Discuss Are you replacing type AC RCD's with Type A? in the Electrical Forum area at ElectriciansForums.net

HappyHippyDad

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Just looking for a bit of clarification regarding RCD's.

A type AC RCD is no longer acceptable for offering additional protection for socket outlets. If you are (for example) adding one socket to an existing circuit are you all updating the RCD to a type A? I can see this being a bit tricky sometimes. It's ok if its a brand of consumer unit that does type A RCD's but this will not always be the case.

Do the regulations mean that if you are extending an existing socket circuit you cannot use an existing type AC RCD?
 
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I think it would depend on the circuit or circuits & what equipment the RCD is protecting. I guess changing it will cover further additions or changes of equipment that would need DC protection.
 
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Julie.

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Technically yes, it should be replaced, it's no different from before, if you needed to add an additional outlet or circuit, and the existing protection wasn't up to spec you would change the existing, or add something such as a rcd where there wasn't one previously.

It isn't something I quite agree with as there are always circumstances where this ups the price beyond what the customer is willing to pay.

For example, grandson finds granny fallen due to tripping over an extension lead (for the Xmas tree), so suggests adding a socket near the corner where the tree goes, - but, it needs rcd, none available for the existing cu etc - basically a single socket results in a new cu etc.

The end result is that nothing gets done to improve the situation, and granny goes back to using and tripping over extension leads!

I do sometimes think the distance we have to go in order to be compliant is a bit too far at times, I would much rather a half way there improvement to none at all - although of course we have to make sure this isn't abused
 
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HappyHippyDad

HappyHippyDad

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You could always list it as a departure on the certificate. Not great but I think for a small job, the addition of a socket etc its okay, as long as you have offered the RCD change
I used to think the departures box was for this sort of use (ie get out of jail free). However, thanks to one @davesparks posts I realise this is not it's intended use.

The departures box is simply if you have done something that departs from BS7671, but (and this is the crucial bit) "The resulting degree of safety of the installation shall not be less than that obtained by compliance with the regulations" (120.3)

It would be less safe by using a type AC than a type A, so this isn't suitable for the departures box.
 

Mike Johnson

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Same with all BS, if you depart from the content of the BS it must be to go "above and beyond" the requirements in that standard, this is quite clear from the HSE and has been tested in Court on a number of occasions.
 
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I used to think the departures box was for this sort of use (ie get out of jail free). However, thanks to one @davesparks posts I realise this is not it's intended use.

The departures box is simply if you have done something that departs from BS7671, but (and this is the crucial bit) "The resulting degree of safety of the installation shall not be less than that obtained by compliance with the regulations" (120.3)

It would be less safe by using a type AC than a type A, so this isn't suitable for the departures box.
Yes, I agree.
I was just thinking what could/would i do. This is going to be something we will all have to deal with over the next few years
 

Vortigern

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I absolutely replace with A type RCBO. In fact you can't really get any other now. But aside from regs, if something can produce a safer installation then of course use it. I am a bit concerned that places like screwfix, b&q are selling dual rcd cu at pretty cheap prices. Recently I was asked to do a cu installation and the guy had bought two dual rcd which were the old AC type and I said he would have to take them back and get a refund as they don't meet regs now. I wonder how many have a go DIY are fitting these. And should such stores even be selling them. It does seem rather irresponsible of them to do so.
 

Pretty Mouth

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I think I may use a degree of common sense.

If I am able to change the existing type AC to a type A (fairly easily) I will factor this into the quote.

If it means a board change I may choose to give them that as an option rather than make it mandatory.
I'll be taking the same approach. It makes sense to install type A on new installations etc, but I don't feel that existing circuits protected by type AC are going to be a great deal safer by installing type A.
 

Pretty Mouth

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I absolutely replace with A type RCBO. In fact you can't really get any other now. But aside from regs, if something can produce a safer installation then of course use it. I am a bit concerned that places like screwfix, b&q are selling dual rcd cu at pretty cheap prices. Recently I was asked to do a cu installation and the guy had bought two dual rcd which were the old AC type and I said he would have to take them back and get a refund as they don't meet regs now. I wonder how many have a go DIY are fitting these. And should such stores even be selling them. It does seem rather irresponsible of them to do so.
I think amendment 1 will be withdrawn on 28th September, so AC still valid for the time being
 

happysteve

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NAPIT did a FAQ video, accessible from their installer portal (where you do the notifications) addressing this scenario, and their view is that if you're doing additions and alterations to a circuit, and where the new Regs would require a Type A RCD (i.e. unless it's a fixed load that could not leak DC under fault conditions) then a Type A RCD is required, i.e. if there is an existing Type AC RCD then this is not sufficient, and you need to do something about it.

A lot of my work involves minor works - additions and alterations to existing circuits.

A lot of the consumer units I come across were manufactuered by the likes of GET, Vytec, Steeple, GE, F&G, Contactum (the old ones with the brown MCB levers), MEM, CED, Legrand, "Plug-in-Systems", Tenby; or old Wylex/Crabtree boards with BS4293 RCDs and BS3871 MCBs. Chances of getting an RCBO or even a Type A RCCB to fit in those boards is pretty much nil (with the possible exception of the MEM RCBO pods). With a few notable exeptions, getting information from manufacturers about whether they approve the fitting of current (Type A RCBO/RCD) devices into older boards is like pulling teeth. Sometimes they're happy to talk to you on the phone, but they're rarely - if ever - willing to put anything in writing, and writen enquiries are ignored.

So if a new board is not wanted/economically unfeasible, then it's either a Type A RCD spur if it's lights, or I guess an external metal enclosure with a Type A RCCB if it's sockets (like doing minor works on a circuit off an old BS3036 fuse board).

It's a lot harder to explain to clients why it's necessary, too. When RCDs in general were introduced, and became required in more and more circumstances, it was easier to point out the difference in how an RCD will protect you where a fuse or circuit breaker won't. I suppose you could go along the lines of, "Well, it's not that the old RCDs are not safe any more, it's more that the things we plug into the circuits have changed," route, but then they point out that LED lights, and power supplies etc have been around for many years so why didn't they do this sooner, it feels a bit like the sort of uncomfortable conversation you'd have with someone in the 1990's who'd bought a garage with an asbestos roof a few years earlier.

One of the things that the CPSes could actually do that's useful is to collectively go round all the manufacturers of all the devices, and get written documentation about what is compatible with what. Their advice to "contact the manufacturer to confirm compatibility" is all very well but my own experience is enquiries go unanswered; and there must be so much duplicated waste of time when everyone's asking the same questions.
 

timhoward

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Nothing to state they are precluded.
There is nothing stating type AC rcds do not meet 'the Regs'.
Agreed. As you know my head is filled with a lot of rubbish collected over the years and more recent study of the regs.
Every now and again a clear out is helpful. My musings….

531.3.3
Type AC RCDs shall only be used to serve fixed equipment where it is known the load contains no DC components.


For new installations that’s crystal clear.
For anything else, I don’t see it as any different to other reg changes we have previously navigated. We could be talking about extending domestic lighting circuits without RCD protection, SPDs or any number of things, the same two regs apply.

reg 132.16:

no addition or alteration, temporary or permanent, is made to an existing installation, unless:
  • the rating and the condition of any existing equipment, including that of the distributor, are adequate, for the altered circumstances, and;
  • the earthing and bonding arrangements, if necessary for the protective measure applied for the safety of the addition or alteration, are adequate
reg 610.4: For an addition or alteration to an existing installation, it shall be verified that the addition or alteration complies with the regulations and does not impair the safety of the existing installation.
(My bold)

Whatever our personal feelings about Type A bring a lot more desirable I don’t see a justification in the regs for automatically upgrading Type AC if the addition or alteration can be achieved in a compliant and economical way without doing so.

We just need to look at what we’re doing. A new shower circuit could arguably added to a Type AC protected board couldn’t it?

I also don’t think Type A is specifically mentioned for impact protection, so don’t currently see why you can’t run a new cable to an RCD socket outlet.
 

Mike Johnson

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Does the team think that these caveats are driven to be written that way due to manufactures pressure and so continue sales of on the shelf outdated equipment?

If installing new would you put in type AC or type A, not much of a quandary is it?
 

Gavin John Hyde

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Its an interesting debate and makes eicrs a judgement call, if house is empty with nothing in it then as you are testing as its found c3 but if occupied and full of dc devices do we c2 it? Napit go c2 niceic suggest c3
10 tears from now i expect every circuit will be on its own afdd. Possibly even radials for everything.
 

Mike Johnson

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Its an interesting debate and makes eicrs a judgement call, if house is empty with nothing in it then as you are testing as its found c3 but if occupied and full of dc devices do we c2 it? Napit go c2 niceic suggest c3
10 tears from now i expect every circuit will be on its own afdd. Possibly even radials for everything.

The cost will bring most customers to tears. 🤣
 

westward10

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What would you do in this particular scenario though Westward?

You're installing a socket. The circuit has a Type AC RCD. Is this ok, or would you find some way (however expensive) to change to a Type A?

Caveat... You're not allowed to be awkward in any way 😉
It is a good question and unless replacement rcd/rcbos are straight forward to fit then to strictly comply with the Regulations it going to be a whole lot of grief. Things like Hager boards should be straight forward albeit with additional costs but older styles of consumer units then as I said a whole load of grief.
 

Lucien Nunes

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A new shower circuit could arguably added to a Type AC protected board couldn’t it
I also don’t think Type A is specifically mentioned for impact protection, so don’t currently see why you can’t run a new cable to an RCD socket outlet.

The problem is that although the hazard that needs protecting against (cable penetration or water inside the shower) doesn't itself generate DC leakage, the RCD could be blinded by DC leakage from elsewhere, in which case it becomes unresponsive to any type of fault. If you are going to rely on an existing type AC, not only the new load but all existing loads need to be non-DC-leakers.

It would be interesting to know what percentage of installed type ACs are at this moment blinded by DC. I doubt it's very many.

On the general subject of frequent upgrades, here's the beginnings of an idea:
How about a mandatory information plate at the origin that shows what version of regs the installation complies with, in a simple way that is intelligible to the user. This would help distinguish an installation in good condition but lacking some recent safety developments, from one that is bang up to date with the latest regs. This might be simpler than trying to categorise obsolete and obsolescent features between C3 and C2 and users having to deduce the level of safety offered by the details within an EICR. Not unlike the emissions standards on vehicles, e.g. My little Euro-6 van is greener than the big one which is Euro-5, and I need look no further to know which can and cannot be driven freely within the ULEZ. I don't have to study the the MOT emissions test results.
 
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timhoward

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The problem is that although the hazard that needs protecting against (cable penetration or water inside the shower) doesn't itself generate DC leakage, the RCD could be blinded by DC leakage from elsewhere, in which case it becomes unresponsive to any type of fault. If you are going to rely on an existing type AC, not only the new load but all existing loads need to be non-DC-leakers.
So in a nutshell a non functional RCD due to existing leakage might as well not be there, and then the addition isn’t RCD protected.
To what extent can we rely on a type AC test with all loads on to detect this before we start? Or a DC clamp meter.

Maybe we just have to tell customers it’s getting impossible to comply with regs without changing the board.

We’ll be going around in circles otherwise - can’t extend a domestic lighting circuit that’s non the non RCD side, can’t move it to the other side without adding DC leakage from the LED downlights, so only options are find an RCBO, or new board.
It would be interesting to know what percentage of installed type ACs are at this moment blinded by DC. I doubt it's very many.
I’m sure you know already that the Robin loop testers used to rely on this characteristic for low current loop tests (saturating the coil with DC)
I believe that the later electronic RCDs and most RCBOs were immune to this behaviour which makes me think it will be older devices most affected.
How about a mandatory information plate at the origin that shows what version of regs the installation complies with
Bring it on….!
 

Lucien Nunes

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To what extent can we rely on a type AC test with all loads on to detect this before we start? Or a DC clamp meter.

Two competing influences there: generate as much DC leakage as you can to test whether it is being desensitised, but at the same time generate more AC leakage to move it closer to the trip threshold and invalidate the results of the test as proof of its sensitivity.

What I'd like to see is a heat map of typical DC leakage sources under non-fault conditions, other that known high-risk loads such as EV charging. Most functional leakage is capacitive and inherently AC, whether at line frequency or inverter frequency. Obviously if the leakage doesn't occur without a fault, simply energising the existing loads doesn't quantify the risk of an existing type AC being blinded.

Then under fault conditions, leakage from the rectified non-isolated bus of SMPSUs and inverters is clearly a possibility e.g. if they get wet or damaged, but how often does it actually happen? Are there identifiable hotspots, perhaps class I integrated LED fixtures with non-isolated LED chips, or VSDs used outdoors, with a disproportionate risk of leaking DC at levels of interest?

Here's another idea: Put a big capacitor in series with every type A RCD :) Some hairdryers won't then work on the low heat setting (which puts a diode in the mains lead) but that's a nasty trick anyway.

A diversionary side note:

Obviously we're used to the idea of rectifying the incoming AC mains to provide line-voltage DC within a device, and hence the idea that earth leakage from the rectified bus can be can be DC. What about deliberately drawing DC current from the AC mains by rectifying it asymmetrically? It was standard in the era of transformerless AC/DC valve radios and TVs, which took AC for the heaters but half-wave rectified the mains for the HT DC supply. But there were are talking about small loads, of arbitrary polarity, that cancelled out in bulk. In 60Hz countries, filament table lamps sometimes used a diode for a dim setting, as the resulting flicker of half the waveform being missing was less noticeable than with 50Hz. The hairdryer low setting is another.

In 1947, Strand Electric, the UK's premier manufacturer of theatre lighting equipment, tried to move forward from electromechanical dimmers to electronic ones using thyratrons. This had already been done by George Izenour in the US but the Strand guys, chiefly James Wood, came up with an idea to make the thyratrons easier to drive and the light flicker-free. Instead of a single-phase bridge, each lamp circuit was driven with a 3-phase, 3-pulse, controlled rectifier, passing moderately smooth DC through the lamp. Unfortunately being only half-wave meant the the mains supply current was pulsating DC also, and that that neutral current was the sum of the line currents, not the difference. Unlike a town full of radios and TVs this was a single point load of hundreds of kW pumping the full load current as DC into the neutral. I am not sure how they managed to overlook this during design and testing but the first installation cooked its supply cables and the concept was soon discontinued.
 

timhoward

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Two competing influences there: generate as much DC leakage as you can to test whether it is being desensitised, but at the same time generate more AC leakage to move it closer to the trip threshold and invalidate the results of the test as proof of its sensitivity
I’ll have to try giving type AC devices a hammering using a Type A ramp test. If they still trip with reasonable AC fault current plus 6ma DC then arguably they are as effective as the device we are being encouraged to replace them with!
It would be rather fun to prove that and write it up as a departure then show it to a Napit assessor…
 

happysteve

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Question, based on this scenario:

A Type AC RCD protects 5 circuits (maybe one of 2 RCDs in an old board). From one of the circuit breakers, you add an external Type A RCD. So the circuit that has the extra Type A RCD on it, if there is DC upto 6mA downstream of this extra RCD, it (the Type A RCD) will still trip in the event of a fault. So far, so good.

My question is, could the upstream Type AC RCD (which protects 4 other circuits) be blinded and rendered ineffectual by something on the circuit which is also protected by the Type A RCD?
 

loz2754

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Question, based on this scenario:

A Type AC RCD protects 5 circuits (maybe one of 2 RCDs in an old board). From one of the circuit breakers, you add an external Type A RCD. So the circuit that has the extra Type A RCD on it, if there is DC upto 6mA downstream of this extra RCD, it (the Type A RCD) will still trip in the event of a fault. So far, so good.

My question is, could the upstream Type AC RCD (which protects 4 other circuits) be blinded and rendered ineffectual by something on the circuit which is also protected by the Type A RCD?
Yes
 

happysteve

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Yes, because a pulsating DC fault that is sufficient to blind the upstream type AC won't necessarily be high enough to trip the downstream type A.
Well then, we're stuffed.

If the additions and alterations require that the circuit is protected by a Type A RCD because there's the possibility that something plugged in to the bit you've added would blind a Type AC RCD, and there is an upstream Type AC RCD that we can't remove and which also protects other circuits.... There's no option but to change the board (or at least split the tails and add a second board), because any additions and alterations can't make the existing installation less safe...

Or am I barking up the wrong tree?
 

timhoward

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I’m not worried about adding Type A RCD socket or RCD spur and sockets being added.
It complies with letter of regs as far as I can see and while a dc leaky device could be plugged in and blind an upstream device they could equally choose any other socket in the house and achieve the same thing so I don’t think it makes the installation less safe.

I actually see more issues with lighting circuits as adding LED down lights is more certain to add permanent dc leakage.
I can imagine convoluted testing reassuring me, e.g measure dc leakage of lights and then check upstream RCD tolerates that much leakage. But more likely a board change if no RCBO is available.

Maybe TT systems deserve more respect as it’s not ‘only’ additional protection we are jumping through hoops to comply with.
 
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HappyHippyDad

HappyHippyDad

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Well then, we're stuffed.

If the additions and alterations require that the circuit is protected by a Type A RCD because there's the possibility that something plugged in to the bit you've added would blind a Type AC RCD, and there is an upstream Type AC RCD that we can't remove and which also protects other circuits.... There's no option but to change the board (or at least split the tails and add a second board), because any additions and alterations can't make the existing installation less safe...

Or am I barking up the wrong tree?
There have been a few discussions about a 'lower grade' RCD being upstream of a 'higher grade' (poor wording but couldn't think of anything else). All the literature states that you should not do this.
Are you replacing type AC RCD's with Type A? 20220807_191802 - EletriciansForums.net

However, @pc1966 did a homemade test which seemed to indicate 'blinding' was pretty unlikely. I cant find his thread though.
 

Lucien Nunes

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The question I suppose, is whether the existing parts of the installation are made less safe by the addition. If you are adding a socket-outlet, you might argue that in its absence, whatever would have been plugged into it would have been run from an existing socket-outlet via an extension lead. Therefore any DC leakage from that load would still have been drawn through the original type AC. OTOH If the new circuit is specifically for a known possible DC leakage source that could not otherwise have been used, then in theory the existing installation is indeed less safe.
 
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If you have a Type AC RCD at the D/board & decide to install an extra circuit or spur with a 13 Amp 2 Gang RCD Socket.
Are the RCD sockets Type A now as I guess there are old stock AC types about ? According to this diagram co-ordination is vital.
 

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timhoward

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If you have a Type AC RCD at the D/board & decide to install an extra circuit or spur with a 13 Amp 2 Gang RCD Socket.
Are the RCD sockets Type A now as I guess there are old stock AC types about ? According to this diagram co-ordination is vital.
Yes, you can get Type A. One example:

You are right about coordination, but sometimes we may have no choice. Points have been made above regarding the load being plugged into an extension lead or into another existing socket anyway , so actually any DC leakage will exist in the installation whether or not you install the new socket.
 

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