Cabling from Meter box to C-bus distribution cabinet

Hello there,
I am about to wire my first c-bus install.
I have done the c-bus basic training etc and got the certificate.
I will probably have 2 C-Bus cabinets - one on the groung floor and one on the first floor. Each cab will have 2 din rails, one for dimmers and one for relays.
I plan to split the power to these two cabinets over 2 circuits from the meter box and was going to run 2.5M twin and earth to power each cabinet protected by a 20amp breaker at the meter box and label the MCBs - C-bus,1 and C-bus,2. I was then planning to install a combination MCB/ELCB at the C-bus cabs to protect each din rail ie one for the dimmers and one for the relays.
These would be 10amp each.
I woukld then run all power circuits to each light using 1.5M T&E.
Can anyone (experienced) tell me if this is compliant and/or a better method?
Thanks
Graham

 

Hi Graham, and welcome,
Not sure of your country of residence but, there a few basics that need to observed.

Firstly, I presume that this is a domestic install and by 'meter box' you mean the customers fuse board/ consumer unit? If so, the cable between this and each C-BUS panel should be selected as to suit the total connected load allowing for diversity, volt drop etc.

For example, here in the UK the IET (formerly the IEE) wiring regs are the law, and they rate 2.5mm flat T&E as worth 20-27Amps depending on how it?s installed. A couple of 4x2A or 8x1A dimmers, plus a 12x10A relay could soon be pushing close to these limits, it is essential therefore that cables are sized correctly, so as to ensure circuit protection works effectively.

On the output side, the same is true, (sized to suit the total connected load allowing for diversity, volt drop etc), 1.5mm flat T&E is worth 14-20A, again dependant on installation method. Given that most C-BUS dimmers used in a domestic setting are 1-2Amps per channel this is not only a bit of an overkill, but given the cost of copper these days, also expensive, so you may want to look at smaller cable sizes.

That all said, if I was doing the spec, cable and MCB sizes apart, I would do the following:

1, Feed each C-BUS Panel from the non earth leakage protected side of the customers Fuse Board/Consumer Unit via a suitably sized RCBOs, this provides both good separation and protection. (essential to comply with UK regulations if lighting sockets are used, plus it?s good practice).
2, In each C-BUS Panel provide a means of local isolation, a manual, double pole, DIN rail mounted switch of the type found in domestic consumer units is ideal for this as it can be ?locked off? during maintenance (again to comply with regs). These are two modules wide, and are of the same form factor as an MCB so will fit nicely in the cabinet.
3, As you already intend, provide a suitably sized and classed MCB to protect and isolate each individual C-BUS device.
4, Finally, I would strongly recommend that you follow Clipsal advice and provide each output (especially dimmers) with its own suitably sized and classed MCB, this will, in the event of a fault, save you the expense of replacing a C-BUS device.

Hope that?s of help,

Regards Paul (Eeng)

 

Hi Graham, and welcome.

Not sure of your country of residence but, there a few basics that need to observed.

Firstly, I presume that this is a domestic install and by 'meter box' you mean the customers fuse board/ consumer unit? If so, the cable between this and each C-BUS panel should be selected as to suit the total connected load allowing for diversity, volt drop etc.

For example, here in the UK the IET (formerly the IEE) wiring regs are the law, and they rate 2.5mm flat T&E as worth 20-27Amps depending on how it?s installed. A couple of 4x2A or 8x1A dimmers, plus a 12x10A relay could soon be pushing close to these limits, it is essential therefore that cables are sized correctly, so as to ensure circuit protection works effectively.

On the output side, the same is true, (sized to suit the total connected load allowing for diversity, volt drop etc), 1.5mm flat T&E is worth 14-20A, again dependant on installation method. Given that most C-BUS dimmers used in a domestic setting are 1-2Amps per channel this is not only a bit of an overkill, but given the cost of copper these days, also expensive, so you may want to look at smaller cable sizes.

That all said, if I was doing the spec, cable and MCB sizes apart, I would do the following:

1, Feed each C-BUS Panel from the non earth leakage protected side of the customers Fuse Board/Consumer Unit via a suitably sized RCBOs, this provides both good separation and protection. (essential to comply with UK regulations if lighting sockets are used, plus it?s good practice).
2, In each C-BUS Panel provide a means of local isolation, a manual, double pole, DIN rail mounted switch of the type found in domestic consumer units is ideal for this as it can be ?locked off? during maintenance (again to comply with regs). These are two modules wide, and are of the same form factor as an MCB so will fit nicely in the cabinet.
3, As you already intend, provide a suitably sized and classed MCB to protect and isolate each individual C-BUS device.
4, Finally, I would strongly recommend that you follow Clipsal advice and provide each output (especially dimmers) with its own suitably sized and classed MCB, this will, in the event of a fault, save you the expense of replacing a C-BUS device.

Hope that?s of help,

Regards Paul (EEng)

 

Hi Graham

There are no restrictions to the minimum size of submain (Australian Standard)
I have a feeling that 2.5mm Sq 20A would be too small for the number of circuits connected to the C-Bus outputs.
A simple way is to add up the total load consumption connected, taking into account the length of the runs from your main switchboarde, to the ground and second floor cabinets.

Regards NewLine

 

cable must also exceed the rating of the protection device - very important.

What newline is suggesting is a maximum demand calculation (albeit not as the standard gives examples for).

You size your cable based on maximum demand and circuit protection rating (and other things but we wont go into it here)

Mick

 

Hi, I'm new to these forums (based in UK) and find myself in pretty much the same situation as Graham. The house is already wired with the appropriate cabling for switches/PIRs and lighting circuits and I'm now finalising my equipment order for the 2 (connected together) control cabinets. As well as an 8 channel dimmer and 12 channel relay at each cabinet I'll be installing the Wiser Home controller unit at one of them (haven't found much in the way of installation instructions for that yet).

With regards our point above, I'm finding that 1Amp Type B MCBs are pretty hard to find and can be rather expensive. Is it an option to say have 3 dimmer circuits share a 3Amp MCB? This will help me determine whether a 36 module cabinet will be sufficient space for the dimmer, relay and all required MCBs.

Also, can someone tell me why the dimmers and relays are available with and without power supplies? The instructions aren't clear on this point and I assume I need them all with power supplies? Is this correct?

Thanks for your help.

 

No it isn't possible for 3 dimmer circuits to share a single MCB as the MCB goes on the load side to protect the dimmer. So to share a single MCB you would be joining 3 loads which doesn't work at all.

As to why some dimmers and relays have power supplies and others don't I would say it comes down to cost and giving the installer flexibility. Clearly those without a PS are cheaper, so for example if every unit had a power supply you would over supply the network, so by mixing and matching you can provide what us required and reduce the costs.

As to weather you need them, yes you need power supplies, but weather you need or want standalone or integrated power supplies depends upon your design and how much current you need to give the C-bus network. Once you have that figure (done by adding up the current draw of each switch, releay or other device) then you can work out how much power you need to give.

This could be done by ordering output units with power supplies, or by buying standalone power supplies. If you look at the specs you will see the integrated power supplies are 200ma, whilst the standalone ones are 350ma.

 

Yes it is clipsals recomendation

C-Bus Hardware Installation Handbook V1.1 - Page 15, section 4.1.2

"To protect the C-Bus dimmer unit and meet the safety requirements of IEC60669-2-1, a MCB should be installed in each output channel"

A very old statement that has been there as long as I can remember. It was only advice form this forum that made me not install them.

Not only does it cost money for the breaker, but it also costs money for the cabinet sapce - a cost that can go unforgotten.

Mick

 

Thanks to everyone for their feedback, really helpful.

I can see a number of people don't agree with the need for the MCBs on each channel but I understand that you do run the risk of needing to replace an entire dimmer unit if you don't have any spare capacity within it (which I won't for now).

 

can I mention work must be carried out by a licensed electrician to? well definitely in Australia anyway

 

Josh, it will be but most don't have any experience of lighting control systems never mind Clipsal so I'm really just confirming a few doubts that they have and it's great to know there is such a good community here to assist if the need arises.

 

My sparky has got me to lay 2.5mm core wire from the consumer unit to my cabinet housing my 4 channel dimmer and relay. These 2 devices will supply a few sets of lights and a extractor fan. The draw will be less than 8amp and i see no further exspansion evr rquired,

Due to personal problems he can no longer attend to cable up.

I've have had another sparky come to see me this weekend and he's
saying i need to feed the clipsal unit cabinet with with 6mm wire from the consumer unit , because of the earth fault loop.

I would appreciated peoples thoughts on that

 

earth fault loop calculations require cable distance. I would expect earth fault loop impedance to be an issue for longer runs and almost anything in a resedential install should be short enough

You can improve it by using a spereate larger earth cable.

If the run is short, then the cost is not significant and you should just do it. Bigger cable is not going to hurt (except for the extra money)

Mick

PS - Rusty on my calculations as it has been quite a while so please correct me if I am wrong.

 

What is the actual distance?

 

Thanks for replies so far.

From consumer to clipsal cabinet is probably no more than 12 metres.

 

Hi Ian

In Australia I believe it was previously a requirement to run minimum 6mm submains.

I could not find the rule anymore but it's what I would run to a sub board and probably a small cost in the scheme of things.

Regards
Daryl

 

Daryl; thanks. So can you confirm that you would use 6mm in a domestic install, drawing less than 8mp for a short run.

The cost of the cable is not an issue, running a new cable is a pain, but I want this to be right .

thanks in advance to all of you that have comment.

 

Is it really a sub board?

Hi Ian
What needs to be done depends on many circumstances, other desisions & existing infrastructure. Anyway....

If the C-Bus controls are at a separate location and only for the lighting controls and dosen't have any circuit breakers for cable protection/ change of cable size, then it is not really a "sub-board", it is more a switching point.
If the subcircuit is protected by a 10 or 16A MCB/RCD at the origin of the circuit then the 2.5mm should be fine. (provided the cable sizes on the output side of the C-Bus are suited for this protection, or just use 2.5 mm there as well.)

note: There used to be a less then 25m in domestic = no voltage drop concerns rule in Australian Standards 3000, but it seems to have been removed. showing my age now...

Cheers

 

With my existing 4 dimmers I feed each clipsal dimmer box from the Consumer unit/Main fuse box ( 4 cables)

The 4 dimmers are split over 2 rcd's at the Consumer Unit.
Each feed is protected by a 10amp MCB at the Consumer Unit and an 10amp MCB at the clipsal dimmer box ( you could argue the later should just be a switch)
Each dimmer output channel is protected by a 1AMP MCB . The cabling on the output to the lights is either 1cm or 1.5cm core

Currently 50W halogen bulbs are on the above lights but slowly replacing with 12W led.

With the new kit I have a 4 channel dimmer and 12 channel relay coming off of the same new 2.5mm core feed (not yet connected at mainfuse , given this disscussion) . This is being protected at the Main fuse box by a 10amp MCB and rcd . I will also use this feed to power a switched cooker hood(3 amp fuse) ( so in some sense this is a sub board).

The clipsal output channels will be protected by 1AMP and the output channels all have 1.5mm core.

The draw will be less than 8amp and i see no further exspansion ever required,