Memera 2000 A100HE RCD 100A 30mA

Discussion in 'Electricians' Talk' started by rmc, Dec 23, 2021.

  1. rmc

    rmc Member

    I think I have an intermittent tripping fault caused by the unit not a circuit. Would anyone know the best replacement for this obsolete unit other than a second hand one?
     
  2. MGW

    MGW Screwfix Select

    I have found testing of RCD's a little hit and miss. I have had units which have passed but were tripping, and swapping stopped the tripping, when replacement also passed, and also units tripping due to strain on the cables, had 100 mA RCD's tripping when the test button on a 10 mA RCD socket pressed (MK not cheap) but in the main RCD's which show OK with a RCD tester are OK, the times when this was not the case are rare.

    The older RCD does seem to be affected by spikes, so likely a SPD would stop it, but a consumer unit is a type tested distribution unit, and to retain the type testing only items recommended by the manufacturer can be used, even if they seem to fit.

    So a botch up to keep things running can come back to bite one. Yes I have done it, when working in house, when working in house it is unlikely anyone is going to try it on, but I have been that electrical engineer who on finding a botch up has insisted the contractor corrects it. Likely if one of my own guys had done it would have turned a blind eye, unofficially told him don't do it again.

    So question one does it pass when tested with a RCD tester? If so what makes you think it is faulty? I am sure the one in my old house was tripping due to surges when a neighbour was welding. Two identical RCD's would hold for 18 months without a problem, then trip for seeming no reason for couple of weeks, then again two years no tripping.

    The RCD's were not built into a consumer unit, Wilex-board-with-RCD.jpg but mounted above the old Wylex fuse boxes, however done before the rules changed as to electrical equipment in the control of an ordinary person. But still today we have isolators before the CU to comply with HSE rules an live working, so not sure if we can still mount SPD or RCD in separate box before or after main CU?

    But I would not have done the above if at the time I could have bought a split load consumer unit. It was done around 1992, today would not be worth the effort, I would just change the CU.
     
  3. The Happy Builder

    The Happy Builder Screwfix Select

    A complete new consumer unit ;)
     
  4. Tony Goddard

    Tony Goddard Screwfix Select

    As Happy alludes to, a Memera 2000 is an old unit and probably due replacement, but there are two options if you don't want that expense. First is buy an SH RCD from ebay and hope its OK, you should have it tested by someone with an RCD tester to ensure it is working.

    Second option, if this is a fully RCD protected board with just 1 RCD, you could replace the RCD with a main switch and fit a new separate RCD on the incoming tails.

    Third option, change the lot for a new board!
     
  5. adgjl

    adgjl Active Member

    Do you have a smart meter close to the rcd?
     
  6. rmc

    rmc Member

    Many Thanks for the various replies. Sorry for my delay in responding, I wasn't being ignorant, but the ******* RCDO failed completely shortly after posting this, taking out Router and plunging me back into 1970s era, except with the lights still on...:(

    RCDO simply would not reset even with all three circuit fuses (Kitchen; Sockets; Cooker) pulled out.

    A helpful eBay Company got me a second hand (but tested) RCDO for this morning, ordered just before blackout here, and an equally helpful local sparky spent a couple of hours fitting it then dealing with nuisance trips that still followed during testing. Bit of a confusing couple of hours for both of us really. Don't think there's much doubt the old RCDO was faulty given it wouldn't reset even with all circuits disconnected. Spent a bit of a wild goose chase trying to find why some appliances sometimes did/did not trip the new one, which he'd ramp tested and confirmed worked. Also checked insulation which seemed fine.

    He discovered the garage has (obviously wrongly) been fed from a spur from Kitchen ring by previous owner. He wasn't impressed. But this garage also has two fridge/freezers bringing the total count with kitchen to three. He tended towards saying I have 'pushed my freezer luck' too far, as these can leak to earth a bit and surge at start-up, and with the knackered old RCDO perhaps even less tolerant. He's going to quote for running a separate spur to garage from the outside meter box, with external armoured cable around front of house, not from the old and fairly full Memera 2000 box.

    For the person who asked about Smartmeter, yes one fitted in last year and quite close to CU (2 meters?). Though similar episode of nuisance tripping preceded its installation and went away of its own. What are you thinking about this?

    Otherwise, I'm not quibbling the need for proper spur to garage, which will separate off two freezers from kitchen, but how do you people feel about this diagnosis? My own insulation tests with mega meter to each unplugged appliance have found no resistance issues, which given he found no wiring issues, leaves no obvious cause except as he thinks maybe too much total freezer earth leakage. Intermittent faults like tripping can send you mad as we all know, is this a good course of action?

    He didn't seem to have an Earth Leakage meter but I intend to get one myself and see if anything is misbehaving only whilst running and not whilst off with mega meter attached.
     

    Attached Files:

  7. The Happy Builder

    The Happy Builder Screwfix Select

    A leakage meter that is of any use will probably be a couple of hundred quid and is not guaranteed to solve your problem, so don’t rush to buy one.
     
  8. Bazza

    Bazza Screwfix Select

    Don’t forget that you also need the experience to be able to interpret the test results!
     
  9. rmc

    rmc Member

    Granted decent Earth Leakage Meters aren't cheap, and results may indeed need skilled interpretation, but I had rather hoped the Electrian I called out would have provider both of these. But he seemed unaware of what these meters were. So he could only run wiring tests (fine) and swap around appliances seeking a pattern.

    Two more festive RCDO blows happened this Xmas morning, first with microwave + kettle going; second one with just a substitute old kettle alone boiling. My suspicion is that the background total leakage is too close to the RCDO's limit, with maybe a rogue appliance somewhere eating up most of it, so otherwise fault-free Kitchen appliances push it over with no clear pattern.

    Hence Leakage measurement, both of circuit as a whole and of individual appliances running (the Earth wire of extension lead moved outside clamp jaws method) seems my best hope of demystifying this.

    Anyone agree or disagree?
     
  10. Lectrician

    Lectrician Screwfix Select

    Disagree.

    smacks of a sparky who has no idea how to fault find.

    Sounds like the usual low ins res N to E fault to me. The more load you apply, the quicker it trips.

    get a decent spark.
     
    Sparkielev likes this.
  11. rmc

    rmc Member

    Lectrician - agreed the Sparky was poor at fault finding, after a couple of hours I sensed he just wasn't sure what to do. And this was Xmas eve....

    Can you clarify if you mean the low resistance N to E fault you suggest is in an appliance or in the wiring? He claimed the wiring was OK after various meter tests.
     
  12. Lectrician

    Lectrician Screwfix Select

    Wouldn’t know without testing. Could be either. Test both. That’s what fault finding is.
     
  13. adgjl

    adgjl Active Member

    Did your electrician test the first RCD, or did they just assume it was faulty. Your original tests weren’t relevant as you still had the neutral connected to the installation.
     
  14. rmc

    rmc Member

    He did test the old one still fitted, finding it tripped at 26mA which he felt slightly high. As it had taken 6 hours disconnected from all circuits to even reset the previous evening, I regarded it as untrustworthy.

    He also ramp tested the new RCDO once fitted and confirmed the seller's recent test of 21mA which he thought better. But the old one was not apparently tripping early.

    He did disconnect wires in the CU for the later insulation and wiring resistance tests.
     
  15. adgjl

    adgjl Active Member

    For an RCD to be in spec, it must not trip at 15mA, and must trip at 30mA. Your original RCD was in spec, as is your “new” one.

    The outgoing wires (including the neutral) must be disconnected from the RCD before the test.
     
  16. rmc

    rmc Member

    Yes I agree nuisance tripping doesn't appear to be a RCDO fault. He tested the new and old RCDOs whilst in the CU via a Megger brand tester, it looked like a Megger MFT1731 Multifunction Tester, plugged into a socket on the ring. Why should the Neutral have been disconnected first?
     
  17. The Happy Builder

    The Happy Builder Screwfix Select

    It doesn’t.

    If there is leakage of 7 mA within the and the RCD trips at 23 mA then the tester will show a trip with 16 mA rather than 23 mA.

    If the tester doesn’t indicate a low test result there is not much point in disconnecting the RCD to test it.

    With the best will in the world an electrician cannot always find intermittent faults.
     
  18. rmc

    rmc Member

    I take your point. But in making it, that the ramp trip current with neutral connected is normal, that suggests no great baseline earth leak exists, i.e. no wiring related resistive breakdown. Which suggests a plug-in appliance must be at fault?
     
  19. adgjl

    adgjl Active Member

    It doesn’t, but ramp tests with the installation connected and disconnected will identify the leakage if you subtract one from the other, or better, a sensitive clamp meter round the phase and neutral tails from the meter.
     
  20. Lectrician

    Lectrician Screwfix Select

    When you say disconnected, do you mean neutrals too? If not, you’re not testing the RCD in isolation on its own. Turning MCBs off is not enough. Neutrals must be removed from neutral bar.
     

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