Earthing

[LastManOnline]

A 2.5mm2 wire is considered the minimum size that may get damaged if it is reasonably well protected, and a 4.0mm2 wire is considered strong enough to survive if it is strung across a loft, and some clumsy individual trips over it.

That is the only scenario I can envisage, although my thought was that rather than a "clumsy individual" tripping over and dragging an earth wire, (though conceivable) I could more easily picture a suitcase been retrieved from the attic for the annual holiday and dragging a cable with it. In whatever scenario though I cannot imagine a 4 mm earth providing any advantage over a 2.5mm earth.
In fact I could not possibly see someone breaking a 2.5mm earth by dragging it with their foot, no matter how hard they tried. It would surely be pulled free from the ceiling rose or switch it was connected to before physically breaking itself.

 

[LastManOnline]

I've always taken the reasons to be exactly for that reason......... and a 4.0mm2 wire is considered strong enough to survive if it is strung across a loft, and some clumsy individual trips over it.

I think all of us would be inclined to agree that such a scenario must be the reasoning, be it "a clumsy individual" or the "suitcase" scenario. Then by definition there should be no requirement for having to increase the earth size when running the cable in a ceiling void or a wall cavity, stud etc

 

[timhoward]

I think all of us would be inclined to agree that such a scenario must be the reasoning, be it "a clumsy individual" or the "suitcase" scenario. Then by definition there should be no requirement for having to increase the earth size when running the cable in a ceiling void or a wall cavity, stud etc

It's been helpful discussing this - thanks.
I'm (now) inclined to agree that "mechanical protection" in this context could be taken to mean "no one can easily get to it", so at least the smaller size can be used.
In other contexts in the regs the level of "mechanical protection" is more precisely specified, e.g. "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like".
The fact that the earthing section (and the supplementary bonding section) don't define the level of mechanical protection probably gives us license to apply common sense.

 

[Mike Johnson]

Today we mourn the passing of a beloved old friend, Common Sense, who has been with us for many years. No one knows for sure how old he was, since his birth records were long ago lost in bureaucratic red tape. He will be remembered as having cultivated such valuable lessons as:

• Knowing when to come in out of the rain;
• Knowing not to stick a screwdriver into a socket;
• Why the early bird gets the worm;
• Life isn't always fair; and
• Maybe it was my fault.

Common Sense lived by simple, sound financial policies (don't spend more than you can earn) and reliable strategies (adults, not children, are in charge).

His health began to deteriorate rapidly when well-intentioned but overbearing regulations were set in place.

Reports of a 6-year-old boy charged with sexual harassment for kissing a classmate; teens suspended from school for using mouthwash after lunch; and a teacher fired for reprimanding an unruly student, only worsened his condition.

Common Sense lost ground when parents attacked teachers for doing the job that they themselves had failed to do in disciplining their unruly children.

It declined even further when schools were required to get parental consent to administer sun lotion or an aspirin to a student; but could not inform parents when a student became pregnant and wanted to have an abortion.

Common Sense lost the will to live as the churches became businesses; and criminals received better treatment than their victims.

Common Sense took a beating when you couldn't defend yourself from a burglar in your own home and the burglar could sue you for assault.

Common Sense finally gave up the will to live, after a woman failed to realise that a steaming cup of coffee was hot. She spilled a little in her lap, and was promptly awarded a huge settlement.

Common Sense was preceded in death, by his parents, Truth and Trust, by his wife, Discretion, by his daughter, Responsibility, and by his son, Reason.

He is survived by his 4 stepbrothers;

• I Know My Rights
• I Want It Now
• Someone Else Is To Blame
• I'm A Victim

Not many attended his funeral because so few realised he was gone. If you still remember him, pass this on. If not, join the majority and do nothing.

 

[LastManOnline]

In other contexts in the regs the level of "mechanical protection" is more precisely specified, e.g. "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like".

Agreed. There appear to be 2 concepts of mechanical protection catered for in the regs.
The first is what you mention above. It's easy for us to relate to the need for protection of cables against damage from penetration, impact etc.
The second is a little more abstract and is based on the perception of the powers that be, for a need for greater mechanical strength in the earthing conductor. This perception is a vague and unexplained (in my experience at least) and is the reason for this thread.
For example, I have seen the earthingc cable to the earth electrode go from 2.5mm to 4mm to 6mm to 10mm.
2.5mm is all that's required electrically. . So what's changed over the years that's required the enlarged size? Soil conditions are the same. The earth electrode is the same. It's the "perception" among the powers that be that's altered. It would be helpful to know what fed into that perception

 

[littlespark]

A bit late in the day, but how about this;

OP wants to take a cpc from a socket to earth a metal switch when there is no cpc on the lights?
Suggestions of a 4mm unsheathed, unprotected single core. Ok. That makes sense and I’m sure it’s been done like that many times.

Going to the lesser size extreme, could a length of 1.5 t&e, or 6241 single and earth be used, and the live cores cut short?
The cpc would be no lesser size than it would be if the lights were wired in t&e, and it’s sheathed.

the remarks about whether cables are mechanically protected in a stud wall? No, they’re not… they would catch on splintered wood, sticking out nails and whatever else the wood butcher decided to leave in there…

apologies of this has already been covered, just scan read through previous messages.

 

[Mike Johnson]

Am I loosing the plot, why can't the OP use 6491X in GY in what ever c\c he wants, we just seem to be making the whole thing very complicated?