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RCBO Energy Consumption/Losses
statter 16416862
53 Posts
Question
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.
20 Replies
keylevel 83562202
16 Posts
I wonder how much of that is down to the electronics. I can understand that resistive losses will be there (and increase with load), but I would have hoped that the electronic "standby" use had been minimised (along the lines of reducing standby current for things like TVs). However, this probably won't happen if there is no legislative drive for it.

Of course, the "standby" use will be a very low percentage if the circuit has a significant load most of the time, but I can see a lot of domestic installations where that won't be true (your figures would add about 3.5% on to my house bill).
perspicacious 20955492
327 Posts
Has anyone measured the standing losses on these and other 'electronic' devices? 

I've posted several times about parasitic USB outlets built into double sockets which in a typical domestic, probably exceed your figures..................

Regards

BOD
mapj1 80733779
2070 Posts
Part of the problem is that there is limited space for a 'proper ' power supply, transformer and so on, so it ends up being a capacitor and resistive dropper, with attendant inefficiency, and it has to be able to fire the actuator, so the active devices have to be quite bosky, not 1.8volt microamp CMOS logic. A custom chip on a mixed voltage process,  could be a solution to that, but I suspect there is not the market volume to justify that yet.

 
wallywombat 11001209453
225 Posts
Realistically, for an establishment big enough to require 20 circuits, the cost of installing and running those circuits is going to absolutely swamp the £13 pa overhead.
gkenyon 82239607
1038 Posts
perspicacious:
Has anyone measured the standing losses on these and other 'electronic' devices? 

I've posted several times about parasitic USB outlets built into double sockets which in a typical domestic, probably exceed your figures..................

Regards

BOD

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 🙄

OMS 615869
646 Posts
Given that the values quoted are per pole, I suspect these are I2R losses, predominantly - with a small contribution to the operating op amps

At the other end of the scale, a 3200A ACB could easily be putting about 800W into a switchboard cubicle

Fuses also have quite significant I2r losses as a comparison - often more than ACB's

Regards

OMS
GeorgeCooke 11001210072
42 Posts
gkenyon:
perspicacious:
Has anyone measured the standing losses on these and other 'electronic' devices? 

I've posted several times about parasitic USB outlets built into double sockets which in a typical domestic, probably exceed your figures..................

Regards

BOD

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.

Hello Statter. Thank you for posting this, and thank you to the forum members that have replied! I had cause to tidy up my 19-way full-RCBO Wylex plastic consumer unit 18 months ago, and replaced it with a corresponding Wylex metal-cased unit.  As always, I took great care to make sure that all terminations were correctly made and secure. I subsequently noticed the metal case was always about 2 deg C above ambient and this has puzzled me until I read your post and the replies.  I never noticed the thermal gain on the old plastic consumer unit as it would not manifest itself to the same level on the plastic case. Now I know why - interesting!
Regards,
           Colin Jenkins.
statter 16416862
53 Posts
Thanks Colin, interesting that you saw a 2 degree rise.  Were these SP RCBOs or double?
This level of static dissipation with no load is ridiculous, I would expect a few mW maximum as there really is nothing which needs any power in an MCB or RCBO. A few cmos op amps need a few microamps, and the supply should be via capacitive dropper and simple zener stabilizer. This sounds like another design problem which needs to be sorted.  A few measurements of an electric nature rather than temperature are indicated.
mapj1 80733779
2070 Posts
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.)
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.
statter 16416862
53 Posts
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.
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. 
mapj1 80733779
2070 Posts
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.
John Peckham 68348
395 Posts
Wait until you get a consumer unit full of AFDDs!
Chris Pearson 11001208764
1452 Posts
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.
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.
statter 16416862
53 Posts
Yes good point.  The CU I refer to was in a very large ( 4 cubic metres) otherwise empty cupboard.  Reasonable ventilation for a cupboard.
gkenyon 82239607
1038 Posts
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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