cooker wiring?


Postby roberto » Mon Feb 02, 2009 8:28 pm

after switching off the switch in my fuse box labelled cooker i though it would be safe to remove the cooker switch...it went bang! would there be power coming from anywhere else into this cooker switch? there is a plug socket about 800mm underneath with wires going into the cooker switch. ...would that be wired into the ring and also into the cooker switch, therfore making the cooker switch live still? please help if you understand?
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Postby singer » Tue Feb 03, 2009 12:54 am

Hi roberto
I'm just wondering what were the consequences of the cooker switch going bang.
Obviously it was live when you took it off but was it still live after it went bang?
If not then check which MCB or fuse has operated at the fuse box to determine which one is protecting that circuit.
If none have operated then you have a dangerous situation as cookers are usually wired in fairly big cable protected by a 32 or maybe a 40 amp device either of which should operate on short circuit.
It could be that you have a rewireable fuse protecting this circuit which has had oversized wire installed in it following an earlier fault, which would hold on short circuit if not for too long.
The tester you refer to in your other post is very unreliable for verifying safety as they pick up all sorts of spurious voltages on neutrals and even earthwires and give a confusing picture of the situation.
Best to buy a decent set of test lamps - not too expensive - verify they work on a known power source before verifying the circuit you are working on is dead, and then verify working again to double check.
Your problem might be the fuseboard has been labelled up wrongly so what you thought was the cooker isolation was in fact another circuit - never assume with electrics - always test to verify circuit is dead!!
Put test lamps on cooker switch live and neutral and then pull fuses one by one until lamps go out. Removed fuse is cooker protection.
Socket below cooker switch with wires going into cooker switch was probably the old cooker outlet point which has been removed and replaced with a socket.
Check what I've said & post back.
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Postby roberto » Thu Feb 05, 2009 8:42 pm

thanks for your reply..I'm in total confussion??! the cooker switch was off when i took the switch out...it went bang...after purchasing a good power tetser i then tested the live wire with it...the switch was the correct one. it turned the lamps on and off through the fuse board. the cooker is wired with what looks like 6mm cable..i'm pretty sure it goes straight to the fuse box, but without chasing it back through the wall i cant be positive. it has a 30 amp fuse in the fuse box.
it could be that you have a rewireable fuse protecting this circuit which has had oversized wire installed in it following an earlier fault, which would hold on short circuit if not for too long.?
what does this mean?

the socket below the cooker switch was only wired into the cooker switch, spurred off with 2.5mm cable...is that allowed?
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Postby singer » Sat Feb 07, 2009 12:06 am

Hi roberto
I'm confused as well.
[quote]the cooker switch was off when i took the switch out...it went bang.[/quote]
Which switch do you mean was off? Do you mean the cooker switch itself or the main switch at the fuseboard(I'm assuming its not a circuit breaker as you go on to say its protected by a 30amp fuse)
Simply turning the cooker switch off doesn't mean its not alive when you remove it from the wall.
You still haven't said whether the bang caused the fuse to blow or not.
What kind of fuse is it? Is it the type that uses fuse wire? This is what I was refering to in my previous reply that you didnt understand.
When cartridge fuses blow due to a fault you simply remove the blown fuse and replace it with same so a 5amp fuse would be replaced with a 5amp fuse a 15 with a 15 and so on. Colour coding of fuses helps with identification so this replacement is usually straight forward.
However with rewireable fuses, when one blows the fusewire has to be replaced with the correct size wire depending on the size of the fuse.
So if your cooker is protected by a rewireable fuse which has blown before for some reason, it may say 30amp on the fuse carrier, but the wire that has been replaced in the fuse may be too big and capable of carrying much more than 30amps before blowing.
Did you remove the fuse from the fusebox before attempting to remove cooker switch from wall?
If as you say you've tested the cooker switch with a tester and the 30amp fuse makes it dead when removed then I fail to understand why it went bang.
[quote]the socket below the cooker switch was only wired into the cooker switch, spurred off with 2.5mm cable...is that allowed?[/quote]
This would be OK as long as the 2.5mm cable was not able to be overloaded, and this would be limited by the protection in the fuseboard.
A 30amp fuse wouldn't do this and would need to be reduced to a 20amp.
.
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