All RCBOs?

[He who knows]

Does the team think that as Type B and Type F RCBOs can't be had, that we might see a "return" to RCCB+MCBs?

Yes, I know we never "left" that, hence the quotes, but all-RCBO has been the "gold standard" for a while. Now though?

 

[ericmark]

Unless the regulations change, most users want an interrupted supply, and the multi-MCB's on a single RCD simply tripped too often for no good reason, so once all RCBO has been installed there is little chance of returning to one RCD for many circuits.

 

[RF Lighting]

Should the regulations or necessity require the more widespread use of these devices then I’m sure the manufacturers will devise a product to capitalise on the demand.

 

[JohnW2]

Does the team think that as Type B and Type F RCBOs can't be had, that we might see a "return" to RCCB+MCBs?

If the demand proves to be great enough, I'm sure manufacturers will move us to a situation in which Type B and Type F RCBOs can "be had".

Whether or not there ever 'should' be a large demand (for something which would probably be pretty expensive) is, however (in my opinion!) not quite so certain!

Kind Regards, John

 

[JohnW2]

Unless the regulations change, most users want an interrupted supply, and the multi-MCB's on a single RCD simply tripped too often for no good reason ...

It seems that they did for some users. However, as I've often said, for well over 20 years I have lived with many (probably about a dozen) multi-MCB RCDs and, during that period, have experienced almost no 'trips for no good reason'.

From what you've often said, it sounds as if you have been particularly unlucky in experiencing many of these 'trips for no good reason', so I would be interested to know how many others have had similar experiences.

Kind Regards, John

 

[ericmark]

It seems that they did for some users. However, as I've often said, for well over 20 years I have lived with many (probably about a dozen) multi-MCB RCDs and, during that period, have experienced almost no 'trips for no good reason'.

From what you've often said, it sounds as if you have been particularly unlucky in experiencing many of these 'trips for no good reason', so I would be interested to know how many others have had similar experiences.

Kind Regards, John

I think you have to remember I fitted all RCD protection back in early 90's when they were quite new, so maybe my RCD's are not to modern standards and more like to trip with a spike, and fact resetting one RCD could cause the other one to trip if I did not turn off the MCB's first also points to a spike causing the trips.

I have been lucky in a way that in 30 years of use, only lost around 4 freezer full of food, 9 times out of 10 we have been able to reset in time, or at least think we reset them in time.

Today my freezers if they lose power show the temperature reached before power was restored, so without opening doors to check, I know if de-frosted, except for the chest freezer, and to be frank a chest freezer can be without power for nearly 24 hours and OK, in the main because they are not frost free. The problem with the frost free upright freezer is the time it can be without power depends where it is in regards of the de-frost cycle. It may last 10 hours if just before de-frost cycle is about to start, but if just when de-frost cycle is about to conclude then lucky if it lasts an hour.

Now when you find the RCD has tripped you clearly reset it and don't open the freezer door as want the heat kept out until it has had a chance to cool, so there is a danger food has defrosted but you have not noticed, once power is lost the circulating fans in the freezer stop, so food at top can defrost but food at bottom still OK, so there is a very real chance that an inspection will miss the fact food at top has defrosted.

I used an old fridge/freezer to brew beer in, and was surprised how long it took in freezer compartment to cool beer at 24°C to 19°C talking about a couple of hours or more. Yes it was 40 pints so a big lump, but when you lose power with a full freezer and it does warm up, it also takes a long time to freeze again, and there is a very real danger of damage to the food.

In the early days of RCD protection it was permitted to have selected designated sockets without RCD protection for things like freezers, but that has been removed.

When I fitted my RCD's in the 90's they were new, and we had not really worked out what should be done before fitting them, I did use an insulation tester but these use DC, today we know we should measure the leakage, as with AC there is always some leakage, and in use a 30 mA RCD should not with no fault supply circuits with over 9 mA of leakage, this is with every thing turned on. I will hold up my hands and admit I have never done this, simple reason my clamp on ammeter will only go down to 100 mA, so I have never been able to measure leakage of whole circuit, the PAT tester measured it for individual items, but not as a group.

I know from the PAT tester some filters have resulted in a high leakage even with new items, which will not show up with insulation testing as that uses DC, so the leakage is often luck, and we have all in the early days of PC's had problems where multi PC's were used in one room. I can not recall a single 100 mA RCD tripping without good reason, even when whole house on one RCD, so it would seem even if 3 x 30 mA RCD's supplied whole house so total of 90 mA it is unlikely they will trip without reason, so 30 mA must be just on the edge, do remember 30 mA is between 15 mA and 30 mA with most RCD's I know the X-Pole RCD claimed tripped between 90% and 100% but the standard is between 50% and 100%.

My RCD tester was ½, full, and x5 there was no ramp test, so I don't know if my RCD's were tripping at 16 mA or 30 mA I had no way to test. I do know where a RCD was tripping and could not find any fault with either RCD or installation swapping it cured the problem, hind sight was likely tripping at 18 mA and new one at 26 mA and had I had a clamp on meter able to measure 1 mA then I would have seen the problem, or a RCD tester with a ramp option.

Clearly part of the problem with just twin RCD's is down to testing, and this has been highlighted with the discussions on type AC, A, F, and B RCD's, we have been always told to test with no load, we test the RCD not the circuit as a whole, and clearly with some equipment we don't want to turn off the supply without logging off. And it is the equipment which requires logging off from which is likely to cause problems, either with unwanted tripping or failure to trip.

So we have always said don't put all your eggs in one basket, be it equipment/s which stops a RCD tripping or causes it to trip when it should not, if the CU is like mine with 16 RCBO's the risk of not tripping with fault, or tripping without a fault is reduced. So if my TV is drawing a DC component stopping the RCD tripping, then the other circuits are still RCD protected.

So I have one circuit which I have found feeds just one FCU, I would assume originally supply to shed, if I use that to charge an electric car, it may be a 16A type AC RCD but there would be a RCD built into the charging pod, so there would be around 2 meters of twin and earth which if damaged when a faulty car was on charge may not trip the RCD, the risk of that happening must be very very low. But if one RCD feeds multi outlets then not 2 meters of unprotected cable as a result of fault on car, but 100's of meters, so with RCBO's the risk of DC stopping them tripping is very low, but with just 2 RCD's the risk is much higher.

But in real terms until we are required to test RCD's with a DC component, and test for a DC component on the supply, it is all guess work, yes we have all seen the demo videos, but in real life how often does the RCD protection require the 40 mS or the 30 mA for genuine wanted tipping two main causes are human error, not checking for cables, and water, and with the latter a 100 mA type S would trip and protect one, the speed is not really required, and with the former even 40 mS gives one a nasty belt, it makes no never mind if 30 mA or 300 mA it still takes around 20 mS to trip, and you get full current during that time.

 

[He who knows]

Should the regulations or necessity require the more widespread use of these devices then I’m sure the manufacturers will devise a product to capitalise on the demand.

Both requirements (the first following on as a consequence of the second) are upon us.

The problem is that it's a "creeping" requirement - people are gradually installing more and more equipment which makes even Type As unsuitable, but may be blissfully unaware that their RCD is no longer providing the protection it should. EV charger circuits are easy to split off from the main CU, but as people start filling their homes with LED lights and dimmers, white goods with variable speed drives they start making Type Fs, at least, a necessity, and therefore a regulatory requirement.

Maybe we'll see hybrid CU designs - kitchen/utility room circuits on MCBs behind a Type F RCCB and the rest of the house on Type A RCBOs, and the emergence of small "EV consumer units", a la "shower CU" or "garage CU" with a single MCB and a Type B?

A nice overview: https://electrical.theiet.org/wiring-matters/years/2019/77-september-2019/which-rcd-type/

 

[He who knows]

If the demand proves to be great enough, I'm sure manufacturers will move us to a situation in which Type B and Type F RCBOs can "be had".

Whether or not there ever 'should' be a large demand (for something which would probably be pretty expensive) is, however (in my opinion!) not quite so certain!

Kind Regards, John

See above for demand.

Maybe someone should organise a sweepstake for the date of the first complaint from a landlord who has got a nice refurbished property with all new appliances, an EV charging point, and an all RCBO CU who has picked up a C2 for not having Type B or F RCD....

But as you say, they aint cheap. Not done much looking for Type B RCCBs, partly because with no plans for an EV charger or a PV installation or an escalator (although that would be fun) they aren't of much interest, and partly because so many search results pick up Type B MCBs or RCBOs (a curse on the houses of all those who decided to make "Type B" mean two different things within a context of related items). But a Schneider single-phase 40A Type B RCCB is £260 from Rapid.

Size is also a problem - will they ever be able to get Type F or B RCBOs down to 18mm?

 

[JohnD]

Does the team think that as Type B and Type F RCBOs can't be had, that we might see a "return" to RCCB+MCBs?

Yes, I know we never "left" that, hence the quotes, but all-RCBO has been the "gold standard" for a while. Now though?

i'm not in touch with these things, but I have type "A" RCBOs.

What's the difference?

 

[JohnW2]

i'm not in touch with these things, but I have type "A" RCBOs. What's the difference?

BS7671 currently says (the red highlighting is mine, despite the views of some here) ..

(i) RCD Type AC: RCD tripping on alternating sinusoidal residual current, suddenly applied or smoothly increasing

(ii) RCD Type A: RCD tripping on alternating sinusoidal residual current and on residual pulsating direct current, suddenly applied or smoothly increasing.
NOTE 1: For RCD Type A, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 6 mA.

(iii) RCD Type F: RCD for which tripping is achieved as for Type A and in addition:
(a) for composite residual currents, whether suddenly applied or slowly rising, intended for circuit supplied between line and neutral or line and earthed middle conductor
(b) for residual pulsating direct currents superimposed on smooth direct current.
NOTE 2: For RCD Type F, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 10 mA.

(iv) RCD Type B: RCD for which tripping is achieved as for Type F and in addition:
(a) for residual sinusoidal alternating currents up to 1 kHz
(b) for residual alternating currents superimposed on a smooth direct current
(c) for residual pulsating direct currents superimposed on a smooth direct current
(d) for residual pulsating rectified direct current which results from two or more phases
(e) for residual smooth direct currents, whether suddenly applied or slowly increased, independent of
polarity.
NOTE 3: For RCD Type B, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current
up to 0.4 times the rated residual current (IΔn) or 10 mA, whichever is the highest value. For general purposes, Type AC RCDs may be used.
NOTE 4: For guidance on the correct use of RCDs for household and similar use, see PD IEC/TR 62350.
NOTE 5: Some typical fault currents in circuits comprising semiconductors are given in Annex A53, Figure A53.1.

Kind Regards, John

 

[JohnW2]

The problem is that it's a "creeping" requirement - people are gradually installing more and more equipment which makes even Type As unsuitable, but may be blissfully unaware that their RCD is no longer providing the protection it should. EV charger circuits are easy to split off from the main CU, but as people start filling their homes with LED lights and dimmers, white goods with variable speed drives they start making Type Fs, at least, a necessity, and therefore a regulatory requirement.

Maybe. However, as those here know, I have been trying for months to find some 'chapter and verse' which helps me to get at least a vague idea as to how 'real' the hypothesised issues (giving rise to the the 'requirement' for different types of RCD) actually are in practice, so I currently don't know how I convinced I am about any of this.

... and it's part of a bigger picture. You presumably won't have seen, but I am one of those who has been known to quite often question the 'need' for RCDs (benefit of having) RCDs of any type!

I can't deny that the increasing regulatory requirement will march on relentlessly, regardless of any thoughts I may have, but I don't think one should necessarily assume that, in terms of 'big pictures', the 'advances' are necessarily all that 'sensible'.

Kind Regards, John

 

[JohnW2]

Maybe someone should organise a sweepstake for the date of the first complaint from a landlord who has got a nice refurbished property with all new appliances, an EV charging point, and an all RCBO CU who has picked up a C2 for not having Type B or F RCD....

It will undoubtedly happen!

... (a curse on the houses of all those who decided to make "Type B" mean two different things within a context of related items).

Quite so. Crazy!

Size is also a problem - will they ever be able to get Type F or B RCBOs down to 18mm?

Who knows - I never cease to be amazed by the degree of 'miniaturisation' that has been achieved, in so many areas, over the years/decades! I've never looked inside anything other than a Type AC RCD, but I suspect that some of the 'more clever' types may well effectively have to have multiple 'devices' within the same item, all operating the same trip mechanism?

Kind Regards, John

 

[ericmark]

Maybe someone should organise a sweepstake for the date of the first complaint from a landlord who has got a nice refurbished property with all new appliances, an EV charging point, and an all RCBO CU who has picked up a C2 for not having Type B or F RCD....

I would agree, however more to the point is how to measure the 6 mA or 10 mA DC component.
I have seen just two items which state what what type of RCD should be fitted, EV charging points, which often have a detection device to auto disconnect if the DC exceeds 6 mA so can be used with type A, and Worcester Bosch boiler installation instructions which also stipulated type A.

I know some early EV charging points asked for type B, but in the main it seems the 6 mA detection units have got around the problem, and that could be used with other equipment, so the jury is still out as to if you will every need better than type A.

But not all boilers say needs type A, and as an inspector how would you know if any appliance needs type A or not, and with a TN supply does it really matter?

This is an old diagram for a three port valve

that clearly will result in DC even if very small, they have been used well before we got LED lights and inverter drives, so we have always had some DC, it all started in the home with the front loading video recorder, the heat from the pre switch mode power supply was too high for units to be put under the TV, so well before the desk top computer came in we had the switch mode power supply, not sure of date, but likely still using the ELCB-v when they first arrived, well before the regulations told us to use 30 mA RCD's.

It is being talked about as if something new, and on a demo utube video it talks about electric trains and DC, trains and trams have used DC for years, it is not some thing new, in early 1990's when I fitted RCD's to my home we already had a DC component, so what has changed is how many, so what we need is a way to measure, so reading this we have the ability to measure and auto switch off the supply when it exceeds 6 mA, so maybe we can include this into the RCBO rather than making it type F or B?

So there is simply nothing we can do, as we are not designing and making RCD's, back in the 90's when I fitted RCD's there were no high integrity duel RCD consumer units, or single width RCBO's so who knows what the 30's will bring.

 

[JohnW2]

I think you have to remember I fitted all RCD protection back in early 90's when they were quite new, so maybe my RCD's are not to modern standards and more like to trip with a spike ...

That, ion itself, cannot explain our different experiences, since my period of 'living with RCDs' goes back a bit further than yours (to 1987). In fact, for the first several years (from 1987), I effectively 'lived with' just a single RCD protecting an entire installation (well, one pwe phase, but one of my phases is roughly comparable with a 'standard domestic installation').

Despite that, as I've said, I have experienced incredibly few 'nuisance trips' (trips 'for no good reason'). Other than in the name of testing, virtually all of the trips I have experienced have been due either to my lack of care in allowing neutral conductors to touch 'earth' or, in one sense or another, due to ingress of water/moisture into something. In fact, I'm not convinced that I have ever experienced an RCD trip for which there was not 'a reson', although there may have been the occasional one.

I have been lucky in a way that in 30 years of use, only lost around 4 freezer full of food, 9 times out of 10 we have been able to reset in time, or at least think we reset them in time.

We have never lost freezer contents, not the least because (a) we don't have any freezers on anything remotely like a 'dedicated' circuit and (b) for very many years all our freezers have had 'over temperature' alarms - which, between them, mean that malfunction of a freezer will never go 'unnoticed' whilst the house is occupied. Such precautions obviously don't help when the house is unoccupied for significant periods of time, but (at least for us) that is the situation for such a tiny proportion of time as to represent an extremely small risk. For what it's worth, on the very few occasions on which the freezer alarms have been activated, it has been due to freezer malfunction, rather than loss of power.

However, given that, statistically speaking things are much more likely to happen (protective devices being tripped) when the house is occupied, I would say that this is a good reason NOT to have freezers on dedicated RCBOs (or even 'dedicated' MCBS) - since the more circuits are protected by the same devices as the freezer, the sooner will the occupants become aware of the fact that the freezer has lost power.

I suppose that if one wanted to be particularly clever/cautious, one could arrange things so that one could 'switch' the freezer over to a dedicated RCBO if/when the house was going to be unoccupied for a significant period - since such is probably the 'safest' when the house is unoccupied.

... we know we should measure the leakage, as with AC there is always some leakage, and in use a 30 mA RCD should not with no fault supply circuits with over 9 mA of leakage, this is with every thing turned on. I will hold up my hands and admit I have never done this, simple reason my clamp on ammeter will only go down to 100 mA, so I have never been able to measure leakage of whole circuit ...

You may 'hold your hands up', but I think you are in the good company of virtually everyone in not even thinking of measuring leakage currents - and, returning to my own experiences, I am far from convinced that (despite the 'theory'), in practice, RCD trips due to accumulated leakage from multiple loads 'in normal operation' is even remotely 'common'. I'm certainly not aware of ever having experienced it,.

.... and we have all in the early days of PC's had problems where multi PC's were used in one room.

You can count me out of that "all" . Over the years (well into the distant past), I have often had half a dozen PCs, plus all associated equipment, operating on a circuit protected by the same 30mA RCD, without ever having 'had problems'.

So we have always said don't put all your eggs in one basket, be it equipment/s which stops a RCD tripping or causes it to trip when it should not, if the CU is like mine with 16 RCBO's the risk of not tripping with fault, or tripping without a fault is reduced.

That is true in relation to devices tripping 'for good reason' (excessive leakage 'in normal operation') or devices not tripping 'for good reason' (e.g. DC components from something else). However, you keep talking about trips "for no good reason", and if that is just some 'random happening', then it's probably the case that the more devices you have, the more likely you are to experience 'trips for no good reason'.

Kind Regards, John

 

[JohnW2]

.... two items which state what what type of RCD should be fitted, EV charging points, which often have a detection device to auto disconnect if the DC exceeds 6 mA so can be used with type A, and Worcester Bosch boiler installation instructions which also stipulated type A. ...... I know some early EV charging points asked for type B, but in the main it seems the 6 mA detection units have got around the problem, and that could be used with other equipment, so the jury is still out as to if you will every need better than type A. .... so what we need is a way to measure, so reading this we have the ability to measure and auto switch off the supply when it exceeds 6 mA, so maybe we can include this into the RCBO rather than making it type F or B?

I'm getting increasing confused by all this. What you say above, and what Amd1 of BS7671:2018 says (as below) all seem to be talking about DC residual currents ('due to a fault) ...

Faults resulting in DC residual currents (L-N imbalances, due to DC current leakage to earth) are obviously one potential issue. However, I thought (perhaps wrongly) that the main/major issue was that a DC component of current flowing during 'normal operation' (equally in L and N, hence no imbalance/residual current) could (perhaps by 'magnetic saturation' or a similar mechanism) impair the ability of the device to operate as it should in the event of a residual (L-N imbalance) AC current due to leakage to earth.

Is that not the case? Can someone help me understand?

Kind Regards, John