Fuses/Connections "Warm To The Touch"

[sw-uk]

Hi,

Is it normal for fuses and connectors to get warm "just warm never hot" when their in operation and current is flowing even with clean and solid connection with solid continuity.

I've found on higher fused circuits like on a car, the blower fan on my vehicle fused for 30amp and when its been on full, you'll find the fuse legs are slightly warm never hot though, no signs of burning or melting. It's the same with my 12v car vaccume cleaner, it draws 6.5amps, after use the tip of the cigarette plug is fairly hot but never any sign of melting or burning etc. The plug on is it 16amp rated.

 

[Lightium]

As low a resistance, they still resist electron flow and radiate heat.



Heating of a mass:
V I t n = c m (delta t)
V=volts
I=current
t=time
n=efficiency
c=specific heat
m=mass
delta t=differance in temp

 

[Pommie]

Yes, it's normal. In the UK they placed fuses in 13A plugs. If you use something like an electric heater, the live pin of the plug gets so hot that the colour of the plastic surround goes brown (yellow?).

Like this,

The fuse is connected to the end of the burnt leg.

Mike.

 

[Diver300]

A fuse will always get warm if run near it's rating. The rest depends on the quality of the connector.

There shouldn't be any burning on a 13 A plug like Pommie showed, so I would have said that was a faulty one, but of course the same plug would have been fine on most loads. UK plugs will usually take 13 A / 3 kW continually without burning, but the plug will be warm as the fuse will heat up.

Car cigar lighter connectors are often poorly designed and will overheat at their rated current. They often have fuses in the them that may generate some heat as well. As the cigar lighter is designed to pop out when hot, the plugs can't have a sliding contact on the middle pin, so there is just a push contact and that's more difficult to get a good connection with.

The plug-in chargers for electric cars usually have temperature sensors in the wall plug so that they can shut off or cut down the charging current if the plug gets hot, as that can be caused by a worn socket.

 

[Pommie]

There shouldn't be any burning on a 13 A plug like Pommie showed, so I would have said that was a faulty one, but of course the same plug would have been fine on most loads. UK plugs will usually take 13 A / 3 kW continually without burning, but the plug will be warm as the fuse will heat up.

Not lived in the UK for 20 years but remember well the brown ring on the live pin of the 13A plugs. Check your kettle lead/plug as they run close to 13A.

Maybe they just got better at making them. I'd guess the're all moulded on plugs now with better production facilities. In my day (hate that saying) they were all screwed together like in the above picture.

Mike.

 

[Nigel Goodwin]

Not lived in the UK for 20 years but remember well the brown ring on the live pin of the 13A plugs. Check your kettle lead/plug as they run close to 13A.

Maybe they just got better at making them. I'd guess the're all moulded on plugs now with better production facilities. In my day (hate that saying) they were all screwed together like in the above picture.

Mike.

13A plugs shouldn't (and don't) do that - if they do the plug was badly fitted, or the fuse 'clamps' were loose, making a poor contact on the fuse. Or, the socket it plugged in to had loose contacts, and the heat transferred up the pin.

If a plug ever goes like that, replace it - if it's because the fuse 'clamps' were loose the metal of the clamp will have been 'de-tempered', and even if you squeeze it to make it tight again it will tend to loosen off and overheat again.

We used to take work experience kids from school where I used to work - one of the things I always did was try to teach them to fit a 13A plug - with them only there for a week it was unusual to find one able to do it satisfactorily.

As for heaters, you really need a decent quality plug - the MK ones were usually the best.