For what it is worth the owner of a private museum of recording equipment has installed power condtioning equipment to protect some of the exhibits when they are powered up.
Is My Masterplug RCD Safe? Please Help!
- Thread starter JonathanP
- Start date
This might be a help if you are having supply problems.
http://www.hager.co.uk/news-exhibit...ive/2012/surge-protection-kit-guide/13389.htm
http://www.hager.co.uk/news-exhibit...ive/2012/surge-protection-kit-guide/13389.htm
I've done my research on all the clamping voltages, reaction time and all the rest of it and I've decided on the Belkin MasterCube surge protector (although on the front it says SurgeMaster - another brand of their products).
About £10 or so at PC World and Curry's, it's just a single socket adapter so there's no trailing cables for extension leads. Next to it, for all my keyboards, I have a surge protected Belkin extension lead so for now I'll just plug it into there until I get this MasterCube. I prefer the organ plugged in on it's own because A). I have a spare plug socket so I may as well and B). It completely eliminates the risk of overloading (although Hammonds actually don't draw that much power, believe it or not).
The MasterCube seems to have quite impressive figures all round, coupled with a guarantee if it fails. I'm not sure if it would cover goods as old as 46 years old, I'll have to read up on that, but it doesn't matter as it proves their confidence in their product.
On the side of RCDs, my music room is actually in the annexe (a garage conversion). There is a small fuse box in the lobby there, about 4/5 years old I think (put in before I moved in, but is modern looking with RCD flick switches anyway. Has been tested by an electrician last year, just to make sure it's safe). So there's RCDs there, but there's also an additional RCD on the fuse box in the main house which switches off that fuse box completely. So, there are basically 2 RCDs to do with anything that side of the house already. On the side of RCDs, I think I'm pretty well protected!
About £10 or so at PC World and Curry's, it's just a single socket adapter so there's no trailing cables for extension leads. Next to it, for all my keyboards, I have a surge protected Belkin extension lead so for now I'll just plug it into there until I get this MasterCube. I prefer the organ plugged in on it's own because A). I have a spare plug socket so I may as well and B). It completely eliminates the risk of overloading (although Hammonds actually don't draw that much power, believe it or not).
The MasterCube seems to have quite impressive figures all round, coupled with a guarantee if it fails. I'm not sure if it would cover goods as old as 46 years old, I'll have to read up on that, but it doesn't matter as it proves their confidence in their product.
On the side of RCDs, my music room is actually in the annexe (a garage conversion). There is a small fuse box in the lobby there, about 4/5 years old I think (put in before I moved in, but is modern looking with RCD flick switches anyway. Has been tested by an electrician last year, just to make sure it's safe). So there's RCDs there, but there's also an additional RCD on the fuse box in the main house which switches off that fuse box completely. So, there are basically 2 RCDs to do with anything that side of the house already. On the side of RCDs, I think I'm pretty well protected!
Dear Riveralt.
Good morning and best wishes to you.
I humbly apologise if I have offended you in this or a former life.
I did give some generalisations ref RCDs without many caveats and limitations in order to simplify my comments and not over-complicate them.
Otherwise my post may have been twice as long winded as it was.
When I mentioned the "possible" RCD trip failures I was including all the research I am aware of including a suggestion that it could be as high as 7%. I am not aware of any more than this figure and am aware of some lower figures.
However I feel that more research should be done (and last I heard there were plans to do this) the "true" figure whilst may well be less than 7% is still I feel a lot higher than some would think.
___________________
If ,just for example, say 7% or thereabouts was a "true" figure (and I`m not saying it is, but I`m not totally ruling it out yet) and this was representative over a wide range of conditions where a fully functioning RCD could be expected to trip (there are conditions where any number of RCDs would not trip but I was ignoring this for simplicity) then purely on a mathematical probability of an even spread (not real life I know) then a theoretical figure of 0.49% of two cascading RCDs with a probable faile rate of 7% each is the calculated result. Yes it is simplistic. No I do not think it totally realistic. It`s just a pure calculation but I think it demonstrates how that risk might be further reduced and worth a thought.
As an example of a recent case .
I was asked by a friend to advise on the loan or purchase of a electric hook up for camping.
I discovered that there are some hook ups that have no RCDs and just rely on the pitch socket RCD.
I advised against using any such set up that did not have its own RCD of 30mA (or less) .
Beside being a reg and also rules of most authorities and camping organisations it, to me, makes sound sense.
The pitch supply is most often a TT supply . If so then reliance would almost exclusively be on the site RCD. This would cover the "commando" plug of the user and the flex to their customer box.
At the customer box their own RCD would give protection to their sockets and equipment which (hopefully) would be enjoying the protection of the site RCD too.
A failure of either site or customer RCD would be mitigated to some degree by the other RCD.
Obviously the same could not be said of the "commando" plug, socket & flex.
_______________
Ref the 95% saved therefore 5% not saved. I did not explain that fully in order to keep simplistic. So apologies again my friend.
I know that with TN systems we generally rely on ADS/(EEBADS) fuses/breakers for disconnection for "indirect contact" and RCDs for additional (or back up if you like) protection for "direct contact" but with TT it is usually RCD for both unfortunately.
I did not mean to imply that without RCD protection then all earth faults could well be fatal but merely that , if all else fails to protect, then RCDs could save 95% of those who would otherwise not be saved (I`m refering to the suggestions of Beiglemire & Lee with is widely used as a source of reference. (I`m sure I spelt the name wrong)
_____________
No I did not say you must have two/three or more RCDs in cascade .
One would be fine if it works, two might be better and if you really want to reduce the risk further well I think 3 or more is definately starting to get a little OTT but if someone feels safer with two and one goes faulty I think they should consider replacing it as a good alternative to just getting rid of it. Compare the cost and the extra protection it might (or might not ) bring and it is worth considering.
_____________
They are not the catch all devices some folk think but they are good as additional protection (back up protection if you like) and usually necessary for TT sytems.
_____________
In my experience (and some may differ) RCDs fail in the following ways
1/ they are over-sensitive (I`ve never found one such yet but I`m sure they must exist)
2/ They do trip but outside the specified times.
3/ they do not trip at all when tested.
If they trip but outside the specified times then pressing the test button at regular intervals may help mitigate this by helping to free up the mechanism from "stiction".
OK I know that in real life such test buttons rarely get pressed even if we advise it and put stickers on to that effect but I still keep on advising that anyway.
_________
I always use my RCD adapter even when the CU or socket has an RCD but to make it a bit more fail-safe but not to make it infallible.
_____________
Tin hat on and ducking down for avoidance of incoming flak.
Good morning and best wishes to you.
I humbly apologise if I have offended you in this or a former life.
I did give some generalisations ref RCDs without many caveats and limitations in order to simplify my comments and not over-complicate them.
Otherwise my post may have been twice as long winded as it was.
When I mentioned the "possible" RCD trip failures I was including all the research I am aware of including a suggestion that it could be as high as 7%. I am not aware of any more than this figure and am aware of some lower figures.
However I feel that more research should be done (and last I heard there were plans to do this) the "true" figure whilst may well be less than 7% is still I feel a lot higher than some would think.
___________________
If ,just for example, say 7% or thereabouts was a "true" figure (and I`m not saying it is, but I`m not totally ruling it out yet) and this was representative over a wide range of conditions where a fully functioning RCD could be expected to trip (there are conditions where any number of RCDs would not trip but I was ignoring this for simplicity) then purely on a mathematical probability of an even spread (not real life I know) then a theoretical figure of 0.49% of two cascading RCDs with a probable faile rate of 7% each is the calculated result. Yes it is simplistic. No I do not think it totally realistic. It`s just a pure calculation but I think it demonstrates how that risk might be further reduced and worth a thought.
As an example of a recent case .
I was asked by a friend to advise on the loan or purchase of a electric hook up for camping.
I discovered that there are some hook ups that have no RCDs and just rely on the pitch socket RCD.
I advised against using any such set up that did not have its own RCD of 30mA (or less) .
Beside being a reg and also rules of most authorities and camping organisations it, to me, makes sound sense.
The pitch supply is most often a TT supply . If so then reliance would almost exclusively be on the site RCD. This would cover the "commando" plug of the user and the flex to their customer box.
At the customer box their own RCD would give protection to their sockets and equipment which (hopefully) would be enjoying the protection of the site RCD too.
A failure of either site or customer RCD would be mitigated to some degree by the other RCD.
Obviously the same could not be said of the "commando" plug, socket & flex.
_______________
Ref the 95% saved therefore 5% not saved. I did not explain that fully in order to keep simplistic. So apologies again my friend.
I know that with TN systems we generally rely on ADS/(EEBADS) fuses/breakers for disconnection for "indirect contact" and RCDs for additional (or back up if you like) protection for "direct contact" but with TT it is usually RCD for both unfortunately.
I did not mean to imply that without RCD protection then all earth faults could well be fatal but merely that , if all else fails to protect, then RCDs could save 95% of those who would otherwise not be saved (I`m refering to the suggestions of Beiglemire & Lee with is widely used as a source of reference. (I`m sure I spelt the name wrong)
_____________
No I did not say you must have two/three or more RCDs in cascade .
One would be fine if it works, two might be better and if you really want to reduce the risk further well I think 3 or more is definately starting to get a little OTT but if someone feels safer with two and one goes faulty I think they should consider replacing it as a good alternative to just getting rid of it. Compare the cost and the extra protection it might (or might not ) bring and it is worth considering.
_____________
They are not the catch all devices some folk think but they are good as additional protection (back up protection if you like) and usually necessary for TT sytems.
_____________
In my experience (and some may differ) RCDs fail in the following ways
1/ they are over-sensitive (I`ve never found one such yet but I`m sure they must exist)
2/ They do trip but outside the specified times.
3/ they do not trip at all when tested.
If they trip but outside the specified times then pressing the test button at regular intervals may help mitigate this by helping to free up the mechanism from "stiction".
OK I know that in real life such test buttons rarely get pressed even if we advise it and put stickers on to that effect but I still keep on advising that anyway.
_________
I always use my RCD adapter even when the CU or socket has an RCD but to make it a bit more fail-safe but not to make it infallible.
_____________
Tin hat on and ducking down for avoidance of incoming flak.
Well for my case, it seems I have two RCDs already, so maybe a plug-in RCD adapter was the wrong thing to buy.
I don't have any added protection against surges - cuts and surges are the worst things for a Hammond. So I should get something to protect against surges. To some people it may seem over the top, but for a 22 stone object you love that you've paid into 4 figures for (well, the Hammond M100 and my Leslie 145 which draws it's power from the Hammond amp), the added protection isn't OTT. It's like someone getting all the protection they can for their £3000 TV, I'd be inclined to say "Get a life", being happy with my old tube TV if I didn't have to get rid of it due to a lack of space (replaced with a £50 Samsung TV), but for others that TV may be their "baby". So do remember that with me, my organ is what you may think of your TV or Computer as. The only difference, if your TV or Computer packs up you can lift it's replacement into the house yourself. Mine involves £100s on removal companies and usually more scratches/dents in my floors and walls. That's after sourcing an increasingly hard to find object (hard to find in a good condition, easy to find trashed). Also they aren't being made any more, so their owners have a duty to protect them.
If I'm not mistaken, I basically have 2 RCDs. I'm sure the fuse box RCDs should be adequate, we test them quarterly. This just leaves surge protection, which has no added protection. So if I get the Belkin MasterCube, I am very protected against Surges and any other unnecessary trips. Does this sound the best way to go to people experienced in electrics?
I don't have any added protection against surges - cuts and surges are the worst things for a Hammond. So I should get something to protect against surges. To some people it may seem over the top, but for a 22 stone object you love that you've paid into 4 figures for (well, the Hammond M100 and my Leslie 145 which draws it's power from the Hammond amp), the added protection isn't OTT. It's like someone getting all the protection they can for their £3000 TV, I'd be inclined to say "Get a life", being happy with my old tube TV if I didn't have to get rid of it due to a lack of space (replaced with a £50 Samsung TV), but for others that TV may be their "baby". So do remember that with me, my organ is what you may think of your TV or Computer as. The only difference, if your TV or Computer packs up you can lift it's replacement into the house yourself. Mine involves £100s on removal companies and usually more scratches/dents in my floors and walls. That's after sourcing an increasingly hard to find object (hard to find in a good condition, easy to find trashed). Also they aren't being made any more, so their owners have a duty to protect them.
If I'm not mistaken, I basically have 2 RCDs. I'm sure the fuse box RCDs should be adequate, we test them quarterly. This just leaves surge protection, which has no added protection. So if I get the Belkin MasterCube, I am very protected against Surges and any other unnecessary trips. Does this sound the best way to go to people experienced in electrics?
No need to apologise or wear a tin hat - just some of things you are saying are wrong and more than a little over the top.
If your thoughts are taken literally for TT (RCD) systems then every person who has one will have loads of rcd adaptors on all their appliances - clearly an absurdity.
I am currently rewiring a number of TT earth cottages - 2 out of the three are now protected by dual RCD's and the third is RCBO protected across all circuits. Ze's all in the 15/25 Ω range.
There is absolutely no need to introduce more RCD's which you seem to imply is required for all TT systems.
Regarding your 7% failure rate (Italy 1996)- this a 2007 report but closer to home study which shows a different lower figure:
http://www.esc.org.uk/fileadmin/user_upload/documents/industry/rcd_research/Final_Report.pdf
When you read it you will find that the major problem is the lack of testing the test button on a regular basis (which this OP is not guilty off) and the ingenious (no dangerous) way some 'electricians' circumvent 'faulty' RCD's.
Your maths is awry because you are taking the average of averages in coming to your 0.49% figure - when in actual fact you are using the 7% figure from data set of CU RCD's and assuming that the same figure applies to the socket fitted RCDs - when we don't know what value that is.
I must admit I cannot fathom out how you got to 0.49% since adding one more working RCD to the original sample size will not make much of a dent in the overall results of the Italian data set.
I agree that the 7% figure (albeit 'all we seem to have') is very suspect (and almost certainly far too high) and that much of this discussion appears to show a lack of understanding of the functioning and purpose of RCDs, but what do you think is 'bad' (or 'rubbish') about the maths?
Exactly. Without commenting on the actual 95%/5% figures, what the purveyors of such statistics are saying is that 95% of those who would not have survived without an RCD (i.e. '100% not survived') will survive with one.Using your logic then before RCDs 100% would not be saved.
There are probably never going to be any reliable statistics on electrical fatalities and the effects of RCDs on them. Even before RCDs, the number of UK deaths per year due to electric shock didn't get far into 'double figures', and at least some of them (e.g. L-N shocks) would be such that an RCD couldn't make any difference. The numbers are just too small. There's more scope for statsitics in terms of 'serious injuries', but they are so poorly documented that we'll probably never get reliable statistics for them, either!
It 'makes sense', in terms of actual safety (reduction in risk), but most of us don't do it. Three would obviously be even 'more sure' than two, but that's really going a bit far! The fact is that, as above, the actual risk is so small that we usually don't bother. If there were 5000 'RCD-relevant' electrocutions per year without RCDs, and it could be shown that a single RCD would reduce that to about 583 (assuming 7% of RCDs non-functioning and 95% 'saved by RCD') and that a second cascaded one would reduce it to about 274, then we might think differently - since, in the language of the media, your risk of dying from such a cause would be almost 'halved' by having a second RCD..
Kind Regards, John
Ah, I guess this is what you meant when you referred to 'bad maths'.
It's the most basic of probability theory. If the probability of one RCD picked at random being faulty is 0.07 (7%), and if the probability of a second one being faulty is independent of whether the first one picked is faulty, then the probability of two picked at random both being faulty is 0.07 x 0.07 = 0.0049 (0.49%).
The premises on which the calculation is based are extremely iffy, but the calculation itself is correct. In terms of the discussion, we don't know whether plug-in devices have the same 'faulty' rate (assumed 7%) as ones in CUs, but there's nothing else we can assume.
Kind Regards, John
If the premise is wrong (iffy) then the calculation is wrong and the conclusion is wrong = bad maths.
That's not just semantic, but (IMO) unusual semantics. I would say that the maths is good, but that the data (hence result and conclusions) fed into the maths are quite probably wrong! Whatever, you clearly had no understanding of what the correct form of the mathematical calculation would be, since you wrote:
... which has absolutely nothing to do with how the probability of two RCDs both failing should be calculated.
Kind Regards, John
Its still bad maths whichever way you twist and turn or insult my intelligence.
As I said, it's just sematics. If you feel that applying correct mathematical calculations to bad data is 'bad maths', then fair enough.
I did not insult you intelligence, and had no intention to. I merely pointed out that it was quite obvious from what you wrote that you didn't know how the calculation should be undertaken (indeed, you wrote yourself "I must admit I cannot fathom out how you got to 0.49%"). That's to do with your knowledge, not intelligence, and none of us have, or can be expected to have, knowledge of everything.
Kind Regards, John
You seem to be mixing up arithmetic with the wider subject of mathematics - I never mentioned arithmetic I simply said it was bad maths.
Fair enough - we obviously have different views of what "bad maths" means. To me, 'mathematics' refers to the computational process - whether arithmetic, algebra, trigonometry, calculus or whatever - which can be undertaken correctly (which I would call 'good maths') even if the figures being fed into those calculations are incorrect.
We can agree to disagree about the semantics, but this semantic discussion is really not very important or useful. In context, I think we can probably agree that a calculation of the probability of two RCDs both failing which is based on an assumed 'faulty rate' of 7% (and various other assumptions) is not going to give a 'good answer', since the correctness of the underlying data and assumptions is very uncertain.
However, whatever the true 'faulty rate' is, we do know that (all other things being equal), if one cascades two identical RCDs each with a probability of being faulty of x, and if the probability of one being faulty is independent of whether the other is faulty (hence not from the same batch etc.) then the probability of both being faulty will be x². So, if there were a 1% probability of one being faulty, then the probability of both being faulty would be 0.01%, if there were a 0.1% of one being faulty then the probability of both being faulty would be 0.0001% etc.
Kind Regards, John
Yes I did mean that if we take a figure (any figure) as being the correct across the board failure rate, and in this instance we take the (possibly incorrect) figure of 7% then ,in this case, a failure rate of something as low as 0.49% (or certainly a lot lower than 7%) might be achievable.
I think we all agree that regular testing of RCDs helps to mitigate one factor causing failure - "stiction " - it helps free up the stickiness of the mechanism, it also is one indication of whether the RCD might work at all or not.
I think if we did two surveys - one with RCDs as found installed and the other with RCDs tripped prior to testing then we might well find a remarkable difference in failure rates.
To my mind, the best survey would be as in actual use - ie not tripped prior to testing because if give a more accurate "real world" scenario.
Two RCDs in tandem is worth a thought on some items and especially for outside use. For the relatively low cost of an RCD adaptor if using outdoor equipment is not lost and it just might make a bit of difference.
The reports of a 95% success rate of a working RCD meaning 5% are not saved is the best assumption we can use. As said it might be well out but it`s the only figure we can go on .
I think we all agree that regular testing of RCDs helps to mitigate one factor causing failure - "stiction " - it helps free up the stickiness of the mechanism, it also is one indication of whether the RCD might work at all or not.
I think if we did two surveys - one with RCDs as found installed and the other with RCDs tripped prior to testing then we might well find a remarkable difference in failure rates.
To my mind, the best survey would be as in actual use - ie not tripped prior to testing because if give a more accurate "real world" scenario.
Two RCDs in tandem is worth a thought on some items and especially for outside use. For the relatively low cost of an RCD adaptor if using outdoor equipment is not lost and it just might make a bit of difference.
The reports of a 95% success rate of a working RCD meaning 5% are not saved is the best assumption we can use. As said it might be well out but it`s the only figure we can go on .
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