Auto resetting RCD? help please...

[Engineer54]

I'm sorry too...lol!!! By all means, if you feel comfortable relying totally on an RCD device for yours and your families protection, ....Me, i definitely won't be!! lol!!

By the way, that MCB recall was for a single rating of a single make as far as i know. RCD failures are far far more numourous, and affect all makes and manufacturers. MCBs and HRC fuses are by far, a more reliable means of disconnection, albeit at a courser level than an RCD...

MG by the way, were the SOLE provider of all of my last projects LV Distribution from the main MC enclosed type Switchboards, through to the local DBs. Failures in the RCD devices were to say the least, ...Alarming!!! Oh and that included substantial numbers of the add-on vigi units too...

Not disputing in anyway the superior properties of a functioning RCD device mate, just that to my mind, as well as i'm sure most other Engineers ....There should always be a good earthing system in place, Safety is something you don't fool around with, and total reliance on RCDs at this present time is foolish...

 

[malcolmsanford]

We will have to agree to disagree old mate .................lol but did you read the ERA report on RCD mate ?

 

[Engineer54]

Nope, ..... But i know what i've witnessed with my own eyes. I had to counter sign all materials that were being removed from site. I can assure, you it was quite alarming at the numbers of RCDs that failed during testing and normal use, during warranty periods. Not just on my last project, but on quite a few of my projects.... More than enough, to convince me Not to rely totally on any RCD for earth fault protection....

So, yeah, ....we'll agree to disagree on this one then ...lol!!!

 

[malcolmsanford]

have a read mate good bedtime reading

http://www.esc.org.uk/pdfs/news-and-events/research/rcd/Final_Report.pdf

 

[BlueToBits]

Malcolm,

The total reliance on the various RCD devices as a means of protection against earth faults is a little foolish to be honest. Yes RCD devices are a very welcome addition to safety, in the home and throughout the industry, but there really is no alternative or substitute to having a good earthing system present at any type of earthed electrical system....

A TT earth system relies on an RCD for ADS in any event. Are we to condem TT earth systems as unsafe?

...France, Spain, and most other countries rely totally on RCD protection for earth faults. We have in fact now brought ourselves in line with them, and they are so confident in them that they have no heistation in fitting socket outlets in bathrooms as they have total faith in them. I have worked here in saudi with Merin Gerin and their "wigi" system and have yet to find a problem with them.
....

They use Double Pole MCBs so the user can easily isolate the faulty circuit and restore power to the healthy circuits whilst they wait for an electrician.

The highest risk to the consumer is the use of candles, trip hazards, falling down the stairs etc. because a faulty circuit has taken out an RCD which in turn has taken out multiple healthy circuits. Bring on RCBOs or DP MCBs. Let us stop messing around with dual and split boards once and for all.

 

[malcolmsanford]

A TT earth system relies on an RCD for ADS in any event. Are we to condem TT earth systems as unsafe?



They use Double Pole MCBs so the user can easily isolate the faulty circuit and restore power to the healthy circuits whilst they wait for an electrician.

The highest risk to the consumer is the use of candles, trip hazards, falling down the stairs etc. because a faulty circuit has taken out an RCD which in turn has taken out multiple healthy circuits. Bring on RCBOs or DP MCBs. Let us stop messing around with dual and split boards once and for all.

Agree Blue but the double pole MCB is still not used for fault protection but overload protection and isolation. As you say if there was a fault on the installation the front end RCD will activate and then by using the double pole MCB your going to isolate both Lives. They still totally rely on the RCD for fault protection as we are doing by making RCD circuits in the home mainly compulsory to have it.

Though in theory RCD protection is still classed as additional protection, the regs are moving to a situation where in the next few years they will be compulsory in domestic installations in all instances, as in locations containing a bath and a shower are now.

That is just my opinion, I may be totally wrong and it wouldn't be the first time lol

 

[Engineer54]

have a read mate good bedtime reading

http://www.esc.org.uk/pdfs/news-and-events/research/rcd/Final_Report.pdf

Malcolm,

I have just read your above link. Now i have to tell you up front, that i take reports and surveys by commercial institutions with a good pinch of scepticism and salt...lol!!

While i'm not going to say that the survey undertaken here is not valid in several areas and aspects, i did find that it went quite a ways in erring on the side of commercial interests rather than taking a neutral stance throughout. And that's basically the problem i have with commercial type surveys, the authour(s) will always be trying to lean results towards those they want to promote...

Now the survey was based in the main, on 607 RCD devices throughout the whole of the UK, now that's not really anywhere near a representative figure to base the reliability of any type of device. ...Hell we had more than 5 times that number of RCD devices on my last project alone. It also came accross (to me anyway) that the report was doing it's best to excuse some of the failures reported, passing them off as human error in cases (no, i'm not talking about the defeated devices) such as failure to operate the ''test button'' at recommended periods of time. Now we all know that pushing the test button has no affect on the operation of an RCD device, it at best proves or otherwise the devices mechanical operation.

I'm not going to go through this survey report point by point, that'll take forever!! ..lol But towards the end of the survey, they included contractors experiences, which seemed again, not taken that seriously by the authors, We don't know how many of these contractors and other industries contributed, and we are only given a few such examples. Were the examples representative of the contributors findings in this area?? .....We will never know!! it was as if the authours had already made up there mind that the RCDs in question were probably fine and that the contributions were making unsubstantiated claims.

Now, hardly a week passes by, do you not get threads or a posts on this forum (and plenty of others too) where the OP is talking about an RCD device failing in one way or another, some straight out of the box and others that have been in service for various periods of time. Well basically that's the same as my own experiences with RCDs, so i will, i think continue to be just that little bit wary on the ''total'' reliance of RCD devices for earth fault protection....

Thanks for the link though, it's always good to these sort of things....

 

[BlueToBits]

We don't test the operation of MCBs. We only ever detect a faulty MCB in those situations an MCB has failed to protect the circuit following a real, actual fault. It can't be said that an MCB is better or worse at fault protection than an RCD because there no comparitive data for MCBs.

 

[telectrix]

nobody has, so far , mentioned the effects on a RCD due to exceeding the rated current. as we all know, RCDs are made up of contacts, springs, and various bits of plastic and metal, metal parts and especially springs are subject to adverse stresses through use, overlhaeting thrpugh overloading, and as such, can alter their characteristics, sometimes to the extent of a small part affecting the correct operation of the device. i, for one, would not stand in a bucket of water and grab a live conductor in the faith that an RCD would save my life.

 

[Engineer54]

A TT earth system relies on an RCD for ADS in any event. Are we to condem TT earth systems as unsafe?

BlueToBits,

This is one of my main beefs with what's happening in the UK these days.... The willingness to create TT systems at the drop of a hat, for no good electrical reason. On top of that, the misguided idea that bunging a rod in the ground willy nilly and getting an Ra reading of under 200ohms is a TT system and is a good-un ...It isn't a TT system and it certainly isn't a ''Good-Un''!!!

It seems in these modern times there are very few electricians that really understand TT systems, and even less on how to create/install them. I personally wouldn't leave a TT system with more than a 20ohm Ra reading, and be aiming for even less!!! You Need a value that will, if an RCD device fails trip out a protective device (MCB) on an earth fault. It may not trip out the MCB in times associated with other earthing systems, but it will trip it!!!

I know of small rural areas in Essex, that have TT systems that have Ra that are better than the local town/village on TN-S systems with Ra's going down to 0.6 ohms. I'm sure there are other areas in the UK where similar favourable ground conditions can be found. But generally in a typical domestic setting you will probably be struggling to get a decent Ra value. But there are several things you can do to improve initially high Ra readings...

Let it be said, a TT system should ALWAYS be considered as a LAST choice and not a first choice, as so many of these PME sceptics promote.

 

[malcolmsanford]

We don't test the operation of MCBs. We only ever detect a faulty MCB in those situations an MCB has failed to protect the circuit following a real, actual fault. It can't be said that an MCB is better or worse at fault protection than an RCD because there no comparitive data for MCBs.

Blue are you saying that there is no failure data to prove if a MCB is more reliable that an RCD or are you saying that a MCB will provide better fault protection mate?

 

[Deleted member 26818]

In my experiance, faulty MCBs tend to fail open, rather than closed.
The ERA report indicates that 17 out of 601 RCDs were faulty, i.e. that they would not have opened in the event of an earth fault.
Hopefully the MCBs would have operated, so no real danger was present.

 

[Engineer54]

haha!! Only if there was a decent earth system in place!! ...lol!!