UK AC RCD’s C2? Absolutely!

[J Sparks]

Given the advancement in technology and the high amount of potential DC in electrical systems. An AC RCD that won’t work, invokes so many further regulations for circuits that need RCD protection that no longer do! 100% C2 in my opinion

 

[nicebutdim]

It also says that coding is entirely at the discretion of the inspector and the document is merely a guide. I would rather be fussy and improve a system than be lazy and have someone’s death on my conscience. Honest question, if you know an AC rcd may not work in a fault situation, explain why you would code it as a C3 and negate the need for someone to fix it. Imagine a child sticks their finger in a lamp holder? But the rcd fails…

A short while back we established that you were commenting on failed units, but now the conversation seems to have shifted to RCDs that 'may not work in a fault situation'.

How are you establishing that an RCD may fail to operate?

As for coding being at the discretion of the inspector, that's the sort of argument applied by testers who blanket code insulated CUs as C2.

Coding should be back up by regulations and sound engineering judgement. It should not be whimsical in nature.

 

[westward10]

Sure…

Sure what?

 

[J Sparks]

A short while back we established that you were commenting on failed units, but now the conversation seems to have shifted to RCDs that 'may not work in a fault situation'.

How are you establishing that an RCD may fail to operate?

As for coding being at the discretion of the inspector, that's the sort of argument applied by testers who blanket code insulated CUs as C2.

Coding should be back up by regulations and sound engineering judgement. It should not be whimsical in nature.

It’s common knowledge that DC current in a circuit with an AC RCD impairs it’s ability to work. Domestic properties have numerous electrical items, induction hobs, led lighting, EVCP’s that all can present this within an installation. There are loads of videos on YouTube explaining the logic behind it. It’s in the regs check out 531.3.3! As for sound judgement I’m an electrical technician with an electrical engineering degree and twenty years testing experience. I think I’m suitable to make the decision. There is a reason they are banned in half the world!

 

[nicebutdim]

It’s common knowledge that DC current in a circuit with an AC RCD impairs it’s ability to work. Domestic properties have numerous electrical items, induction hobs, led lighting, EVCP’s that all can present this within an installation. There are loads of videos on YouTube explaining the logic behind it. It’s in the regs check out 531.3.3! As for sound judgement I’m an electrical technician with an electrical engineering degree and twenty years testing experience. I think I’m suitable to make the decision. There is a reason they are banned in half the world!

Yet for most of those 20 years you were completely unaware of the issue, until Youtube broadened your knowledge?

I was hoping for an explanation of your testing process, rather than coding on the basis of assumption and that's the problem I have with this sort of blanket coding. 'Potential' exists for failure of Type A RCDs. Where they are used for fault protection, do you mandate that additional protection be provided on the basis of 'what if'?

While I don't disagree with the basic premise that Type A protection would be preferable, I do disagee with the idea of coding on the basis of assumption where no potential danger can be demonstrated in a particular installation.

A failed RCD needs to be replaced, regardless of whether that failed unit is Type AC, A or other. A working RCD does not need to be replaced, unless evidence exists to suggest that it will fail to operate (whether that be for the reasons you outline or for any other reason). The average house does not have an induction hob or EVCP and basic LED lamps aren't likely to introduce sufficient DC current to prevent operation of a Type AC RCD. In short, while it may be the case that Type AC protection isn't suitable for a modern installation, most homes do not possess what might be considered a 'modern installation'. Coding should be appropriate to each installation inspected.

 

[nicebutdim]

I'd like to qualify my previous comments as the OP probably knows nothing about me and might consider them to be argumentative or harsh. The comments weren't intended to be either, but as an apprentice I find myself disappointed and frustrated when no logic is apparent behind blanket statements.

We're all entitled to our opinions, but equally we should be able to substantiate them as bold opinions are likely to be challenged.

Tl;dr... No offense intended, but I want to learn and want to do so in an informed manner.

 

[davesparks]

Honest question, if you know an AC rcd may not work in a fault situation, explain why you would code it as a C3 and negate the need for someone to fix it.

If the RCD is there for additional protection then it is possible that it should be a C3 as it is additional protection and not the primary protection which is potentially compromised.

If there is a definate, confirmed presence of DC leakage currents which will alter the operation of a type AC RCD then that is a different story to guessing that there maybe might be an issue.

Imagine a child sticks their finger in a lamp holder? But the rcd fails…

An RCD is unlikely to assist in that situation anyway. If a child sticks their finger in a lampholder then they are more likely to make contact with both the live and neutral, this will result in current flowing through their finger which the RCD will see as normal load current.

 

[Risteard]

If you read the Best Practice guide #4 for EICR coding (Nov 2022) from Electrical Safety FIrst, it states for "A Type AC RCD installed where a Type A RCD required" to be coded as C3.

Indeed they do, but I must admit I find this suggestion somewhat questionable. Surely if an RCD is required, and the circumstances of the installation dictate that it needs to be a minimum of a Type A RCD because a Type AC RCD could be disabled by circulating DC currents then a C3 Observation seems overly lenient. But alas, you are correct that this is what that Best Practice Guide suggests.

 

[Pretty Mouth]

It’s common knowledge that DC current in a circuit with an AC RCD impairs it’s ability to work. Domestic properties have numerous electrical items, induction hobs, led lighting, EVCP’s that all can present this within an installation. There are loads of videos on YouTube explaining the logic behind it. It’s in the regs check out 531.3.3! As for sound judgement I’m an electrical technician with an electrical engineering degree and twenty years testing experience. I think I’m suitable to make the decision. There is a reason they are banned in half the world!

Common knowledge indeed, but one thing that remains mostly unanswered is how the DC current comes to be passing through the RCD in the first place? Presumably a circuit must be completed for it to flow, so is it deliberate, or is it due to faulty equipment? And what route does it take? Any answers (with sources) appreciated

 

[oscar21]

Another reg that I think is daft and has been changed for changes sake. I would have thought that in 99% of situations an AC RCD will be just fine, certainly in all the EICR's that I've done over the last few years and all the installations that I've done with AC ones they all tripped off no problem under test, the ones that didn't were physically faulty (BG ones for eg) despite houses being full of LED lamps, TV's, phone chargers, HOB's, washing machines etc etc.

My house is a perfect example, I have lots of electonic goods, your typical house, probably more so with my computer stuff, yet the 10 year old RCD trips off every time the oven is on for more than 30 minutes, its needs a new element.

From what certain people are saying I have a C2 problem in my consumer unit which is potentially dangerous, no RCD at all would be a C2 as well, so going by that logic I might as well ditch the RCD altogether and be no less safe than I was before, then I could have a roast dinner and not just a pizza.

 

[davesparks]

Another reg that I think is daft and has been changed for changes sake.

It has been changed because the older RCD technology is no longer appropriate in a modern installation.

I would have thought that in 99% of situations an AC RCD will be just fine, certainly in all the EICR's that I've done over the last few years and all the installations that I've done with AC ones they all tripped off no problem under test

Tripping under test conditions is different to tripping under real world conditions.

My house is a perfect example, I have lots of electonic goods, your typical house, probably more so with my computer stuff, yet the 10 year old RCD trips off every time the oven is on for more than 30 minutes, its needs a new element.

I think you've misunderstood some basics here.
The RCD tripping due to a faulty oven element does not prove whether or not it has been affected by any DC leakage.

 

[davesparks]

Common knowledge indeed, but one thing that remains mostly unanswered is how the DC current comes to be passing through the RCD in the first place?

DC leakage occurs from electronic loads, especially switch mode power supplies and the like.

Presumably a circuit must be completed for it to flow, so is it deliberate, or is it due to faulty equipment? And what route does it take? Any answers (with sources) appreciated

Lucien wrote a pretty good explanation of the DC leakage subject relatively recently. It should be possible to find it with a search.

 

[loz2754]

Can anyone explain type A RCD's

So after reading that other thread would I be correct in saying type A RCD's actually trip if it detects DC current thus disconnecting upstream RCD's from the DC fault anyway? I was under the impression that type A could only cope with DC leakeage as opposed to detect it.

www.electriciansforums.net

 

[oscar21]

It has been changed because the older RCD technology is no longer appropriate in a modern installation.

Tripping under test conditions is different to tripping under real world conditions.



I think you've misunderstood some basics here.
The RCD tripping due to a faulty oven element does not prove whether or not it has been affected by any DC leakage.

Well if it has been affected by DC leakage then it still tripped so all is good and if it hasn't been affected by DC leakage then all is good too. My house has all the possible scenarios that could cause DC leakage but the RCD still trips merrily away.

 

[MJPD29]

It’s common knowledge that DC current in a circuit with an AC RCD impairs its ability to work. Domestic properties have numerous electrical items, induction hobs, led lighting, EVCP’s that all can present this within an installation. There are loads of videos on YouTube explaining the logic behind it. It’s in the regs check out 531.3.3! As for sound judgement I’m an electrical technician with an electrical engineering degree and twenty years testing experience. I think I’m suitable to make the decision. There is a reason they are banned in half the world!

Sorry on behalf of everyone else we didn’t realise you had a degree, I’ll be the first to bow down to you. Our years practical experience working on site years means nothing when the piece of paper enters the room.

 

[timhoward]

I think there are valid points on both sides of this debate.

In general if an RCBO seems to work (and I usually try a type A test too even though it isn't required) then I feel I have no evidence that it isn't doing it's job, and it's a C3.
In practise I find most Type AC RCBO's will trip if tested on a Type A setting, and normally within required times. (Using the x5 test they sometimes didn't quite make 40ms but only by a few ms.). So far the only ones that didn't trip also didn't trip on a type AC test because they were stuck or broken.

If you remember the older No Trip loop testers used to used DLOK and deliberately inject DC to blind the RCD, and it's telling that this technology had to be abandoned as it fails to work on almost all RCBOs.

In general I'm more concerned about older shared RCD's where the cumulative DC leakage from multiple circuits can be higher, and the older ones seem to be more susceptible to DC blinding in the first place (backed up by the fact that older loop testers could successfully 'fool' them).
I'd love to get a DC leakage clamp meter to help make better informed decisions but it hasn't made it to the top of the wish list yet.