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Posted By Topic: Caravan Main Switch

jasont
Oct 21 2017 11:00

Can I use a 40A 30mA RCCB as the main switch to a caravan or does it need to be an RCBO?

My current arrangement is

1x 2pole 40A 30mA RCCB
1x 10A 6KA MCB
1x 20A 6KA MCB

mounted in a 4-way surface enclosure.

Thanks,

Jason
   

pluto
Oct 21 2017 11:43

jasont Oct 21 2017 11:00

Your question
Can I use a 40A 30mA RCCB as the main switch to a caravan or does it need to be an RCBO?

My current arrangement is

1x 2pole 40A 30mA RCCB
1x 10A 6KA MCB
1x 20A 6KA MCB

mounted in a 4-way surface enclosure.

My reply
No this would NOT comply with AS/NZS 3001.

If you look at Figure 2.1 of AS/NZS 3001 you will see an arrangement that complies.

1 - 16 A ECBO 2 pole as main switch and socket outlet over current protection; AND

1- 10 A MCB for the lighting circuit (or could be 6 amp if desired).

These devices would be able to be mounted in a 4 way housing; double DIN width RCBO + a single DIN width MCB and this allows the N and E busbars to be mounted in the 4th way, put a blanking piece in the 4th way of the enclosure cover.

Commentary
A 40 A RCCB with the 20 A MCB will NOT provide discrimination with service piller socket outlet which will be a 16 A RCBO (or equal).
   

jasont
Oct 21 2017 13:25

Thanks for the reply.

If I down-rate the MCB protecting the socket outlets to a 16A MCB, coupled with the RCCB I am achieving the same earth leakage + over current protection correct?
   

Sarmajor
Oct 21 2017 13:46

The sum of the protective devices is not allowed to exceed the current rating of the supply connectors
So that limits you to 16 amps.
Option 1.
Replace the RCD with a 16 amp RCBO as a main switch and protection of the power points and then fit a 6 amp MCB to the load side of the RCD for the lighting. As per the right hand side of fig 2.1 & 2.2 in AS/NZS3001:2008.

Option 2.
Use a 10 amp MCB for the power points and a 6 amp MCB for the lighting.

Download 3001 it is free for all electricians.
   

jasont
Oct 21 2017 14:18

Excellent, thanks.
   

AlecK
Oct 22 2017 08:05

Option 3:
16 A RCBO and nothing else.

There are three functions that must be provided:
- main switch
- RCD protection of all final subcircuits
- current limitation to protect supply lead and associated fittings
16A RCBO does all three.

There's no need to have a separate mcb for the lighting, as per 2.5.3.4 of "3000".
   

Sarmajor
Oct 22 2017 11:30

Yes, option 3 is ok as well. Probably half of the motorhomes that I inspect these days only have the 16A RCBO and all 12 volt dc lighting.
   

toyoto
Oct 24 2017 18:42

I've seen option 2 used a few times but the way i read 3.3.1.1 is that there is a single current limiting circuit breaker, so option 2 would not comply.

or is this a case of, it doesn't specifically say you can't, so you can.


   

pluto
Oct 24 2017 21:53

toyoto Oct 24 2017 18:42

Your comment (part only)
I've seen option 2 used a few times but the way i read 3.3.1.1 is that there is a single current limiting circuit breaker, so option 2 would not comply.

My comment
May I suggest that you read the heading of the clause3.3.1.1 "Current Limiting of the incoming supply" that tells you the area of the installation being considered.

Then a later clause 3.3.1.3 covers the final sub circuit over current protection which also has a cross reference to clause 3.3.1.1.

The important message you need to read the whole section to get all the information required about over current protection 9in the connectable installation.

   

Jacks
Oct 25 2017 09:47

So Pluto , what is the point you are making or trying to make ? are you saying Option 2 is OK or not ?
   

pluto
Oct 25 2017 11:18

option 1; AS/NZS 3001 figs 2.1 and 2.2 both comply in respect of the use of a 16 A RCBO + one MCB can be 10 Amp or 6 amp depending on the size of lighting wiring in the caravan.

Option 2: 1 16 A RCBOs + 1 10amp MCB + 1 6 amp MCB complies if 6 A MCB used for lighting.

Option 3: the use of a 16 A RCBO only depends on the size of lighting wiring in the caravan, it is only satisfactory if the lighting wiring in the caravan is rated at 16 amps. If the lighting wiring rating is less then 10 amps it will not comply with AS/NZS 3001.

Remember the thermal insulation derating when checking the cable current rating for the wiring in the caravan shell.

   

pluto
Oct 25 2017 11:21

A correction to option 3 of the lighting cable current rating

Option 3: the use of a 16 A RCBO only depends on the size of lighting wiring in the caravan, it is only satisfactory if the lighting wiring in the caravan is rated at 16 amps. If the lighting wiring rating is less then 16 amps it will not comply with AS/NZS 3001.

   

AlecK
Oct 25 2017 13:02

Balderdash.

the RCBO complies with 3.3.1.1 for current limitation at rating of supply fittings.
It also complies with 3.3.1.3 by providing overcurrent protection for the final subcircuit. Bear in mind that under option 3 there is only ONE final subcircuit, comprised of all the cables departing to a variety of loads.

The branches of that subcircuit supplying socket outlets will be rated for 16A. Any lighting cables not rated for 16 A are still protected against overload by the nature of the connected load. 3001 does not require them to have a separate protective device (which would make them a different final subcircuit). They are effectively a reduction in CCC, which just happens to occur immediately after the origin of the subcircuit. By default a reduction in CCC requires another overcurrent device; but can be protected as per "3000" 2.5.3.4 (omission of overload protective device) for overload and 2.5.4.3.2 for short circuit. Note also that "3001" is "additional" requirements to those of "3000" [1.1.1]; and nothing in "3001" switches "off" these particular provision of "3000".

Only likely to apply to older caravans being upgraded, typically having lighting wired in 1/0.044 (solid) conductor. But could apply for a new-build as well.
   

toyoto
Oct 25 2017 14:30

What about this arrangement:

1×40a RCCB feeding
1×10a mcb and 1×6amp mcb
   

AlecK
Oct 25 2017 15:07

Complies with the requirements we've been discussing.
But uses more fittings than necessary, at increased cost; and limits the load on all sockets to 10A, reducing usefulness.

The most common "fail" I find is current limitation. For example, I've come across a number with 40 A RCCB, plus 16A and 6A mcbs. Often with existing / expired WoEF; meaning both the person who wired / certified it, plus at least one Inspector, didn't read the rules.
The quick / easy cure is replace the RCCB with 16A RCBO; but often cheaper to re-wire so the 16A mcb acts as current limiter. Either way they can have a WoEF today, and not have to come back for a re-check after finding someone else to fix it.
   

Jacks
Oct 25 2017 15:12

Eeemm just as I suspected Pluto's option two is not the same as option two quoted earlier in the thread,the original option two was basicly saying load limiting by 1 10A MCB and 1x6Amcb,so looking at the arrangement originally posted and changing the MCB's to a 10 and a 6 instead of a 10 and a 20 along with a 40A RCCB as the main switch then is this acceptable as load limiting ? this is also what Toyoto also just asked .

In theory the answer would be yes , but in practice if you read 3001 3.3.1.1 correctly it says there needs to be a separate load limiting device for the supply so it doesn't look like that is an option .

Clearly the best option is an 16A RCBO as the main switch then at the end of the day it doesn't matter what the heck is downstream.
   

AlecK
Oct 25 2017 16:21

That's not a correct reading of the clause - but I can see how you arrive at it.

When it says "separate" it means "separate" for each supply. The word separate is really redundant, because 3.2.4 covers the point.
Not common to have multiple supplies, but it does happen; and when it does each needs its own supply current limiter.
The word "separate" can't mean "separate from other mcbs used on that supply"; because 3.3.1.3 specifically allows the limiter to also act as subcircuit protection.

Also remember that while 16A single phase supply fittings are most common, other ratings and configurations exist and the wording allows for these.

Having met the limitation-to-protect-supply-fittings requirement; move on to following clause for final subcircuits, which
a) requires overcurrent protection for each subcircuit; and
b) allows this to be done by using the supply current limiter; provided there is only one subcircuit. The proviso is also redundant, because if you have a single mcb, there can only one subcircuit (per supply). That's a function of the definition of final subcircuit [3000 clause 1.4.88]. The only way to have more is for each to have its own protection device.

Next come labelling requirement.
Then on the RCD protection 3.3.2: enough Type A to protect as many subcircuits as there happen to be, and specifically can be combined with the device(s) required by 3.3.1.
So by using an RCBO, all boxes ticked with only one device. But any combination devices that ticks all three boxes is compliant.

There is one aspect of present wording that could be taken as making combinations of mcbs non-compliant as load limiter, and that's "a...circuit breaker". That's singular, so could be argued to exclude combinations.
However given that the required result - protecting the supply lead & inlet - can be achieved by some combinations, I don't place much weight on that. And when it comes to issuing a WoEF, no weight at all; because the wording in C 6.4 doesn't require a single mcb but instead allows any combination.
Which I believe shows the clear intent of 3.3.1.2; but in any case allows issue of WoEF for an appropriate combination.

As Pluto noted, a caravan park pillar will have a 16 a device, either mcb or RCBO. So why do we have this current limitation rule at all?
Because connectable installations don't always plug into caravan park pillars. They also plug into sockets in other environments, including generators, homes, and building sites, where there is may well not be current limitation on the socket. There may also be older caravan park sockets that don't have close current limitation (1976 Regs Appendix N clause 12 called for 15 a rating of mcb, but didn't make it mandatory).
Today's clause 2.3.3 calls for all sockets intended to supply connectable installations to be protected, but that doesn't stop people plugging into whatever there is.


   

Jacks
Oct 25 2017 17:10

Aleck, your part comment

There is one aspect of present wording that could be taken as making combinations of mcbs non-compliant as load limiter, and that's "a...circuit breaker". That's singular, so could be argued to exclude combinations.

I completely agree with your take on this ,but as you have said in the past and on other topics the words are the words , we might not agree with them but the "a" certainly makes it a single item so I can see why the Toyoto thought that option two would not comply.
We don't really know if that was intentional or not when the standard was re written but the main thing is that there is load limiting and how that in the Installation itself and how that is achieved I agree doesn't really matter,

So back to the original post, so if this ia a existing set up and cost is being considered , then the most economic option is to replace the 20A MCB with 16 and reconfigure the wiring so its downstream of the RCCB but upstream of the 10 A MCB.


   

AlecK
Oct 25 2017 17:46

I don't think I've thought about that singular wording closely before. It's easy to read what you expect to see. My mindset was perhaps based more on App C, 'cos I spend more time working with that than with Section 3.
Often not until someone else points out what they see that you realise you're interpreting and not doing a straight reading.
Maybe this bit will be tidied up to be absolutely clear in next amendment.
   

pluto
Oct 26 2017 08:17

I wish to make some comments that has been glossed over which effects the way that as/nzs 3001:2008 + A1 has been drafted and it also effects some of the comments made above.

I was one of drafting team of the as/nzs 3001 2001 and 2008 and 2008 + A1 verisions, so I am are well aware of the "why" that as/nzs 3001 has been drafted the way it has been published.

Some key points
(a) In Australia it very common to have up to three 15 A supply leads, the first for the air conditioning unit, the second for the instantous water heater and the 3rd for the balance of the loading. While not all caravans have three supply leads, the use of two supply leads is very common.

The supply lead is not supplied with a new caravan in Australia, you go to the local hardware oe electrical shop and buy a 15 A extension cord (3 pin flat pin fittings) which becomes your supply lead(s).


(b) In Australia the use of transportable structures is mainly for caravans, motorhomes and the like, the use for portable installations for other types of portable or semi-portable electrical installations is considerably behind the use in New Zealand, in which New Zealnd provides for supply to mobile workshops, mobile medical vehicles, etc.

In at least one state the use of transportable structures for electrical installations is NOT covered by the local electrical legislation at all, they are considered to be portable appliances.

(c) There is NO warrant of electrical fitness system as used in New Zealand in any state or territory, but at least one state does have initial electrical inspection with a "all of service life" sticker to indicate what is installed when built, the sticker does not cover any changes made to the electrical installation after manufacture.

(d) In Australia there never been the neutral to earth link which limits the application of RCDs in caravan park service pillars.

These points are reason that some requirments of as/nzs 3001 use in New Zealand seems to be a bit different.