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Posted By Topic: Converting Meter Box to MEN Board

Phazor
May 06 2018 14:48

Whats the points we need to cover when we are converting a standard outside meter box to an MEN switchboard? Reason we are doing this is that the main switchboard is landlocked inside with no access to add circuits.

Its your standard modern install master switch, plywood backing, meter, fuses, and switch/es surface mounted with primary insulation exposed. Cover is screwed shut.

Earth Electrode is below meter box.

Just on a side note should all meter boxes be screwed shut when the primary insulation is available? Sometimes meter boxes just have a latch holding the door shut.

Also when we make it the MEN board we should have an accessible latch arrangement on the door ?

   

Satobsat
May 06 2018 20:37

Would it not be easier to add a new main switch board on the inside wall adjacent to or back to back with the meter box?
   

Andrew
May 07 2018 11:39

The meter box doesn't need screwed shut, but it should require a tool to access it - even if that tool is just a coin or thin piece of metal.

A main switch on the other hand must be readily accessible.
   

Phazor
May 07 2018 19:44

A lot of meter boxes just have the latch on, are these non compliant.
   

mf51to1
May 07 2018 20:17

The ones with the latch on NORMALLY have a panel inside which covers any single insulated wiring.
   

AlecK
May 08 2018 08:38

It gets a bit complicated, as you have to meet all of the requirements for a MSB and most meterboxes aren't designed for that. For starters:

Before something can be an MSB, it first has to meet definition of "switchboard" by having subcircuit and / or submain circuit protection. For which you'll need to consider discrimination between those devices and the supply fuse, and also between those devices and the protective devices in any DBs supplied from the new MSB.[2.5.7.2]

Then it has to have one or more "main switches" [2.3.3, also 2.3.2.2]. Among other things, this means the lid can't be screwed shut as the main switch has to be "readily accessible". So now you've got a problem with having too easy access to the primary insulation for the cabling related to meters & load control.

Then because it's the MSB, it needs to contain the MEN link and be the origin of the MEC. At this stage you;ll need to run a PEC for the cable supplying the old switchboard (was mains, now submains); and remove the MEN link and MEC from that existing swbd.

And of course because you're altering both "mains" and "main earthing system", some of the work is high risk and requires inspection.

Probably best to either follow Satobsat's suggestion of a separate but adjacent MSB, or replace the existing meterbox with an enclosure designed for both duties.


   

dbuckley
May 08 2018 09:02

Alec notes AlecK


> Before something can be an MSB, it first has to meet definition of "switchboard" by
> having subcircuit and / or submain circuit protection.

1.4.91 states: An assembly of circuit protective devices...

Thus the rules state that to be a switchboard there must be a plurality of circuit protection devices, therefore surely a single circuit protective device does not meet the definition?


   

Andrew
May 08 2018 11:12

1.4.91 also states: ...protection of, one or more submains or final subcircuits or a combination of both.

Perhaps that means it can protect only a single submain/subcircuit, but needs at least 2 devices to do so.

I seem to recall a discussion on here about adding a socket-outlet to a meter box (tapped off the load side of the meter), which would make it a switchboard by virtue of the protection of that subcircuit even though no additional protection was added for the main house supply (which becomes a submain).
   

AlecK
May 08 2018 11:51

just because "devices" is a plural doesn't mean there has to be more than one. The wording has to be plural, otherwise (if it said "a circuit protective device") it would stop being a switchboard if there were two or more.
Which is why those following words (as noted by Andrew) are there.
So a single submain does comply.

But if that's what was going on, there would be no reason to make the change. The reason for the change must be that someone wants to run another submain to anorher DB, as well as turn the existing MSB into a DB.

   

Andrew
May 08 2018 11:54

Found the thread I was thinking of.
https://www.electricalforum.co.nz/index.php?action=more_details&id=1433665866
   

dbuckley
May 09 2018 09:47

There is chapter and verse on plurals: the Interpretation Act 1999.

Section 33, Numbers: Words in the singular include the plural and words in the plural include the singular.

Its been this way since at least 1924.
   

SaintAlan
May 09 2018 10:35

Wow.