RCD for garden equipment, would it work?

Discussion in 'Electricians' Talk' started by MGW, Jul 3, 2020.

  1. MGW

    MGW Screwfix Select

    My consumer unit is populated with 14 RCBO's 30 mA 40 mS curve B type AC, and on the web site for the CU it seems you can't get type A, so big question if I use a 10 mA 40 mS type AC socket for the garden, would a faulty USB charger on a different socket stop it working?

    In fact if any inverter controlled item goes faulty causing a DC injection on the supply will it only affect that RCD (RCBO) or will it affect them all?

    Little peeved it only went in last year, and it seems they are still permitted in UK, although banned in Germany did look at paperwork and saw type B and though great, then latter realised they were curve B type AC this is what you get buying cheap gear.
     
  2. spinlondon

    spinlondon Screwfix Select

    I don’t know that the issue is about faulty anything.
    More like a fully functioning USB charger being a problem.
     
  3. MGW

    MGW Screwfix Select

    I said USB charger as an example some boilers and washing machines actually stipulate if an RCD is used it should be type A or better, with 14 RCBO's should one be swamped only a limited number of items would loose RCD protection, but the cost of swapping all is rather high, so what is only the one feeding the inverter drive freezer, fridge/freezer and washing machine, is that enough?
     
  4. sparky steve

    sparky steve Screwfix Select

    Pity you never thought about all this at the design stage? Key point, do your homework at the design stage;)
     
  5. MGW

    MGW Screwfix Select

    I did consider it at design stage, the box said type B, it was only latter I realised type B was really curve B it was type AC.
    I will change the 32 amp RCBO for front sockets in house for a type A RCBO, at £16 it seems prudent to swap the one feeding the freezer, fridge/freezer, and washing machine which all have inverter drives.

    But lights is another question, may be simpler to return to tungsten, I have a draw full of them, and in any case in real terms do we really need RCD protection on lighting circuits?

    With 14 RCBO's I think the chance of faulty equipment stopping a RCD working at the same time it is needed is slim. However the video is an eye opener, and when many circuits go through one RCD one has to ask how many will fail to work? Also should we test the RCD with all normal stuff still running? We tend to turn off the PC before testing the RCD, but that PC may be stopping the RCD from working.
     
    Teki likes this.
  6. spinlondon

    spinlondon Screwfix Select

    With regards to the PC, my understanding, is that earth leakage should be restricted to 3.5mA AC current, and that d.c. leakage is generally only around 0.05mA.
    As for d.c. leakage on one circuit affecting the operation of RCBOs on adjacent circuits, I suspect, that it may well do.
    I do know that with solar panels, if a B type RCD is recommended, then all RCDs in the installation should be B type.
     
  7. MGW

    MGW Screwfix Select

    I have looked and I have not found any RCBO's type B, although I have now found the make I have now do a type A which when I hunted about 9 months ago before I realised how little DC would stop the RCD tripping were not on the market, only the 6A were made as type A.

    Since making this post I have found type A curve B at £16 32A so the idea of using a RCD socket has been dropped, from what I read the problem is where a full wave rectifier goes faulty so working as a half wave rectifier, if there is no fault than the RCD will still work, and as far as I can tell it will only affect that circuit.

    So I now wonder how one would fit all type B when it seems they are not available? It seems many countries have banned use of type AC, just like the ELCB-v was banned, but not as yet the UK.
     
  8. spinlondon

    spinlondon Screwfix Select

    Back to dual RCD boards.
     
  9. MGW

    MGW Screwfix Select

    Oh I hope not, well not an option with my house if lights in any room and not on same RCD as sockets, as lights split up/down and sockets split front/back, three levels so two cooker circuits, two electric showers, three ring finals, and three lighting circuits, plus immersion heater etc so 14 RCBO's would not want that lot on just to RCD's.
     
  10. spinlondon

    spinlondon Screwfix Select

    MGW likes this.
  11. MGW

    MGW Screwfix Select

    The report seems to say no problem, who do we believe?
     
  12. spinlondon

    spinlondon Screwfix Select

    The study was conducted at the time when the 17th edition was being prepared.
    I wonder how many of the requirements for RCD protection would have made it into the 17th, if the study had concluded type AC RCDs were not fit for purpose?

    One of the reasons cited for introducing so many requirements for RCD protection, was the relative cheapness of RCDs.
     
  13. MGW

    MGW Screwfix Select

    I have to accept that 14 RCBO's covering every circuit must be better to the fuses and MCB's it replaced when only around 3 circuits were RCD protected. And that RCD was type AC anyway. In my old house I think the RCD tripped once for good reason, I sawed through the three and earth going to a light switch, which went around 4 corners so had never expected it to be there.

    This house they have tripped twice, both because the roof leaked, and likely would have tripped the old system, as those sockets were on the RCD. And the sockets were not on circuit with inverter drives.
     
  14. phill jackson

    phill jackson New Member

    I appreciate this is a bit of an old thread :)
    From my own diy investgations, type AC rcds will still trip with pulsed DC, but at higher, sometimes, much higher, values than their rating. In the report they are limiting distortion to 5%, so probably the AC rcds will still work, if a bit less well. They hardly touch on the idea of affecting rcd function, probably too much of a hot topic.

    It all seems to depend on the brand, the method (electronic or electromechanical), which side of the waveform the pulsed fault is on, etc. I've just retrofitted my 17th edition board with A type 30mA rcds for about £23 each. I have a TT setup and the main 100mA AC type rcd trips at 90mA AC fault, but 448mA pulsed DC (A type) fault. With a pure DC injection somehow from a usb socket, i imagine it wouldn't work at all :/

    Every house has LED lamps now at the very least, I'm not sure how I feel at having fitted hundreds of AC type rcds over the last few years!
     
  15. The Happy Builder

    The Happy Builder Screwfix Select

    My understanding is that for current to flow there has to be a complete circuit.

    For example current flows from a battery out through a lamp and back to the battery.

    So for the DC current from an appliance to flow it has to have a full circuit and it will take the easiest route. So it flows from the appliance it is coming from through the circuit neutral, out through the RCD then back into the DNO network around the transformer windings and then back it through the RCD to the appliance to complete the circuit, passing through the RCD in both directions. I don’t think it takes a detour to go down the garden.

    Is that a too simplistic view of what happens or is it more complicated?
     
  16. The Happy Builder

    The Happy Builder Screwfix Select

    @phill jackson

    From experience the 30 mA RCD will be blocked and not trip at all, whilst the 100 mA RCD will trip frequently. I have had that happen with Bosch Direct Drive washing machines and also solar PV with storage batteries.

    If the 100 mA RCD is upfront in a separate enclosure you can generally swap it for a 300 mA Type A which aren’t expensive.
     
  17. The Happy Builder

    The Happy Builder Screwfix Select

    The only difficulty with buying 300 mA Type A RCDs is that they are made for European countries and there’s not many rated above 63 amps, as they don’t have 100 amp single phase supplies into homes like the UK and have lower capacities as well as three phase supplies in their homes.
     
  18. spinlondon

    spinlondon Screwfix Select

    There’s a couple of videos on You Tube where Paul Meehan provides his test rig for people to demonstrate.
    In one video, they inject 250mA of d.c. into the set up, which prevents the trip switch from operating, the RCD then goes on to fail the 1 x and the 5 x test.
    In the other video with John Ward, John uses 250mA and 50mA.
    I think in both videos they ramp test the RCD.

    MFTs inject d.c. when testing Zs on ‘No Trip’ setting.
    Not sure how much they inject though.
     
  19. MGW

    MGW Screwfix Select

    Although some LED lamps use pulse width modulated current regulation, most use a capacitor to limit the current, and DC can't pass through a capacitor so LED lamps are not really a problem.

    The fridge/freezer, freezer, washing machine or any other item with inverter drives could be a problem i.e. some thing where the AC supply is rectified before it goes through a transformer or capacitor. It seems to be claimed as a new problem however this motorised valve mid-position-valve.jpg has been used for years, clearly it will result in a DC component, I note some Worcester Bosch boilers actually stipulate type A RCD protection. I know now manufacturers instructions only need to be taken into consideration it no longer says they must be followed, but when I do an EICR I don't down load the installation instructions for all installed equipment and read to see if anything asks for type A.
     

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