Hot plug !?

flynnboy

Hi

I have a 3kw convector heater and the plug at the socket is getting hot. Today I smelt plastic and when I opened up the plug the top end of the fuse holder was scorched and had almost welded itself to the plastic !

Does anyone know why this should be happening ? I have another heater exactly the same and it's plug is NOT getting hot. The heater in question was recently repaired.

Thanks for any advice

davelerave

i thought 2.5kw' was the max for 13amp portable appliances.
i think a 3kw sustained load will overheat plugs and socket probably

flynnboy

davelerave wrote: »

i thought 2.5kw' was the max for 13amp portable appliances.
i think a 3kw sustained load will overheat plugs and socket probably

I don't think that is the reason. As I said I have another identical heater running on the same circuit and it's plug is not getting hot.

Davy

flynnboy wrote: »

The heater in question was recently repaired.

Might be a place to start. Bring it back to where you got it repaired

davelerave

replace socket and plug is the solution to the problem

but only if there's no overload issues ,otherwise prob will recur

i assume heater is still 3kw ,check with meter or clamp

meercat

Agree with davelerave. Replace socket and plugtop.

kevez

flynnboy wrote: »

I don't think that is the reason. As I said I have another identical heater running on the same circuit and it's plug is not getting hot.

2 running on the same cirsuit ? thats not good for the circuit. just change the fittings (socket and plugtop) they might have a loose connection

fizzynicenice

change le plug

kaizer13

3kW appliance should be connected in through a switched and fused spur unit and not through a plug and socket. The fact that you are getting away with it on one of the heaters does not make it correct. The one that is overheating the plug is a clear warning of why it should not be done that way.

2011

kaizer13 wrote: »

3kW appliance should be connected in through a switched and fused spur unit and not through a plug and socket. The fact that you are getting away with it on one of the heaters does not make it correct. The one that is overheating the plug is a clear warning of why it should not be done that way.

This is not correct. 3kW appliances are often pluged into socket circuits. A good example is an electric kettle, these are often rated at 3kW.

http://www.coopersdirect.com/pageview.php?page=show_product&ecommerce_stockcode=5011423121437

The BS1363 plugtop is designed for a maximum load of 3.2kW, see link:

http://en.m.wikipedia.org/wiki/BS_1363?wasRedirected=true

A 3kW resistive load (which is essentialy what a heater is) will only draw 13 amps. The 13A fuse in the plugtop (BS1362) is able to take this.

Dimplex sell their full range of electric heaters in Ireland, here is an example of a 3kW plug in heater:

http://www.uk-plumbing.com/brochure/dimplex/contrast.pdf

http://www.choiceful.com/choiceful-id-104076-Dimplex-Electric-Fan-Heater-3Kw-DXFF30TS.html

The heat generated in the plug= I^2 R

Which is the square of the current times the resistance. So what does this tell you? It tells you that if the resistance in the plug (or socket) is low then the heating effect at that point will be low. In your case it there is a high resistance here. For that reason I would do as Dave suggested and replace the plug and socket (just to be sure). You may find a loose connection here or perhaps the plug and socket are just not connecting to each other properly.

Solair

Sockets have springy contacts inside them which make contact with the pins of the plug. Over time, with use, these springs wear and loosen.

The result of this is that the pins start to make increasingly poor contact with the terminals in the socket as the springs deform.

You will notice that an old socket may not really grip plugs very firmly anymore.

The pin will still make contact, but the surface area touching the terminals of the socket will be significantly reduced.

The power has to flow through this reduced surface area, which causes the pins to heat.

Other potential causes:

Loose connections at the back of the socket.
Loose or poorly wired connections in the plug.
Damaged / loose / deformed fuse holder in the plug.


I would strongly suggest changing the socket, and preferably get a good brand like MK to replace it.

If the plug's not a moulded-on type, you should also replace that using a good quality plug.

danjo-xx

flynnboy: As I said I have another identical heater running on the same circuit and it's plug is not getting hot.

On mature recollection:D if my memory serves me right, the maximum load for a standard 2.5mm cable circuit is 3kw and you have 2x3kw heaters on same circuit so no wonder the plastic is melting....but why didn't the fuses blow, I dunno.


just my 2cents worth.

2011

On mature recollection if my memory serves me right, the maximum load for a standard 2.5mm cable circuit is 3kw

That would be a good design guide! In the real world the electrician has no control over what will be plugged into the socket cicuit. A 2.5 T&E can take 26A for which is the load from 6kW of heaters with a PF of 1

Also of all the heaters will have built in stats so they may not be consuming 3kW 100% of the time.

and you have 2x3kw heaters on same circuit so no wonder the plastic is melting

The load of both heaters should not be flowing through a single plug. There should not be a melting plastic situation if all sockets and plugs were in good condition and installed properly.

....but why didn't the fuses blow, I dunno

When both heaters are drawing 6kW between them the current drawn will be 26A (if they are both turned up fully). The chances are the circuit is protected by a 20A B type MCB. This level of current for long periods of time is not sufficient to cause a 20A MCB to operate due to it's caracteristics. From the link we can see that it would take about 60 seconds to operate at 30A! From the shape of the graph it can be seen that 26A would take a far longer period by which time one of the heaters may have switched off due to its stat.


The OP may have 32A ring socket circuits!

RoundyMooney

Or DZII fuses at the board, they're still out there :eek:

M cebee

Was thinking.;)
If the ring circuit is being 'phased out,we'll be in a better position to adopt
a 'better' european style unfused plug/socket system at some stage.
http://en.wikipedia.org/wiki/IEC_60906-1

Can't see the UK bothering with it though

flynnboy

Hey guys ! I didn't know there had been all of these replies as I have not been informed of any ?

Anyway, thanks very much. In fact since I posted I have taken it back as I believe it has a loose connection somewhere. It is a Dimplex and the instructions mention connecting with a plug, not a fused unit.

And yes I was wondering myself why the fuse hadn't blown...... I'll wait and see the outcome of the new repair.

Thanks again

Bruthal

kaizer13 wrote: »

3kW appliance should be connected in through a switched and fused spur unit and not through a plug and socket. The fact that you are getting away with it on one of the heaters does not make it correct. The one that is overheating the plug is a clear warning of why it should not be done that way.

I would`t agree with that, the 13 amp fuse is there to protect the appliance cable and so 3 kw should be useable. 3 kw is very close to 13 amps so the plug connection to the socket was the problem here or fuse holder in plug was a bad connection etc.

Id say a 13 amp socket would take a bit more than 13 amps in reality. They are rated to connect and disconnect 13 amps, but would probably carry more once in contact.