How many sockets have I fitted incorrectly?

[JohnW2]

John, I don't see where you are reading any difference (apart from the BS compliance spec). Both statements posted about "only TN-S" to me say the same thing, only we yours states single sockets only, and we don't know where you got yours from. Would you mind clarifying?

The bit I posted about 9 posts back indicating that single-socket ones were 'only suitable for use with TN-S...' came from:

Untitled

• JohnW2
• 24 Jul 2013
• 1

MK are devils for not putting dates (at least, not dates I can find) on their Technical Documents, so I'm not sure whether this one is earlier or later than the one which Lectrician posted (which didn't 'single-out' single-socket ones, if you'll excuse the pun!).

Kind Regards, John

 

[JohnW2]

Who knows about BS EN 61543: 1966?

Seems I'm needed here!

Your name did flit through my mind

EN 61543 is titled "•Residual current-operated protective devices (RCDs) for household and similar use - Electromagnetic compatibility". I can't see why that would apply to double SRCDs and not single.

Thanks. I wasn't suggesting that the Standard might apply to double ones but not single ones. Rather, I was wondering whether there might be something about MK's single-socket ones which is not compliant with the Standard, but that there double-socket ones were compliant with it.

As I sort-of asked, does this Standard perhaps call for double pole interruptuon as a result of operation of the RCD?

Kind Regards, John

 

[mfarrow]

As I sort-of asked, does this Standard perhaps call for double pole interruptuon as a result of operation of the RCD?

I would hope you could deduce the answer to that by my posting the Introduction to the standard.

 

[stillp]

Who knows about BS EN 61543: 1966?

Seems I'm needed here!

Your name did flit through my mind

EN 61543 is titled "•Residual current-operated protective devices (RCDs) for household and similar use - Electromagnetic compatibility". I can't see why that would apply to double SRCDs and not single.

Thanks. I wasn't suggesting that the Standard might apply to double ones but not single ones. Rather, I was wondering whether there might be something about MK's single-socket ones which is not compliant with the Standard, but that there double-socket ones were compliant with it.

As I sort-of asked, does this Standard perhaps call for double pole interruptuon as a result of operation of the RCD?

Kind Regards, John

It's not easy to answer your question about double pole interruption, since the standard has multiple amendments, and refers to several other standards that have themselves been amended. However I shouldn't think so, since that would have nothing to do with EMC.
I was also wondering if the single sockets fail the tests of the standard, or perhaps it's just that they haven't tested them yet to the newer standard.
Anyway, the bar beckong, so goodnight all!

 

[stillp]

As I sort-of asked, does this Standard perhaps call for double pole interruptuon as a result of operation of the RCD?

I would hope you could deduce the answer to that by my posting the Introduction to the standard.

Missed that, sorry!
There doesn't seem anything that can be deduced from that though.

 

[JohnW2]

As I sort-of asked, does this Standard perhaps call for double pole interruptuon as a result of operation of the RCD?

I would hope you could deduce the answer to that by my posting the Introduction to the standard.

You're right. I didn't read it, not even the title, carefully enough

So the Standard business is essentially a red herring, but we still have ('my' version of) the MK Technical Document in which the comment about 'suitable only for TN-s...' appears to relate only to single-socket devices.

Kind Regards, John

 

[JohnW2]

However I shouldn't think so, since that would have nothing to do with EMC.

Indeed, and I stupidly totally missed the fact that it's about EMC. It's clearly a red herring in relation to what we're discussing.

Kind Regards, John

 

[mfarrow]

There doesn't seem anything that can be deduced from that though.

It's applied (or so it says) in the product standard for 61008/9, from both are manufactured predominantly SP devices (for the domestic market that is).

 

[JohnW2]

... from both are manufactured predominantly SP devices (for the domestic market that is).

Are you sure that's true (genuine, not rhetorical, question - I don't know)? If it is, then I suppose that, as BAS suggested way back, they might be saying it's unsuitable for TT because it's a SP device.

Kind Regards, John

 

[mfarrow]

Are you sure that's true (genuine, not rhetorical, question - I don't know)?

Well most of the MCBs and RCBOs in our houses are only single pole, or at least they are in mine. They're compliant with BS EN 61008 and 9 respectively. I can't see anything to reference 61543 in those standards, but I'm not saying it isn't there (the 'secured' versions aren't very searchable) and I'm not sure how BS ENs are designed with respect to cross-referencing each other.

BAS suggested way back, they might be saying it's unsuitable for TT because it's a SP device.

Certainly for isolation, but they are still OK for functional switching. If they're trying to be extra cautious though, they're the only manufacturer who would be doing so, and would drive them out of the market if they didn't clarify that statement with regards to isolation/functional switching.

In addition I should add that BS 7671 does not specify double pole switching for RCDs providing Additional Protection.

 

[JohnW2]

Well most of the MCBs and RCBOs in our houses are only single pole, or at least they are in mine. They're compliant with BS EN 61008 and 9 respectively.

That's obviously true, but we're talking about SRCDs and, as I implied, I haven't a clue as to whether they are SP or DP (to be honest, I don't recall ever having thought about it, but probably 'thought of them as probably DP', since domestic RCDs {as in CUs etc.} invariably are)

BAS suggested way back, they might be saying it's unsuitable for TT because it's a SP device.

Certainly for isolation, but they are still OK for functional switching. If they're trying to be extra cautious though, they're the only manufacturer who would be doing so, and would drive them out of the market if they didn't clarify that statement with regards to isolation/functional switching.

Yes, I agree it's a fairly weak case, but I'm struggling to think of anything else about the 'earthing system' which has any relevance at all in terms of the 'suitability' of a certain SRCD.

In addition I should add that BS 7671 does not specify double pole switching for RCDs providing Additional Protection.

Again, I think that's true, so it weakens the case again. However, MK obviously had something in their minds and, as you imply, felt it was sufficiently important to risk potentially having a major impact on their sales by saying it - so I guess we're not going to know the answer until someone asks them. Of course, in view of the 'no date' issue with MK documentation, we could all be looking at obsolete documents/ information, for all we know!

Kind Regards, John

 

[ericmark]

Well seems I have started something here. As said already lack of dates and other data means I have no idea if RCD sockets I have used were to a TT supply or MK or if MK RCD sockets were always unsuitable for a TT supply.

But with a RCBO it's quite obvious when they are single pole but with a socket one relies on some information written on the socket to tell one. Looked at Time Guard RCD socket and it states double pole. Also nothing about using on TN system only.

It would seem this is only something stated for MK RCD sockets.

I looked up Clipsal Filtered Sockets and nothing about only able to take 13A for the pair of outlets as stated with MK.

There has been a lot said about the current that a double socket can handle personally I feel the finger protector fitted on the new plugs reduces the amount of heat the plug and socket can get rid of and now no 13A socket can take 13A over an extended period and where as with for example an immersion heater is supplied either a FCU or a MCB with a non fused plug like the old 15A should be used. But in general we consider the limit for a pair of sockets to be 20A not 26A over an extended time.

However a double socket with only 13A really needs a FCU supplying it and I have never seen any warning on the packets that they are only good for 13A.

I feel it's unreasonable to expect people to down load the data sheets to find these limitations and things like this could cause the demise of the 13A plug and socket. Which to me would be a pity.

To limit a double socket to 16 or 20 amp is understandable and we would then supply from a 16 or 20 amp MCB. But 13A means fitting FCU as well as the socket so why not just include a 13A fuse in the socket?

 

[JohnW2]

Looked at Time Guard RCD socket and it states double pole....

Indeed it does - but I note that it also says "Breaking Capacity 250A". Does this mean that one should theoretically not use it if Zs is less than about 0.92Ω ? (I'm far from convinced that, in the case of an L-E fault, one could rely on an OPD in the circuit to operate before the RCD attempted to break it).

Also, I've just located a double-socket MK SentrySocket on my shelves and tested it. The RCD certainly does do 2-pole disconnection. I have no single-socket one to test, but maybe someone out there does?

Kind Regards, John

 

[ericmark]

My worry is more that when one looks at averts in the likes of screwfix for these products there is nothing warning about TN-S only it's only when one goes to likes of RS that one gets the information as to how they are to be used.

I see point on current but not sure of the let through value of a B32 MCB? It's not just the loop impedance it's also the let through value looking here it would seem to be around 800 to 10000 but to read between 8 x 10² and 10 x 10³ in such a small graph is not really easy.

Reading 434.5.2 I think we take t as = 0.1 seconds so I²t = 102.4 amps which seems wrong as a B32 will not trip until 160 amps I will guess both added together so 262.4 amps but only a guess.

If that was correct the 250A is close enough to 262.4A not to really worry but I am baffled as to how one calculates the let through value. I have only needed it with a fuse and then it's from graph.

 

[JohnW2]

My worry is more that when one looks at averts in the likes of screwfix for these products there is nothing warning about TN-S only it's only when one goes to likes of RS that one gets the information as to how they are to be used.

I suppose it's for the buyer to satisfy him/herself that the specification of a product meets their needs, and can't necessarily expect the adverts of a retailer to provide all of the necessary information.

However, in this case there is certainly confusion about what the specification/ instructions for the MK products really are, and the reasons for what they say. The lack of dating of the documentation is a particular problem, but the actual MK statement is fully of confusing uncertainies - reference to TN-S when they probably at least mean TN, talking about supply neutral and supply earth being connected with a TN-S supply, the reference to a 127V L-N supply - and, with one version of the documentation, the apparent difference between single- and double-products. Until someone gets clarification about all that, you'll not even know whether you have ever fitted one of these products 'incorrectly'.

I see point on current but not sure of the let through value of a B32 MCB? It's not just the loop impedance it's also the let through value ...

I don't think 'let through' is relevant to what I was talking about (maximum breaking current) - it's simply a matter of the magnitude of PEFR (dependent only on Zs) and disconnection times - which, in the case of the MCB, is simply a function of the fault current (hence, again, Zs). The RCDs you were talking about will tolerate a 'through fault current' of 1500A - so provided the MCB disconnects the supply before the RCD attempts to break the current, there's no problem. However, if the MCB does not disconnect quickly enough, the RCD will attempt to break the current, and if that fault current is >250A (again, dependent only on Zs), the RCD's breaking capacity will have been exceeded. Hence, as I said, if one cannot be certain that an OPD will operate before the RCD contacts attempt to open, then the only safe course would be to avoid using the product if the PEFR is above 250A (hence Zs is below about 0.92&#937. Is that logic wrong?

Kind Regards, John