Melted 13amp Spur switch

[luke teague]

Feed a storage heater on economy 7. The 13amp spur switch for it is to the side of it wasn't working properly and the phase input looked a bit melted.

I have tested all the wiring IR is fine and so is continuity and Zs thats without the melted broken switch as it fell apart in my hands.

It felt loose as if the mechanism had come apart inside, so I took it apart to see. It hadn't come apart, but melted and feel apart. there was a hair line crack all the way up the switch.

The most melted part is the neutral supply connector, the cable covering had even melted slightly an inch or so up the cable.To me this is quite alarming, it doesn't look that far away from starting a fire.

The circuit is on a 16 amp mcb and not all that old. but even the 13amp fuse spur never blew.

I will change the switch and reposition it as its very near the heater and the heat can not help things.

I'm worried that the same thing is going to happen again, has anyone seen anything like this before, or know what could be causing it?

The storage heat tested out of and i was thinking if it was that surely the cable for the heater would be damaged instead.

 

[nickblake]

Something similar has just happened to me.

See picture:

The fuse didn't blow, but the jumper lead between the fuse and switch has melted. I think its a cheap switch that can barely cope with 13amps - but surely the fuse, even though it might carry a bit more than 13amp, should blow BEFORE the switch starts to melt!

The jumper lead was preinstalled in the switch and appeared to be fitted professionally at manufacture - I confess I assumed it was and didn't check whether it has been installed correctly (i.e. insulation properly stripped) so this could be a possible cause i.e. poor connection.

This is a screwfix varilight FCU switch BTW.

Wont blow unless there is a short ,or a fault to earth, especially as its on the incomming side of the fuse

 

[nickblake]

Exactly.

However, fuses do tend to rate lower than they can handle.

Some could sit for days letting 14-15 amps through.

Exactly my point

 

[///ajd]

Wont blow unless there is a short ,or a fault to earth, especially as its on the incomming side of the fuse

How many amps do you think caused this melting - less than needed to blow the fuse surely? I thought the point was that a serious short or earth would lead to very high currents - hence blowing the fuse. My point is the fuse should surely be the weak point, not another part of the switch!!

 

[nickblake]

or overload sorry missed that one brains switched off, i was refering to load fault the melted cable wouldnt cause the fuse to blow ,but if there was a fault on the out going it should have , where the melted cable is is before the fuse so the fuse in the fcu wouldnt protect the melted cable what is protecting that would be the protective device at the CDU ,which could be a rewireable fuse whch requires greater currents to blow especially if its a 3036 30 amp suppling a ring

 

[///ajd]

probably not cause by overload or current more likley to be a loose or faulty conection ,looking at the picture i was refering to and as i have stated its on the incomming side of the fuse so wouldnt blow that fuse ,not knowing where this was connected to radial or ring if it was the ring then the cable which has melted would be protected at 32 / 30 amps depending on type of protective device if its a rewireable fuse it could take 40 plus amps to blow it and as 2.5 is rated less than that its going to melt ,if you get a fault thats less than the tripping fault of the protective device and more than the cable rating

On reflection I think you're right to assume its may not be due to excess amps (>13), but perhaps it has melted at 8 amps or whatever do to this poor/loose melted connection, well before the fuse which should go at "13" amps, or thereabouts.

It looks to me as though the factory wire in the switch (it came fitted like that and neither me nor tyhe electrician who fitted it touched that part) was less able to take the ampage than the fuse - which just seems a nonsense, and unsafe.

 

[RexT]

Hi Luke teague,

I have come across a high resistance value in a new switch before and also in switch plates for lighting.
I guess its always worth a check of a switch before you install it.
I agree that a suspect would be lose connections and I have seen damage to the neutral terminals of showers and main switches.
Hope this helps,

Best wishes

Rex

 

[hopkins85]

But most storage heaters draw more than 13amps thats why a 20A DP switch is better. The SW/FS could of been getting hot for ages. Also the fuse could of been faulty

 

[Andyfm]

If its a 3.4 kw heater it should not be on a fused spur