Immersion heater info.

[Toddius]

Hi.
we have an immersion heater that we have had a few problems with. It was running on economy 7 , we had meter changed which disabled the Spurs which was powering immersion heater. we had a electrician come and he installed the two elements on flex with plug tops and changed Spurs to sockets. The bottom one melted ,luckily we was in and smelt the burning. Called him. He denied any blame and said that is ok to do with immersion heaters and he does it all the time.
we had a different electrician come round to rectify. He changed plug sockets to Spurs , and rewired elements. I’m guessing he didn’t use the correct flex as today when heater wasnt working I opened it and the live cable insulation had corroded away And cores inside was very weak.
if I get someone else round what should the correct method be for him to get these working. I’m guessing a certain cable rating and heat proof,should it be on any particular type of spur.from reading online I’m assuming it should also have its own rcd on distribution board. I want to be armed with correct information for when electrician visits.
Thanks.

 

[johnb2713]

Heat resistant cable should be fine 2.5mm2

 

[poni]

I’m guessing a certain cable rating and heat proof,should it be on any particular type of spur.from reading online I’m assuming it should also have its own rcd on distribution board

Yes, heat resistant three core flex , 2.5mm2 as John says, in all cases
Fused connection unit (not a plug and socket) if not on its own circuit,
best case, would be its own circuit (16A RCBO) with a 20A double pole switch with neon, and heat resistant three core 2.5mms flex,

in the photo it looks like a poor(lose/bad) connection has cased the cable to over heat, this can happen to any cable if poorly installed

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[Murdoch]

Burnt out connections like those are nearly always due to poor or loose connections.

 

[Geoff1946]

Once it's burned up the terminal needs thorough cleaning with abrasive to show clean metal, not just a new wire fitted. If there dirt and oxidation still there it will cause resistance and go again.

 

[BorisJ]

Yes, heat resistant three core flex , 2.5mm2 as John says, in all cases
Fused connection unit (not a plug and socket) if not on its own circuit,
best case, would be its own circuit (16A RCBO) with a 20A double pole switch with neon, and heat resistant three core 2.5mms flex,

in the photo it looks like a poor(lose/bad) connection has cased the cable to over heat, this can happen to any cable if poorly installed

​

2.5 mm cable is over the top and harder to terminate. 1.5mm heat resistant cable is what is required. 20A switch on its own circuit is good but no need for a neon.

 

[johnb2713]

2.5 mm cable is over the top and harder to terminate. 1.5mm heat resistant cable is what is required. 20A switch on its own circuit is good but no need for a neon.

2.5mm2 has never failed me yet, a neon is good advice for a high consumption load, a good reminder to switch it off etc, it adds very little to the cost. 1.5mm2 is plenty for the current carrying capability but the mechanical strength isnt as good, 2.5mm2 IMHO would be a much better job.

 

[Murdoch]

2.5 mm cable is over the top and harder to terminate. 1.5mm heat resistant cable is what is required. 20A switch on its own circuit is good but no need for a neon.

If the circuit is E7 then a neon indicator is a very handy way for the customer to see if the circuit is actually getting power when it supposed to