correct method of stripping twin & earth?

[Hardy Sparky (Mvc)]

How about the stanley knife method hmmmm

 

[ian932]

How about the stanley knife method hmmmm

If you like the sight of your own blood.

 

[Sidewinder]

Can't believe that -considering the breaking strain of a CPC compared to the small force needed for stripping by the cheese wire method.

It's not the breaking strain only it is also the structural change caused by the work hardening of the material generated by the deformation forces.

 

[pewter]

CK stripper all the way. Cheese wire if its low grade and the stripper does not work. I cant understand why anyone would not have the CK stripper in the tool box

 

[Sidewinder]

but you do? :coat i use a mixture of ck auto strippers and the "cheese wire" method

No I don't "cheese wire" it.

I strip it with a knife.

Last time I was in college, the lecturer tried to pull me up as he was unhappy and felt that I would skin the live conductors.

EVERY time he could he checked any T&E I had stripped and never could pull me for nicking the insulation.

He was also unhappy about me scoring perpendicular to the cable axis, but never managed to pull me on that either.

---------- Post Auto-Merged at 22:53 ---------- Previous post was made at 22:52 ----------

Never affected anything in practice though has it.

Nicky,

Is this aimed at my comment?

 

[Manator]

For those who have answered without knowing what terms are what, Cheese wire is when you snip the cable off center, then grab the cpc with pliers or side cutters and pull to the extremity of your conductor length. This works but leaves a very "untidy" cable end, the risks are, greater train is imposed on the pulled "cheese wire" (cpc), this can also alter its overall diameter, which is what sidewinder suggested in his post. Lets just say that on an engineering aspect, if you pull a 1.00mm cable at a force greater than so many newtons, you in fact pull the cable, and indeed stretch it, so that it is no longer 1.00mm but .75, or lower.

 

[Sidewinder]

Manator,

There is also the structural change to the crystal lattice that can occur, which can, increase the specific resistivity of the material, which could be more of a concern, and more difficult to detect!

 

[Manator]

Indeed, but for our use as electricians this change is miniscule, and providing circuits are designed properly have very little impact. Indeed the example I posted, in most circumstances would have very little impact on any standard installation. However it should at all times be acknowledged, and treated accordingly.

 

[Sidewinder]

Manator,

Quite true, but, I guess it depends on how "value" engineered the install is, or how close to the max loading, Zs etc. the installation design parameters are...

 

[davetheglitz]

Appreciate the idea - but despite what I like to think I'm not Superman and don't believe I could physically distort the cpc to any significant extent.

 

[Sidewinder]

You do though Dave, in the process of bending it back on itself.

Copper is very susceptible to work hardening, and it is this process that increases the specific resistivity.

The bending radius encountered when using the cheese wire method is less than that required to work harden the base material, thus less than that required to increase the resistivity.

 

[electrician786]

I don't think the cheese wire method has affected many installs sidewinder because almost every spark i have worked with has used that method also. But that said, you also have a valid point.

 

[davetheglitz]

See your point - but I don't think a one off operation is likely to cause work hardening to the extent where the csa is decreased at any point in the cable. Also - assuming less than a right angle pull - the sheath is pretty pliable - so not sure the bend radius would be compromised. Perhaps it's all down to method - which is worth highlighting.

Once again-I've only got gut feel to work on here - does anyone know of any definitive research?

 

[Sidewinder]

Dave,

Work hardening will not change the csa, any bending of any sort to a copper cable during its manufacture, or installation will subject it to a degree of work hardening.

Too much and the resistivity increases.

In an isolated single incident probably insignificant, in a long run with many terminations undertaken this way and an identical run stripped correctly I suspect that there would be a measurable difference even with the rubbish instruments we normally use!

 

[green-hornet]

Honestley Dave you would be surprised if you saw how much you stretched the cpc, I sat in a lecture where this was measured during time trials, It is unberleavable how elastic, and stretchable a thin strand of copper is.

Do not get me wrong, in normal situations the anormorphic change is negligable for domestic, and small commercial, but if crucial Zs, and volt drop calcs were required, it could have a tremendous impact, even on the miniscule measurements.

 

[Ash]

with the physics side of the CPC, the CPC in T+E is normally oversized by quite an amount if you do the adiabatic equation for the circuits you're wiring, so even if you were to do damage to the structure of the conductor, it's probably still miles within the limits

 

[IzzyS]

...but if crucial Zs, and volt drop calcs were required, it could have a tremendous impact, even on the miniscule measurements.

Surely any design that close to the edge needs a re-think?

 

[elec dept]

Cheese wire for me(and the students I teach), however there is a train of thought that by doing this method you MAY "stretch" the CPC therefore affecting its current carrying capacity in the event of a fault, alledgedley!

 

[Badger]

but with the introduction of rcd protected circuits it has a tripping time of 0.4 secs not 5 secs now so current carrying capacity on the protective conductor isnt going to be needed to be as large as a true live and neutral carrying conductor.

 

[ProDave]

I use the cheese wire method.

I don't buy this "stretching the CPC" theory.

I challenge anyone to take a bit of 1mm CPC from some scrap cable. Measure the diameter with a micrometer. Clamp one end of the CPC in a vice, and pull the other end as hard as you can with a pair of pliers. Then re measure the diameter and tell us how much it changed. Bare in mind this test will be pulling it a lot harder than needed to zip down the insulation when stripping.