day, MEC onto N-bar, and PECs connected to MEC. When adding a new PEC (or EBC) it van be connected to MEC ; as long as you can be sure it actually is an MEC, and not something else (or even just a conductor-to nowhere).
You must not connect to the existing single N(&E)-bar, even though there may be other PECs already connected there.