SY Cable containment

The "not true" was regards "provide considerable extra protection from knocks and sharp objects" - patently not true, I have used a craft knife to easily slice through the sheath of SY with the steel braid embedded in the outer sheath ... and there is no penetration protection.

I agree there's the possibility of fire due to penetration of an SY cable, if the overcurrent protective device is not selected carefully. An RCD might well operate, though, if one were used to protect the circuit.

Overcurrent protection also depends on the braid being properly terminated (preferably in the correct gland).

Having said that, I've seen SY terminated in industrial plugs and socket-outlets, where the braid is not terminated at all !!!!

Perhaps you have not realised Graham but the braid is not usually mild steel, and the EMC aspect (perhaps it is in the standard none of us have) is somewhat dubious due to significant braid resistance and reactance, and the coverage is less than 100%. In my experience SY is much tougher than plain PVC cable, and using the braid as a CPC (not a G/Y (GNYE is not well known except to panel builders and electronics)) is very unwise as I have witnessed a fire due to exactly this, it has a high resistance and not a lot of current carrying capacity. I did point out that it is not "flexible SWA" Graham, and the braid often does not have anything like the equivalent copper cross section of the conductors. I have never seen (as far as I remember) a piece of SY without a bedding layer under the braid, and such would be very unwise.

SY cables do not have the braid embedded in the outer sheath Graham, that is something else entirely, and is some other type of screened cable, larger sizes of SY are quite difficult to cut, even with large proper cable shears, and a craft knife would stand little chance with the braid.

Whether SY is tougher than larger sizes of rubber cables which might otherwise be used is also interesting, it is probably a fairly close run thing, and just depends on the mechanical or chemical abuse.

SY will be used by every electrical installation apprentice in the land when they do their AM2. They also have to complete an EIC where the cable is already marked up as a departure. 
Miles of the stuff used in industry here but I think many employing it believe the braid is definitely for robust mechanical protection and, as GK says, it is often connected to an industrial plug for that very reason!

David Stone said:

Perhaps you have not realised Graham but the braid is not usually mild steel, and the EMC aspect (perhaps it is in the standard none of us have) is somewhat dubious due to significant braid resistance and reactance, and the coverage is less than 100%

David, I have many years' experience using the stuff in relation to Machinery and Controls.

I am fully aware that CY has a far better coverage than SY, but it really depends on the application (and budget). In fact, the coverage of SY varies, and some types wouldn't even offer, in reality, any mechanical protection, and only a little help with radiated emissions. SY is usually OK for short distances, and up to the frequencies used by inverter drives.

CY is more effective on longer runs, and where frequencies are higher (hence "coverage" is more important than "simple Faraday cage") ... also where there are high protective conductor currents and a lower inductance of the functional earthing down the cable is more important.

David Stone said:

(GNYE is not well known except to panel builders and electronics)

Hence, its inclusion in BS 7671:2018+A2:2022 (following the example of BS EN 60445:2017 and BS EN 60445:2021) ... although "I didn't know" doesn't mean "It doesn't exist" or "It doesn't matter".

David Stone said:

SY cables do not have the braid embedded in the outer sheath Graham, that is something else entirely, and is some other type of screened cable,

Some definitely out there. And definitely was sold as "SY" ... and there being no constructional standard for the cable, who is to know, or even argue (no standard, no argument really)?

David Stone said:

larger sizes of SY are quite difficult to cut, even with large proper cable shears, and a craft knife would stand little chance with the braid.

Agreed. But it doesn't stop people thinking the smaller csa cables have added mechanical protection somewhat equivalent to SWA, which is absolute nonsense. What's more, I see a lot of (rusting) SY cable used outdoors, not UV stable, and certainly not suitable for the wet environment.

David Stone said:

Whether SY is tougher than larger sizes of rubber cables which might otherwise be used is also interesting, it is probably a fairly close run thing, and just depends on the mechanical or chemical abuse.

Agreed - H05RN-F is good stuff for a rather wet environment, and with a range of other contaminating materials that might affect other cable types.

Direct personal experience over many years taught me that SY is more abrasion and crush resistant than any other flex I know of.

I lost count of the number of times a 440V extension in SY was run over by a heavily loaded forklift truck, yet continued to function. W e used to use rubber flex with a braided inner, then another inner sheath but it always seem to get cut up more easily by machine shop turnings embedded into the solid tyres of the truck. SY seemed to stand it much better. And no, the FLT driver refused to be educated.

whjohnson said:

And no, the FLT driver refused to be educated.

Oh dear ... but is it the FLT driver's issue or the H&S duty holder's? I think the legislation would say the latter in this instance, inadequate risk assessment and controls (SY cable was not really the "correct" answer here, if there actually ever was one).

No one was really too concerned, other than for production to restart as quickly as possible! The leads were 3 phase 110V which fed what we used to call ''man fans', basically semi-portable floor standing fans which were used to keep the machine operators cool. If a fan packed up, they sat down until it was repaired - usually FLT damage to either the fan itself, or more often than not a severed trailing lead. No RCD, just Crabtree C50 type C 3 pole mcbs.