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Posted By Topic: Is this legit? MEN & Multiple DB Switchboards

fungus
Nov 01 2015 23:21

Hi all,

I went through the wiring rules and my old paperwork back when I was an apprentice -still not confident if this setup is correct. Just want you guys to double check if this alright? Since I haven\'t done anything like this before. See attachment for further details.

I got a project on a lifestyle block. The main MEN switchboard and meterbox is going in an outbuilding garage/workshop first.

A house containing 2x 2bedroom units, each unit will have a 20way switchboard. The 1st unit (Tenancy 1) will be occupied by the land owner with a MEN DB installation. The 2nd unit (Tenancy 2) will only be a DB with no MEN link feed from Unit 1 board.

Another house (House 2) will be built later on, it will have a MEN DB installation.

Qs:
1)Is this setup legit, based on my drawing (see attachment)?
2)Not too sure if that earth conductor link between the Main MEN board to Tenancy 1 MEN DB is necessary?!
3)Can I get away with doing MEN with its own electrode rod on all switchboards?

Notes:
-Red phase will cover garage/workshop & House 1.
-White phase will cover House 2 only.

   

fungus
Nov 01 2015 23:29

https://drive.google.com/open?id=0B-I5zuqM36OLQlh4TjJ5RFFRS00


Link of my drawing.
   

AlecK
Nov 02 2015 08:37

can\'t access the drawing, but based on description I understand you have 2 separate structures, and another separate structure to follow.

1st structure has MSB; also has meters.
An MSB must be MEN.

2nd structure has 2 DBs; DB1 MEN, DB2 not MEN and fed from D1.

That\'s allowable under \"outbuilding\" rule.
But having both these DBs MEN would not be compliant.

3rd structure to have MEN D3
Again allowable as long as it is a separate structure, both from the one with the MSB and the 2-nit one.

The PEN submain to MEN DB setup is usually not the best, running a PEC in the submain is usually a better option.
PEN requires great care to ensure there are no alternative paths between the different earthing systems, such as bonded pipework.

Unfortunately it often gets used just to save a few dollars worth of submain PEC.

   

fungus
Nov 02 2015 15:20

I have changed the access to my drawing -should be able to see it now.
   

AlecK
Nov 02 2015 16:49

OK can see it now.
Matches the description (always a plus).
noting illegal in it.

Fine as long as there are no controlled loads / different tariffs, and as long as all 3 (or at least both units of house 1) are on same revenue account

May be a problem if unit 2 is to be on a different account(separate metering).



   

fungus
Nov 02 2015 17:22

AlecK: I don\'t really need that earth conductor link between the Main MEN board to Tenancy 1 MEN DB -since the Tenancy 1 MEN has its own earth rod?!
   

DougP
Nov 02 2015 18:33

You\'re showing an earth stake and MEN link on both house 1 and house 2. So you don\'t need the PEC to either of them.

But just keep in mind that doing it that way will require inspection on all MEN switchboards.

Depending on the distance, if you do run a PEC to both houses, then no MEN and no earth stake will be required.
   

DougP
Nov 02 2015 18:34

But as AlecK said, what\'s the story with the revenue metering? All on one account?
   

fungus
Nov 02 2015 20:03

Is all on one meter at this stage but I\'m guessing House 2 will be on a different phase and probably has its own meter.

MSB (workshop) to House 1 is roughly 40m+, maybe I can do PEC. I will have to work out the cost putting in a heavier earth cable in a conduit comparing MEN - earth stake, inspection and etc.

MSB to House 2 is 80m+ so I might just stick to the original plan with this one.

Thanks for all your help!
   

DougP
Nov 02 2015 21:18

You might want to clarify with the customer about their usage of the \"tenancy\" areas.

If they are renting them out, under the tenancies act, they can\'t charge the tenant for power unless the usage is metered. For example, if those two tenancies were on one revenue meter, they can\'t just charge each tenant half the usage.

So you might need to include check meters at each tenancy.

It\'s good that you have separate switchboards (Each individual occupier shall have ready access to an isolating switch or switches that isolate that occupier’s portion of the electrical installation) - that would also make it easier to install check meters, although a central location might be better.
   

AlecK
Nov 03 2015 08:28

I\'m embarrassed to admit, but I was wrong to say \"nothing illegal\". Didn\'t look properly at the drawing & only noted the Ns.
If Rule one is: ask \"where does it say that?\" ; Rule 2 must be \"pay attention\".

DougP is correct, you either run a PEC or install MEN link & electrode.
NOT both; because if you do both there will be load current flowing in the submain PEC (contrary to 8.3.8.1).



   

DougP
Nov 03 2015 15:49

We\'re all allowed the occasional brain fade from time to time.
   

Rhino
Jan 31 2019 13:08

Could House 2 be feed from house 1, using a submain with PEC from tenancy 2s DB Board?.. removing the need for inspection, MEC and electrode.. then could the same be done for a potential 3rd house using the DB of house 2 ?
   

pluto
Jan 31 2019 14:50

From my review of the darawing provided

The first switchboard, LHD side of the drawing, is the main switchboard and requires an MEN link and main earth electrode.

All other switchboards are being provide with a submain neutral and an earth conductor so don't need an link or earth electrode in any other switchboard.

The submain min size earth wire, use table 5.1 of 3000:2007

For the neutral conductor same sizs as the active conductor single phase or largest active conductor three phase.

The use of neutral screen cable as the subain is good as the screen size used for the earthing conductor gives a full sized earthing conductor (same as active) instead of a reduced size earth of the active conductors when using TPS cables.

From an electrical engineering point of view the use of submain active, neutral and earth conductors is the best solution by far.

BTW the use of the outbuilding solution PEN conductor link and earth electrode for each other switchboard is only permittee if the buildings which contain the switchboard meet the definition of an outbuilding.

If an electric vehicle charging is to connected to any of the installation switchboards they require a submain earth conductor, use of the PEN conductor used by the outbiulding provisions is NOT permitted.