Dimmer Output Protection

I would like to know,under what kind of normal situation, we should install protective device (MCB, Fuses, even RCBO...etc) at the output of the dimmers? What kind of protective devices shall we use and would work with dimmed signal?

 

My views are that no output "protection device" is required, and it is not common practice to do it in Australia. Here's been a lot of previous discussions - you can read my (controversial) comments and the reason I think it's a complete waste of money :

http://www.cbusforums.com/forums/showthread.php?t=1952&highlight=mcb

It's all to do with the tripping characteristics of protection devices - if they are sized so they handle the inrush current, then they simply don't trip fast enough to be of any great use.

So, I am yet to be convinced that they will offer any protection whatsoever - but I'd like to hear an official response from the CIS team (who always stay out of discussions on this subject)

Cheers, John

ADDED 12th July 06 : SEE POST BY znelbok FURTHER DOWN THIS THREAD

 

Thanks. My colleague agrees what you said.

I asked the question because I had seen some other dimmers have fuses at output to protect their coils. I have also seen client specifications which have circuit breakers at outputs as well as inputs. Since there is nothing for the Professional Dimmers, I am wondering if I should need one.

I am not worrying about over-loading due to reworks because this is not supposed to happen. I always reserve buffers for loading. With the margine professional dimmers have, there is no way the dimmer will be overloaded. However, there are still unusual cases that something might have happened after our installations but before commissioning. (we may not be doing the e&m part of the site ourselves) We expect the dimmer is good enough to have protection itself against minor faults. But sometimes I think we need to protect the dimmer and ourselves money wise.

 

Apart from a wide variety of client's installations, our company has 2 commercial ighting showrooms (in 2 states, separate locations to my office) with at least 300-400 independant loads in each showroom, all run via C-Bus. Whilst I look after programming, I have almost no control over how things are wired up when I am not there (once every 3-4mths at most).

Electricians are employed to come and change lights, move things around, etc... and it is amazing how "wrongly" things get wired up. The main cause of this is that most of the dimmers and Relays are mounted remotely from the luminaires, so all the electrician sees is a 3-core cable sticking out of the wall. The people requesting the work are non-technical showroom staff, so if the electricians are asked to fit a fluorescent light to replace a halogen one, they do what they are told.

High-wattage Metal Halide units connected to 1A dimmer channels. Trailing edge electronic transformers connected to C-bus (leading edge) dimmers, and then dimmed continuously. Tracks allowing almost unlimited amounts of lights to be added, so dimmers are overloaded (we usually have 2xRelay and 1xDimmer on each 3 circuit lighting track). Fluorescent lights with electronic and conventional ballasts connected to 1A dimmers which are programmed to dim (not just go 0% or 100%). Continual blowing of halogen and incandescent lamps. The list goes on and on - it's probably the ultimate in "totally uncontrolled" end-user wiring reconfiguration !

In 4 years of this abuse - guess how many blown up dimmers there are ? NONE whatsoever ! The only failure we've had is ONE channel of a 4x2A refusing to dim (it still switches on and off, but won't do anything else) - but this is probably be a control problem rather than a dimmer overload.

Perhaps that is because some *other* brands require that kind of protection. Also note that (for reasons detailed elsewhere in this forum) it is almost de-facto for UK installers to have fuse or MCB-protection on each output channel of dimmers.

I can only make comments based on my experience - and nothing I have seen (in our own installations, or stories from other users) even slightly suggests that C-Bus dimmers are "frail" or easy to blow up. And I simply will not accept anecdotal evidence from anyone that the addition of fuses or MCBs does anything at all to protect the dimmers.

Let's stick to the facts and not get caught up in urban myths...To anyone else who is reading this and disagrees with me, I welcome your PROOF about the subject.

LOL - JC

ADDED 12th July 06 : SEE POST BY znelbok FURTHER DOWN THIS THREAD

 

Ok, my thoughts on this subject, (coming from a professional lighting for large events/concerts/etc background), are that the reason that the professional "touring" dimmers, the kind that are the (usually) 12 channels, 10 Amps per channel, controlled by DMX from a lighting desk, and plug into a 32A 3-phase outlet kind, have MCB's on the output of each channel because that is the only protection they have for each individual channel. There normally is a 32A MCB/RCD protecting the 3-phase outlet the dimmer is plugged into, but this provides no overload protection for each 10A channel.

If a C-Bus dimmer already has a MCB/RCD protecting it from the Line/Switchboard side of it, and this MCB/RCD is the correct rating for the loading of the circuit, (which should HOPEFULLY mean a rating that is under the maximum rated ability of the particular dimmer channel) then an additional MCB/RCD after the dimmer, before the fixture, would provide absolutely ZERO additional protection.

If you had for instance a dimmer, lets make it a hypothetical one for the sake of this discussion, that was an 8 channel dimmer, with a rating of 2 Amps per channel. If the dimmer had been wired by a sparky who had simply installed a 16 or 20 Amp breaker to protect all 8 channels of the dimmer, then yes, it would most definately be an intelligent move to protect each channel of the dimmer with a 2 Amp breaker per channel, BUT... These should be installed BEFORE the dimmer, not after it anyway. (And by before, I dont mean time-wise, I mean before the dimmer as in between the dimmer and mains supply)

Just some food for thought, hope it helps

 

Good points, Darpa

The difficulty with the 1 & 2A Cbus dimmers is that they only have 1 input circuit (ie: a 8 channel has 1 active in, and 8 dimmed actives out). So, on the input side there is really only the possibility to protect it with 1 x MCB, probably a 6 or 8A.

Therefore, people (mostly in the UK) think that to "protect the dimmers" you should have MCBs on every output channel. Not only does this add considerably to the cost, wiring complexity and physical space required - it also is doubtful to me that it offers any protection of the dimmers anyway.

The reason I keep saying this is because the tripping characteristics of MCBs is DESIGNED to be "slow" so they don't accidentally trip (refer my previous posts). So, they react far too slowly to provide any protection to those so-called "delicate" dimmer channels (which are amazing robust actually, and will survive amazing amounts of overload).

Also, a big difference between Stage / Touring Lighting and Hard-wired Domestic anyway - in stage lighting there is the distinct possibility that too many lights could be plugged in and a dimmer channel overloaded, since it's basically a "portable" installation. However, in a domestic house, all the wiring is fixed, and the wattage of the loads is KNOWN (at design stage of the system) - so there is no possibility of overloading the dimmer.

Therefore, what exactly are those proposed MCBs on the C-bus Dimmer Outputs actually trying to protect against?

When CIS advises me that Output Channel Protection is recommended, I will install it - But until then I (and almost every other installer in Australia) will leave well alone... if and when a dimmer channel blows up, then I'll claim it under warranty.

John

ADDED 12th July 06 : SEE POST BY znelbok FURTHER DOWN THIS THREAD

 

I stand corrected JohnC,

And to be bluntly obvious with you, I am such a newbie, that I am only in the early stages of looking at becoming a Systems Integrator. I havent even signed up for C-Bus training yet, and am mainly on here to do as much research as I possibly can about every facet of C-Bus before I commit myself to this career path.

I had not taken the earlier points of your post into account, as I have not actually ever installed or handled a "yet-to-be" installed piece of C-Bus equipment, so I was not aware that the C-Bus dimmers only had the one mains input for all channels.

So thankyou for correcting me on the mistakes in my post, it only helps me to learn

 

It would appear that this advice from Clipsal now exists.

http://www2.clipsal.com/cis/__data/page/2850/C-Bus_Hardware_Installation.pdf

this document was refeenced in another thread wrt selv and lv on a relay, and in reading it, it appears tha Clipsal are recomending MCB's on the output channels.

Mick

 

outputs

we have been installing c-bus since it came out and i install a 2 pole rcd/mcb
on each dimmer or relay etc.
up untill 1 month ago - no problems
last month a clever builder put his chisel through a cable feeding 4 downlight
in the roof on 1 channel of a 2 amp dimmer.
rcd/mcb tripped - o.k.
but it stuffed up any control of that channel- ie channel on all the time (cant
dimm or turn off)
might have to look at load side protection!!!
darpa i wouldnt hold your breath on being an intergrator
its a very long drawn out process and it seems to be who you know not what
you know.

 

Thanks, Mick. I actually read that document today, but completely missed that (was looking for something else re: RJ45 wiring). And yes, I agree that CIS is making some reference to protection of the outputs, in a somewhat strangely worded kind of way.

And then further on within Figure 4 (of a ProDimmer) there's a comment

That wording makes me think that you HAVE TO (must) do it in Europe ? As far as I am aware, there is no such specific requirement in Australian Standards.

Anyway, the CIS document then goes on to state in Table 3 the various ratings for the MCB/Fuses. And it makes a somewhat obscure comment :

I can't comment on why it's worded that way - I could read it that the fuse/MCB WILL PROBABLY be suitable to protect the channel, or should I read it that you have to select some special type of Fuse/MCB that is especially suitable to protect the output?

I haven't read EN60669, but I initially thought that the Euro Stds require that the OUTPUT CABLES be protected - because if you wire them directly to the dimmer then there isn't actually anything providing (safety) protection of those cables between C-Bus Output and the Loads.

But then again, why does Tables 2 and 3 state that protection of Relays is "N/A" ? To comply with EN60669-2-1 do you only need MCBs on the outputs of Dimmers, but not of Relays ?

Would someone please clarify this.

Cheers, John

 

From my quick scan of AS3000, there is no mention of either IEC60669 or EN60669, so I would say that there is no need in AUstralia to comply with them, hence there is no need to add this protection on the output for compliance.

As for the coment in table 3, I read it as you should select protection suitable for the output load, ie a 60W load (~260mA) should have say a 500mA fuse to protect it. This would meant that fuses would be needed as i dont believe that MCB's exists for such low values and using a 1A MCB (regardless of the load) is just a waste of money.

As for the relay, I thingk it shoudl say "By determination" rather than N/A.

As you know - standards are all about interpretation, as they are less descriptive these days, so it can mean different things to different people and still be "right".

Just my unexperienced opinion

Mick

 

One reason I would always use dimmer output protection is it also gives an easy way to Isolate a feed so that you can work on it
Unlike a relay the dimmers always appear to have a voltage on them even when dimmed to zero.
Mike

 

I can do that much cheaper with din rail terminals with knife blades much cheaper than using MCB (both cheaper for each terminal and space used). While it offer does not offer protection to the circuit it does allow a point of disconnection. If you want fuses you can get a different type of terminal for that.

I think individual isolation is overkill in a domestic situation, commercial/corporate maybe, but they can afford it as well.

Mick

 

An earlier comment on this discussion indicated a new document “C-Bus Hardware Installation”
http://www2.clipsal.com/cis/__data/page/2850/C-Bus_Hardware_Installation.pdf

The following comments are based on an installation in Australia.

On page 18 of this manual a cable size of 2.5mm2 on the supply side and 1.5mm2 on the load side is recommended. A little caution needs to be exercised here.

Firstly a 2.5mm2 is an overkill for a DIN rail dimmer, assuming it is supplied via its own MCB. The total maximum load permitted on the dimmer is 8 amps. A 2.5mm2 cable is rated at 20 amps (except when completely surrounded by thermal insulation). A 1.5mm2 cable is rated at 10 amps (even completely surrounded by thermal insulation) when used for lighting.

For an installation using an MCB on the supply side but no protection on the load side, the MCB MUST be rated to suit the size of the supply AND load cables. If the load cables are 1.5mm2, the MCB on the supply side must be rated at 10 amps even if a 2.5mm2 cable is used.

The above comments are based on an informal discussion with the Technical Regulator in SA.

 

That sounds correct to me Leigh. We all must remember that AS3000 is primarily a Safety Standard. The section regarding Fusing is mainly based on protection of the CABLES within the installation, not any particular device connected to those cables. What I mean by that is that you always select the MCB / Fuse rating based on the cable sizes that have to be protected, it has little to do with the actual load that will be connected to it.

Therefore, any upstream (from the Cbus Dimmer) protection is there ONLY to protect the wiring going down to the dimmer. It is NOT there to protect the dimmer itself, nor the loads either !

Unfortunately that doesn't really answer the original question, nor the question of whether MCBs on the outputs are actually effective to protect the dimmer channels. But it's a good discussion never the less !

Cheers, John

 

No not correct - The MCB does not have to be rated for the load cable.

It is more the otherway around, the load cable has to be rated to at least the MCB.

Remember this in AS3000 In<Ib<Iz (or something like that - cant remember the subscripts with out pulling the standard)

Anyway, the load (maximum demand) has to be less than the protection device which has to be less than the cable (derated of course as applicable).

As an example you may have a 40 MCB on a 70m cable, the cable will have to be upped in size to suit voltage drop and short curcuit performance, the resulting cable will handle well in excess of 40 amps, but sizing a cable at 40 amps only (cloest above 40) will ensure that your isntallation fails to meet the standards.

Mick

And of course this is all off topic.

 

Thanks znelbok, that clarified it much better - I intended to say that same thing but explained it exceptionally badly - serves me right for typing late at night from home without a copy of the Standards to refer to.

What I think Leigh was trying to say was that irrespective of what sized cables are supplying power to the dimmer (or relay or whatever), if you use (unprotected) 1.5mm cables on the Output (load) side then you can only use a maximum 10A MCB on the Supply side. That is because, as you said, the load cable has to be rated to at least the MCB.

So, we're all saying the same thing, but looking at it differently

Paraphrasing all that into a real world application... for example a 4x5A dimmer. The dimmer can theoretically draw a total of 20A with all channels fully loaded. So, you'd be right in considering a (maximum) 20A MCB to protect the Input Side of that unit, providing that the cables associated with the Input are rated to (minimum) 20A.

However, that Technical Regulator in SA is saying that in order to use a 20A MCB on the Input side you MUST use 2.5mm (or 4.0mm or 6.0mm if derating applies) on all the Output channels, even though each channel is only drawing a maximum of 5A each. If you are using 1.5mm Load side cables, then you can only use a maximum 10A MCB for the whole dimmer !

However, if you use individual (say) 6A MCBs on each output channel, then you can use 1.5mm cables (providing no major derating applies) on the Output channels and then use a 20A MCB upstream on the Input side.

The above is my limited understanding of the situation - Please be kind if I've (again) explained it badly or incorrectly, as I am not an expert in all this stuff by any means and I am guided by the various Standards, Rulings and also other more experienced people's advice.

Cheers, John

PS : Anyway I don't think it matters that it's a bit off topic... we all learn something one way or the other from these exchanges !

 

I cant see anything wrong in what you have said.

The only thing I would add is that in your example where you can theoretically draw 20A, you can possibly design it for real world use i.e. if one light is a lounge room and another is a bedroom etc etc, the chances of all four load being on together are xxx. In a dwelling it would not be hard for this situation to arise, but it is something to think about at least when at the design stage. The other is that you may not actually have a 5A load on the channel and so you can take that into consideration as well.

I think I asked a similar question years ago in regards to the 12Ch relay. 10A x 12 - If fully loaded (10A load on the channel) then my supply cable would need to handle 120A!!! Bringing it back to real world, a fluro at 1A is a long way from 10 A and typically I am seeing 15-25A on a relay, so the cables are sized as such.

The remote overide is to easy to use (and has a mind of its own when the mice pee in the output units as well) and allow all channels to be turned on so I class an all on scenario as quite possible.

Mick

 

Could you let me know which brand, model and rating of knife blades you are using?

Thanks,

Fleetz

 

weidmuller - plenty to choose from in the w series.

Mick

Sorry for the late reply - missed the post