Correct selection of RCD with regards to EICRs

[GBDamo]

The picture is a section of text from the October edition of Professionals Electrician, NAPIT Codebreakers.

I have an issue with coding 'incorrect RCD type selected'.

1, is it now expected that all permanently connected equipment is assessed and MIs consulted to determine if the correct type of RCD has been used?

2, in general purpose circuits are we now to assess what DC leakage is likely?

3, are we expected to test DC leakage with the installation at full normal usage.

The selectively of RCDs is easy to spot and is most likely to be no more than a C3.

As far as installations this is all easily covered in the design and the correct RCD type can be selected but when it comes to EICRs how does it work in practice?

 

[HappyHippyDad]

That's interesting. Using the correct type of RCD is now something that is being examined more closely than before, so it's a relevant discussion. They have clearly said it is 'potentially dangerous' which is a C2. However, they then go go to talk about scenario's which indicates it could be any code depending on what you find. Perhaps we do need to give it a little thought when carrying out an EICR.

I have just fitted a type B RCD for a tesla EVCP. A type AC RCD would not have detected any DC leakage so 'could' be deemed as potentially dangerous and therefore a C2.

Ps.. I haven't answered any of your questions, sorry

 

[GBDamo]

That's interesting. Using the correct type of RCD is now something that is being examined more closely than before, so it's a relevant discussion. They have clearly said it is 'potentially dangerous' which is a C2. However, they then go go to talk about scenario's which indicates it could be any code depending on what you find. Perhaps we do need to give it a little thought when carrying out an EICR.

I have just fitted a type B RCD for a tesla EVCP. A type AC RCD would not have detected any DC leakage so 'could' be deemed as potentially dangerous and therefore a C2.

Ps.. I haven't answered any of your questions, sorry

No, but you've illustrated my point.

If your fixed installation was inspected as part of an EICR and it had AC type RCD you could safely code it C2.

Likewise you could go and give the socket ring a visual and find a USB socket outlet on an AC type. It is not inconceivable that this device could fail in such a way as to saturate the AC type device, is this a C2? Maybe.

Then we have a look in the kitchen and they have a fancy inverted washing machine, again DC saturation is not inconceivable so is this also C2? Again, maybe.

But now we are coding the installation on what is plugged in, not the fixed wiring.

If we are coding on what IS plugged in then does it then not follow that we should code on what MAY be plugged in?

Have I jumped the shark here or are we now in the situation where type AC Devices should be coded C2 in domestic EICRs.

Thoughts please.

 

[Pretty Mouth]

Would a C3 code not be more appropriate, with a C2 if DC leakage was found to be preventing it from operating under test?

 

[Dartlec]

The picture is a section of text from the October edition of Professionals Electrician, NAPIT Codebreakers.

I have an issue with coding 'incorrect RCD type selected'.

1, is it now expected that all permanently connected equipment is assessed and MIs consulted to determine if the correct type of RCD has been used?

2, in general purpose circuits are we now to assess what DC leakage is likely?

3, are we expected to test DC leakage with the installation at full normal usage.

The selectively of RCDs is easy to spot and is most likely to be no more than a C3.

As far as installations this is all easily covered in the design and the correct RCD type can be selected but when it comes to EICRs how does it work in practice?

This sounds like rather a can of worms, especially when there are so few type A RCDs out in installations yet.

According to the ESF guide, sockets without RCD protection would usually be a Code 3 (assuming RCD not needed for fault protection and socket not likely to be used to supply outdoor equipment)

Most of the 2000s flats I've inspected have grid switches to appliances under cabinets, with flex outlet plate and no RCD protection as it wasn't needed.

So assuming a socket or flex outlet set aside for a washing machine that isn't likely to be used for outdoor equipment and has a low Zs - Code 3 if no RCD, and Code 2 if there is an type AC RCD?

If they want us to go down that road, surely they will have to start publishing tables of the 'guilty' appliances.

Not to mention the fact that EICRs are often done with the flat empty between tenants, so it's impossible to know what will be plugged in where...

 

[Dartlec]

Would a C3 code not be more appropriate, with a C2 if DC leakage was found to be preventing it from operating under test?

Trouble is that unless the tenant is doing a wash cycle while you EICR, it probably won't show up anyway?

Of course, one solution might be to ask appliance manufacturers to find a way to stop injecting DC into the supply, but presumably they would be against such madness! (I don't actually know if there is a way to stop it, to be fair)

 

[Lister1987]

I'd go C3 with an FI to examine the RCD for DC leakage with an appropriate clamp meter. If the investigation doesn't show DC leakage then C3 (with a note on how DC leakage can have a negative effect on Type AC RCDs and how the client should consider RCD type when making future purchases (EV charger, DC heavy white goods), but if it does show a sizable amount of DC leakage (potentially enough to blind the RCD and prevent proper operation) then I'd C2 then I'd look to replace the RCD for a more suited type.

 

[GBDamo]

This sounds like rather a can of worms, especially when there are so few type A RCDs out in installations yet.

According to the ESF guide, sockets without RCD protection would usually be a Code 3 (assuming RCD not needed for fault protection and socket not likely to be used to supply outdoor equipment)

Most of the 2000s flats I've inspected have grid switches to appliances under cabinets, with flex outlet plate and no RCD protection as it wasn't needed.

So assuming a socket or flex outlet set aside for a washing machine that isn't likely to be used for outdoor equipment and has a low Zs - Code 3 if no RCD, and Code 2 if there is an type AC RCD?

If they want us to go down that road, surely they will have to start publishing tables of the 'guilty' appliances.

Not to mention the fact that EICRs are often done with the flat empty between tenants, so it's impossible to know what will be plugged in where...

Another problem is manufacturers are specifying type AC RCD protection for plug in items, like washing machines.

Simply inserting a statement in the War and peace that has become the modern instruction manual is not good enough.

The consumer buys it, plugs it in and if it works that it. Many don't know what an RCD is let alone what type it is, it simply isn't consumer level knowledge.

Retailers need to be forced to point this out at point of purchase.

 

[GBDamo]

I'd go C3 with an FI to examine the RCD for DC leakage with an appropriate clamp meter. If the investigation doesn't show DC leakage then C3 (with a note on how DC leakage can have a negative effect on Type AC RCDs and how the client should consider RCD type when making future purchases (EV charger, DC heavy white goods), but if it does show a sizable amount of DC leakage (potentially enough to blind the RCD and prevent proper operation) then I'd C2 then I'd look to replace the RCD for a more suited type.

An EICR is a snapshot in time, similar to an MOT for car.

You simply cannot certify DC leakage as it is dependant on factors not within the remit of an EICR.

It can also be influenced by simple and expected actions by the uneducated.

We, as electricians, have a duty to keep abreast of these changes and take all reasonable steps to ensure our installations reflect changes in the regulations.

The general public do not, we should know to put the correct protective device in where required, and know to look to see if a special requirement is needed.

As said above, can of worms.

 

[Dartlec]

Another problem is manufacturers are specifying type AC RCD protection for plug in items, like washing machines.

Simply inserting a statement in the War and peace that has become the modern instruction manual is not good enough.

The consumer buys it, plugs it in and if it works that it. Many don't know what an RCD is let alone what type it is, it simply isn't consumer level knowledge.

Retailers need to be forced to point this out at point of purchase.

Retailers can barely get the measurements right in my experience, let alone much else.

Though did see a pump the other day that comes with a plug, but states in the manual that a Part P installer can cut it off and wire to a spur without it affecting the warranty.... I'm sure that will please all the highly qualified electricians who aren't a member of a scheme

 

[GBDamo]

I'd go C3 with an FI to examine the RCD for DC leakage with an appropriate clamp meter. If the investigation doesn't show DC leakage then C3 (with a note on how DC leakage can have a negative effect on Type AC RCDs and how the client should consider RCD type when making future purchases (EV charger, DC heavy white goods), but if it does show a sizable amount of DC leakage (potentially enough to blind the RCD and prevent proper operation) then I'd C2 then I'd look to replace the RCD for a more suited type.

Think of it as half a dozen sockets on an unused spur off a 32A ring.

You wouldn't, on inspection, say there was no overload at point of inspection, or even evidence of previous overloading, therefore C3.

You would say there is potential to overload an insufficiently protected circuit, therefore C2.

Its about what can reasonably be expected.

 

[Lister1987]

Think of it as half a dozen sockets on an unused spur off a 32A ring.

You wouldn't, on inspection, say there was no overload at point of inspection, or even evidence of previous overloading, therefore C3.

You would say there is potential to overload an insufficiently protected circuit, therefore C2.

Its about what can reasonably be expected.

As you say, an EICR is a snapshot in time and we can only code by what we can see.

If we get an idea of present DC saturation (based on what is installed) then we are in a position to C2 (if saturation is present) or C3 (if none present). We can only code what we can see. Obviously if MIs state an RCD type and they aren't being followed then you could code as a C2 citing 134.1 and 510.3 - By not following instructions them there is the potential for danger, and the C2 then forces that MIs to be followed, whereas a C3 can be 'ignored'

If we are coding on what IS plugged in then does it then not follow that we should code on what MAY be plugged in?

No, because we don't know what the client is likely to buy, all we can do is educate or future proof by changing the RCD (which may need changing as a result of the C2 for 134.1 and 510.3

 

[Pretty Mouth]

Think of it as half a dozen sockets on an unused spur off a 32A ring.

You wouldn't, on inspection, say there was no overload at point of inspection, or even evidence of previous overloading, therefore C3.

You would say there is potential to overload an insufficiently protected circuit, therefore C2.

Its about what can reasonably be expected.

Subtly different to your example IMO.

A cable unprotected from overload could be dangerous in normal use - there are no additional failures required, just equipment drawing a heavy load.

An incorrect RCD has 2 points of failure before it becomes a dangerous situation - DC leakage from faulty equipment, and an AC earth fault. Hence why I'd code C3.

 

[GBDamo]

Subtly different to your example IMO.

A cable unprotected from overload could be dangerous in normal use - there are no additional failures required, just equipment drawing a heavy load.

An incorrect RCD has 2 points of failure before it becomes a dangerous situation - DC leakage from faulty equipment, and an AC earth fault. Hence why I'd code C3.

Fair point, but some equipment produces DC leakage current during normal operation it is not necessarily a fault that caused the RCD saturation. C2 now?

I'm not saying I have the answer and will be having a word with NAPIT before my next EICR, when ever that is.

 

[GBDamo]

As you say, an EICR is a snapshot in time and we can only code by what we can see.

If we get an idea of present DC saturation (based on what is installed) then we are in a position to C2 (if saturation is present) or C3 (if none present). We can only code what we can see. Obviously if MIs state an RCD type and they aren't being followed then you could code as a C2 citing 134.1 and 510.3 - By not following instructions them there is the potential for danger, and the C2 then forces that MIs to be followed, whereas a C3 can be 'ignored'




No, because we don't know what the client is likely to buy, all we can do is educate or future proof by changing the RCD (which may need changing as a result of the C2 for 134.1 and 510.3

I don't disagree with any of that.

However 513.3.3 states "Where DC leakage current is confirmed to be present or may be produced by equipment....."

Now, on fixed equipment, we have a known unknown a case of finding out if DC current leakage is likely under normal operation or a likely fault product.

With socket circuits we have an unknown unknown. That is, we know there is potential for appliances to be used but we don't know what they are and how they could affect DC current levels.

Also many appliances work in cycles so you could have the situation where it is only when appliances are at the correct point in their cycle that they leak DC current. How do you measure this? How do you account for the cumulative effects of various appliances?

To me this doesn't pass the reasonableness test, which is, could it reasonably be expected that a normal person ,acting normally, is highly unlikely to introduce a saturating DC current to a circuit?

When any person can go out and buy an appliance with a plug on it that can satuate an AC type RCD then the answer has to be, no.

 

[Dartlec]

If as it seems, Type A RCDs will become the standard in the next BS7671 which won't be fully in force till 2023, then that would seem the time to introduce this level of consideration for RCD types.

If we can still get a satisfactory EICR on properties without RCD protection at all, then I don't see how we can give an unsatisfactory to one that does - unless there is a clear case like a car charger, PV, etc. where a Type A is mandated.

I'm also a little wary of manufacturers of 'end user' white goods specifying things when it is often to avoid them having to make improvements to their products. As far as the end user is concerned, if it comes with a 1363 Plug, then it fits into a 1363 socket - and is either rated at 3A or 13A.

What would happen if a washing machine manufacturer makes a deal with Wylex and states that only a specific Wylex model RCD must be fitted?

Have there been any real world incidents of injuries caused by this situation as yet? It's hard to grasp how much of a practical risk it is, even though the theoretical risk is clear enough. If there is actually a significant risk out there now, then more should be done than expecting EICRs to always pick up the issue.

 

[GBDamo]

If as it seems, Type A RCDs will become the standard in the next BS7671 which won't be fully in force till 2023, then that would seem the time to introduce this level of consideration for RCD types.

If we can still get a satisfactory EICR on properties without RCD protection at all, then I don't see how we can give an unsatisfactory to one that does - unless there is a clear case like a car charger, PV, etc. where a Type A is mandated.

I'm also a little wary of manufacturers of 'end user' white goods specifying things when it is often to avoid them having to make improvements to their products. As far as the end user is concerned, if it comes with a 1363 Plug, then it fits into a 1363 socket - and is either rated at 3A or 13A.

What would happen if a washing machine manufacturer makes a deal with Wylex and states that only a specific Wylex model RCD must be fitted?

Have there been any real world incidents of injuries caused by this situation as yet? It's hard to grasp how much of a practical risk it is, even though the theoretical risk is clear enough. If there is actually a significant risk out there now, then more should be done than expecting EICRs to always pick up the issue.

It seems to be the latest fad to have an inverted motor on washing machines, certainly the high end ones, with EV chargers, home batteries and PV.

It certainly looks like we are heading this way.

 

[Dartlec]

It seems to be the latest fad to have an inverted motor on washing machines, certainly the high end ones, with EV chargers, home batteries and PV.

It certainly looks like we are heading this way.

Sure - and Type A don't have any disadvantages that I know of, so makes sense to make the change.

But with EV chargers, home batteries and PV there is usually (hopefully) a competent installer who will be certifying that work and can either upgrade the whole installation, or install new consumer unit for that bit with the correct RCD.

Washing machines are the tricky one, since they are almost never supplied or fitted by an electrician, but sold to the customer directly who will just plug it in.

I wonder if the "installation services" that Currys, AO etc offer, check whether the installation is correct for the appliance and notify the customer if there are issues. (hint: I doubt it).

I had to attend a flat earlier in the year where the people "installing" the washing machine wouldn't do so because there was a flex outlet plate under the worktop, not a socket.

 

[Pretty Mouth]

Fair point, but some equipment produces DC leakage current during normal operation it is not necessarily a fault that caused the RCD saturation. C2 now?

I'm not saying I have the answer and will be having a word with NAPIT before my next EICR, when ever that is.

I didn't know that. Yeah, could be a C2 then. What sorts of equipment does produce DC leakage in normal operation?

 

[Pretty Mouth]

What sorts of equipment does produce DC leakage in normal operation?

terrible misuse of the English language

 

[pc1966]

I don't think there is any equipment in normal use that has "DC leakage" as such. That would imply a semiconductor between L & E which is not going to pass the likes of class-Y safety for a capacitor under impulse over-voltage, etc.

As mentioned above, this is only going to show under double-fault conditions, such as an open CPC on a washing machine with a DC drive and a motor insulation fault to earth.

EV chargers are a bit of an exception, as they have a big DC power source and are often in wet areas with the true Earth present.

PV install possibly as well, though the inverters tend to monitor the panel's insulation resistance and shut down otherwise. Also PV setups should be properly earthed by the fixed wiring, where as cars depend on plug/socket/flexible cables.

 

[Dartlec]

I don't think there is any equipment in normal use that has "DC leakage" as such. That would imply a semiconductor between L & E which is not going to pass the likes of class-Y safety for a capacitor under impulse over-voltage, etc.

As mentioned above, this is only going to show under double-fault conditions, such as an open CPC on a washing machine with a DC drive and a motor insulation fault to earth.

EV chargers are a bit of an exception, as they have a big DC power source and are often in wet areas with the true Earth present.

PV install possibly as well, though the inverters tend to monitor the panel's insulation resistance and shut down otherwise. Also PV setups should be properly earthed by the fixed wiring, where as cars depend on plug/socket/flexible cables.

The electrical design is slightly above my pay grade, but is there a way that washing machine manufacturers could protect their devices from such a fault happening? That would seem to be a better solution given the number of Type AC RCDs that are going to be around for 20 years still.

 

[pc1966]

The CPC is really the protection as such, it would either trip a DC-sensitive RCD, or more likely just take out the OCPD (supply MCB, or plug's fuse in the UK).

It is possible to reduce the risk by having the DC isolated, but that pushes up the cost. Some older members might remember the "live chassis" TVs and radios of years gone by then the metalwork was connected to neutral and the supply half-wave rectified for the HT feed (or not, for series connected value heaters). Thankfully those days are more or less gone, and the resulting need for work areas to have isolated supplies, etc, for safer testing.

But the move to DC operated motors is almost certainly going to be cheaper (and slightly more power-efficient) by rectifying the mains and then chopping the resulting DC directly to feed the motor. In those cases a motor insulation fault will cause a DC component, but very pulsed as 100Hz (most likely), hence the "type A" as being OK.

Things like USB power points theoretically have the same risk, but for a small high-frequency transformer it is cheap to achieve quite high isolation voltages. And they don't work with water normally!

True DC systems like PV panels or EV batteries don't have any ripple, so they can't be detected by a transformer arrangement and that really pushed up the cost for a "type B" RCD detection system.

 

[Dartlec]

The CPC is really the protection as such, it would either trip a DC-sensitive RCD, or more likely just take out the OCPD (supply MCB, or plug's fuse in the UK).

It is possible to reduce the risk by having the DC isolated, but that pushes up the cost. Some older members might remember the "live chassis" TVs and radios of years gone by then the metalwork was connected to neutral and the supply half-wave rectified for the HT feed (or not, for series connected value heaters). Thankfully those days are more or less gone, and the resulting need for work areas to have isolated supplies, etc, for safer testing.

But the move to DC operated motors is almost certainly going to be cheaper (and slightly more power-efficient) by rectifying the mains and then chopping the resulting DC directly to feed the motor. In those cases a motor insulation fault will cause a DC component, but very pulsed as 100Hz (most likely), hence the "type A" as being OK.

Things like USB power points theoretically have the same risk, but for a small high-frequency transformer it is cheap to achieve quite high isolation voltages. And they don't work with water normally!

True DC systems like PV panels or EV batteries don't have any ripple, so they can't be detected by a transformer arrangement and that really pushed up the cost for a "type B" RCD detection system.

Do Type A inherently cost more to make? or is it just an economy of scale thing?

Given that a lot of Consumer Units in new builds etc are not likely to be changed for many years, it would make sense for them to have some marketing pushing replacement Type A RCDs for their existing units - but most manufacturers seem to be very bad at supporting retrofit on anything other than their very current range.

 

[pc1966]

Do Type A inherently cost more to make? or is it just an economy of scale thing?

I can't see them costing more than a few percent.

The issue is with the current balance (differential) transformer saturation on high DC-component currents, that can be largely mitigated by choosing a larger core and/or lower permeability material. You do need a more sensitive detector then, but that is a design cost and not something recurring as high part cost.

So I think it is down to scale and/or off-loading old stock or old designs for UK market. I suspect type AC will dissepear in a couple of years as Type A becomes the norm everywhere (even if only 80% of the markets regulate for it).

 

[Dartlec]

I can't see them costing more than a few percent.

The issue is with the current balance (differential) transformer saturation on high DC-component currents, that can be largely mitigated by choosing a larger core and/or lower permeability material. You do need a more sensitive detector then, but that is a design cost and not something recurring as high part cost.

So I think it is down to scale and/or off-loading old stock or old designs for UK market. I suspect type AC will dissepear in a couple of years as Type A becomes the norm everywhere (even if only 80% of the markets regulate for it).

If there is no case in which an AC would be chosen in preference over an A, then it would make sense for everyone to switch over and AC to stop existing.

Since they've been the standard in Germany for a while I believe you'd think that someone like Schneider might have an advantage - but then perhaps they are using us to clear out their old stock - pretty sure their Screwfix dual RCD boards are still type AC.

But how much DC could a washing machine leak? Type A covers up to 6ma so what if you have 3 washing machines in a large house - when do you need to start splitting them.

Perhaps we should just ban washing machines and go back to tubs and mangles...

 

[pc1966]

I don't know for sure why they make both type AC and type A RCDs, as Hager do the same. Sadly the market will, in the majority of cases, go for the cheapest option even if it is only a couple of percent so I suspect that is the underlying reason. But if the IET regs move to marginalise type AC it might just kill them off.

The thing about the "DC leakage" is it not likely to be cumulative like AC is. With most appliances having some form of noise filter they (along with the cables) always have some AC imbalance, even if only a fraction of a mA.

However, I seriously doubt that any normal bit of machinery will have a DC leak as part of "normal" operations, and if they have an insulation fault then is most cases the CPC diverts it and quickly it descends in to an over-current situation taking out the OCPD anyway.

So really it is a loss of CPC integrity and a DC fault combined that might lead to a person becoming the path for the AC+DC leak and that is when you rely on the additional RCD protection for safety. So for anyone worries I would be a bit less concerned about the type A/AC debate and more strict on verifying the socket used has a good CPC connection and the appliance is properly earthed (as PAT testing ought to verify).

Here the ring final has the advantage of double paths for CPC, but not all kitchens use rings. Also you might just have the CPC fault at the outlet socket used. Socket testers are not good in this respect, they will show an open CPC but only a few of the more expensive types show a high Z one. Also few private households will do PAT testing, though it is something that most electricians could offer.

I guess TT installs might have a bit higher risk as the rod's Ra may not be able to take out the OCPD, but again with proper bonding of utility pipes it is unlikely that a high CPC potential to true Earth would present much of a risk within the house.

 

[richy3333]

All of this has been discussed at length by e5 if anyone wants to look it up. Hager stated in their instagram cast this week that all their split load boards have type A rcds fitted. We’ve been fitting type A RCBO’s for quite a while now. The cost difference to us on Hager or Fusebox is only a couple of pounds per device.

 

[Dartlec]

All of this has been discussed at length by e5 if anyone wants to look it up. Hager stated in their instagram cast this week that all their split load boards have type A rcds fitted. We’ve been fitting type A RCBO’s for quite a while now. The cost difference to us on Hager or Fusebox is only a couple of pounds per device.

Yep, I watch all the E5 stuff and it's very informative. Their EICR coding ones were some of the best 'training' I've seen on the subject.

However, if the issue is as significant as they suggest, it seems more sensible to put pressure on the manufacturers who sell to screwfix etc, to stop pushing out their cheap boards with Type AC in, rather than to expect inspectors to start coding things that the landlord/tenant/homeowner won't understand.

One thing that they (E5) do seem to have been pushing recently is that adding RCDs is not (or should not be) a solution to poor practises elsewhere - within the fixed wiring and within appliances.

A self-testing RCD that doesn't require reliance on the end user to press 6 monthly (or monthly as some manufacturers seem to recommend) would probably add more to safety. I've personally run into a couple of RCDs just in the last month that weren't tripping on test button until 'unstuck' by flicking on and off several times.

 

[GBDamo]

All of this has been discussed at length by e5 if anyone wants to look it up. Hager stated in their instagram cast this week that all their split load boards have type A rcds fitted. We’ve been fitting type A RCBO’s for quite a while now. The cost difference to us on Hager or Fusebox is only a couple of pounds per device.

I was led down this rabbit hole by Sparkyninja but have since watched the E5 stuff, all very informative.

And

 

[richy3333]

@Dartlec we never buy CU’s or DB‘s from the likes of Screwfix. They have very poor choice and sell to a price. The whole point about screwedfix and tooledupstation is selling at a price point first and specification second.

 

[Dartlec]

@Dartlec we never buy CU’s or DB‘s from the likes of Screwfix. They have very poor choice and sell to a price. The whole point about screwedfix and tooledupstation is selling at a price point first and specification second.

Of course - though it's that much harder to explain to some customers why you are quoting more when they can say - well Screwfix sell it so it must be safe...

 

[Lister1987]

I was led down this rabbit hole by Sparkyninja but have since watched the E5 stuff, all very informative.

And

This is why in my recent posts I'm going on about checking for DC leakage just as a part of what you do, whether it's a complete fullscope analyse of every item on every circuit or just part of fault finding

 

[newfutile]

If the inverter has no isolating transformer or other form of simple separation I assume the worst and code a C2 as such ;”Solar power on type AC RCD reg: 712.411.3.2.1.2”