Two revenue meters fed from one main

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Nite_Shift
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Two revenue meters fed from one main

Post by Nite_Shift »

I have a customer that has converted part of their house into a (council consented) flat. There is currently one revenue meter for both dwellings, and the flat runs off a check meter.

The electrical system is now getting an upgrade, and they want to relocate the revenue meter. They have asked me to have a second revenue meter installed for the flat at the same time.

Running a new main for the flat is not an option due to civil works involved.
Both dwellings have a combined maximum demand below the current 60A supply.

I have contacted the supply authority who have advised me it is "illegal according to the act" to have two revenue meters running off one main, and a new main must be installed in order to install a second revenue meter. I didnt push the point with them, but would like to ask on this forum if anyone can point me in the direction of this legislation? I did ask them if this was just their rule or law, and they advised it was law. It just doesnt sound right to me, it would mean an apartment block of 50 units would need 50 main supply cables!

Does anyone here have any experience in this situation?
AlecK
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Re: Two revenue meters fed from one main

Post by AlecK »

I don't believe any such rule exists.
What DOES exist is a rule that separate installations can't share mains [ 3.9.8.2 of "3000"].
Everything fed off the point of supply (PoS) for an installation has to be for that installation only.

Presumably in this case the PoS is at the street.
And since everything upstream the PoS is the responsibility of the network, they won't want to move the PoS to anywhere else (eg the meterbox).
And unless the PoS is moved, that length of cable from street to metering point will remain "mains" and can't be shared between different installations.

A case could be made for multiple meters.
Think of it like any block of shops / offices / flats that has multiple separate tenants each supplied from their own switchboard (and each having own meter).
But for better or worse, networks have some very rigid ways of seeing the world; and they don't like being argued with (especially when they're wrong).
And since the local network has a monopoly; regardless of whether they're right or not, we generally have to toe their line.

So the question is, will the "convenience" of each consumer being able to choose their own retailer, and get their bills directly; make up for both the initial cost of running new mains & setting up a new main earthing system, plus the endless monthly cost of 2 lots of line charges ?
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Re: Two revenue meters fed from one main

Post by Nite_Shift »

Thanks for that, your reponse is very much appreciated.

The crazy thing here is that there are already two installations running off the one mains cable, its just there is only one revenue meter installed currently. And the supply authority is happy with the current setup.

3.9.8.2 seems a bit hazy to me for this situation. It does not state that mains cannot be shared. It says that conductors of different installations should not be grouped together within the same multicore cable or enclosure, and goes on to say how to segregate them properly. That makes sense.

Sharing one conductor between two installations doesnt seem to be addressed here to me, although I may have been looking in the wrong place!

This does not seem to be an act/regs requirement from my searching thus far.

I think im going to politely ask them to reconsider the situation in this case. Worst case they stick to their guns, best case we might get a favourable result.
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Re: Two revenue meters fed from one main

Post by Sarmajor »

There are two dwellings sharing the mains but as far as the rules go they are one installation.

There are high level definitions of an Installation in several Acts that cover electricity supply in NZ.

If there is only one point of supply then there is only one installation as far as Section 162 of the Electricity Industry Act 2010 is concerned.

The same definition is used in the Electricity Act 1992 section 2

As Aleck points out it is all about the point of supply.

Council consent does not create an electrical installation.

There is only one Revenue meter and most likely only one ICP associated with that address. Good Luck.
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Re: Two revenue meters fed from one main

Post by AlecK »

true 3.9.8.2 doesn't directly address sharing conductors-in-common; it's about sharing a common wiring system between installations.
What prevents using common mains is simply the definitions referred to by Sarmajor.

Every installation starts at it's own PoS (another definition in the Act) .
That's where "mains" start, too; 'cos the definition (in ESRs) excludes any fittings that are not part of an installation from being "mains".
For a typical single installation, with the supply crossing the boundary (overhead or underground), that crossing point is the PoS;
where both "mains" and 'installation" start.
Everything downstream of that is the same installation, no matter how it's configured.
Which makes it impossible for "mains" conductors to be shared between installations, because if the conductor is shared then, by definition, it's either not a "mains" conductor; else - again by definition - it's not being shared by more than a single installation.

Side issue:
In this typical scenario, there's a length of conductors from the supply fuse(s) & N to the PoS.
Those conductors are dedicated to the installation, generally they're part of the same physical cable as the "mains", and we mostly treat them as part of the "mains"; but technically they are not "mains". They're part of "works"; and - like the supply fuse(s) - they are what the Act calls "exclusive fittings". As far as I'm aware, there's no special term for them.

What 3.9.8.2 prohibits is things like a 2C or 3C N/S being used to supply multiple installations, eg each installation on a different phase and all sharing the N . Can't even have separate cables sharing a duct.

It's important to keep the definitions in mind, because they are fundamental to the correct interpretation of ESRs.
In my experience, networks (and retailers) often don't. Instead they go with what they are used to; and what they perceive to be usual practice.
They usually deal with the ICP as the demarcation point between "works" and "installation". But firstly that (wrongly) assumes there's only ever one ICP per installation; and secondly it assumes the ICP and the PoS are in the exact same location - again not always true.

As I suggested before; they have the power to reach an agreement about having the PoS at a different location - but they are unlikely to be willing.
If they agreed to the PoSs being at a common metering point (as it is for plenty of other multiple installations) instead of at the default position at boundary; then the existing mains would stop being "mains". They might become part of the network, but more likely would become private "works".
And of course your 2 part-installations would have to be correctly configured, each with its own main earthing system (including MEN), and no "master' switch controlling both.
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Re: Two revenue meters fed from one main

Post by DougP »

AlecK wrote:
Tue May 19, 2020 9:22 am
What 3.9.8.2 prohibits is things like a 2C or 3C N/S being used to supply multiple installations, eg each installation on a different phase and all sharing the N . Can't even have separate cables sharing a duct.
Funny you should mention that one specifically, as I've seen installations exactly like that. 2 actives and one neutral to mains box, then 2cNS to the first switchboard with the first ICP & meter, then a twin to the second switchboard with its own meter. Each switchboard with its own main earth.

I had to replace the first switchboard, so I lugged the incoming neutral, outgoing neutral and a tail for the first board main neutral, along with the meter & ripple shunts.

As an existing installation, there wasn't much else that could be done other than replacing all the mains, the mains boxes and lines.
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Re: Two revenue meters fed from one main

Post by gregmcc »

Ive seen exactly that as well at a retirement village, there were a whole lot of 2 unit dwellings, 2c NS from the pillar to the meter board, then 1c N/S to the inside DB, looks like these were built late 80's to early 90's
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Re: Two revenue meters fed from one main

Post by AlecK »

Those configurations were permitted, and I believe common, under earlier regulatory regimes.
From a purely engineering viewpoint; electrically sound.
But from a safe work viewpoint, not so good.

Remember compliance with all of "3000" has only been mandatory since 2010; before that only some clauses were listed as mandatory.
And before 1993 there was only the (' 76) Regs, no Standards or CoPs.
The Act itself only came in in 1992; to give us the definitions for "installation" & "PoS" that apply now.
Prior to the '92 Act, all these matters were controlled by entities known as Electrical Supply Authorities; who could - and did - decide how things "must" be done in their area. Which would be automatically accepted by the inspector, because ESAs were also responsible for inspection of (all) installation work.

And of course what was acceptable when installed can remain in service under ESR 113.
But - as in Doug's example - it can be difficult to find a way of making alterations to these configurations without breaching today's rather different requirements. I think his solution is probably the best for the situation, as it ensures continuity of the (still live) N to the 2nd installation when anyone is working on the 1st MSB.
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Re: Two revenue meters fed from one main

Post by DougP »

Thanks Alec.
The configuration did't seem to be a surprise to the inspector.
One change we did make was removing the control of the water heating from the second installation, as it was switched using a channel in the ripple of the first installation. That seemed to be just too confusing for anyone working on the metering, as it involved two separate supplies into the ripple switches.
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Re: Two revenue meters fed from one main

Post by AlecK »

Metering is another area where the old ESAs made up their own rules. Mostly was treated as a sort of add-on to the installation; associated with it but not actually part of it.
These days it's definitely part of the installation, and so must comply with Wiring Rules.
(Not that '3000" sets any specific requirements).

I'm presuming a switch-loop system, running the w/h subcircuit(s) through the switch channel(s).
It would have been logical back then to use second channel of single ripple control; rather than another unit.

Difficult to see how the arrangement could be made compliant with today's requirements; eg 3.9.8.2
Today's metering providers like to have their equipment associated with only one installation & one consumer.
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Re: Two revenue meters fed from one main

Post by TPower »

So are we saying, due to that rule, 3.9.8.2, we aren’t allowed to have one three phase cable supplying a MEN switchboard/central supply, which then supplies multiple separately metered units. This set up isn’t uncommon. Or am I not reading this correctly?

I would’ve thought you would just consider the entire set up as one installation? Or is each metered supply considered its own installation?

A revenue meter is just an electrical fitting isn’t it? So doesn’t necessarily make the boundaries as to where an installation starts and finishes?

I think I must be reading this wrong?
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Re: Two revenue meters fed from one main

Post by TPower »

So are we saying, due to that rule, 3.9.8.2, we aren’t allowed to have one three phase cable supplying a MEN switchboard/central supply, which then supplies multiple separately metered units. This set up isn’t uncommon. Or am I not reading this correctly?

I would’ve thought you would just consider the entire set up as one installation? Or is each metered supply considered its own installation?

A revenue meter is just an electrical fitting isn’t it? So doesn’t necessarily make the boundaries as to where an installation starts and finishes?

I think I must be reading this wrong?
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Re: Two revenue meters fed from one main

Post by AlecK »

You are correct that a meter is just another fitting; and is part of the installation
Officially metering has zero to do with determining whether the particular set-up constitutes one installation or several.

An installation has a PoS.
The default location for the PoS is set by the location of the first "exclusive fitting(s)" for the installation.
This is generally the supply fuse(s), and the PoS will be
- either: at the load terminals (if the fuse is on the property)
- or: where the mains cross the boundary (if the fuse is external to the property).
Under current rules; each "installation" must also have a "main switch" and a "main earthing system"; ie an electrode, a MEC, and a MEN link.
The "main switch(es) & MEN link must be at "main switchboard" ; which may or may not be co-located with the meters.

A collection of occupancies can be set up as a single installation, in which case 3.9.8.2 has no effect.
So eg 3 parts can each be fed by one phase each; or they can all have 2 or 3-phase supply.
And they may or may not be metered separately.
Basically the scenario you describe fits easily within ESRs & Wiring Rules.
It may fit less well with network and / or retailer, who may not accept new examples of this sort of set-up; even though there are plenty of legacy examples.

If the occupancies are set up as separate installations, each with "main switch" & "main earthing system"; then they will also each have their own PoS; and 3.9.8.2 (a) prevents conductors of these separate installations from being in the same multicore cable or in same pipe / tube / duct.

So it's more common for such a situation to have supply fuse(s) for each installation within the building, eg at a common metering point.
The supply fuses will be the first "exclusive fittings" and become the PoS for each installation.
The conductors from distribution to this collection of PoSs aren't part of any installation, so don't have to comply with wiring rules;
meaning again 3.9.8.2 can't apply.

An example of what 3.9.8.2 prevents is a common cable run down a common driveway to supply three buildings, each on a separate property and containing a separate installation.

Currently the restriction applies to common "wiring enclosure".
When 2018 edition is cited; even if each installation has separate mains conductors run down common trench; the words will change to "pipe, tube, or conduit". So shared ducts will be banned even if they are not "wiring enclosures" but only provided for mechanical protection.
Not even for a short distance, eg crossing under a path or from trench up the wall to the meter enclosure.

There may also be legal issues arising from how the land has been subdivided / cross-leased;
eg if the driveway has been split so that each property includes a strip of it; then the mains for each installation may need to run down their own strip.
But that's a whole other minefield; and nothing to do with ESRs / wiring rules.

The fact is everything is governed by the PoS; so establishing location of PoS is the key issue case-by-case

When the various occupancies involved are all within one structure, eg a block of flats / offices etc; it can get tricky working out the demarcations.
All such occupancies are required to have their own isolating switch [2.3.3.3(b); but whether this is a "main switch" depends on whether the occupancy is set up as a separate installation.
If it's fed PEN and has it's own "main earthing system"; then it may be.
If it's fed by cabling including a PEC, then probably not.
These days we're not allowed more than one N-E link in same structure of a single installation, but used to be common; so just having a N-E link doesn't help decide.
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