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Posted By Topic: Wiring of RCCB/MCB with no indication of L/N

Apr 15 2018 17:40

I\\\'m wriing a small distribution board for a tiny house and want to get as much done before I get an electrician in to check it out and sign it off.

There is a one pole MCB which Live from mains would go into the bottom and then out of the top into the top left of the RCCP I think. Not sure about the rest though.

I\\\'m not connecting this to mains btw, just putting in some wires to a junction where the mains will come in from. Wont be live until an electrician signs it all off.


Can anyone please suggest how these should be wired up?

Apr 15 2018 17:45

here is a picture of how I think it goes

Apr 15 2018 17:49

you need an electrical inspector, NOT just an electrician, to sign this off.
And even then, installing the switchboard is beyond the limits of what a homeowner is allowed to do [ESR 57 of the Electricity (Safety) Regulations].
So either get the inspector to do this bit, or get an electrician in.

Apr 15 2018 19:33

I must have misread NZECP 51:2004 Electrical code of practice for homeowners, I thought this mean I could but on reflection I think it just refers to the wiring up to the distribution panel??

Electricity Regulation 47:
(e) Install, extend, and alter subcircuits (including submains),provided that–
(i) The person must not enter (whether personally, by holding any material or equipment, or otherwise) any enclosure
where live active wires are likely to be present; and
(ii) The work is tested by a registered electrical inspector, in accordance with NZS 3019, and the work is certified by
that inspector in accordance with regulation 39, before being connected to a supply of electricity by such an inspector.


Apr 15 2018 20:38

If this is a tiny house that is on wheels so it is relocatable it is a no go for the home owner to do his own wiring

Apr 15 2018 21:49

ESR47 is no longer the relevant Regulation. It s now Reg 57

The domestic exemption from the Electricity Act Section 79 applies only to Domestic Installations. It does not apply to Connectable Installations or Caravans / Mobile Homes / Busses or anything similar.

The requirement for an inspector comes from ECP51.
The Act requires a person authorised to test and certify Prescribed Electrical Work. Regulation 57 requires a person authorised to Inspect Mains Work with no reference to High Risk (which is the only Mains Work that requires Inspection)

So as long as ECP51 is cited in the ESRs domestic work has to be inspected certified and connected by an Inspector.

Oh and if L/N is not specified on a RCCD/MCB (more commonly an RCBO) then the choice is yours.

Apr 16 2018 00:00

Do I see a 40A RCD protecting 16+16+10=42A of MCBs?

Also if this \"tiny\" house is not on wheels, then its a residential, (b) 2 comes to mind.

Apr 16 2018 08:42

The problem here is that someone doing what they should - reading the relevant ECP - is getting incorrect information because the ECP is itself out of date by many years and several amendments to the Regulations.

The current set of rules is as follows:

The Electricity Act (Section 79) allows the owner of \"premises tat are occupied, or intended to be occupied, by that person as a residence for that person\" to do \"any\" electrical wiring work; provided the work is within limits set by Regulation, and carried out in accordance with regulation, and that no part of it is connected to a power supply while being worked on. The Act also requires testing, certification and connection by someone who holds a current practising licence that authorises them to certify prescribed electrical work(ie an electrician).

Now to the ESRs; where ESR 57 places limits on the work, and requires it to be done i.a.w ECP 51.

The limitation is to a list of work types, the relevant one in this case being \"(e)installing, extending, and altering subcircuits\"; with specific exclusion of entering any enclosure where live conductors are likely to be present.

That doesn\'t apply to a new switchboard, and a new switchboard will not yet have been connected to supply 9so could be allowed by Section 79. But \"subcircuitds originate at the load side of the overcurrent protective device(active) and the neutral bar(neutral); so this \'subcircuit\' rule does not cover assembling the switchboard components, nor wiring them up. Nor do any of the other work types listed in ESR 57. Accordingly that work must be done by someone with an appropriate PL.

Interestingly while this work-type item includes the \"test/certify/connect\' requirement, by a person authorised to inspect \"mains work\" (ie an Inspector, which is a step up from the \'certify\' PL required by the Act); none of the other items do, including relocating switches, sockets, and lighting points wired in TPS. The way I see it, these two items have to be read in tandem; because relocating under item (c) is by definition making an alteration under item (e). What this pair is really saying, when taken together, is install/extend/alter; but in TPS only, while the Act itself requires total disconnection from supply (active and neutral) before any alteration / extension is carried out.

Even though all three documents are available free, it\'s not really acceptable that people have to refer to all three at once to arrive at a correct understanding; nor that the one intended for homeowners to use has been allowed to become so out of date that it is wrong, and quotes from an obsolete section of the Act, and from a set of Regs that were revoked in 2010.

Apr 16 2018 09:00

dbuckley - you should know better than that. The rating of the RCD doesn\'t have to be more than the sum of the connected MCBs. That\'s not how the RCD rating is calculated.

Apr 16 2018 09:02

True, but the wiring to / from the RCD has to be fully protected, so in this case will need a CCC of 42 A.

Apr 16 2018 10:48

Doug notes

> dbuckley - you should know better than that

I should, shouldn\'t I. That\'s what happens when one posts in the middle of the night, one forgets all about MD calcs and just posts bollocks :)


Apr 16 2018 11:56

Only fools & liars claim they can get everything 100% right 100% of the time.

The rest of us are allowed the odd memory lapse.

Apr 16 2018 14:05

A Momentary Lapse of Reason.