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Posted By Topic: portable building

Nov 03 2013 13:57

We have a potable building with a caravan plug all brand new.inside the building is a 4way surface mount switchboard with a 30ma 20amp rcbo as a main switch and a 16amp breaker for power and a 6anp breaker for lights.Is this rcbo all right for a main switch for this subboard.We have been told that all we need to connect the power to it is a c.o.c from the electrician who wired it,or does it need to have a electrical wof on it from an inspector.Cheers.

Nov 03 2013 16:39

The RCBO is fine as a main switch. However the rating of that RCBO depends on the rating of the connector on the building.

Generally, the preferred connector in NZ is a 16amp round pin complying with IEC60309 for use at caravan parks. However there is no specific rule, apart from the minimum size being 15amp.

If your building has a 20amp connector, then the sizes of the RCBO and circuit breakers is fine. But if it has a 15amp or 16amp connector, then it should really be 16amp RCBO, 10amp power and 6amp light to give you some discrimination. (In my opinion, this isn’t actually compliant discrimination, but it is accepted in practice).

A connectable installation requires a warrant of electrical fitness (ESR76). A warrant of electrical fitness can only be issued by an inspector (ESR78). I’m pretty sure they will need to see the COC from the electrician who wired it.

See NZS3001 for more information.


Nov 03 2013 18:02

I think people are getting confused over the main switch. Just because it is a r c b o doesn\'t mean it has to limit the amps. It\'s function is main switch so it only has to have the ability to carry full load current. The fuse in the house protects the cable to the outlet and the 2 fuses in the outhouse limit the current to the size of the 16amp connector. Remember that most main switches are 60 amp rating. The higher rating means that it is not going to fail in its role.

Nov 03 2013 18:05

You should read 3001 to get the correct information.

Nov 03 2013 18:38

Hi Doug. The last house you wired. Did you fit a main switch rated either 60or80 or 100 amps or did you fit a r c b o . Just interested because I normally fit main switch.

Nov 03 2013 19:09

In the last house, I fitted a main switch.

In the last portable building, I fitted a RCBO as per AS/NZS 3001

Nov 03 2013 20:02

There are four functions required
1 = isolator
2 = overcurrent protection of cabling within connectable installation\\
3 = current limitation to no more than rating of supply fittings
4 = RCD protection of all final subcircuits
A 16 A RCBO can do all four for a typical caravan.
But it\'s equally valid - though more expensive - to use separate fittings for each function.

Nov 04 2013 17:31

AS/NZS 3001
states that the use of a mcb is ok for the purposes of limiting the current. The 10 amp and 6 amp mcbs mentioned limit the current to 16 amps so the rcbo which is also acting as the main switch can be larger than 16 amps and is much better if it is. As mcb cost only about $6 and a 63amp rcb costs only $34 the cheapest way would be to have the 63amp rcd acting as main switch and residual current device and either the total of mcbs adding up to no greater than 16 amps for a plug situation or fitting an additional 16 mcb to fulfil requirements. A much larger rated RCD acting as main switch is less likely to fuse closed when running at peak loads for long periods.

Nov 04 2013 20:00


The cost of the switchboard enclosure has been left out why not use a 16 A RCBO and 6 A MCB for the lighting. Total space taken 3 units total and use a 4 way housing and 2 devices and room for a N and E bar.

Your 63 A RCBO + 10 A MCB + 6A MCB takes 4 units and no room for a N and E bar.

Nov 04 2013 20:36

how long have N & E bars taken a pole space in a enclosure for ????

Nov 04 2013 21:36

The cost of the enclosure is only $24 so no big cost. In fact the whole lot costs less than the price of 1 good quality rcbo without enclosure

Nov 05 2013 08:40

Why use a 6 A mcb?

overcurrent protection is for the cable, not the load type.

The wiring must be 7-strand minimum and 1.0 mm2 minimum [3.4.1], so it will usually be 1.5 mm2 and so good for 16 A.

In many cases lighting is ELV, but where some 230 V lighting is included, using 1.5 mm2 for all sucircuits means a 16 A RCBO can do all required functions.

Nov 06 2013 16:56

@ Blair , The original poster stated the MCB\'s were 16 amp and 6 amp , so If the portable building has a 16amp caravan plug on it as also stated then the 20amp RCBO in NOT legal and will need to be swapped out with a 16 amp one ,

@ WillCal : To get right back to your first question Then, as per above the RCBO is not correct , in order for you to connect it you need a COC form the Sparky that wired the portable building and the Building also needs
an Electrical WOF which can also be issued by the sparky that intially wired it .
Sounds like you need to point out though that it is non compliant,and needs to be done in accordance with AS/NZS 3001, 2008 A1

Nov 06 2013 18:37

@Jacks, states the rating of protection is for the supply cable to the outbuilding. Therefore the cable size and length needs to be stated to determine if the 20 amps is too high or not.


Nov 07 2013 21:49

@Blair , if you are going to quote then you should quote all of it , if you bother to read the rest you will see it says supply lead or supply lead fittings which ever is the smaller , I made my assumption because it was clearly stated originally that it had a caravan plug on it. So I think I\'m safe in saying a 20 Amp RCBO is to big and does not comply .