RCDs

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  • Ric
    Automated Home Jr Member
    • Apr 2004
    • 25

    RCDs

    OK, I've bought some C-BUS kit and one thing that I cant seem to ind in the documentation is whether or not you should put an RCD in line with the load on a dimmer unit.

    I know that I will need an 8A RCD for the feed to the dimming unit itsel but is this sufficient to cut the power if one of the load circuits shorts?

    Probably a simple Q but better safe than sorry.
    Ric Charlton

    always trying but not always successful
  • CBusShop
    Automated Home Jr Member
    • Apr 2004
    • 22

    #2
    If possible, I would recommend having a RCD in series with each output channel before the load. Without the output RCD protection, it is possible that the dimmer channel could be damaged by the short-circuit condition.
    Kwong Li
    Laser Business Systems Ltd.
    http://www.laser.com
    http://www.cbus-shop.com

    Comment

    • Ric
      Automated Home Jr Member
      • Apr 2004
      • 25

      #3
      Re: RCDs

      Thanks for the reply!

      This does move me on quite nicely to my next couple of questions:
      • What size MCB should I place in line? - i understand that each channel is a max. of 1A
      • Where can I find 8A MCBs? - or should I use a size that I can get? (6A or 10A)
      Ric Charlton

      always trying but not always successful

      Comment

      • Ross
        Automated Home Jr Member
        • Apr 2004
        • 34

        #4
        Re: RCDs

        Originally posted by Ric
        Thanks for the reply!

        This does move me on quite nicely to my next couple of questions:
        • What size MCB should I place in line? - i understand that each channel is a max. of 1A
        • Where can I find 8A MCBs? - or should I use a size that I can get? (6A or 10A)
        Normally circuit protection should be in front of the dimmer not after. If the dimmer is an L5508D1A for example then a 10amp RCDMCB should be used. The chance of a fault taking out the group leg of the dimmer is remote at best. If this does occur you can have your dimmer repaired by Clipsal for a nominal fee.

        The concept of RCD protection on a group by group as suggested by CBusShop is not recommended practice.

        A short circuit condition does not necessarily mean you are going to toast that particular channel either. Of the hundreds of dimmers we have fitted, and yes I do mean hundreds, I can think of only one instance where a short circuit caused a group to fail.

        If you build some redundancy into your project (ie; have a couple of spare groups left on a dimmer as well as a relay) you can also just move the output of that circuit to a new group output and reprogram.

        Hope that helps.
        Austalian Integrators Forum
        http://www.integrate-oz.net/forum/index.php
        http://www.cbussales.com/index.php

        Comment

        • CBusShop
          Automated Home Jr Member
          • Apr 2004
          • 22

          #5
          The question that I was trying to answer was "I know that I will need an 8A RCD for the feed to the dimming unit itself but is this sufficient to cut the power if one of the load circuits shorts?". I was not advocating not having circuit protection on the input mains feed but rather, in addition of.

          Having RCD protection after as well as before the dimmer, although not mandatory, is recommended practice by Clipsal UK and I have known at least one instance of a short-circuit taking out the dimmer channel in far fewer dimmers than Ross has fitted. Having a dimmer repaired might be a cost-effective option in Australia but not in the UK because Clipsal UK do not have a repairs department at the moment and unlikely to for some time.

          Apart from the small additional cost and space involved, there is no disadvantage in having circuit protection fitted to each output dimmer channel. Indeed, having output channels individually protected as well as the incoming mains feed would allow maximum flexibility in isolating either the whole dimmer or channel by channel basis.
          Kwong Li
          Laser Business Systems Ltd.
          http://www.laser.com
          http://www.cbus-shop.com

          Comment

          • FrankMcAlinden
            Automated Home Guru
            • Feb 2004
            • 109

            #6
            Re: RCDs

            Hi Ric
            As Ross has mentioned in a previous post its not normal practice here in Oz to put circuit breakers or rcds on the cbus loads. If i was going to put protection on each output i would use a hrc fuse which is much quicker than a normal domestic circuit breaker... I had one channel of one of my dimmers go down and Clipsal repaired it in a resonable time..
            I would imagine as Ross stated that the dimmer units would be quite robust...I do recall someone mentioning that there are now circuit breakers available which are fast acting like hrc fuses ....

            HTH
            Frank
            Home of FirM - the Multi Zone IR Transport System
            http://www.armaghelectrical.com.au/index.html

            Comment

            • Ross
              Automated Home Jr Member
              • Apr 2004
              • 34

              #7
              Originally posted by CBusShop
              The question that I was trying to answer was "I know that I will need an 8A RCD for the feed to the dimming unit itself but is this sufficient to cut the power if one of the load circuits shorts?". I was not advocating not having circuit protection on the input mains feed but rather, in addition of.
              The answer to that question is Yes. RCD and MCB protection is sufficient to protect the dimmer. Circuit protection on the input mains side via MCB is manditory not optional. RCD on the input side could be optional in the UK however in Australia all lighting circuits require and RCD as well. An RCD on the input side will offer greater protection. The point is the upstream RCD will see the short before the downstream RCD every single time. Why double up? Only one will trip and it will be the upstream unit.
              Having RCD protection after as well as before the dimmer, although not mandatory, is recommended practice by Clipsal UK
              Do you have a reference for this statement? Clipsal Australia do not have this as recommend practice. I would be very suprised if CIS UK did. The only reference to circuit protection I have every found is on the line side of the dimmer. The installation data sheet for an 8 channel dimmer can be found here http://www.clipsal.com/cis/pdf_files...NSTRUCTION.pdf and nothing about load protection is mentioned or recommended.
              Having a dimmer repaired might be a cost-effective option in Australia but not in the UK because Clipsal UK do not have a repairs department at the moment and unlikely to for some time.
              That may well be the case and I accept that fully. That should further the cause to have some redundancy built into the design of the project.

              Apart from the small additional cost and space involved, there is no disadvantage in having circuit protection fitted to each output dimmer channel.
              Can you give me a figure in pounds as to the cost of having this protection? I would be interested to hear an amount quoted. My experience says more cost, more space, more time, no gain.
              Indeed, having output channels individually protected as well as the incoming mains feed would allow maximum flexibility in isolating either the whole dimmer or channel by channel basis.
              This is hardly worth mentioning. Isolation of channels from the dimmer is a simple affair and can be achieved with a screw driver and a connector.

              Well thats my 0.02c worth. I'll let you chew on that for a bit while you find me this reference from CIS UK.
              Austalian Integrators Forum
              http://www.integrate-oz.net/forum/index.php
              http://www.cbussales.com/index.php

              Comment

              • CBusShop
                Automated Home Jr Member
                • Apr 2004
                • 22

                #8
                You have an interesting style of debate, Ross. I shall answer your points in the same order.

                The upstream MCB will not protect a dimmer from a fault condition downstream. By the time the upstream MCB trips due to a fault downstream, the dimmer channel could already have been damaged. By fitting a downstream MCB (as well as the upstream one, of course), it should protect the channel from over-current and short-circuit fault conditions. It also allows easy isolation of a particular dimmer channel to carry out work on. As you are aware, C-Bus dimmer channels are not isolated from the mains feed even in the off state.

                There is no written reference to my statement except that it is endorsed by the CIS UK Technical Manager, Steve Gordon. Also, on a number of CIS quotations to customers that we have copies of, the lack of any downstream channel circuit protection was explicitly stated. Steve has advised that any damage caused by inadequate circuit protection on both sides of the dimmer is not covered by CIS standard warranty. He further confirmed that damaged dimmers are currently not repairable by CIS UK for the foreseeable future.

                If a customer has 8 circuits to control with a C-Bus 8-channel dimmer, I hope you are not suggesting that he or she should install an additional dimmer module as redundancy. A protective MCB for the purpose costs less than 3 British Pounds per channel and a suitable DIN rail enclosure costs around 35 Pounds (all plus VAT) if additional rail space is required.

                May be it is not worth mentioning the quick circuit isolation feature of having downstream MCBs for electricians and people that are electrically competent. For the rest of us, poking around inside a live DIN rail enclosure with a screwdriver rearranging potentially live wires is hardly a simple or desirable activity. Swapping channels and reprogramming the C-Bus dimmer unit, for most people, involves a chargeable visit by the installer/integrator whereas an MCB will provide the protection automatically and conveniently.

                The C-Bus dimmers, as you have stated, are good units but they are not infallible. Dimmer channels do get damaged under certain fault conditions and the occurrence is higher that you are experiencing. For the sake of a few extra Pounds per channel, I maintain that fitting appropriate dimmer channel circuit protection is a sensible and cost-effective precaution.
                Kwong Li
                Laser Business Systems Ltd.
                http://www.laser.com
                http://www.cbus-shop.com

                Comment

                • Ric
                  Automated Home Jr Member
                  • Apr 2004
                  • 25

                  #9
                  Re: RCDs

                  OK - so, if I go with the protection on either side of the dimmer, what size MCB should I be looking at for the load?

                  Each channel has a 1A rating and the smallest standard-size MCB I have seen is a 3A. This would therefore allow 3 times the rated current flow before tripping.

                  Ideas? :roll:
                  Ric Charlton

                  always trying but not always successful

                  Comment

                  • FrankMcAlinden
                    Automated Home Guru
                    • Feb 2004
                    • 109

                    #10
                    Re: RCDs

                    Hi Ric
                    Had a quick look in the Clipsal Catalogue and they do 1amp circuit breakers 6ka or 10ka .. here in Oz.....So i would imagine Merlin Gerin or others would manufacture 1 amp ones as well.... I still would recommend hrc fuses maybe using fused terminals ;-)
                    Frank
                    Home of FirM - the Multi Zone IR Transport System
                    http://www.armaghelectrical.com.au/index.html

                    Comment

                    • Ross
                      Automated Home Jr Member
                      • Apr 2004
                      • 34

                      #11
                      Originally posted by CBusShop
                      You have an interesting style of debate, Ross. I shall answer your points in the same order. .
                      Well I didn’t know I had an interesting style of debate, but thanks for pointing that out.
                      The upstream MCB will not protect a dimmer from a fault condition downstream. By the time the upstream MCB trips due to a fault downstream, the dimmer channel could already have been damaged. By fitting a downstream MCB (as well as the upstream one, of course), it should protect the channel from over-current and short-circuit fault conditions. It also allows easy isolation of a particular dimmer channel to carry out work on. As you are aware, C-Bus dimmer channels are not isolated from the mains feed even in the off state.
                      Perhaps you should revisit my last post. I stated “The point is the upstream RCD will see the short before the downstream RCD every single time.” You seem to be confused with the use of an RCD over an MCB, and the combinations thereof.
                      Furthermore what you are endorsing is just complete rubbish. As for fault currents and their dark secrets, we shall leave for another time. Suffice to say any quality MCB RCD with a fault current rating of 6kA or better WILL protect the dimmer in the majority of cases, that is the fact weather you choose to accept it or not. There is no guarantee that a dimmer will survive any short circuit however, sanity says use a quality product and get on with it. The point on the additional benefit of having groups individually isolated is complete rubbish. Turn the line side breaker off. Problem solved. What is the issue with that?

                      There is no written reference to my statement except that it is endorsed by the CIS UK Technical Manager, Steve Gordon. Also, on a number of CIS quotations to customers that we have copies of, the lack of any downstream channel circuit protection was explicitly stated. Steve has advised that any damage caused by inadequate circuit protection on both sides of the dimmer is not covered by CIS standard warranty. He further confirmed that damaged dimmers are currently not repairable by CIS UK for the foreseeable future.
                      Like I said before I can appreciate the problems with getting equipment repaired. As for Steve Gordon’s take on things, I would suggest he get up to speed with the CIS documentation as should you. Perhaps Steve would like to discuss this with us. I would welcome the opportunity. As for no written documentation from CIS, (the company that manufacture the products) supporting your installation methods, need I say more.

                      If a customer has 8 circuits to control with a C-Bus 8-channel dimmer, I hope you are not suggesting that he or she should install an additional dimmer module as redundancy.
                      No, I am suggesting, if possible use another dimmer that will switch things like bathrooms and laundry and external lighting and leaving 2 spare in lieu of using a relay. Or a combination of both or taking a “chance” as the rest of the world does and use quality equipment and deliver a quality installation. As I’ve said before my experience with product failure is rare at best. I will state however that the majority of all C-Bus installation problems stem from incompetent installers playing with things they have little understanding of.

                      A protective MCB for the purpose costs less than 3 British Pounds per channel and a suitable DIN rail enclosure costs around 35 Pounds (all plus VAT) if additional rail space is required.
                      Let’s see. One of my company’s current projects is a residence on the beach and has 4 off 8 channel dimmers and 2 off 4 channel dimmers (as well as 6 relays). That’s a total of 40 dimming groups to protect and using your method is hardly justifiable, nor sensible. Geez I could toss in an 8 channel dimmer cheaper than going down that road.

                      May be it is not worth mentioning the quick circuit isolation feature of having downstream MCBs for electricians and people that are electrically competent. For the rest of us, poking around inside a live DIN rail enclosure with a screwdriver rearranging potentially live wires is hardly a simple or desirable activity. Swapping channels and reprogramming the C-Bus dimmer unit, for most people, involves a chargeable visit by the installer/integrator whereas an MCB will provide the protection automatically and conveniently.
                      Please, this is just complete rubbish. If you have no idea what you are doing then leave well enough alone. Trained systems integrators and endorsed and qualified installers are the only people who should touch a C-Bus installation in any case. That is the whole point, if you aren’t qualified then don’t touch. You may want to check that one out with CIS as well.

                      The C-Bus dimmers, as you have stated, are good units but they are not infallible. Dimmer channels do get damaged under certain fault conditions and the occurrence is higher that you are experiencing. For the sake of a few extra Pounds per channel, I maintain that fitting appropriate dimmer channel circuit protection is a sensible and cost-effective precaution.
                      And I say that this is complete tripe. It would appear we shall have to agree to disagree. I could go on but I feel I am kicking a dead horse.
                      Austalian Integrators Forum
                      http://www.integrate-oz.net/forum/index.php
                      http://www.cbussales.com/index.php

                      Comment

                      • Ross
                        Automated Home Jr Member
                        • Apr 2004
                        • 34

                        #12
                        Re: RCDs

                        Originally posted by Ric
                        OK - so, if I go with the protection on either side of the dimmer, what size MCB should I be looking at for the load?

                        Each channel has a 1A rating and the smallest standard-size MCB I have seen is a 3A. This would therefore allow 3 times the rated current flow before tripping.

                        Ideas? :roll:
                        Save your money Ric. You would be just adding components that are not required. Read my post below for clarification.
                        Austalian Integrators Forum
                        http://www.integrate-oz.net/forum/index.php
                        http://www.cbussales.com/index.php

                        Comment

                        • Ross
                          Automated Home Jr Member
                          • Apr 2004
                          • 34

                          #13
                          Re: RCDs

                          Originally posted by FrankMcAlinden
                          Hi Ric
                          Had a quick look in the Clipsal Catalogue and they do 1amp circuit breakers 6ka or 10ka .. here in Oz.....So i would imagine Merlin Gerin or others would manufacture 1 amp ones as well.... I still would recommend hrc fuses maybe using fused terminals ;-)
                          Frank
                          Frank,
                          A 1 amp 6ka circuit breaker has a trade price of 12.72
                          A 1 amp 10ka circuit breaker has a trade price of 27.59

                          Besides the cost of breakers and switch boards to house them, what do you gain? Nothing. A fully loaded group may well trip a 1 amp breaker with no fault at all.

                          This is just not a valid consideration.
                          Austalian Integrators Forum
                          http://www.integrate-oz.net/forum/index.php
                          http://www.cbussales.com/index.php

                          Comment

                          • Darbyweb
                            Automated Home Jr Member
                            • Mar 2004
                            • 25

                            #14
                            Re: RCDs

                            Interesting topic

                            I've arrived a bit late in the proceeding but'll add my 2p's worth anyway.

                            Firstly there seems to be a bit of confusion with terminology.

                            RCD - Residual Current Device.
                            MCB - Miniature Circuit Breaker.

                            In the UK we do not need to have RCD protection on lighting. IEE Regs require protection for all outlets which could be deemed for use outside the equipotential zone, i.e. Garden.

                            Standard practice in the UK is to protect all sockets throughout, leaving Cooker, Appliance Ring, Heating, and lighting circuits off the RCD.

                            I would certainly class a standard, quality, CBus installation in the UK to include outgoing protection of all Dimmer ways.

                            As correctly detailed a 10amp MCB would be suitable to feed each dimmer, and then on the outging side fit single 1a Type B MCB's.

                            These are easily obtainable from good wholesalers.

                            Part number as used by ourselves.

                            Hager NB101 1amp 10kA.
                            Also available in 0.5, 2, 4, 6 and onwards.

                            Good practice would always dictate that the local circuit has an immediate means of isolation that is clear to the end user.

                            To say that they would need to isolate 8 circuits to work on a single light would be a little unfair, as would suggesting a screwdriver and connector as another means of isolation would also be a little foolhardy and down right dangerous - one dead customer later :cry:

                            Likewise telling them to remove the offending 8 channel dimmer - send it away to Clipsal and leave them with 7 more non functioning circuits would certainly not be on..

                            From a customers point of view (he's always right remember) to blame him for damaging his own equipment, whilst correct, would probably end your relationship with him all for the sake of £2.50 per channel.

                            We have recently taken over an install where the client had used a 'qualified' CBus installer. He had not recommended inline MCB's - customer has already lost 2 x channels and is not a happy bunny !!

                            From my own perspective, in a rush to do work at home i stuck in an additional 8 channel dimmer without fitting MCB's - cut through the wrong cable, and bang goes 1 channel - local MCB goes out (10amp) as does ELCB protection (1960's overhead supply)

                            As a professional installer, we cannot do anything less the 100% - perhaps the Blame/Claim culture has not hit Aus yet, but anything that looks like a shortcut and consequently affects what has been installed, will come back and bite you in the arse.

                            Thanks for your time



                            Dean.


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                            Comment

                            • FrankMcAlinden
                              Automated Home Guru
                              • Feb 2004
                              • 109

                              #15
                              Re: RCDs

                              Hi Dean



                              I would certainly class a standard, quality, CBus installation in the UK to include outgoing protection of all Dimmer ways.

                              This appears to be UK specific standard practice from information i have received from others...Going on the cost of the cbus stuff im not surprized.
                              For Example 15 years ago when plc,s were very expensive we had to incorporate a mcb for each output which went to a field device ie solenoid. This was a requirement from the customer...Today mcb,s would only be required for groups of outputs .....

                              If you have a dead short on a dimmer load i dont believe the rcd/mcb on the line side of the dimmer would be quick enough to protect the triac ....To give the dimmer a good chance of survival i would prefer to use a quick acting fuse and if i had the room in my electrical box i would have installed terminal fuses...
                              Frank



                              Home of FirM - the Multi Zone IR Transport System
                              http://www.armaghelectrical.com.au/index.html

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