Braided earth strap

[Unkel Kunkel]

The one that runs from neg. battery terminal to bodywork and then on to a bell housing bolt.

It’s become a bit  frayed in the2 inches near the battery end.

Regarding replacing it - I suppose there must be a reason for it being a braided strap,  

but originality issues apart, is there a case for  replacing it  a heavy duty multi- strand copper insulated black cable with the appropriate terminals transferred?

[NonMember]

There's nothing special about braided copper. The braiding merely holds it together in the absence of insulation, and not bothering to insulate an earth strap makes it cheaper. Also easier to fit the body fixing eyelet part-way along it, which is probably the best (only?) reason not to replace the whole lot with black insulated starter motor cable. You want a continuous run from battery to engine, not a (possibly resistive) join in the middle.

[Mjit]

Braided rather than insulated cable's used for sound engineering reasons, rather than financial ones.

Braiding gives you a cable that can hold itself together and give a large cross sectional area of conductor but without putting any single strand under 'stress'.  This means it can wind its way around the back of the battery tray without actually bending any of the wire strands and also handle relative movement between the engine and car body without any of those strands being loaded.  With a more solid insulated cable you're going to have to kink the wire (and so copper strands inside it) to get around tighter corners and could get fatigue fractures over time between engine and body.

[Unkel Kunkel]

That's, very interesting thanks.

I can’t recall seeing braided earthing straps on “modern” vehicles or have I just not encountered  them?

[JohnD]

Present, for instance, on Ford Transits, as seen on recent Fb thread.   That one rotted through too.

There are sound engineering reasons for using such tat, mainly production economy, cheapness.    There are sound engineering solutions too, like NOT kinking a sheathed copper stranded cable by routing it by a larger curve if it must traverse a small angle, and a coil - one turn will do - if one end will vibrate.

John

[NonMember]

The whole thing about vibration hardening is fairly obviously moot because the starter live cable is subjected to all the same conditions but they used an insulated cable.

[Mjit]

Ideally the live would be braided too but braised and insulated is tricky - for a start the flexing braiding the cable permits would mean wear between cable and insulation and when the insulation wears through on your unfused, direct batter positive cable and it earths out on, well anything metal...  Not going to end well.

There's a few differences between the starter live and battery earth cables.

Over life the 'normal' live cable will degrade due to vibration - but if correctly routed/clipped that will be to the copper conductors and not the insulation.  As a result you're unlikely to run out of insulation and short out, just run out of enough copper to power the starter.  At that point the worst case is you can't start your stationary car.
On the other hand if that was your earth cable as the copper strands break internally you have less copper to carry power back to the battery that way.  As the whole body is part of the negative circuit that just means the electrons will find another route, through the choke/throttle cables for example.  None of those are meand for that load so will get hot and you have the risk of a fire.  Also while the starter live failing's only really an issue when you're stationary with the engine off the earth could fail while you're doing 70MPH on the motorway with an Audi right up your arse.  Lose the earth and would could lose the ignition circuit and have the engine just cut out (or find another earth and start a fire).  Neither great at 70MPH.