13A plugs will not carry 13A !

[ricicle]

I have a Bain Marie at work that has a full setting on the simmerstat. When this is set to full (which is always) the appliance takes 12.8 amps continuously.
I have tried various makes and combinations of plugs and sockets, same make together, different makes together. The most frequent combination I have used is Duraplug plugs and MK sockets. Whichever is used the plugs are always burning up through heat created at the connection between the fuse and the L pin. I have tried tweaking the cradle to grip the fuse tighter but to no avail. Has anybody else experience this with high loads ?

The appliance is supplied with a fitted plug and says it is rated at 13A

 

[JohnW2]

I have a Bain Marie at work that has a full setting on the simmerstat. When this is set to full (which is always) the appliance takes 12.8 amps continuously. I have tried various makes and combinations of plugs and sockets, same make together, different makes together. The most frequent combination I have used is Duraplug plugs and MK sockets. Whichever is used the plugs are always burning up through heat created at the connection between the fuse and the L pin. I have tried tweaking the cradle to grip the fuse tighter but to no avail. Has anybody else experience this with high loads ?

I've certainly experienced plugs getting quite warm with sustained high loads, but never to the extent of causing obvious damage or 'burning up'. I can't say that what you describe surprises me and I imagine the reason we don't see a lot more of it is that long-term sustained loads anything like 13A on a plug/socket are fairly unusual.

I take it that, as well as 'tweaking the cradle', you've also tried clean the end of the fuse. If it's always occuring at the pin end of the fuse (slightly surprising, given that it's usually much better heat-sinked than t'other end) are you sure that the pin/socket contact is not generating at least some of the heat?

I suppose this all goes to support the adage that loads >2kw which operate 'continuously' should ideally be fixed wired, and ideally on their own circuit - but, there again, I suppose you could experience the same problem with the fuse of an FCU! I supposed a dedicated circuit with a 16A MCB and no FCU would be the safest!

Kind Regards, John.

 

[xr4x4]

I was going to say, maybe hardwiring is a better option and a FCU might cope better.

 

[JohnW2]

I was going to say, maybe hardwiring is a better option and a FCU might cope better.

Indeed - although, as I said, the FCU might present a similar problem - since the receptacles for the (same type of) fuse can't be much different - and there's probably a bit less heatsinking in an FCU than with a plug+socket.

Kind Regards, John.

 

[ban-all-sheds]

How about every time it happens reporting the seller to Trading Standards for selling items not fit for purpose?

 

[westie101]

It all depends on definitions is it 13A continuous or 13A max? I have no idea

 

[JohnW2]

It all depends on definitions is it 13A continuous or 13A max? I have no idea

I think their documentation usually says 'maximum' but that's really a bit ambiguous, since it could mean (and many would take it to mean) "maximum continuous". I don't remember precisely what BS1363 says, but I seem to recall the temperature rise test is over a long enough period for temperature stability to be achieved - so effectively 'continuous', I guess.

Kind Regards, John.

 

[JohnW2]

Whoops; duplicate.

 

[westie101]

It's just something from my side of the meter where we are used to, at times, having 3 or more different ratings for the same situation for the same equipment. These are usually connected to the expected "loss of life expectancy" of the equipment if operated at a higher rating for a short time!

e.g we know a 100A cut-out can carry 146A (the fuse overload) for a short time, it will carry 100A for an extended time (8hrs +) but we would only rate it at 80A continuously.
The limiting factor we have found is that overheating anneals the spring contacts on the fuse carrier.

A network transformer has a rating of up to 136% in cold (below 5C) conditions, it can carry this continuously without any loss of expected life

 

[333rocky333]

We get it a lot with commercial griddles. and plug in friers rated at 13amp and supplied with fitted plugs.
I found the best combination was Mk socket with an Mk TOUGHPLUG However ive seen them burn up to, when tong tested they were running at just under 13 amps though

 

[ericmark]

I think the problem is the 13A plug now has a plastic sleeve to stop fingers touching pins when being withdrawn and this has reduced the firmness of the plug and contact area.
For items taking near to full load then the blue 16A plug and socket is far better the longer pins make better contact.

 

[JohnW2]

It's just something from my side of the meter where we are used to, at times, having 3 or more different ratings for the same situation for the same equipment. These are usually connected to the expected "loss of life expectancy" of the equipment if operated at a higher rating for a short time!

Yes, the same is true in many fields I've been associated with. The problem in this case is that neither you nor I are certain of what sort of 'maximum' 13A is for a BS1363 plug+socket. Given that such items are intended for widespread use by totally unskilled people, one would hope it should be a truly 'continuous' rating, but I don't know for sure that is teh case.

Kind Regards, John.

 

[mfarrow]

Have you tried dielectric grease? I won't help the connection, but may stop the corrosion that ultimately leads to it failing.

Other than that, I guess soldering it in may be a last resort, though never done this so I don't know whether they pop or not. Also, they may contain solder at the ends, so use a 60:40 solder, a modern fuse, and as little heat as you can.

 

[bernardgreen]

Back in the 1970's the GPO regulations set a maximum load of 9 amps on 13 amp plugs used in GPO buildings. The reason was lower cost plugs were melting or burning.

Where it was necessary to have more than 9 amps special permission had to be obtained and only a specific brand could be used. If I recall correctly MK branded plugs were the only ones allowed fro more than 9 amps


Westie is correct about the spring clips being annealed by the heat that the fuse generates when carrying 13 amps. Reduction in the amount of copper / brass in the plug ( and sockets ) has reduced the ability of the plug to dissapate this heat and keep the temperature low.

For 3Kw continuous load a 13 amp plug is not suitable ( in my opinion ) and a 13 amp FCU using a normal 13 amp fuse will have tbe same problem of softening fuse holder clips.

An FCU with a bolted in fuse would be better.

Alternatively provided the manufacturers will confirm that internally the equipment can safely withstand 16 amps then I would use a dedicated supply circuit with a 16 amp MCB ain the circuit and no fuse at the point of connection

 

[JohnW2]

Alternatively provided the manufacturers will confirm that internally the equipment can safely withstand 16 amps then I would use a dedicated supply circuit with a 16 amp MCB ain the circuit and no fuse at the point of connection

Indeed, as I said, that would clearly be the best option for a high semi-continuous load.

As discussed before, equipment manufacturers shouldn't really rely on external overcurrent devices to protect their equipment, but I know that many do specify an MCB/fuse rating for the circuit. The type of equipment we're talking about is likely to come with instructions saying that it should be connected with a plug fittted with a 13A fuse - so someone hard-wiring it would have to decide whether they were happy to disobey those instructions!

Kind Regards, John.