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RCBO Energy Consumption/Losses

statter
Just refitted a large consumer unit with Wylex miniature RCBOs.  Looks like a decent compact product.  When energised on no load the metal CU casing ran about 5 degrees C above immediate surrounding ambient (in a very large cupboard).  Wylex spec says full load losses are 1.5 to 2.6W per pole and these are two pole devices.  I think this would break down between no load loss and a loss that varied with current (along the lines of copper and iron losses with a t/f).

Given the temperature rise I observed (which so far as I can tell with my cheap IR thermometer) is uniform across 20 devices the standing no loss dissipation is likely around 0.5W plus each.  Whilst this will keep consumer units warm it will also add to bills.  A 20 device CU with 0.5W per device will use 87kWh costing about £13 pa.  

I haven't got the kit to measure the losses accurately but this is certainly something to think about when specifying larger installations.

Looking across other manufacturers I see Hager quoting 3W for a single pole RCBO at full load so the Wylex unit does well by comparison.

Has anyone measured the standing losses on these and other 'electronic' devices? 

I expect we will see a new section in the Regs on losses before long given the increasing focus on energy efficiency.
  • 0
    You have to fire triac to pull in the the actuator coil, which is several mA, a  simple shunt regulator,  like a dropper  and Zener diode combination  needs to pull this all the time, so that it is ready when required you'd need a series reg or a switcher to allow you to draw less current on standby - as I said earlier a custom chip could do this,  with a high voltage pass transistor process.  You could even integrate the firing SCR onto the same die - ideally a biCMOS process that allows transistors and both polarities of FETs, but that would give you a higher ultimate cost per chip. (MOS only or bipolar only are cheaper as there are less foundry steps.)
  • 0
    No Mike, that does not need a fixed current, it is a pulse and can come directly from the supply. The sense electronics need a few tens of microamps, the firing electronics can get as much as they want direct from the mains for the short period under consideration. A custom chip is irrelevant, and easy once there is volume, without a need for a significant standby power. A pounds worth of discretes would do this job, and save the million or so design and process cost of full custom. There are a number of RCD chips available on the market already, and none of them are big enough to loose more than 100 mW or so. There is something odd about this temperature rise, if it is real.
  • 0
    I do think this level of no load dissipation is high.  There will be millions of these devices and MW across the country as a result.  Measured about 10mA (very rough - just showing on meter and lots of scope for error) on 5 of these devices with no load this am.  Granted some may be reactive but 0.5VA per device feels high.  I will have a think about further measurements with the kit I have to hand.
  • 0
    I've just measured the temperature rise on my Wylex consumer unit metal case, and it's 6.8 deg. C. above ambient at the warmest point; much more significant than I had previously estimated.  It's a 19-way consumer unit fitted with 17 single-module switched-neutral RCBOs, one MCB and one timer module. The supply tail to the consumer unit was carrying 1.25 amps at the time of the measurement, so there was very little load at the time of the temperature measurement.  This means that inside the case the temperature will be even warmer.  I keep a pipe thermometer on the case and this indicated a maximum case temperature of 38 deg C. in last month's heatwave.  Not good. The issue this gives me is that the individual modules are so closely packed together on the bus bar that thermal dissipation from each individual RCBO unit is restricted - the internal elements in the ones in the central area must have a significant temperature rise, and this indeed corresponds with the warmest temperature reading I have made.  Thank you for raising this Statter - I was largely unaware of it.
  • 0
    We'd like losses due to contact resistance to dominate, it sounds like it is not the case. However given there is no room for any electrolytic caps for energy storage, or clever electronics, I suspect this is just an example of wasteful shunt regulator design. The reason I mention custom chips is that this is the way to get the size right down -the compact designs do not have room for conventional PCBs and large  passives like 0603  resistors.

    It could be better capacitor dropper and reactive, but the temperature rise says it is not.
  • 0
    Wait until you get a consumer unit full of AFDDs!
  • 0
    Are these warm CUs exposed or in insulated cupboards? I don't have the knowledge to do the maths, but to maintain a temperature rise of a few degrees above ambient must take a significant (i.e. more than trivial) amount of energy.
  • 0
    Hello Chris.

    A good point -thank you.  My consumer unit is on a clear and open wall space in a domestic utility room, but is only 20mm down from the ceiling, above which I have removed the local loft insulation. The location was chosen to meet the Management's aesthetic requirements.  The enclosure is spaced off the wall on a framework of three 25mm battens to both sides and the bottom, with no batten at the top. Cable routing is slotted through the plasterboard ceiling, back-entry to the consumer unit, so some (limited) thermal convection is present.  If I were to tackle this again, I would substantially increase the distance from the enclosure to the ceiling.
  • 0
    Yes good point.  The CU I refer to was in a very large ( 4 cubic metres) otherwise empty cupboard.  Reasonable ventilation for a cupboard.
  • 0
    GeorgeCooke:
    gkenyon:

    My observation ... our kids leave their plug-in USB chargers plugged in and switch on the socket-outlet left on, all of the time anyway ?




    Time to educate them then.




    Education is not the problem ... mind on other things is really the issue.


    Anyway, if we are not careful, we could run the risk of turning this into a debate on corporal (or capital) punishment ?


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