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Type A rcd . EICR coding ? etc

aligarjon
Hi Guys.   Not been on for a long time, just had a bit of a search and couldn't really find anything so thought i would ask and see what you all thought.


1.  Are we or will we be coding type AC rcd's if there are LED's or induction hobs, lots of electronics  etc  present.

2. How much DC leakage does it actually take to saturate an rcd and cause  problem?

3. How much does a standard LED lamp or induction hob  leak ?

If we test an AC RCD with no load and it's fine then re-test it with all LED lights, induction hobs etc turned on and it operates correctly could we then say that it is ok with a note on EICR  OR EIC if installing any of the above.  


Obviously also on an EICR if the RCD then doesn't operate with it all on it becomes a C2 ?


Any thoughts



Gary
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    I would be interested in Paul Skyrme‍ 's opinion on whether an appliance can be sold knowing it could have adverse affects on existing installations. Surely there are rules regarding this.
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    Presumably at some point the savings on your electric bill from having the low energy central heating circulator will cover any additional installation costs, hopefully long before the circulator needs replacing.
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    How do I select the correct Type of RCD?



    It is important to select the correct Type of RCD for the equipment to be used. The Type of RCD will depend on the characteristics of the equipment. Where necessary, equipment manufacturers should specify the RCD Type required. If the information is not available, the manufacturer should be contacted and asked to provide it. It is a legal requirement of UK Product Safety Regulations for manufacturers to provide clear installation instructions to enable safe installation.

    https://electrical.theiet.org/wiring-matters/years/2019/77-september-2019/which-rcd-type/


    It appears that Worcester Bosch are saying ask the IET and the IET are saying ask Worcester Bosch.

     


  • 0
    It would seem to me that it would be reasonably foreseeable that injury could result from the mal-operation of an RCD caused by residual currents with a DC component. “Reasonably foreseeable” is effectively the benchmark for any  

    claim that due diligence has been properly exercised. However, that rather obvious contention hinges on an equally obvious contention that situations may arise where DC current will indeed be deleterious to the operation of an RCD. 

    It would be unwise to disregard the weight of opinion that would uphold such a contention but I do applaud David for challenging it. 

    I would also like to know how the tester is rigged as most MFTs inhibit tests where the ground resistance exceeds touch voltage limits and most simply fail to display a definitive time when maximum disconnection times are exceeded.
  • 0
    Hi Lyle


    The reasonably "foreseeable test" should not apply if the appliance is manufactured in compliance with the LV directive because this gives specific requirements to prevent these kinds of faults. I do not see any of the fault types suggested as reasonably foreseeable because the manufacturer should have designed the possibility out of the product. If the fault is foreseeable he should provide protection against it IN THE PRODUCT, not expect it to be provided by a third party, and particularly as the instructions do not admit this danger. It is fairly easy to fit a "crowbar" across the supply which is triggered by such leakage which removes the danger by blowing the mains fuse (and I note that internal fusing appears not to be fitted, which I would expect). The instructions keep on referencing BS7671 in areas where it is out of scope, pushing overall safety onto someone else. This is a bit like saying I make a class 2 appliance but someone else must protect it against an Earth fault to the casing because I have not designed the class 2 insulation to be adequate under all foreseeable conditions.


    Washing machines and similar appliances have used phase control etc. of their motors for many years, yet I have not heard of any accidents due to RCD failure because of leakage. Is this just luck or is it because the design is adequate? Unfortunately, I think that BS7671 is being asked to deal with all possible dangers from "the use of electricity", including the appliances connected, which is way out of scope. We are seeing that "Risk Shifting" is becoming common, particularly in areas such as product liability. There is an easy solution available, if you need a DC supply, then isolate it via the electronics. It may cost slightly more, but for low-power devices not very much. Just as an example I recently bought a new 300W power supply for £25, and 10W supplies cost £5. I have just been quoted £3000 to fit a replacement gas boiler, and I can buy it for £1000. Realistically a few pounds extra for the boiler to be properly isolated is not a problem because a 50W transformer would cost £5 in volume. Perhaps this is all too simple? (And I should get Gas Safe registration!).


    I have several RCD testers including the Megger MFT as I said. One of these gives readings up to 2 seconds for disconnection, the MFT just says TRP if longer than 100 ms.


    The solution to this is to add a regulation to BS7671 which simply states that "Appliances which may leak DC currents into the Mains wiring system may not be connected to RCD protected circuits". This puts the problem back with manufacturers to ensure that their products are safe and cannot affect our safety measures.


  • 0
    davezawadi (David Stone):

    Hi Lyle



    Washing machines and similar appliances have used phase control etc. of their motors for many years, yet I have not heard of any accidents due to RCD failure because of leakage. Is this just luck or is it because the design is adequate?


     


    No, you won't have heard of any issues with RCDs with phase control.


    Quite simply because the Type AC RCD is unaffected by Phase Control - see item 1 in Figure A53.1 of BS 7671


  • 0
    Sparkingchip:

    It appears that Worcester Bosch are saying ask the IET and the IET are saying ask Worcester Bosch.

    Exactly so! At least their customer services people respond quickly. It seems that the online manual concerning type A RCDs was out of date and it is now worded as in Sparkingchip's posting about 7 before this one. Here is what they wrote:


    "The information provided in our previous email is taken from the latest manual versions, we no longer specify a type A should be used. We now reference the latest IET regulations as different types of RCD can now be used for low energy DC modulating pump. The information in our latest manual is now in line with current IET regulations for using RCD on the type of pump used, they will be able to advise you further on reasons behind this regulation." ??
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    davezawadi (David Stone):

    Hi Lyle


    The reasonably "foreseeable test" should not apply if the appliance is manufactured in compliance with the LV directive because this gives specific requirements to prevent these kinds of faults. ............


    The solution to this is to add a regulation to BS7671 which simply states that "Appliances which may leak DC currents into the Mains wiring system may not be connected to RCD protected circuits". This puts the problem back with manufacturers to ensure that their products are safe and cannot affect our safety measures.


     


    I am with David on this. BS7671 is being changed to ensure that the fixed wiring can catch faults induced by poor design of plug in appliances. The messing around we have with earthing car charger supplies on PME installations because car manufacturers have tried to save a few pounds on a >£30,000 car is a typical case. 


    While I am all for safety the cost in a simple installation is becoming excessive and the need to change protective devices every few years to remain compliant, especially if the property is rented, is not in my opinion the solution. 


    Last week I was called out to change the fuse wire in a  blown fuse in a >£600,000 house. The kitchen fitters had managed to blow the fuse. The owners will spend over £10,000 on a new kitchen but despite many years of trying I have not convinced them to fit a new consumer unit, or even RCD protection. As the costs of a new CU increase especially if AFDDs are required my chances of convincing them decrease even further. I am sure this scenario is being repeated in many properties around the country. 


  • 0
    Comments on a few recent posts:


    Testing of type-AC RCDs.  I've done some of this in a variety of ways last year, as a side issue to an assignment about testing type-A with smooth dc.  (Where I am, there's no type AC anyway. The AC interest was because of my UK connections.)  

     1:  I saw, as I've mentioned here earlier, that some AC-branded RCDs basically behave as type A. So don't be too confident from testing a single unit, e.g. about what levels and waveforms cause a trip. A really classic type AC with hard magnetic core may be different: identify them by failure to trip on one polarity of half-wave rectified residual current, even at many times the rated tripping level.  When standards about installations and appliances specific RCD types, they appear to focus on how an standards-comformant RCD must behave, rather than how a typical one actually does. 

     2:  I'd recommend against MFTs if you've an oscilloscope available. Or, at least, use the oscilloscope too. Otherwise, you're guessing at what the MFT responds to, or what currents it applies at different times. If you want a simple variable resistor for leakage currents, a wire dipping in a saucer of water gives quite good control. 


    When this manufacturer says it doesn't any longer require type A, I assume it means there are others (such as F, B, etc, etc) that would be ok, not that AC is suitable. 


    Yes, it gets complicated between standards and manufacturers, and meat-in-the-sandwich as was mentioned some months ago.  If I remember right, the opposite happened with PV inverters some 10 years ago, after the competition to have high efficiency had caused them to drop the isolating transformer that older models had. Then there was fuss about needing type B RCDs in case of internal faults.  Given the availability and cost of these RCDs, there was a definite benefit for inverter manufacturers who could state that (rather like some EV chargers) they already had suitable protection built in to prevent DC into the AC side or at least to detect low levels and disconnect. (I'm only going by distant memory .. should look this up better if I had time.)  The special feature there is that an electrical-specialised person probably chooses the components (inverter etc) to suit the customer's project and give overall lowest cost, so they see the advantage of paying x more for the inverter to save 2x on the RCD.  With boilers, washing machines etc the item is typically chosen by others, and the electrician gets, too late, the job of fulfilling the manufacturer's requirements or the wiring-regs requirements in view of what leakage currents the manufacturer says could arise.


  • 0
    EICR ,how do you know what type of RCD is fitted if not stated , I have one or two spare no markings as to what type they are. Can we give a code for that.


    Now even 13amp socket outlets with one or two USB type A charging points are out of date , you now need sockets with USB charging points Type C . You can buy outlets with one Type C  and one type A, witch covers both charging leads ,but of course more money and bother for customer to change existing ones.

    The whole regulations are getting out of hand.

    jcm

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