Live and neutral melted inside shower casing.

[topher67]

Hi guys, looking for some help on this.

Heres an idea of setup.

The shower supply is separate from the old CU as there are two sets of tails coming from the key meter. 1 set going to the old CU and 1 set going to the double pole 40a RCD shown below.

This is the sequence from the key meter.

Keymeter - tails - double pole 40a RCD - tails - connector block inside CU taped up - 6mm T&E - 45a Pull cord - 6mm T&E - Shower connection.

The live and neutral have melted inside the shower casing. This is only only the shower side of things. this in turn has melted part of the shower casing.

The RCD has never tripped and the only reason this was even noticed at all was due to the smell of burning.

I am going to replace the shower. I need to know if the correct thing to do is......

keymeter - tails - double pole 40a RCD - 10mm T&E - 45a pullcord - 10mmT&E - 8.5kw shower.

Any help on this would be great. And also any idea as to why the shower continued to operate without tripping.

Thanks.

 

[bernardgreen]

The insulation melted because the terminals clamping the wire had become loose and the joint cable to connector became a high resistance joint. Current passing through resistance causes heat.

The RCB trip didn't trip because no current was leaving the wires and reaching earth so there was no earth fault.

The MCB did not trip because although the heat was being generated in the terminal and not in the element the element was still determining how much current was flowing so it was still the same as normal current for the shower when working nromally.

The copper in the cables will have been softened by the heat and MUST not be used for the new shower. Although it may appear that the softened copper has been clamped tightly after a short time the softened copper will change shape and the pressure in the terminal clamp will reduce and the joint will fail, get hot and melt the new shower.

 

[ban-all-sheds]

The MCB did not trip.....

Bernard....

What MCB?

This is the sequence from the key meter.

Keymeter - tails - double pole 40a RCD - tails - connector block inside CU taped up - 6mm T&E - 45a Pull cord - 6mm T&E - Shower connection.

Oh dear oh dear oh dear.

You have no overcurrent protection on that 6mm² cable apart from the supply fuse.

Very dangerous.

I need to know if the correct thing to do is......

keymeter - tails - double pole 40a RCD - 10mm T&E - 45a pullcord - 10mmT&E - 8.5kw shower.

No - you must provide protection for the 10mm² cable - either in the main CU, or in the same enclosure as the RCD or by replacing the RCD with an RCBO. The latter would be the neatest, and would also let you have a more powerful shower than the 9.6kW you're currently limited to (subject to cable installation details).

 

[bernardgreen]

Oh dear

I assumed "inside consumer unit" meant there was an MCB in circuit.

Slap wrist... do not assume.....

Good thing the terminal went high resistance before the element went short circuit........

Good thing the smoke was noticed before the insulation melted from the cable in the shower and the live and neutral shorted out....

BIG BANG

 

[Taylortwocities]

Untitled

• Taylortwocities
• 5 Jan 2010
• 2

 

[ban-all-sheds]

OK **** - some more questions for you to provide rational, logical, intelligent and mature answers to.

It will be hard to interpret failure on your part as anything other than confirmation that you are irrational, illogical, stupid and immature.

Bernard....

What MCB?

Why should I not have asked Bernard what MCB he was talking about, when the OP described not having one?

Oh dear oh dear oh dear.

You have no overcurrent protection on that 6mm² cable apart from the supply fuse.

Why should I not have expressed dismay that the OP has nothing apart from his service fuse protecting a 6mm² cable?

Very dangerous.

Do you not think that is dangerous? If not, would you please explain why?

No - you must provide protection for the 10mm² cable - either in the main CU, or in the same enclosure as the RCD or by replacing the RCD with an RCBO. The latter would be the neatest, and would also let you have a more powerful shower than the 9.6kW you're currently limited to (subject to cable installation details).

Would you please explain which parts of that advice you believe to be wrong, and if so, in what way?