Dodgy trade pictures for your amusement! - 1 Million Views!

[Pretty Mouth]

So bending a multi cored cable or a solid core which is worse, bending a solid core at right angles introduces massive tension and compression to the core which would be spread over a multi core cable.

They come manufactured like this Mike, the installer doesn't bend them to shape. I guess the manufacturers have done their tests and are happy.

 

[nicebutdim]

Out of interest; has anyone ever seen one of these solid links fail at a bend?

 

[Raptor0014]

Out of interest; has anyone ever seen one of these solid links fail at a bend?

Nope. I’ve changed a few boards with them in too.

I generally only see failures occur when connections are loose or broken in the terminal.

 

[nicebutdim]

Nope. I’ve changed a few boards with them in too.

I generally only see failures occur when connections are loose or broken in the terminal.

It's those images of loose terminations that made me wonder if anyone had ever encountered an issue with factory formed bends.

 

[littlespark]

Just once.

Wasn’t the link that failed, it was a badly designed system where too much power was going through a link somehow, melted the insulation on the neutral link and the incoming live…..

Bang flash, out goes the DNO fuse and a Sunday call out for me.

 

[Mike Johnson]

The milage would be in the amount of electricians that bend cables we spool off drums at right angles in an attempt to make the internal cable runs look like they are factory fitted, the amount of pic's on this Forum alone show a large number.

 

[nicebutdim]

The milage would be in the amount of electricians that bend cables we spool off drums at right angles in an attempt to make the internal cable runs look like they are factory fitted, the amount of pic's on this Forum alone show a large number.

I can't think of a single image on this forum that shows anyone having done so. Such basic installation techniques are a fundamental part of any trainee's education.

 

[Raptor0014]

The milage would be in the amount of electricians that bend cables we spool off drums at right angles in an attempt to make the internal cable runs look like they are factory fitted, the amount of pic's on this Forum alone show a large number.

Out of interest how would you deal with a set of tails that come in rear, side or bottom entry? You’d have to bend those to get them into the switch. So curious as to how you’d do it, given your stance on bending conductors.

 

[westward10]

Bending a multi-core cable is totally different to bending a single-core conductor. In a multi-core cable the outer conductors are stretched but the inner conductors are compressed.

 

[Raptor0014]

Bending a multi-core cable is totally different to bending a single-core conductor. In a multi-core cable the outer conductors are stretched but the inner conductors are compressed.

Ok, so how would the termination be done for a single 2.5 conductor?

ESF state this as best practice and it’s what I was taught to do and see most other electricians doing the same. It’s a single solid conductor bent at 180deg.

I’ve never understood how this is fine but some find bending a cable at deg unacceptable.

 

[westward10]

Bending a termination point is fine it is only making for a larger surface are for the screw to compress on as the pictures demonstrate. The bent part is not important.

 

[Raptor0014]

Bending a termination point is fine it is only making for a larger surface are for the screw to compress on as the pictures demonstrate. The bent part is not important.

So how is bending a cable at 90 deg worse?

 

[westward10]

The bend of a termination as shown in your pics is not significant with regard to the performance of the conductor but over bending a multi-core cable can be.

 

[nicebutdim]

The angle of a bend is less important than the radius of that bend. The cables we bend are manufactured to a standard and there are minimum bend radii for cables manufactured to those standards.

As per previous post, bending the end of a solid conductor is simply to increase surface area within a terminal signifcantly larger than the conductor - it's basically a means of avoiding the a situation where conductors aren't properly terminated.

The other issue of solid links within a CU is entirely separate as we don't know what standards those links are manufactured to and can safely assume that all factory fitted components have been type tested.

 

[ipf]

In earlier days I was taught to double up a single terminal cable sized 2.5 or less.
Now rarely do, unless there is bad location in the terminal.
Still see some RFC sockets with two sets of doubled up cables.
In CU's the links are manufactured to suit.

 

[Raptor0014]

The angle of a bend is less important than the radius of that bend. The cables we bend are manufactured to a standard and there are minimum bend radii for cables manufactured to those standards.

As per previous post, bending the end of a solid conductor is simply to increase surface area within a terminal signifcantly larger than the conductor - it's basically a means of avoiding the a situation where conductors aren't properly terminated.

The other issue of solid links within a CU is entirely separate as we don't know what standards those links are manufactured to and can safely assume that all factory fitted components have been type tested.

I’m aware of the reason for the bending of conductor termination and radii of cable bends.

I just don’t understand the aversion of some to bending of cables as long as they aren’t going over the bend radius tolerances.

If they were bent like the termination bends I’d understand.

 

[nicebutdim]

I don't think anyone has objected to the bending of conductors within specified radii.

 

[Dustydazzler]

You have to be pretty ham fisted to bend a cable to the point of snapping it clean in two

 

[brianmoooore]

Copper is a strange material. In its annealed form (heated to a dull red and cooled slowly) it is extremely ductile, and can be bent pretty much how you like, but just the once. After that, it 'work hardens' with each successive bend making it harder and less ductile, until it becomes almost brittle, and breaks easily if bent. The only way to make it ductile again is to heat it to dull red and slowly cool, which can be somewhat difficult if it is covered in PVC insulation.
I play around with copper pipes as well as wires, and have made thousands of bends in 15mm and 22mm tube. The correct wat to do this is to start with Table X copper tube, which is annealed to the correct degree, then to bend it slightly more than you require, before straightening it back to the angle you wanted. This is to leave the tube in a less stressed state than it would be after the initial bend.

 

[Simon47]

Bending a multi-core cable is totally different to bending a single-core conductor. In a multi-core cable the outer conductors are stretched but the inner conductors are compressed.

OK, I'm starting with a significant "IF" here ...
If the cable is at least half decently made, then what should happen is the individual components will slide about within the cable. A core that is on the inside of the bend at one point, will be on the outside a short distance along it - hence by sliding along relative to the other components there should be minimal stress. Within the core, the same thing should happen with the individual strands.
You can see this in action quite well with coarsely stranded cables. Who hasn't nicely prepared an SWA cable, only to find the strands of the armour are all different lengths when you move it into position - and then you curse yourself for not keeping the right bends in place while you were cutting back the armour Similarly with the main tails when the nice neat ends are no longer nice and neat once you get that last bend into it.

The min bend radius will depend on several factors - including how well the components can slide about within the cable. In part, there will be a factor of ensuring that any bend will encompass the twist lengths - a tight bend radius with a long twist length won't guarantee that a component that's in compression inside the bend will also be in tension on the outside a little further round.