fused spurs / double Pole Switches

[stillp]

No, the criteria for passing the test are clearly stated in the standard for either s single or dual socket, the same criteria could be applied to 2 adjacent singles.

 

[mfarrow]

It isn't something I'd thought we needed to worry about.

Most heating loads are cyclic in nature, and a significant majority of washing machines have 2kW elements in them, not 3kW.

Drying your hair isn't going to come close to 4kW; you could heat a room with that.

 

[ban-all-sheds]

No they're not. It isn't a departure.

It is if you take the strict view that 433.1.103 only allows you to connect BS 1363 accessories to a ring final.

 

[stillp]

I've more than once used two 3 kW non-thermostatic fan heaters plugged into a dual socket-outlet to dry carpets after a pipe burst, and I don't remember burning any sockets.

 

[stillp]

No they're not. It isn't a departure.

It is if you take the strict view that 433.1.103 only allows you to connect BS 1363 accessories to a ring final.

I wouldn't call that a strict view BAS, I'd call it a misinterpretation. 433.1.103 doesn't say "Only accessories to BS 1363, nor does it say "Accessories on a ring final circuit shall be to BS 1363...", which they could easily have said, if that's what they meant.
Giving permission for something to be used doesn't forbid the use of something else.

 

[ban-all-sheds]

It does not have the word "Only", but it does say, only, "Accessories to BS 1363 may be supplied....".

The strict interpretation of that is indeed that you cannot use the exemptions from the normal rules for overload current protection and parallel conductors if you are supplying non-BS 1363 accessories.

 

[JohnW2]

No, the criteria for passing the test are clearly stated in the standard for either s single or dual socket, the same criteria could be applied to 2 adjacent singles.

That's true if your only interest was in whether the two adjacent singles would 'pass a/the test' (which I imagine they probably would).

I thought your interest was in a comparison - and since double sockets may, in practice, exceed the requirements for 'passing the test', one would need to actually undertake a comparison if one had that wider interest.

Kind Regards, John

 

[stillp]

If sufficiently close to meet a similar user requirement to a dual socket, I'm not sure they would pass.
You're right though, a comparison would be interesting.

I could set up the test, but I don't have any means of measuring the temperature. Where's RF? He'll probably have some lame excuse like working for a living.

 

[JohnW2]

If sufficiently close to meet a similar user requirement to a dual socket, I'm not sure they would pass.

It's hard to tell. I've always been a little surprised that there appears to be an appreciable difference in thermal behaviour of single and double sockets, so I probably not have a good understand of how these differences come about. Maybe it's an misconception, but, FWIW, the volume/mass of the 'moulding' of the works of a double socket actually looks to me as if it's probably greater for a double than for 2 x singles.

You're right though, a comparison would be interesting. ... I could set up the test, but I don't have any means of measuring the temperature. Where's RF? He'll probably have some lame excuse like working for a living.

Can you remind me what the 'pass criteria' are?

Kind Regards, John

 

[stillp]

It does not have the word "Only", but it does say, only, "Accessories to BS 1363 may be supplied....".

The strict interpretation of that is indeed that you cannot use the exemptions from the normal rules for overload current protection and parallel conductors if you are supplying non-BS 1363 accessories.

Yes, I agree. The subject of the sentence is those exemptions, rather than the accessories' compliance with BS1363.

 

[stillp]

Can you remind me what the 'pass criteria' are?

Maximum temperature rise of 47 K at terminals or terminations, 52 K for accessible external surface.
Another surprising omission is that there isn't a criterion about no visible damage.

 

[JohnW2]

Maximum temperature rise of 47 K at terminals or terminations, 52 K for accessible external surface.

They are pretty (perhaps surprisingly) high figures. 52°K above ambient is hot enough to do significant damage to skin. I can but presume that real world sockets 'more than satisfy' that test, because I don't believe that even fully-loaded sockets normally run at external temperatures anything like that high in 'normal use', do they?!

Another surprising omission is that there isn't a criterion about no visible damage.

Maybe, but the test is of relatively short duration. Even at 52°K above ambient, it would probably take quite a long time for visible damage to appear - so if it passes the temp rise test, I very much doubt that it would become visibly damaged within the duration of the test.

Kind Regards, John

 

[stillp]

Yes, that's pretty hot, but no worse (in fact somewhat less) than the outside of a metal kettle. There's no reason for skin to remain in contact for more than a fraction of a second. I don't know how hot they get, I don't know anyone who's done the test. I assume though that the MK document you referred to earlier implies that at 23A the sockets reach the maximum allowed temperature.

Short duration? It's 4 to 8 hours. I might have expected some plastics to go brown or show charring.

 

[JohnW2]

Yes, that's pretty hot, but no worse (in fact somewhat less) than the outside of a metal kettle. There's no reason for skin to remain in contact for more than a fraction of a second. I don't know how hot they get, I don't know anyone who's done the test. I assume though that the MK document you referred to earlier implies that at 23A the sockets reach the maximum allowed temperature.

To remind you...

... I found the following, posted in December 2009 in the IET forum, purporting to be a direct quote from the MK Catalogue:

All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissible maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time.

Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.

MK recommend that users of their sockets consult professional design Engineers when designing installations to avoid the possibility of heat and mechanical stress to components and installations caused by overloading of MK socket-outlets.

So - 'browning of faceplate and damage of insulation of cable cores' at 22.3A and very significant damage (with a 'very real potential of fire') at 24A ... also possibly of interest....

Following the recent endless discussion about the 'current rating' of double sockets, I have now had the opportunity to discuss this with a technical support engineer at MK/Honeywell. I am therefore now fairly clear as to their position, even if it seems a rather unsatisfactory situation:

• 1. The statement in their technical literature for Logic Plus sockets which reads "Current rating: 13A per socket (except 3 gang, which is 13A total)" is not only confusing and ambiguous, but simply wrong - and his 'explanation' was that this literature was created by the marketing department, over whom the engineers have limited control! MK (MK's engineers) do not intend to imply EITHER that the double socket can only supply 13A total, OR that it can supply 26A total.
  
  2. Similarly, he did not really know why all double sockets have "13A" embossed on the back, again because this is not the intended 'rating' of either half or all of the double socket.
  
  3. MK do not claim, recommend or suggest that their BS1363 sockets have any greater current carrying capacity than anyone else's. In common with all manufacturers, they merely seek to comply with BS1363, in particular the 20A temperature rise test. MK's (engineers') only view on the 'rating' of their (and everyone else's) double sockets is therefore based on the BS1363 temp-rise-test figure of 20A - although he did add that he thought most designers would try to avoid a situation in which one double socket was likley to be loaded with as much as 20A (although it's not all that clear as to how that would be achieved - unless on installed only single sockets!).

So, that really answers the question I posed at the very start of that other infamous thread. The chap I talked to said that he would pass on my 'complaint' about the potentially misleading literature to their marketing department, but I don't think I'll be holding my breath whilst waiting for any changes! There doesn't seem anything more to discuss.

Short duration? It's 4 to 8 hours. I might have expected some plastics to go brown or show charring.

I may be wrong, but I would have expected browning to have taken very much longer than a few hours at the sort of temperatures we're talking about. There's no point in thinking about higher temperatures, because if a socket failed the temp rise test, an additional 'visible damage' test criterion would be superfluous.

Kind Regards, John

 

[plugwash]

Maximum temperature rise of 47 K at terminals or terminations, 52 K for accessible external surface.

Are you sure you don't have those figures reversed? I'd expect terminal temperature to rise more than external surface temperature.