Burned wire end

[drood]

Yesterday I was adding some supplementary earth bonding to the shower switch in my bathroom, and discovered that the end of the supply live wire had blackened and partly melted the terminal in the switch.

The shower is 7.5Kw, 18m from the consumer unit. It is cabled with 6mm, protected by a 40A mcb and a 45A double pole pull cord switch. All other terminals are ok. The cable is not laid within any insulation in the loft or adjoining walls. Any ideas why this may have happened? What can I do to ensure that it doesn't happen again?

Thanks.

 

[Big_Spark]

If there is no overload, then it is likely that it was never tightened up properly, arcing occurred in the terminal under load, generated heat and did the deed.

Change the accessory with the damaged terminal, reterminate the cable and ensure the connections are TIGHT..or you will likely start a fire.

 

[AdamW]

It is all too easy to forget to tighten up a connection. Luckily with plumbing you get a leak that points out the error. With electrics it is generally pretty well hidden until you find blackened cables or fires.

When I used to install silly big stereos in cars I would re-tighten the cables after a few days just to be on the safe side. And quite often I would find that whilst the cable appeared mechanically sound I would be able to do the terminal up a bit more, thus some "bedding in" was required. This is especially true of speaker cables as they are stranded.

Is this practiced in domestic electrics? Obviously not on the order of days but does a good electrician recheck his connections the next morning, for example?

 

[BR]

Maybe if he had been drinking the night before . Generally you tend to get used to fully tightening connections and would do it without even thinking.

 

[Big_Spark]

Adam, a good electrician or engineer will always tighten things up as far as is safe to do so.

I knew one Guy, Chris, who was a mare when it came to tightening connections, the amount of Breakers and main switches that "broke in my hand" was amazing!!

huge screwdriver didn't help either!

Damned fine spark apart from that.

 

[AdamW]

I suppose the advantage of domestic electrics over automotive electrics is the lack of vibration (unless you live within 50 miles of the San Adreas fault!). Vibration is not good for keeping screw terminals done up (probably why so many crimped connections are used).

You see the problem I have with tightening stuff up is that I have witnessed far too many nuts, bolts and screws being overtightened and causing problems (e.g. when I was a kid, people who did up one wheel nut as tight as they could before starting on the other always ended up with misaligned wheels). So I am very concious of this and don't want to overtighten things.

And with some electrical fittings you can feel it begin to give when you have done up the slug screw a fair way. But I suppose this is the point where you should stop!

There can be problems of using tools too good for the job: a flatmate back at uni wanted to try out the screwdriver attachment of his new drill whilst assembling some flatpack. Didn't realise just how much torque a drill has and put the screw straight through! And I have heard stories of people taking the heads off nuts using air wrenches where they shouldn't be.

 

[mildmanneredjanitor]

What next, torque screw drivers????

Calibrated according to BS....

Even the best tools in the world can't help some people, I remember a lad refitting the wheels to my car after having new tyres fitted. Used a torque wrench, lovely, (christ knows what setting?) but proceeded past the 'click'. TWICE!

What's the point!

 

[BR]

Speaking of giant screwdrivers. At a pauwells (company makes industrial transformers for supply companies etc.)training coarse in dublin. We (two of us, the course cost €1500 for two days! easy know the esb were paying for it!) were given a sample set of "oversize" screwdrivers made especially for pauwells by IRAZOLA.

I'm looking at the PZ 2. It is 26" long and the handle is of diameter 75mm! Fully insulated to 10,000V.