Should SY, YY and CY cables be used in electrical installations? NAPIT’s Bill Allan offers his verdict.
SY, YY and CY cables are ﬂexible cables which are being widely used in industrial installations in the UK, and increasingly so in domestic installations. This is due, in part, to them being more robust than standard ﬂexible cables. In addition, no special tools are required, which is an obvious advantage, says NAPIT.
However, they’re non-standard cables so the question must be asked: are these types of cable acceptable for use in electrical installations in the UK?
SY, YY and CY cables
An obvious disadvantage of these cables is that cable data, such as the current-carrying capacity of conductors, isn’t readily available and reference must be made direct to the cable manufacturer. These cables are described in some manufacturers’ literature as ‘control’ cables. The letters indicate:
S – Steel wire braid
Y – PVC
C – Copper braid
These letters don’t indicate adherence to a particular standard. In the case of SY cables, for example, they indicate only that these cables have a steel wire braid with a thermoplastic (PVC) oversheath. SY, YY and CY cables are claimed by some cable manufacturers to comply with the German standard, ‘VDE 0250’.
The VDE Institute is a national and internationally accredited institution in the ﬁeld of testing and certiﬁcation of electrotechnical devices, components and systems (VDE stands for Verband der Elektrotechnik, Elektronik und informationstechnik).
VDE publishes a series of standards covering, among other things, various cable types. However, simply quoting the term, ‘VDE 0250’ is meaningless because it is not a speciﬁcation and the ‘0250’ is just one part of a complete standard number. In order to be meaningful, the full standard number must be quoted. For example, the German NYM type of cable is deﬁned in VDE 0250-204:2000. The full VDE standard to which these cables might conform is unclear.
VDE standards are German national standards. They’re neither Harmonised European (EN) nor International (IEC) standards, therefore their use under BS 7671 isn’t automatic and they would be subject to the required engineering assessment regarding safety, etc.
NAPIT understands that the VDE Institute has issued certiﬁcation to a small number of cable manufacturers for some SY, CY, and YY cables and that this certiﬁcation is based on individual cable manufacturer speciﬁcations which are conﬁdential to both VDE and the manufacturer.
As these speciﬁcations haven’t been published, we’re unable to determine which material and construction speciﬁcations or tests have been applied. Consequently, authoritive literature isn’t available to assist in making engineering judgements.
BS EN 50525-2-11
The UK standard for PVC insulated and sheathed ﬂexible cables is BS EN 50525-2-11 and some manufacturers of SY, CY and YY cables claim conformity with this standard. However, they have different constructions.
There is no provision in BS EN 50525-2-11 for any braid and hence a braided cable, such as SY cable, can’t conform to this standard. BS EN 50525-2-11 speciﬁes various types of PVC ﬂexible cable, such as H05VV-F.
The Approved Cables Initiative (ACI) reported last year that cables designated SY, YY or CY often have lower insulation and sheath thicknesses by comparison with the BS EN ﬂexible cables.
The use of foreign standards
Regulation 133.1.1 requires that every item of equipment (including cable) must comply with the appropriate British or Harmonised Standard. In the absence of such a standard, reference can be made to the appropriate IEC standard or the appropriate standard of another country.
As the VDE 2050 standard is neither a Harmonised European (EN) standard nor an IEC standard, it’s doubtful whether it could be called ‘appropriate’.
If Regulation 133.1.1 isn’t complied with, Regulation 133.1.3 requires that the designer or the person responsible for specifying the cable must conﬁrm that it provides at least the same degree of safety as that afforded by compliance with the Regulations.
A similar requirement for the designer or speciﬁer to conﬁrm the safety of non-standard equipment is given in Regulation Group 511.
This leads to the question: can a designer or a speciﬁer, who has speciﬁed the use of SY, CY or YY cables, give such an assurance? And on what basis would it be given?
Flexible cables in ﬁxed installations
The fact that SY, CY and YY cables are ﬂexible cables brings up a general point on the use of ﬂexible cables in ﬁxed installations.
An obvious use for ﬂexible cables in ﬁxed installations is for the ﬁnal connection to equipment which may need to be adjusted, such as ﬂoodlights or motors. Flexible cables may also be used for overhead wiring between buildings.
Regulation 521.9.1 permits the use of ﬂexible cables for ﬁxed wiring if they’re of the heavy duty type or the risk of damage is low or protection against mechanical protection is provided. However, NAPIT doesn’t advise the use of ﬂexible cables in ﬁxed electrical installations generally.
Several of the manufacturer data sheets state that SY cables aren’t suitable for ﬁxed wiring applications requiring compliance with the regulations, as set out in BS 7671.
There is no doubt that SY, CY and YY cables have their supporters within the industry but the fact remains that they’re non-standard cables and the general industry guidance is to discourage their use.
In order to be certain that cables comply with BS 7671, only those cables which are recognised in BS 7671 should be selected.