Was all of these isolators necessary?

[JohnW2]

Not effective if the fault is a Neutral to Earth fault.

Have you really managed to think up some very contrived way in which such a fault could result in "the plug overheated and welded it self into the carbonised socket" ?

Kind Regards, John

 

[winston1]

How about emergency isolation.......

Faulty appliance, no access to plug and socket without moving the appliance. RCD cannot be reset, house in darkness.

You may not think that rates as a emergency but for the peoplw affest it is very close to being an emergency.

More likely the occupants won’t know what is causing the RCD to trip so will still panic or whatever.

 

[bernardgreen]

Have you really managed to think up some very contrived way in which such a fault could result in "the plug overheated and welded it self into the carbonised socket"

No need to "think it up" it happened a few weeks ago. The plug had to be levered out of the socket.

Fortunately getting the charred plug out of the socket removed the path to Earth and the RCD could be reset.

 

[reds42]

I presume that isolator was 'sensibly' positioned and not (as is only too common) on the wall immediately above the DW, such that it could not be safely operated when the appliance was "on fire".

Yes, it was off to the side from the machine. When I fitted a new kitchen in my house I fitted isolators off to the side of my big appliances after having experienced their value. I didn't bother with FCUs as that seemed uneccesary as I was leaving plugs on the machines.

 

[JohnW2]

Yes, it was off to the side from the machine. When I fitted a new kitchen in my house I fitted isolators off to the side of my big appliances after having experienced their value.

As I've said, that's sensible.

I didn't bother with FCUs as that seemed uneccesary as I was leaving plugs on the machines.

Again, we are agreed that they are unnecessary - but, since there are (to all intents and purposes) any significant downsides, I have no problem with people using them in such situations - any more than I have a problem with the fact that we use 13A fused plugs to plug into a (fused) triple socket or into an extension led fed from a (fused) 13A plug.

Kind Regards, John

 

[JohnW2]

No need to "think it up" it happened a few weeks ago. The plug had to be levered out of the socket. Fortunately getting the charred plug out of the socket removed the path to Earth and the RCD could be reset.

I must say that I still really don't understand how an N-E fault could possibly result in that and, in any event, why the RCD (which would have operated in milliseconds) did not prevent the degree of thermal damage to which you refer,

Are you sure you've "got things the right away around" and that you're not talking about a situation in which overheating of a plug (due to poor connects/contacts etc.) over a long period of time, with currents not high enough to operate an OPD) eventually caused so much thermal damage as to create a N-E fault, which then immediately tripped the RCD, which then couldn't be reset because the N-E fault persisted? In other words, the N-E fault was the result of the situation, not its cause.

If so, although that's not an impossible scenario, I would think it incredibly rare. Plugs overheating to the extent of being irremovable from the socket are rare enough - so for that to progress to creating a N-E fault must be incredibly rare!

Kind Regards, John

 

[bernardgreen]

If so, although that's not an impossible scenario, I would think it incredibly rare. Plugs overheating to the extent of being irremovable from the socket are rare enough - so for that to progress to creating a N-E fault must be incredibly rare!

The fuse in the moulded on plug was the source of heat, Load was a 2.3kW heater, ( verified by measuring the resistance of the element ).

Plastic sleeve on Line pin melted and deformed, then when cooled down the altered shape of the sleeve prevented the plug from being removed from socket without the use of brute force.

It was reported that :-
There was a strong smell of burning and the switch on the socket was immediately switched OFF (1) When the switch on the socket was switched back ON the power went OFF (2)

(1) The heater was still working so RCD had not tripped,
(2) 2.3 kW was not an overload so MCB did not trip

The owner wanted to return the heater for a refund so an investigation of the damage inside the plug was not possible.

It is very probable that the inside of the plug continued to smoulder for some time after the switch on the socket was turned OFF and this had continuing smouldering created a path of carbonised material that created an Earth leakage fault.

Resistance testing on the pins on the plug with the switch on the heater switched OFF indicated a path from Neutral pin to Earth pin sufficient to trip a 30 mA RCD

Deposits of "soot" inside the socket would have also created another path to Earth but the resistance of this was not tested before the socket was taken apart

 

[JohnW2]

The fuse in the moulded on plug was the source of heat, Load was a 2.3kW heater, ( verified by measuring the resistance of the element ).

Fair enough - so exactly as I suggested ...

... Are you sure you've "got things the right away around" and that you're not talking about a situation in which overheating of a plug (due to poor connects/contacts etc.) over a long period of time, with currents not high enough to operate an OPD) eventually caused so much thermal damage as to create a N-E fault, which then immediately tripped the RCD, which then couldn't be reset because the N-E fault persisted? In other words, the N-E fault was the result of the situation, not its cause.

... in which case, as I implied, I think that you rather confused things by responding as you did to my ....

And what to do if the fault is that the plug overheated and welded it self into the carbonised socket

Switch off that one circuit at the CU, I imagine, and then either remedy the fault or send for someone to do so.,

.... with ...

Not effective if the fault is a Neutral to Earth fault.

... which left me wondering (and asking) how on an earth an N-E fault could result in "the plug overheated and welded it self into the carbonised socket". However, you now admit that the primary fault was not an N-E one but a (I would think extremely unusual) complication/result of a primary fault which was over-heating of a plug due to other reasons - so I now understand what you have been trying totalk about!

Kind Regards, John

 

[skspark]

I've been called upon to change a few multiple ganged kitchen grid switches lately - usually just after a new kitchen has been fitted. Yes, they can be a right pain in the arse. The worst case scenario is when the outgoing circuits are in a downward direction, and you have hardly any space to get your screwdriver between the top of the worktop and the terminals of the switch. Because the worktops were not installed when the gridswitches were fitted. They can be a tad involved, but most are straightforward if you are methodical in your work. Try not to overwork the cables - they work harden and the job becomes more difficult. If you are lucky, you may get away without changining the backbox. Most were MK anyway. It usually takes me a minimum of 3 hours. Maybe 4 if I have to change the backbox. Identifying the ring ends should be easy got the grid out.