BS 1363 13A Socket Continuous Max Load

This is undoubtedly an interesting discussion. It points out a number of defects with the standards system, and the use of these by manufacturers. I was having a discussion with a well-respected standards Engineer the other day, about the FACT that MCBs can become very hot at their nominal current, not even a current which will at some point cause tripping in some cases sufficient to cause the cases to brown and even become distorted. At one time (quite a long time ago) the cases were made of thermosetting plastic,  whereas I have just tested an new MK Sentry RCBO and the case is a thermoplastic and melts at about 200C or less. It is not labelled with a recycling type so identification is a bit difficult. I think it may well be uPVC, or a similar co-polymer, or possibly from the smell nylon. As you will be aware uPVC and nylon are easily formed by quite limited heat, typically plastic conduit.

All of these ratings, heating and other effects suggests a serious design problem, where the full operating envelope has not been considered properly. Our conversation was started because of the current note from manufacturers that they are unhappy with RCD current ratings not matching the maximum of the protected circuit protective devices. However whilst in Screwfix this morning there were various BG CUs on sale where the protected MCBs did not match this criterion!

It seems from all the comments above that many believe that the published ratings are not the ratings that can be used. This is a ridiculous conclusion, but whilst it may be true, this should not ever be the case, pointing out that specifications and standards are ALL totally unsatisfactory. I have no idea how to get this fixed, as manufacturers seem to be getting away with it, and using instructions to avoid any responsibility for this unsatisfactory situation. Any ideas? 

Sparkingchip: 
 

sparkiemike: 

At a recent Elex “seminar” Darren Staniforth from Scolmore made a comment that BS1363 socket outlets were only tested for 8A continuous load. This was news to me because my 1995 version of BS1363-2 says for the Temperature rise test the connected load will be 14A for a minimum continuous period of 4hours or longer until stability is reached and max duration of 8hours. 

 

The 14 amp test load is beyond the rating of the socket, plug and any appliance that should be connected.

So the test covered misuse of the socket by someone using a multiway socket adapter, which is something I see very frequently, but modern adapters are fused so it is a throwback to the nineties, after nearly twenty years there may be an assumption that people have sufficient sockets in their homes, but that is far from true, I regularly see things like the kettle, toaster and microwave all plugged into a single socket using a multiway adapter or the washing machine and dryer.

Having said that how long does it take for a 14 amp load to blow a 13 amp fuse?

In my view testing at 14 amps is reasonable for a plug and socket rated at a nominal 13 amps. Not for deliberate misuse, but to allow for manufacturing tolerances and mains voltage variations. Consider an appliance designed to use 13 amps but that actually uses 13.5 amps due to manufacturing tolerance at nominal voltage, and that uses 14 amps at 250 volts which is within the permitted range.

13 amps should be regarded as the NOMINAL rating and not as an absolute maximum. A bit like motor car tyres that are marked “110 MPH” planned use at a significantly higher speed would be foolhardy. BUT I would not expect the tyre to burst or come apart at 115 MPH that was reached briefly and inadvertently due to a speedometer reading 5% low.

“What to do about it”

A good start in my view would be testing as follows. Both tests at 35 degrees ambient, to allow for heatwaves.

Firstly an endurance test for 1,000 hours at 14 amps. This to allow for mains voltage variations and manufacturing tolerances.

Secondly, a test at 20 amps for whatever time it takes for the 13 amp fuse to blow. This to allow for overloading of a multi gang extension lead. The plug and socket should withstand the overload for the time it takes for the fuse to operate.

How do they manage abroad ? How many amps can continental 16 amp sockets supply ?

Without a fuse to heat things up, possibly they have less of an issue. However many continental sockets were originally only rated at 10A rather than 16A - which, I suspect, is why we see many appliances limited to around 2.2 or 2.3kW by manufacturers - any more and they cut themselves off from a substantial chunk of their potential market.

   - Andy.

A shucko socket is and as far as I know always has been  nominally 16A (not quite 4kW)  and until the advent of modern MCBs, used to be protected by a 16A fuse, commonly the Neozed style (" bottle fuse" ). With various regs changes the number of sockets and lights per fuse has varied a bit, but in any case to allocate the full 16A to one load would be unusual, as it leaves nothing for the rest of the circuit.

The pins are normally nickel plated so do not go brown/ black and grotty over time like plain brass would.

(As an aside, the slightly thinner pinned Russian plug that looks a bit like it that used to turn up with East German kit  does however have bare brass pins, and they can certainly corrode, and then go sizzle and pop when they age a bit, but being undersized does not help either.)

Oddly the same pin dimensions as the schucko occur in Swiss plugs (with an earth pin however) but supplied by 13A breakers and called 10 amp points.

Not to be confused with he 2 prong euro-plug with its thin inwardly sprung pins that fits everything badly is nominally rated at 2.5A, and even fits a 13A socket if you open the shutters for it - but please only do that if it is your own fused extension socket used for nothing else afterwards!

Mike.

“using instructions to avoid any responsibility for this unsatisfactory situation. Any ideas? ” Blimey Dave lad, you`ll be blaming manufacturers of plastic consumer units for the let us change towards metalclad consumer unit fiasco next ? ?

broadgage: 
Firstly an endurance test for 1,000 hours at 14 amps. This to allow for mains voltage variations and manufacturing tolerances.

Blimey, that would be over 3 MWh or nearly a whole year's leccy for me.

A few years ago I went to the local German owned WB central heating boiler factory, they had gas boilers that had been running flat out on test for several years, I passed comment that they must never run short of hot water in the cloakrooms, the guy showing us around looked blank then said all the hot water is dumped.

It would seem appropriate to make use of gas and electricity used for testing. 

Secondly, a test at 20 amps for whatever time it takes for the 13 amp fuse to blow. 

Needs to be higher - some 13A fuses will simply not blow reliably at that current.

We could perhaps learn something from the Mil Spec approach, and look at accelerated ageing in a damp atmosphere or after salt-water spray - there are hard gold-plated brass plugs and sockets with far smaller diameter pins than the 13A ones that take quite a bit more current, and they are very reliable indeed.

Mike.

I have a funny story about a well-known UK electronics company now defunct, so I feel not too bad to mention it,  that had complex environmental chambers for this sort of test, where at Christmas some production line technicians sneaked in some mince pies and things for an end of season ‘do’ . The intention was to use the ‘ovens’ to allow  these up to be enjoyed warm.  Due to a most tragic programming cock-up, when the oven doors closed some were given the salt spray treatment, instead of the dry heat that was intended…

Chris Pearson: 
 

broadgage: 
Firstly an endurance test for 1,000 hours at 14 amps. This to allow for mains voltage variations and manufacturing tolerances.

Blimey, that would be over 3 MWh or nearly a whole year's leccy for me.

I do not believe that full voltage is needed when testing current carrying capacity. 14 amps at a much reduced voltage would do the job.