Preferred Method

[fattony]

I don't see anything wrong with using sy in certain situations. If the conductors are adequate to carry the current, if the braid is earthed, if the cpc is one of the cores and not the braid itself, if it is installed indoors or away from UV Rays. The braid can just offer a little more protection rather than using T&E , so for some commercial installations it is fine.

From what Ive read I agree:

Welcome to Doncaster Cables - SY Steel Wire Braid Armoured Flexible PVC Control Cable

This cable is also used by electricians in certain fixed installations where only light mechanical stress may occur. This cable can also be used outdoors (but should be protected); however, it is best suited to dry or moist conditions indoors.

My view

Scenario 1 - 6mm cable from busbar feeding 20A isolator is fine for a short run - 3m
Scenario 2 - I would prefer to see the cable capable of carrying the supply current regardless if the load is limited, especially over any distance
Scenario 3 - I wouldnt do it I think its completely wrong, 2.5mm in a C32A BS60898 over 3m distance

 

[Darkwood]

From what Ive read I agree:

Welcome to Doncaster Cables - SY Steel Wire Braid Armoured Flexible PVC Control Cable

This cable is also used by electricians in certain fixed installations where only light mechanical stress may occur. This cable can also be used outdoors (but should be protected); however, it is best suited to dry or moist conditions indoors.

2 key points ...fixed installation and outdoor use should be protected ..i.e. run in a pipe etc to shield it from the UV

My view

Scenario 1 - 6mm cable from busbar feeding 20A isolator is fine for a short run - 3m
Yes agree
Scenario 2 - I would prefer to see the cable capable of carrying the supply current regardless if the load is limited, especially over any distance
Many of my industrial installs rely on the ommitance for overload protection due to the nature of the load been fixed, this can safe alot of material costs but care needs to be taken that Zs values are still met.
Scenario 3 - I wouldnt do it I think its completely wrong, 2.5mm in a C32A BS60898 over 3m distance
It would probably fail Zs with any large distance and this is the reason why you can't but it could be done over 5m if load is fixed or limited using O/L protection ommitance regulations

It is situation dependent but even variable loads that have a FLC that acts as a limiting factor can be classed as fixed loads but as always a good knowledge of these design methods is essential as a slight error in the design stages can be costly when you find you fail Zs compliance.