Requirement to Earth Armoured Fibre optic cables

I would say yes.

Though strictly speaking it should be called bonding, not earthing.

Any significant length of armoured fibre optic cable should in my view be bonded, Just as one should bond other metallic services such as gas or water supply pipes.


In case of an open PEN conductor then metalwork within a building could be live at a significant voltage. Bonding of pipes and structural elements controls the risks under such circumstances. A not bonded armoured fibre optic cable could introduce a significantly different voltage, with risk of dangerous shock if touched at the same time as say a water pipe.


I see no need to bond relatively short lengths that are entirely within a building. They are then more comparable to say a metallic hand rail on the stairs, and we do not normally bond those.

I think that would need consideration of the context.


How/where is the optic cable terminated?


For example, if its between two buildings.... and you terminate the armour to the buildings earthing system... and that system is PME then you could end up joining the neutrals of the supplies together via the armour - that could get very nasty in the event of an open neutral.


One of the (many) reasons for bonding the armour of a power cable to earth is to assist in fault detection & automatic disconnection. This doesnt apply with an optic cable - the armour is soley for mechanical protection. Indeed one of the reasons for using a fibre might be to deliberately form an insulating connection between two buidings.


Perhaps a better way would be to terminate the cable into an insulating box in such a way that the armour cannot be touched & a suitable warning notice afixed to said box?

So it might be better just to use the armour as mechanical protection and not earth it at all, OR just earth it at one end only if it connects two buildings and two earthing systems.


Z.

Where fibre optic cables have a metallic screen, then yes, this should be bonded at the point of connection. If you are going between buildings on different earth mats, it is conceivable that you have the wrong type of cable. Within the Electricity Supply Industry, we use Kevlar armoured cable (which is non-metallic) between sites as obviously we don’t want fault current down a thin fibre optic cable. in case you are wondering about the strength of Kevlar, it can be used for cut-resistant gloves as well as bullet proof vests. 


Regards,


Alan.

I work as a Highways Maintenance Electrician and all Armoured Comms cables are Bonded to an Earth Bar or MET inside Cabinets