I'll start then. With the braid earthed, it's certainly more robust/safer than say T&E or plain sheathed flex in the same situation - especially with an RCD (or even a low rated MCB) upstream and PFC not too high. Having some sort of screen is probably better than nothing EMI wise too. Leaving the screen unearthed seems to be asking for the worst of both worlds - they might as well have used simple (and cheaper) flex.

For fixed wiring I'd say SY/CY falls into a similar camp to BS 8436 (nail shield) cables (other than the lack of a standard) - mid-way between plain plastic sheathed and SWA - with many but not all of the benefits but with savings (esp. installation convenience). One attraction of CY/SY is that it's far more readily available with larger number of cores than most other cable types. By gut feel is that the braid isn't going to fare any worse under fault conditions than the aluminium foil of BS 8436 cables - and they're OK standards wise for BS 7671 use (within certain limitations of course).

I'm sure I've something in my long term memory about the HSE recommending CY/SY for extension leads (with the braid earthed of course) in environments where ordinary flexes may be damaged - providing some attempt at ADS while retaining the necessary flexibility. Something that neither ordinary flex or SWA would really be suitable for.

The obvious solution is for the cable manufacturers and standards bods to pull their finger out and come up with the suitable standard, so we could all know what we're dealing with.

     - Andy.

fair do's Andy

there is more commentary on needed/wanted standards etc

https://www.basec.org.uk/news/2019/4/25/new-testing-certification-scheme-yy-sy-cy-control-cables/

In your view, does/could the braid qualify as 'mechanical protection' in the case of BS7671  like SWA would/does (arguably)  e.g. if buried in fabric < 50mm without RCD ?

Looking at some examples of the stuff, it appears 'no' to the above, as it looks more like screening on some coax  ... though one can appreciate there is an increase in strength from the braid for other cases where not buried or as a 'flex/extension'

Is the braid suitable to act as a protective conductor, as if not then it could only be for just the [increased to some degree] mechanical protection; but is it ever an exposed conductive part  required to be earthed ?

One supposes not to the above so long as it cannot be touched.

Indeed, metal capping is not ever earthed is it (or is it !).

Thank you

Habs

just to add, this comment was read on a website, "...I have had a direct conversation with the IET about this very topic recently. They confirmed to me that they are not telling electricians not to use it - but they are warning them that the specifier is liable for any associated costs should there be a fault with the cable. As SY does not have a VDE, BASEC or HAR standard, this means the installer is potentially specifying the cable at their own risk. However; the specifier is not liable if the manufacturer of the SY cable has their own quality guarantees. For instance; every cable that Lapp supplies is covered by our 18 month product warranty (t&c’s apply) and £25m product liability. Hence, should their be an associated cost due to the failure of our cable - Lapp are liable for this cost, not the specifier/installer. The IET are warning installers to ensure that their cables are “sustainability sourced” for want of a better word - not telling them that SY must never be used - and quite rightly, when you consider the amount of SY cable in the marketplace that does not have any quality guarantee. ..."

other commentary - 'interesting':

uk.prysmiangroup.com/.../sy-yy-cy-cable

That seems pretty balanced to me.

If there were a particular use for this cable for which other cables were not suitable, would a standard not have been created?

a rhetorical question perhaps  :-)

is it unsafe though to use ... likely not in many cases (or that seems to be the prevailing implication), but going 'off book' on an install requires the designer/specifier take responsibility for making the choice (why etc ) and hopefully to record such (especially if a  deviation from the norm).

when it comes to inspections, is it really an issue though if it is used and what is a fair observation of it ... however if a non-standard is used how can it be assessed and what against and so on  ...

what I would be coming to as a conclusion is,  installation choice (EIC record of deviation or not), when it comes to inspections, is it really an issue though if it is used and what is a fair observation of it ... however if a non-standard is used how can it be assessed and what against and so on  to lead to a safety observation.

in the case I described what would the outcome be !   line up 100 electricians and what would be the prevailing opinion

SY, CY and YY cable is used extensively in Machinery as defined in the Supply of Machinery (Safety) Regulations, and also for interconnecting parts of machinery and its control systems. This is the cable's intended use, and with CY and SY types, the braid is there to help with EMC issues (e.g. VSDs or control circuits sensitive to EMI from associated power cables). CY and SY provide a means of extending the electromagnetic shielding of a metal enclosure, through the braiding, to another metallic enclosure, and this is achieved using 360-degree bonding glands specifically made for these cable types.

Where the cable is part of Machinery as defined, BS EN IEC 60204-1 applies, and this is outside the scope of BS 7671, see Regulation 110.2 (xi).

SY, CY and YY cables are generally safe to use provided that:

• The cable is installed in an application and environment for which it was intended.
  
  • Not usually suitable for outdoor applications
  • Braid of CY and SY should NOT be considered to provided additional mechanical protection as required by BS 7671 for various circumstances (coverage of SY braid may not be suitable to act as cpc for mechanical protection against penetration by fixings etc.)
  • A number of types of SY, CY and YY cables are auxiliary cables (control cables) - these must not be used for power applications.
  • Flexible conductors terminated suitably (i.e. if connected via terminals marked 'sol' or 'r', appropriate ferrules used).
• The cable does not exceed voltage and current ratings in the installation conditions.
• A copper (CY) or steel (SY) braid is not used as a CPC on its own (internal CPC muse be used), but also the braid should be appropriately connected to a means of earthing or bonding at least at the supply end via an appropriate gland.
• The cable has a constructional specification provided by the manufacturer, preferably verified by an independent test body (such as BASEC).
• Where conformity for the installation to BS 7671 is claimed:
  • information required by Regulation 511.2 is recorded on the EIC; and
  • it is recommended evidence is kept on file, demonstrating 'at least the same degree of safety as that afforded by compliance with BS 7671' as required by Regulation 511.2

Guidance along these lines has been provided in the On-Site Guide for many years (see Section 7.9, Page 100, of the 2022 Edition).

Usually, there is a suitable alternative for circuits within the scope of BS 7671, so I'm not sure why the discussion keeps going round and round to be honest.

In your view, does/could the braid qualify as 'mechanical protection' in the case of BS7671  like SWA would/does (arguably)  e.g. if buried in fabric < 50mm without RCD ?

In my view, even the armour of SWA cables doesn't count as 'mechanical protection' (i.e. to 522.6.204 (iv)) - as it's too easy for nails/screws to penetrate between the strands (in one experiment I even got the fairly blunt tine of a garden fork to pierce through SWA to a live core without too much effort) - rather SWA would come under option (i) - i.e. 'earthed metallic covering', that should trigger ADS should the cable be pierced by something metallic though to a line conductor.

Is the braid suitable to act as a protective conductor, as if not then it could only be for just the [increased to some degree] mechanical protection; but is it ever an exposed conductive part  required to be earthed ?

The distinction between a protective conductor and an exposed-conductive-part always seemed a bit strange to me - if there's a fault then the exposed-conductive-part will have to survive carrying just as much fault current for just as long as a c.p.c. - yet we have all sorts of rules for sizing c.p.c.s but apparently none for exposed-conductive-parts. I suppose there is some difference in that generally we'd expect a c.p.c. to remain serviceable after a fault (so for example it can't be allowed to get so hot it permanently damages surrounding insulation) whereas an exposed-conductive-part might be considered more expendable - but all the same we'd not want an exposed-conductive-part vaporizing or burning back to break the circuit before the protective device opens. Yes, the steel braid can provide some useful mechanical protection (especially where the cable might be abraded or cut into by a wide sharp edge, rather than pierced by something pointy) but generally that can't be relied upon without the earthing/ADS approach as well. As I said, my gut feel is that steel (or copper) braid would likely do as least as well as the aluminium foil of BS 8436 cables - but without the numbers available that's hard to prove.

   - Andy.

I think Andy's answers are the generally-accepted wisdom.

AJJewsbury said:

I suppose there is some difference in that generally we'd expect a c.p.c. to remain serviceable after a fault (so for example it can't be allowed to get so hot it permanently damages surrounding insulation) whereas an exposed-conductive-part might be considered more expendable

A good reason to use the correct glands at BOTH ends of the cable, so there are parallel cpc paths in the event of penetration or severing of the outer layers of the cable.