Live pin on tumbler hot even after

[vice]

Hi. Tumble dryer with a new plug plus new socket face. It's on the end of a long run, maybe 20 meters. Could that be an issue?

 

[ericmark]

Obviously, BOTH the Line and Neutral pins and socket contacts are carrying the same current.

You may have fuses in line and neutral in Australia, we did have at one point 110 volt plugs with fuses for both lines, but in the UK the fuse is only on the line pin, the neutral is not fused, so heat from fuse will be concentrated on the line pin.

Having a long run to a heat pump tumble drier could cause a problem, but since only using around 600 watt unlikely. A long run to a resistive heater drier will not affect it.

The pin being hot is normal, but being too hot is not, as @ebee says, easy to miss interpret, cold after all is a measurement of heat.

 

[JBR]

Aha! So it WAS a tumble drier, as I said!
Only joking! Sorry for overuse of exclamation marks!

 

[FrodoOne]

You may have fuses in line and neutral in Australia, we did have at one point 110 volt plugs with fuses for both lines, but in the UK the fuse is only on the line pin, the neutral is not fused, so heat from fuse will be concentrated on the line pin.

Australian Plugs do not have Fuses in them.
While they are rated at 10 A, they are usually supplied by 20 A rated Circuits.
(Power Strips are required to utilize a 10 A Circuit Breaker, which will operate if more than 10 A is drawn by plugging in a number of devices drawing more than 10 A in total.)

As far as I know
(apart from the plugs used on North American 120 V strings of "Christmas lights -
see

- from 15:20 to 16:15 )
BS 1363 plugs are the only ones which contain a fuse - one end of which is connected to the Line pin.

"The operating time (of a fuse) is not a fixed interval but decreases as the current increases.
Fuses are designed to have particular characteristics of operating time compared to current.
A standard fuse may require twice its rated current to open in one second,
a fast-blow fuse may require twice its rated current to blow in 0.1 seconds,
and a slow-blow fuse may require twice its rated current for tens of seconds to blow."

Fuse (electrical) - Wikipedia

en.wikipedia.org

The mass of the "fusible element" is small , when compared to the mass of the fuse "endcaps",
which are both small,
when compared to the Line Pin and the holder - at the other end.
Hence, it is difficult to imagine any cartridge fuse in a BS1363 plug carrying up-to its rated current
transferring any significant amount of heat to the Line Pin,
such that it "was hot hot, like touching a metal kettle." (Post #1)

 

[ericmark]

The British 110 volt (55-0-55) plugs did have fuses which were actually the pins, there was a grove in the outer shell of the fused type, and not in the unfused type, so the fused type would fit in all sockets, the unfused would only fit in individually fused sockets. This allowed one to have a ring final circuit with 110 volt.

Today we need overload protection at the sockets

and I have seen where this is missed out, many site fires, the big problem is the portable transformer the yellow brick should really be banned, they put a thermal overload on the incoming supply,

often rated at 12 amp, so the output can be 12/55x230=50 amp with 1.5 mm² extension plugged into another 1.5 mm² extension which is common on building sites, the resistance of the cable can mean not enough current is drawn with a shorted line to trip the thermal overload, so the cable melts, and set scaffold boards on fire.

If one does a risk assessment of 110 volt from brick transformers compared with 230 volt RCD protected, I can't see how 110 can work out safer, but our rules say it must be used. The larger transformers do have MCB's on the outlets they are OK, it is the yellow brick which is the problem.

However out 13 amp plug and socket is what we are talking about, and again the new safety feature has resulted in the line and neutral pins being reduced in size and insulation put on them to stop one being able to touch live pins when inserting or removing, and this in turn has reduced the heat transfer into the socket, so the plugs tend to run hotter.

Fake 13 amp fuses make this worse

we are told we need to weigh them,

Yes and we are really going to do that? There are other signs but most of us expect fuses bought over the counter to be genuine, I find I buy 3 amp and maybe 5 and 7 amp, but 13 amp I gain as changed when wrong size found, so my 13 amp fuses could come from anywhere.

 

[FrodoOne]

However out 13 amp plug and socket is what we are talking about, and again the new safety feature has resulted in the line and neutral pins being reduced in size and insulation put on them to stop one being able to touch live pins when inserting or removing, and this in turn has reduced the heat transfer into the socket, so the plugs tend to run hotter.

This has been stated before
BUT
how does the "half-insulation" reduce the heat transfer to the socket "fingers"?
These "fingers" are in contact with the bare metal of the pins and are not in contact with the insulation.

The minimum dimensions of the Line and Neutral Pins of a BS 1363 Plug are quite specific and are shown in https://wiki.diyfaq.org.uk/index.php/Mains_plug
These are 6.22 mm * 3.99 mm
giving a CSA of 24.258 mm²
which is 9.7 times greater than 2.5 mm² conductor.

However, I can find no specification for the thickness of the "Half Insulation" for these Pins. (Can you?)
Australian Plug pins now have similar insulation,
although these Australian Pins are only 6.3 mm * 1.6 mm. (CSA 10.08 mm²),
which is 4.034 times greater than a 2.5 mm² conductor.

My examination of a cross section of one of these "Australia" Pins leads me to believe that the insulation is about 0,3 mm
leaving a CSA of 5.7 mm * 1 mm = 5.7 mm²,
2.28 times greater than 2.5 mm² conductor.

If BS 1363 Pins have Half-Insulation thicknesses if 0.3 mm
the CSA will be 5.62 mm * 3.3 mm = 18.546 mm²
which is 7.4184 times greater than 2.5 mm² conductor.
Even if BS 1363 Pins have Half-Insulation thicknesses if 0.5 mm
the CSA will be 5.22 mm * 2.9 mm - 15.138 mm²
which is 6.0552 times greater than 2.5 mm² conductor.
Hence, even at the greatest likely reduction in the "Heat-Sinking" capacity of a BS 1363 Pin,
it is still over 6 times that of a 2.5 mm² conductor.

The "Conduction" to the Socket-Outlet "fingers" will still be the same as it was, in the past.

Since the Electrical Conductivity must remain the same
so must the Heat-Conductivity of these "contacts",
with or without the Half-Insulation of the "Pins".

 

[ebee]

how does the "half-insulation" reduce the heat transfer to the socket "fingers"?

I think it probably does but to what extent I`m not sure.
Take two pins of the same size and CSA, part cover one with electrical insulation should increase a bit of thermal insulation too?
the contact springs on a socket should be the same on both variations therefore heat loss on the insulated pin should be slightly less, how significant I`m not sure though, I would expect that it might run a little warmer as in both variants there will be a bit of air around them.
Just a thought.

 

[FrodoOne]

I think it probably does but to what extent I`m not sure.
Take two pins of the same size and CSA, part cover one with electrical insulation should increase a bit of thermal insulation too?
the contact springs on a socket should be the same on both variations therefore heat loss on the insulated pin should be slightly less, how significant I`m not sure though, I would expect that it might run a little warmer as in both variants there will be a bit of air around them.
Just a thought.

Heat travels by Conduction, Convection and Radiation.
Half-Insulating "Pins" will not reduce Thermal Conduction, if it does not reduce Electrical Conduction.

As I believe that I "demonstrated", a BS 1363 Pin is a significant "heat-sink".

Convection could be slightly reduced.
However, it is hard to see how this heat transfer method could ever have been "significant" (even without Half-Insulation),
given the confined space involved!

Much the same comments apply to Radiation, since the temperature differentials are (or should be) quite small !

 

[Harry Bloomfield]

This has been stated before
BUT
how does the "half-insulation" reduce the heat transfer to the socket "fingers"?
These "fingers" are in contact with the bare metal of the pins and are not in contact with the insulation.

The insulation on the pins, limits the pins ability to radiate the heat, most of which will be produced by the fuse, and in the case of a worn fuse holder, a great deal more from the contacts to the fuse.

Hence, even at the greatest likely reduction in the "Heat-Sinking" capacity of a BS 1363 Pin,
it is still over 6 times that of a 2.5 mm² conductor.

Brass, has much lower conductivity/higher resistance than copper.

 

[FrodoOne]

The insulation on the pins, limits the pins ability to radiate the heat, most of which will be produced by the fuse,

However, the "Radiation" would not be Zero, especially if the Insulation were Black.

The insulation on the pins, limits the pins ability to radiate the heat, most of which will be produced by the fuse, and in the case of a worn fuse holder, a great deal more from the contacts to the fuse.

"a great deal more from the contacts to the fuse."

If this really is true,
it seems to be a case against having fuses -
actually, with miniscule "heat output", while operating below their "rupture" current -
but more against having poorly designed/maintained "push-in" connections in any Plug.
(Virtually) the only situation where this occurs is with BS 1363 Plugs.

Are there any "studies" into this matter?

Brass, has much lower conductivity/higher resistance than copper.

One source (http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thrcn.html )
gives the comparative thermal conductivity of Brass as compared to Copper as
109/385 = 0.283

However, the possible "worst case scenario" which I suggested of
"Even if BS 1363 Pins have Half-Insulation thicknesses if 0.5 mm
the CSA will be 5.22 mm * 2.9 mm - 15.138 mm²
which is 6.0552 times greater than 2.5 mm² conductor."

The "6.0552 times greater" Brass conductor would still have a thermal conductivity of
6.0552 * 0.283 = 1.714 times Greater than a 2.5 mm² Copper conductor.

 

[Harry Bloomfield]

it seems to be a case against having fuses -

Even back in the days, when we had good solid plugs and sockets, with plenty of brass in them, and no insulation on pins - there were sometimes examples of over-heated plugs and sockets. Both are now pared down to minimum cost, so one needs to buy carefully, if a plug or socket is intended to be used regularly for a maximum load appliance.

One source (http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thrcn.html )
gives the comparative thermal conductivity of Brass as compared to Copper as
109/385 = 0.283

I was of course referring to electrical conductivity, and electrical resistance!