First switchboard or metering point.

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Dan L
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First switchboard or metering point.

Post by Dan L »

Is it still OK to have a metering distribution point supplying seperate metered men switchboards.

For example a meter box with a neutral stud and mcbs per metered supply to their own men switchboard.

Or will this distribution point have to be a main switchboard central supply and all metered supplies be to dbs.

Obviously the second option is better practise

Iv seen many older sites like the first option

I feel like iv read somewhere the first switchboard must be MEN.

And this metering point a switchboard?

1.4.91 says to supply sub circuits and sub main so if its to supply mains then maybe not

I'm not asking what's better practise because obviously a main switchboard central supply supplying metered dbs is best but want to kniw is that option still compliant.

Thanks in advance
AlecK
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Re: First switchboard or metering point.

Post by AlecK »

You're right that it depends on what is being fed from the enclosure.
As per definition; it can;t be a 'switchboard" unless it supplies - & protects - either submains or final subcircuits.
So if there are no circuit protection devices, or only for mains, then it isn't a switchboard.

If it's not a switchboard, it can't be the MSB.
Which means it can't include a MEN link, and while it may include one or more isolating switches (eg for isolation of meters) they aren't "main switches".

Basically the options under current rules are
a) set the common metering point up as MSB, c/w main switch(es), MEN, MEC, & electrode ,and provide protection for submains out to the various parts (ie a multiple installation) ; or
b) set it up as metering point only, with the (separate) mains for the various installations just passing through (ie a single installation ).

For option a), the outgoing submains will have PECs (unless going to outbuildings).
For option b), there may be no overcurrent protection devices for all or some of the outgoing mains; and the incoming will either be separate mains from the several PoSs somewhere upstream, or possibly in common shared cable / enclosure with the PoSs being in the meter enclosure (in which case they are not "mains" but private works).

Which brings in the other key aspect: the definition of the PoS.

Remembering that metering has absolutely nothing to do with whether any particular collection of fittings is an "installation" or only a "part installation" - and nor does the ICP system used by networks & retailers to denote their various customers.
Dan L
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Re: First switchboard or metering point.

Post by Dan L »

Why can there be no overcurrent devices at the metering point on the mains?

For example one supply to metering point split into 2 seperate icps and each of the 2 meters with own icp has its own main overcurrent protection before meter (orion requirement meter isolation switch).

Or even a larger supply to metering point then that branched into smaller mains and each individually protected?

Because the overcurrent is protecting mains and not sub mains or sub circuit surely its still not a switchboard?
AlecK
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Re: First switchboard or metering point.

Post by AlecK »

Correct that circuit protection devices for mains don't count for definition of 'switchboard".

didn't say there can't be overcurrent devices on mains at a metering point; just that there may be none.
Which is absolutely normal where there's no reduction in CCC (eg for a controlled mains for water heating); and overload protection is either at origin (pillar / pole / pit) or at MSB.

Requirements set by retailers / networks / metering providers are one instance; but these are generally extra to requirements in Wiring rules.
And often completely unjustified technically; but enforceable through supply contract with consumer.
Dan L
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Re: First switchboard or metering point.

Post by Dan L »

This brings me to my next question. We recently discussed MEN switchboards in same structure and I understand your answer fully

But am I correct in saying there is nothing stopping many MEN points in the same structure if they are completely separate installations?

An example it's very common to see 4 or 8 units all in the same structure. All have own seperate supply from network boundary, own MEN MSB and all have there own earth electrode at the front door meters away from each other.

?
AlecK
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Re: First switchboard or metering point.

Post by AlecK »

Yes, you are correct that a structure can have several distinct installations within it.
Not just a few; sometimes several per floor over many floors.
Each must have own "main switch(es), MEN, and MEC; but can share electrode
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