Burnt Out 13-Amp Plug

[plugwash]

I don't think there's a lot wrong with the "BS1363 plug/socket system" (the Standard), so that a lot of the issue is presumably that some of the products are not necessarily BS1363-compliant.

Well the question is why do other types of plug/sockets, for example BS546 and IEC60309 seem to do much better?

Is it because there is less pressure to drive costs down?

Is it because they avoid heating caused by the fuse and/or fuseholder?

Is it because the pins are bigger (15A BS546 pins are substantially bigger than BS1363 pins, but 16A IEC60309 pins are not)

Is a round pin and sleeve design fundamentally better than the rectangular pin with a clip gripping two of the four sides?

Is it some combination of the above?

 

[JohnW2]

Well the question is why do other types of plug/sockets, for example BS546 and IEC60309 seem to do much better?

Albeit you are responding to something I wrote over 2 years ago ...

Well, assuming that you are right in saying that (and I imagine that you probably are), I suspect that the short answer is that they are appreciably 'over-engineered' than they need to be to satisfy their 'ratings' (which I suppose could be re-worded as 'more expensive than they need to be'), in at least some (maybe most) of the senses that you go on to list.

The point of my 2-year-old comment was that it would be reasonable to expect that the Standard for a "13A plug" would require it to nearly always remain OK if it were carrying 13A almost continuously.

Kind Regards, John

 

[EFLImpudence]

I have said before that I have encountered a 13A plug and socket - with plug-in timer - which had 'for ever' been supplying a 3kW immersion with no damage.

I suppose once one little thing goes wrong, e.g. a fault causing overheating in the fuse holder leading to loosening, then it escalates.

 

[JohnW2]

I have said before that I have encountered a 13A plug and socket - with plug-in timer - which had 'for ever' been supplying a 3kW immersion with no damage.

You have, and that doesn't surprise me. I don't personally have quite that, but I do have plugs which have carried high currents for recurrent relatively long periods for decades without any signs of thermal damage.

I suppose once one little thing goes wrong, e.g. a fault causing overheating in the fuse holder leading to loosening, then it escalates.

Yes, quite probably.

Kind Regards, John

 

[JohnD]

In 5 years the customer need to change the socket or the wiring because the customer no wants to run a heater of that socket made for a lamp.

although some other countries use a universal plug that contains its own (appropiately rated) fuse, and a universal socket.

 

[Deleted member 18243]

One of my regular calls is to a factory which uses infra red heaters (3kw) plugged in to 13 amp sockets, pays for my wine

Why don't you suggest they use a more suitable method of connection?

 

[JohnW2]

Why don't you suggest they use a more suitable method of connection?

... and cut off payments for the wine supply?

Kind Regards, John

 

[ericmark]

when fuse-related overheating occurs in a BS1363 plug or FCU, it seems that it is almost always due to poor connections, not to the fuse per se.

This is what came first argument, did the fuse overheat and anneal the holder causing a poor connection and so a thermal run away, or was the connection bad first? All we know is the fuse and plug, and likely the socket have been damaged, we have no idea which came first.

I have not found many FCU damaged due to overheating compared to plugs, I would assume due to it being larger so can transmit the heat away better.

I would say the larger the plug the better, however there have been some exceptions, before the finger protector there was a version with a very small distance socket to back of plug, I know sold by MANWEB the line pin formed the spring to grip fuse, and was rather good at transferring heat from fuse.

When my dad's house was built (1954) the immersion heater had a dedicated 15 amp supply and the old round pin 15 amp plug and socket, this allowed the plumber to change the immersion heater without him needing to wire a plug, and it did not produce heat as long as in good order so unlikely to overheat in the cupboard housing the immersion heater, I am sure the old 15 amp plug could overheat, but never found one, as to if due to not so many used during my working life, or if they did not suffer from overheating I can't say.

 

[JohnD]

the round-pin plugs have a good contact when new, but, with age, the part-round "tube" in the socket wears and becomes loose. the advantage of a square pin is that you can have a sliding contact of flat surfaces with spring action, the spring will take up any wear.

you don't often see old 15amp plugs and sockets that are worn out, but they are common on theatrical lights prior to modern Led systems.

 

[JohnW2]

This is what came first argument, did the fuse overheat and anneal the holder causing a poor connection and so a thermal run away, or was the connection bad first? All we know is the fuse and plug, and likely the socket have been damaged, we have no idea which came first. .... I have not found many FCU damaged due to overheating compared to plugs, I would assume due to it being larger so can transmit the heat away better.

There's a lot of speculation going on in this discussion

I feel sure that someone must have 'done the experiments' to determine what temperature is reached by BS1362 fuses in various situations, but I certainly haven't seen the results of such experiments. Has anyone seen any such data?

Kind Regards, John

 

[ericmark]

The temperature must be variable depending on ambient temperature and air flow around the plug, I am sure the spec says what energy must be dissipated by the plug, and a new plug in a new socket in free air should clearly be able to remove the energy from the area fast enough to stop overheating.

I note with interest some double sockets rated at 13 amp the pair, and also 20 amp the pair where we all know it could have a 26 amp load.

To be fair the 13 amp total load seems to be for special sockets, be it filtered, USB, RCD or other, but seems to me odd, as how can the installer know what will be plugged in. Also since no fuse in the socket the only heat in a socket is what is transferred from the plug.

In theory a faulty plug should not affect the socket, in practice we know it does. Heat clearly travels through the pins, or a faulty plug would not affect the socket, so reduction in the metal of the pin must have a detrimental effect on the system.

 

[bernardgreen]

For what it is worth

I measured the voltage difference between the caps of a 13 amp fuse when supplying a fan heater

1 kWatt load Vd = 0.034 V
2 kWatt load Vd = 0.073 V

Heat created in the fuse wire assuming 4 Amp current per kWatt load
W = V x I

1kW load-------0.034 Volts x 4 Amp = 0.136 Watt

2 kW load-------0.073 Volts x 8 Amp = 0.536 Watt

Estimating that a 3 kW load will take 12 amps and produce a Vd across the fuse of 0.102 Volt ( 3 times 0.034 )

3 kW load--------0.102 Volts x 12 Amp = 1.22 Watt

The voltage measurement was from the caps of the fuse and therefore did not include any voltage drops ( heat sources ) created by poor contact between fuse holder and the fuse caps or between plug pins and socket receptacles or cable and terminals.

Not recommended for DIY investigations, it is risky if the meter is not safe to use on 230 Volt

 

[FrodoOne]

Well the question is why do other types of plug/sockets, for example BS546 and IEC60309 seem to do much better?

Is it because there is less pressure to drive costs down?

Is it because they avoid heating caused by the fuse and/or fuseholder?

Is it because the pins are bigger (15A BS546 pins are substantially bigger than BS1363 pins, but 16A IEC60309 pins are not)

Is a round pin and sleeve design fundamentally better than the rectangular pin with a clip gripping two of the four sides?

Is it some combination of the above?

It is a strange "myth" that some think that bigger "pins" are better at carrying "current" than smaller "pins", however the "pins" may be defined.
The "current carrying capacity" depends almost entirely as to how the "flexible contacts" in the socket-outlet "mate" with the pins concerned.
This should be obvious, since a 2.5 mm² CSA "conductor" is quite capable of carrying 20 A.
Any "pin" larger than 2.5 mm² CSA is quite capable of carrying more current but the contact with the pin is the "limiting factor".

The overly large pins of the BS 1363 plug are a "bit of a joke" when compared of the "slim" pins used with sockets-outlet such as these (https://commons.wikimedia.org/wiki/...cket_styles_for_different_current_ratings.jpg), where the same relatively thin "pins" are rated to carry from 10 A up to 32 A, with the change of the width of the pins (and the shape of the Earth pin) being related only to the "need" to prevent the insertion of a "higher" rated plug into a "lower" rated socket-outlet.

 

[JohnD]

For what it is worth

I measured the voltage difference between the caps of a 13 amp fuse when supplying a fan heater

1 kWatt load Vd = 0.034 V
2 kWatt load Vd = 0.073 V

Heat created in the fuse wire assuming 4 Amp current per kWatt load
W = V x I

1kW load-------0.034 Volts x 4 Amp = 0.136 Watt

2 kW load-------0.073 Volts x 8 Amp = 0.536 Watt

Estimating that a 3 kW load will take 12 amps and produce a Vd across the fuse of 0.102 Volt ( 3 times 0.034 )

3 kW load--------0.102 Volts x 12 Amp = 1.22 Watt

The voltage measurement was from the caps of the fuse and therefore did not include any voltage drops ( heat sources ) created by poor contact between fuse holder and the fuse caps or between plug pins and socket receptacles or cable and terminals.

View attachment 268269

Not recommended for DIY investigations, it is risky if the meter is not safe to use on 230 Volt

If I understand you correctly,

"3 kW load--------0.102 Volts x 12 Amp = 1.22 Watt

A fuse in good order can release about as much heat as a 1W lightbulb

Which is trivial.

 

[bernardgreen]

Which is trivial

Not in a totally enclosed space where the only route for heat to exit the space is by conduction along the Live pin into the metal of the socket's receptacle.