Hi
My wife works in a school kitchen.
There is a single 13A socket into which is plugged two hot cabinets which are daisy chained together.
When switched off, there is arcing behind the switch.
The electrician who attended says this is acceptable and that the socket is not overloaded.
I find this hard to believe, simply from a reliabity point of view but have ask her to check the ratings on the two cabinet and let me know.
Is there ANY circumstances where arcing is acceptable ?
Andy
Why not use the switches on the cabinets to switch them off? Plug switches are low quality and I wouldn't expect them to last long if you are switching large loads often.
BTW you always get arcing but usually only for a small period, usually unnoticeable.
I assume you mean the socket switches?
Some sockets carry a 20 year guarantee. What evidence have you for this statement?
On Wed, 18 Jul 2007 08:28:42 +0100 someone who may be Andy Cap wrote this:-
There is arcing inside all electrical switchgear breaking a load, except for the relatively rare case of AC switchgear being operated while the current is zero.
This arcing is often not noticeable. If it is noticeable then it may or may not indicate a problem, usually the latter.
Is there a switch on the hot cabinets to turn them off before they're unplugged?
No, apparently not.
Whilst I've never noticed it in normal operation, I've just looked closely at my own kitchen socket whilst switching off a 3KW kettle and when shaded with my hand, about 1 time in 5 there is quite a flash so I guess it really just ' boils down ! ' to a reliability issue, rather than safety, as long as the load is within limits.
Andy
On Wed, 18 Jul 2007 10:43:27 +0100, Andy Cap mused:
That's pretty much it. Although when we wired school kitchens we would fit a double socket for each hot cabinet rather than having them daisy chained. Depends on the loading I suppose, IIRC these were fairly hungry cabinets.
On Wed, 18 Jul 2007 08:28:42 +0100 someone who may be Andy Cap wrote this:-
Do let us know the ratings.
Presumably they are thermostatically controlled.
But they'll be thermostatically controlled?
If there is one then turn this down and then unplug. My iron doesn't like being switched off when its heating up and gives a bit of a spark.
If they are daisy chained, so only one plug is plugged in to the socket, then I assume that plug has a 13A fuse, so can't see a problem.
On Wed, 18 Jul 2007 13:39:32 +0100, "Lyndon" mused:
Then you know f*ck all. A 13A fuse doesn't just blow instantly at the moment it passes 13.01A.
Neither does a 13A socket or a ring main burst into flames or casue any other problems at 13.01A.
Not my experiance at all, but I don't buy low quality wiring accessories.
On Wed, 18 Jul 2007 17:48:05 +0100, "Lyndon" mused:
Who said it did?
You said I know 'f*ck all' because a fuse doesn't just blow at 13.01A, and I never said a 13A fuse would blow at 13.01A.
My point was that it really doesn't matter that the fuse doesn't blow at
13.01A. It is still the weakest part of the socket/swich/plug. The socket will take everything that the 13A fuse can take, and the switch will be rated at about 15A for a resistive load. If you connect a load protected by a 13A fuse into a 13A socket you don't have much to worry about.
Well they're both 240 volts !!! Obviously the word Watts didn't register. :-{ I've sent her back to do further research.
They did experiment by unplugging the second cabinet first but the switch still sparked..
There is no adjustable thermostat apparently.
Andy
Nonsense! The endurance test in BS 1363-2:1995 which all switched sockets are required to pass to be granted approval under the Plugs & Sockets Safety Regulations require the switch to survive 15,000 switching cycles at the full 13 A rated load current (substantially non-inductive). The on-load voltage drop across each switch contact must not exceed 60 mV at the start of the test and 75 mV at the end.
At (say) two switching cycles per day, and (say) 260 working days a year this translates to an operational life of nearly 29 years.
There is also a breaking capacity test for the switch at 25% overload, although this is only for 10 cycles.
The breaking capacity test is followed by an arcing test, again at ~16 amps. The switch is operated slowly by hand, deliberately attempting to cause arcing, and is held in the arcing position for two seconds. The actuator is then released and any arcing must cease. This is repeated ten times.
On Wed, 18 Jul 2007 23:31:49 +0100, "Lyndon" mused:
Yeah, although there are arguments for and against using a 13A plug and socket in this situation. As it's short term loading you could say it was fine, but you could also argue that as it would be used most days of the week then it should have something rated at 16\20A or higher.
Perhaps suggest that they keep an eye on the temperature of the faceplate, and plugtop, as they touch it during switch off. Excessive temperature would indicate a resistive contact somewhere and is grounds for immediate replacement.
I'll mention it.
The loads are 1KW and 0.9KW and one single unit will cause the arcing. I still suspect that the switch is the culprit but it sounds as if they are unlikely to get it changed until it siezes up completely.
Andy
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