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Posted By halesowen Baggie
A young lady in one of our offices has burnt her finger while pulling a standard 3 pin plug out of the wall socket. She burnt the finger on one of the plugs pins.
Has anybody any idea what causes the prongs to heat up, is there a defect with the appliance (a heater) or the socket and electrical wiring.
I need the info for my accident report.
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Posted By John Watson
Hi, note sure which is at fault but suggest you get an electrician in very quickly to ensure you are not complete a "why the building burnt down report" in the near future.
regards
John
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Posted By Alan Hoskins
Electrical connections heat up when there is a poor connection, especially with higher loadings such as heaters.
You need to have the contacts and connections checked in the plug and in the socket.
Alan
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Posted By holmezy
Baggie,
its usually a result of poor wiring connections, probably in the plug, but possibly in the socket. Depending on what else was plugged in or being used at the time, it could also indicate an overloading of the curcuit. Extension cables and multi socket adaptors are easily overloaded.
Good luck with your investigation, and follow the previous advice and get an electrician to check the wiring and appliance etc. type
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Posted By halesowen Baggie
Can somebody explain to me in laymans terms why the fuse in the plug did not trip. It is a 13amp fuse?
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Posted By David Robb
Basically because the circuit was not pulling enough current through the fuse to rupture the element within it.
A 13 amp fuse will not necessarily blow at 13amps although it will be very close to it.
Depending on the fault that has caused the heat to build up, it may well mean that the appliance itself is not faulty and that the socket outlet has a loose connection (this could be on either the live or neutral conductors.
The supply fuse/circuit breaker will be rated at a significantly higher level (probably 32A) and will require a much higher overload before it will trip.
It is likely, in my opinion, that the fault is in the socket rather than the plug.
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Posted By Gareth Butler
Hi. How small are the womans fingers? If it is an old type plug top, with non-sheathed live and neutral pins, it is possible for her to partially pull out the plug, and for her finger to touch the live pin while the current is still passing through it from the socket!
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Posted By Exdeeps
The reason that the fuse did not blow is very simple. Assuming poor contact (dirt etc) then the total resistance of the circuit will increase. Think of the circuit as a pipe carrying water with a partially blocked filter. As the voltage (pressure) is constant and current (Flow rate) is proportional to voltage but inversely proportional to resistance (blocked filter) so the current will fall. At the same time, a current is flowing but has to overcome the high resistance before doing useful work in the appliance, ie it has to do some extra work to be able to do its designed work. In this case doing more work results in heat at the choke point/poor connection/blocked filter. If this were water pipes you would hear the extra work being done as a hissing sound!It is also probable that the output of the appliance is reduced so for instance a water heater will take longer to boil or not make such hot water. Did that make any sense to anyone?
By the way, you really need a sparks to look at this problem now before the heat turns into something really nasty.
Regards,
Jim
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Posted By Chas
Halesowen Baggie - I have more of a plumbing background and understood your water related explanation. I have always hated anything to do with electrics largely because I never really understood the subject. So thank you for your alternative approach to resistance, current etc. i understand now, I think!
Exdeeps - please let us know the outcome of your investigation, I for one would like to know the ultimate cause.
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Posted By Chas
Sorry I got the names muddled - It's too late in the day.
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Posted By seamus
Hello
first of all get an electrician to check it out.
My view is a heater that is on a long time should be wired via a double pole switch, and fused at the correct size. I presume the reason the lady pulled out the plug was to turn off the heater, another reason to have a fixed switch.
If the heater is on a long time the contact between the plug and the socked may heat up, the 13 amp fuse will only blow in the case of an overload/fault and could take in excess of 20 amps to blow, depends on the time involved.
I have seen 13 amp fuses in circuits drawing 25 amps and they have lasted a long time.Often because the electrician did not read the instructions and wired up the machine with a 13 amp plugtop.
A fuse such as this is not designed to blow if a plug top terminal gets hot. They do sometimes melt if the live terminal is loose and the fuse overheats.
Check all similar heaters and I suspect all the terminals will be hot, some hotter than others.
It is unlikely there is a fault in the heater but the electrician will need to check it. Even the best of plugtops have this problem at times.
So perhaps we are back to the idea of a fixed double pole switch with a local fuse.
Hope this helps
Seamus
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Posted By Granville Jenkins
It could be the plug, there again it could be the socket outlet - you need to determine which poste-haste!! Its unlikely to be the appliance as that would have warmed up in the process. Also, if the fault is generating that amount of heat there must be serious problem which needs immediate attention - no point in waiting till the next time and then find there is a fire or someone is electrocuted.
Overheating of the sort that you have described is generally down to a loose connection in the plug which causes arcing (short circuiting) between the cable and the terminal inside the plug. The short circuiting generates heat at the terminal which is then conducted through the terminal post, which is how your colleague got her finger burnt.
A couple of questions!
When was the last time your organisation had their fixed wiring tested i.e. distribution board and socket outlets etc.
Secondly, as the item was unplugged it more than likely falls under the description of a 'portable appliance' - has the item been PAT tested (portable appliance testing)in the last 12 months? Most items rated at 13amps (which can carry up to 3000Watts(3kW)of power should be inspected and tested on an annual basis.
I hope the above comments are of some assistance.
Regards
GJ
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