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Type A rcd . EICR coding ? etc

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
Parents
  • Freezers, type F, time-delay.

    I haven't yet found a modern type A that has the tripping problem with freezers etc - though there might well be some that would.  The F is not one I've tried.  The few type-B I've tested had significant time-delay anyway, apparently taking advantage of the maximum permitted operating times to make them less prone to tripping - but that doesn't mean they'd all be like that. Then I've even seen some type-A claiming a 10 ms delay as an optional feature (it still keeps them within the requirements for supplementary protection, so manufacturers are free to include it if they want). I'm trying to remember where those were, but I suspect they weren't in the UK - and then in the countries that are extra keen on lots of RCD type it's harder to find them in 2-pole 80A rating rather than 4-pole with lower rating. 

    With the large number of types defined in recent standards, and the optional tweaks that manufacturers can do within these, it's horribly messy.  Moving towards getting rid of type-AC is pleasing and overdue. Much of the rest may be going too far, in view of the high cost of more specialized devices and the small proportion of faults for which they'd be needed. I suspect the longer-future situation will be something like an enhanced type-B, at a more reasonable cost, if it becomes mainstream. The extras needed to make a type-B instead of type-A aren't something of particular complexity or necessary cost that would cause anything close to the price-difference we currently see (I know others have pointed this out here earlier too).  

    Trip-happy. 

    Perhaps the permanant magnet getting weaker...? Or dust on the iron-iron contacts, making an air-gap. But then the trip current in normal ac tests should be significantly lower too, if it's made a big difference for the trip-happiness. Generally the story we hear from studies of aged RCDs is of higher current and/or slower tripping, though on the other hand those studies don't usually test and report whether an RCD is operating quicker than its type used to when new! It seems that avoiding tripping on transients just wasn't given such attention in old devices. 

    The source of transient residual currents in some modern appliances. 

    Good question. I should take this up further out of curiosity, except for lack of time - perhaps some much-later month, a little study of some trip-provoking modern appliances. For transients coming in from the supply in a TT system, one can imagine L and N both moving together in potential compared to PE, so making currents (in capacitances to the PE) that add together.  In cases where the appliance causes trouble by itself it's not so clear. In one case I saw (modern washing machine), removing the power-supply filter from the circuit definitely stopped the trouble, until a newer RCD was fitted and the filter was restored; but getting things working was the main aim, and I still don't know what was causing the PE currents in the filter. I could speculate on capacitance to earth from conductors on the load side of an inverter (e.g. motor windings and possible filter capacitors), together with sharp changes of these conductors' potentials which the inverter makes, and possible inverter states where all output conductors are switched to one or other side of the dc capacitor to give zero output voltage but then suddenly switch to another state. I've never yet got round to checking more of what's going on in these modern household devices. Bigger inverters for drives can definitely make a real mess of PE currents, at least on their load side. 


Reply
  • Freezers, type F, time-delay.

    I haven't yet found a modern type A that has the tripping problem with freezers etc - though there might well be some that would.  The F is not one I've tried.  The few type-B I've tested had significant time-delay anyway, apparently taking advantage of the maximum permitted operating times to make them less prone to tripping - but that doesn't mean they'd all be like that. Then I've even seen some type-A claiming a 10 ms delay as an optional feature (it still keeps them within the requirements for supplementary protection, so manufacturers are free to include it if they want). I'm trying to remember where those were, but I suspect they weren't in the UK - and then in the countries that are extra keen on lots of RCD type it's harder to find them in 2-pole 80A rating rather than 4-pole with lower rating. 

    With the large number of types defined in recent standards, and the optional tweaks that manufacturers can do within these, it's horribly messy.  Moving towards getting rid of type-AC is pleasing and overdue. Much of the rest may be going too far, in view of the high cost of more specialized devices and the small proportion of faults for which they'd be needed. I suspect the longer-future situation will be something like an enhanced type-B, at a more reasonable cost, if it becomes mainstream. The extras needed to make a type-B instead of type-A aren't something of particular complexity or necessary cost that would cause anything close to the price-difference we currently see (I know others have pointed this out here earlier too).  

    Trip-happy. 

    Perhaps the permanant magnet getting weaker...? Or dust on the iron-iron contacts, making an air-gap. But then the trip current in normal ac tests should be significantly lower too, if it's made a big difference for the trip-happiness. Generally the story we hear from studies of aged RCDs is of higher current and/or slower tripping, though on the other hand those studies don't usually test and report whether an RCD is operating quicker than its type used to when new! It seems that avoiding tripping on transients just wasn't given such attention in old devices. 

    The source of transient residual currents in some modern appliances. 

    Good question. I should take this up further out of curiosity, except for lack of time - perhaps some much-later month, a little study of some trip-provoking modern appliances. For transients coming in from the supply in a TT system, one can imagine L and N both moving together in potential compared to PE, so making currents (in capacitances to the PE) that add together.  In cases where the appliance causes trouble by itself it's not so clear. In one case I saw (modern washing machine), removing the power-supply filter from the circuit definitely stopped the trouble, until a newer RCD was fitted and the filter was restored; but getting things working was the main aim, and I still don't know what was causing the PE currents in the filter. I could speculate on capacitance to earth from conductors on the load side of an inverter (e.g. motor windings and possible filter capacitors), together with sharp changes of these conductors' potentials which the inverter makes, and possible inverter states where all output conductors are switched to one or other side of the dc capacitor to give zero output voltage but then suddenly switch to another state. I've never yet got round to checking more of what's going on in these modern household devices. Bigger inverters for drives can definitely make a real mess of PE currents, at least on their load side. 


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