Neutral Bounce ? ? ( discussion only )

[bernardgreen]

The effect of very high transient currents on stranded cable is to compress the strands together leading to the strands have flatten sides. The effect is very small but can be seen with careful examination of the cores.

I have seen the strands of a earth grid cable fused together inside the insulation with no obvious damage to the outside of the insulation. That was after a direct hit to an equipment room on a hill top site.

 

[JohnW2]

The effect of very high transient currents on stranded cable is to compress the strands together leading to the strands have flatten sides. The effect is very small but can be seen with careful examination of the cores.

Interesting. Why is that? I would have guessed that, if anything, electromagnetic effects would have tended to move strands apart - not compress them together.

I have seen the strands of a earth grid cable fused together inside the insulation with no obvious damage to the outside of the insulation.

Sure, but you're presumably not suggesting that such 'fusing together' was not due to a considerable (local) temperature rise, are you?

Kind Regards, John

 

[bernardgreen]

Sure, but you're presumably not suggesting that such 'fusing together' was not due to a considerable (local) temperature rise, are you?

There was obviously a massive rise in temperature, possibly (in theory) limited to the skin of each conductor due the rapidly rising current being mostly in the surface of each conductor. Then the heat disipated into the core of the strands after the current had stopped flowing.

 

[chris765]

There was nothing visibly wrong with the conductor, if I go back to that job I will have a look at the CSA to see if there's any change.

I have been to TNC-S faults before where the overhead neutral has broken and somehow made contact with the live conductor.
The only way to earth is through service bonding and 10mm certainly doesn't cope well

In this lightening strike there was nothing remotely close to that extent of damage.