If an RCD fails to operate once, should it be considered faulty and replaced?

F

flex_m

-
I was doing some temp work as a mate, assisting a fully qualified sparks with testing, and an RCD failed to operate. He flipped it off and on, repeated the RCD test and it operated properly, then assured me it didn't need replacing. The fact it failed to operate under fault conditions once makes me think it should have been replaced. Is there a specific regulation that has been ignored here or is it just bad practice to leave an installation that you are aware has such potential faults? Is this serious enough that I should notify the company I was working for (the sparks in question was temp too)?
Cheers
 
First question is where was he conducting the test? Out on the circuit or at the load side terminals with the circuit isolated?
 
Gummed up mechanical levers by the sound of it. IMHO if it has surcummed to this type of failure, it will in time do so again, so personally i'd change it out!!
 
flex_m said:
I was doing some temp work as a mate, assisting a fully qualified sparks with testing, and an RCD failed to operate. He flipped it off and on, repeated the RCD test and it operated properly, then assured me it didn't need replacing. The fact it failed to operate under fault conditions once makes me think it should have been replaced. Is there a specific regulation that has been ignored here or is it just bad practice to leave an installation that you are aware has such potential faults? Is this serious enough that I should notify the company I was working for (the sparks in question was temp too)?
Cheers
Click to expand...

The preferred order of test for an RCD is to do the with-the-meter tests, and then only after that poke the test button on the RCD unit. The reason being that poking the RCD unit first can dislodge a stuck lever, that will then go on to pass meter tests which by rights it should have failed. The clear logic there IMHO is that an RCD which without being freed up fails the meter tests, has failed.

In any case common sense says if it can gum up in the period between its last use and your test, it can gum up again in the period between your test and someone's life relying on it working.
 
whgich is why there'sa label attached saying test quarterly. how many customers are too lazy or too stupid to comply?
 
Though we don't help with CU units often being up there on sky hooks. Wall-mounted test button outside the CU, anyone?
 
Maybe if this remote switch were connected to a mechanism so that when it was re-energised it could operate a system of levers to re-engage the switch on the RCD.
Anyone want to stump up with a research grant?
Nick, this time next year mate.......
:)
 
replacing it without educating (assuming that like 99.9% no quarterly test has been carried out) is pointless. it may well have failed as it hasnt operated in 10 years, replacing it and hoping the next time its used in 10 years is so far from what it was designed for. the best thing to do is educate the user of the installation replace if you wish although there may be nothing wrong with it if used correctly. no guarantees the new one wont behave the same way if the same happened to it.
 
trev said:
Maybe if this remote switch were connected to a mechanism so that when it was re-energised it could operate a system of levers to re-engage the switch on the RCD.
Anyone want to stump up with a research grant?
Nick, this time next year mate.......
:)
Click to expand...

Right then...two pullcords coming out of the bottom of the CU per RCD, one to test the RCD, one to reset it :)
 
Too simple mate, the people on Dragon's Den will never stump up £quarter of a million for that :)
 
wozz said:
replacing it without educating (assuming that like 99.9% no quarterly test has been carried out) is pointless. it may well have failed as it hasnt operated in 10 years, replacing it and hoping the next time its used in 10 years is so far from what it was designed for. the best thing to do is educate the user of the installation replace if you wish although there may be nothing wrong with it if used correctly. no guarantees the new one wont behave the same way if the same happened to it.
Click to expand...
Agreed, if you replace it without educating then you're addressing the symptoms and not the cause so effectively in a few months time the installation won't be any safer than it is now.

Similarly if the RCD passes after the test button has been operated then surely just education on monthly testing is going to leave the installation equally as safe as replacing the RCD.
 
Bit uneasy about that. Aren't they meant to be maintenance free? If an RCD requires user cycling every three months to keep it from seizing up, is it a fit for purpose RCD? Is there a valid reason why RCDs should be treated differently in this respect from MCBs? We don't rely on the user cycling MCBs every three months in order to keep them from seizing up, we expect them to do their job if left for years and if we found one that had failed to operate under appropriate fault conditions we'd chuck it, wouldn't we? Grateful for your thoughts, maybe I'm missing something here.
 
flex_m said:
I was doing some temp work as a mate, assisting a fully qualified sparks with testing, and an RCD failed to operate. He flipped it off and on, repeated the RCD test and it operated properly, then assured me it didn't need replacing. The fact it failed to operate under fault conditions once makes me think it should have been replaced. Is there a specific regulation that has been ignored here or is it just bad practice to leave an installation that you are aware has such potential faults? Is this serious enough that I should notify the company I was working for (the sparks in question was temp too)?
Cheers
Click to expand...
Consider yourself Dismissed
 
flex_m said:
I was doing some temp work as a mate, assisting a fully qualified sparks with testing, and an RCD failed to operate. He flipped it off and on, repeated the RCD test and it operated properly, then assured me it didn't need replacing. The fact it failed to operate under fault conditions once makes me think it should have been replaced. Is there a specific regulation that has been ignored here or is it just bad practice to leave an installation that you are aware has such potential faults? Is this serious enough thatI should notifythe company I was working for (the sparks in question was temp too)?
Cheers
Click to expand...
Consider yourself Dismissed
 
Nick,

It's possibly to do with the amount of Energy required to cause them to operate.
With an RCD, it would be tiny compared to an MCB, hence 'gumming up' stopping them from operating.
I think that's why the Max Zs increases with breaker rating.
Further study require, or some of our esteemed members could enlighten us further! :-)
 
Archy Styrigg said:
It's possibly to do with the amount of Energy required to cause them to operate.
With an RCD, it would be tiny compared to an MCB, hence 'gumming up' stopping them from operating.
Click to expand...

I think the energy to operate the actual opening of the contacts is stored mechanically in the internal spring mechanism when you push it up, isn't it?
 
OK....I'll fess up.

I honestly can't remember the last time (if ever, for 'routine testing') that I've used the test buttons on any installed in my house......like most people, it's just so dull going around resetting everything.....
 
NickD said:
Bit uneasy about that. Aren't they meant to be maintenance free? If an RCD requires user cycling every three months to keep it from seizing up, is it a fit for purpose RCD?
Click to expand...
Good question and I don't have an answer but they all seem to suffer from increased tripping times the longer they're inactive, even the good brand name units are guilty.

NickD said:
Is there a valid reason why RCDs should be treated differently in this respect from MCBs? We don't rely on the user cycling MCBs every three months in order to keep them from seizing up, we expect them to do their job if left for years and if we found one that had failed to operate under appropriate fault conditions we'd chuck it, wouldn't we? Grateful for your thoughts, maybe I'm missing something here.
Click to expand...
RCD's and MCB's have always been treated differently, there's never been a requirement to test that an MCB trips according to the current/time graph for its appropriate curve. You only find out the hard way whether or not an MCB is capable of disconnecting withing the expected time.

I don't think you're missing anything, there's plenty to be uneasy about, it's a point that all the official publications seem to have cunningly avoided giving specific guidance on. :)
 
Best thing is to bring in your nan's kettle/oven/fridge/iron and donate it to them. Then they wont have to worry about the test button ever again...
 
I think the single largest deterrent to testing MCB's is the practicalities of doing so!!!
 
Yep, a Primary current injector test kit can be a little steep to purchase for the average journeyman electrician... lol!!
 
Rockingit said:
OK....I'll fess up.

I honestly can't remember the last time (if ever, for 'routine testing') that I've used the test buttons on any installed in my house......like most people, it's just so dull going around resetting everything.....
Click to expand...

Im with Rockingit on this. It must have been about a year ago since I tested mine. I test my smoke detectors a lot more than I test my RCD. I know its probably a cop-out but I personally think for me its remembering to do it when no one else is in. Cant be arsed with the hassle of getting the kids and missus off the comps, tv, and all the other things. I know its for their own good.... Just telling the truth...
 
NickD said:
Bit uneasy about that. Aren't they meant to be maintenance free? If an RCD requires user cycling every three months to keep it from seizing up, is it a fit for purpose RCD? Is there a valid reason why RCDs should be treated differently in this respect from MCBs? We don't rely on the user cycling MCBs every three months in order to keep them from seizing up, we expect them to do their job if left for years and if we found one that had failed to operate under appropriate fault conditions we'd chuck it, wouldn't we? Grateful for your thoughts, maybe I'm missing something here.
Click to expand...

Where did u get maintenance free from? Far from it, manufactures ask for them to be tested as least quarterly and I believe that to be the same for all manufs , to such a extent a British standard even puts a blanket rule on testing them regardless of what the manuf says. If all this is ignored and it fails after not being touched after 10 years by a few milliseconds the rcd is hardly to blame. The only thing not fit for purpose is the end user as far as I can see and I do realise how bad that sounds. Handover paperwork in a lot of our industry is crap maybe if this was addressed so could the testing of rcds at the same time.

Mcbs work on thousands of amps rcds work on milli amps I'm no product engineer but I can hazard a guess at which one would be more prone to not working ( assuming correct icn,ics). Also would the benefits be that great? Would the MCB have the same life span after and how dangerous and expensive would the testing be? Testing rcds is easy and safe.
 
I read somewhere recently that some manufacturer has developed an rcd / rcbo that tests itself in the middle of the night when there's very little electrical activity and then resets itself, or did I dream it!
 
stantheman said:
I read somewhere recently that some manufacturer has developed an rcd / rcbo that tests itself in the middle of the night when there's very little electrical activity and then resets itself, or did I dream it!
Click to expand...

If it resets all the clocks in my house at the same time then I might get it...
 
wozz said:
Where did u get maintenance free from?
Click to expand...

I didn't, it was just a question about whether RCDs are meant to be maintenance free.

So what it boils down to is, is the quarterly test requirement 1. a safety test only or 2. stipulated as essential maintenance? 1 implies a stuck RCD should be failed, 2 implies should be failed only if quarterly tests have been happening. Answer also affects degree of kicking the end user deserves. Would a relevant BS or product standard tell us the answer? Anyone got one? (Googling comes up with little useful and BSs are rarely to be found legitimately online for free access.)
 
Wow, looks like I opened a mysterious can of worms by asking this question, I'm glad it's sparked a debate, many thanks for all the responses.

MDJ said:
jeez a copper on the forum
Click to expand...

Haha, I didn't mean it in the sense of getting the bloke I was working with in trouble, we were both temping and no longer with the company, more in the sense of is this something that was left unsafe and needs rectifying.
I'm relatively new to the game, in the middle ground between doing everything to the letter at college and the reality of working on site. After the responses on here I will be stressing the importance of quarterly RCD tests to customers in the future.
 

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If an RCD fails to operate once, should it be considered faulty and replaced?
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Periodic Inspection Reporting & Certification
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