MCB on Output side of Dimmer

Hey

Do people normally put 1amp MCB's on the output side of their dimmer control units ? I was reading the installers document and it had

4.1.2 Output side of C-Bus output unit
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 (as in Figure 3 & Figure 4).

But the most of the installations i've seen didn't have mcbs.

It will be really annoying if I have to because I don't have enough space in my switch board for 8 additional breakers. If its a really good idea can we get inline fuses before the light fittings ?

 

I too have often wondered about this.. Saw it in the manual but have never seen it in the field..

 

This dates back a long way and has been discussed back and forth quite a bit.

The points of discussion are whether or not an MCB actually provides meaningful protection to the individual dimmer channel. I think most people agree that it does not, at least in case of a short circuit event.

However, it does help for overloads. For instance, if you do an installation where you load a 1A dimmer with almost its 1A load, and later either higher wattage globes are fitted, or the circuit gets extended by additional globes. You can only hope that the Electrician then does not simply replace the 1A MCB with a bigger one to prevent the "nuisance tripping"

The other benefit is that when you want to work on a circuit, you can switch off that specific MCB only, instead of taking down the entire dimmer.

Cllipsal's stance on this has been a bit confusing, but here we apply the principle of protecting each output channel of the dimmers with an appropriate MCB, so as to circumvent any discussion when it comes to warranty claims.

 

here? Your company ? So you would put in 8 x 1Amp MCB/'s on each dimmer unit ?

Wow makes me wish I had bought a bigger circuit board.

I can't imagine putting in a globe with more than 240watts in a single globe.

I could see the more important risk being a short or adding a lot of downlights ?

 

Hi Trucker,

Here is South Africa, and yes, one 10A MCB for Input, 8 x 1A for output.

If you were to put in a globe of more than 240W into a single-globe circuit, then I would expect that your design would call for a 2A or larger dimmer module.

And yes, your last point is the most crucial one, whereby as stated, the short circuit benefit is quite questionable.

Check with your C-Bus Installer what he has to say about warranty issues in your country, perhaps after that you might worry about a larger DB (or a sub-DB).

 

True, but if you have three @ 60W and someonw replaces them with 100W you very quickly exceed 240W. Another case is a multi globe fitting and they all get replaced with higher wattage globes.

It is not always one globe per channel

Mick

 

Ahh thats what I said above.

The real issue is adding more downlights (eg more globes) or shorting it out.

 

What do Australian installers do? I have a sparky that is going to install this for me but he is not specifically a c-bus installer so I want to be able to tell him which way to go.

My cbus is (will be) already in a (new) sub-board so I'm not particularly wanting to replace a brand new board or get a sub sub board

I have 36 poles 12 is filled by the 8 channel 1am dimmer, 8 is filled with 4 roller shutter relays, another 8 is filled with 4 channel relay (for bigger loads/fans). I also have a logic controller (4 pole) which I can put in my data cabinet which probably makes sense because eventually it will be replaced with a wiser mk2.

Presumably I should put in a 8amp MCB for the dimmer unit on the input side? Although the lighting circuit is already protected in the main board by a 10amp MCB on the main board?

 

Down Under

Hi Tucker
It's all dependant on the local wiring rules. Here in Aus you do not have to protect the output, but in other countries such as England, they do.
Look at it this way, do you put protection after a wall switch mounted dimmer?
Is C-Bus any different in operation (apart from physical form)?
No

 

Matthew has hit the nail on the head! There are a bunch of different rules in different geographic locations.. e.g. another one is in the UK and Hong Kong, there is a need to switch both the active and neutral when using the C-Bus ceiling fan controller hence the neutral 'in' and 'out' connections through the second pole of a double pole relay on the unit. Where possible, the same device is provided for multiple markets. This sometimes means that additional information or additional 'features' may be supplied.

The circuit protection in the Australian market is the that of the upstream circuit breaker that is used to protect the wiring and not the C-Bus dimmer. Any circuit protection downstream of the dimmer is not a requirement in the Aussie market.

 

Can anyone confirm that Clipsal will still honour warranty on dimmers with no fuses on outputs.
Lots of discussions and it appears in Australia we no longer have to fit them.
Thanks

 

This forum is not an official forum therefore what any body says really has no standing.
Having said that being an ex Clipsal employee who could make these kinds of decision I would have typically honoured a warranty claim on a dimmer with no fuses on the output.
There was always exceptions to this, often given away by failed multiple channels where an installer just moved a faulty or overloaded circuit to the next channel or put another dimmer in and blew that one. Instead of fault finding. A 1 Amp fuse in this poor practice would have done little to help, as even if it had blow, chances are the installer would have replaced it or put a large fuse in.