Cable armour earthing

[glendale]

We have LV (415V) 3 core Steel Wire Armoured cable on site where the Steel Wire Armour has been earthed every 30 metres along its length. Has anybody any experience of this practice? The site contains explosive materials.

 

[rovineye]

Shipboard, we use armor cable, but our armor is bronze, copper or aluminum and covered with an outter sheath.

We ground multi-conductor cable at each end, ensuring armor is electrically continuous throughout the length. For single conductor armored cables we ground at the midpoint.

This is the same method we use even if in hazardous locations, and at all voltage levels.

The only exception I have to this are cables that are armored, do not have an outter sheath, and are part of our propulsion system (VFD). I don't have that scenario, but if I did, the OEM requires the armor to be earthed "at frequent intervals".

 

[ElChispa]

Having worked underground in hazardous environment (ie methane) we used stranded copper or solid aluminium armoured sheathed cables which were earthed at both ends but ensuring continuity of the armouring. This was sufficient for the mines and quarries inspetorate.

 

[glendale]

Thanks for your responses, I think this may be down to preferential engineering by past installation designers rather than standards.