Electricity + Control October 2016

CABLES + ACCESSORIES

NEC

– National Electric Code

PV

– Photovoltaic

PVC TUV

– Polyvinyl chloride

– Technischer Uberwachung-Verein

UL

– Underwriters Laboratory

UV – Ultraviolet

Abbreviations/Acronyms

Protection of cables from direct sunlight can be achieved by implementing a safe, reliable and code compliant wire management system. By conveni- ently using the available shade of the modules and other structural members, one can improve on the life of PV cables. The PV cables can be protected by being secured to the module frames, support rails and other rack- ing system components. Where cables are exposed away from the panel covering (where inter row PV cable routing occurs), they can be provided with a special protective covering. Protection of PV cables from heat sources can be achieved by not fixing the cables within sixinches from the heat source. Another method to protect the PV cables from such a heat source is by ad- equately shielding the cable and its protective sheathing or properly selecting a PV cable of special design (heat resistant cable) to with- stand the effects of such exposure. Cable trays’ systems can also be used in lengths of the panel ar- rangements where PV cables run along the trays under the modules. All standard requirements must be adhered to when implementing these installations. In addition to trays, PVC or galvanised metal conduits can be used to protect the solar cables. Protection of PV cables from water PV cables should not be in constant contact with water as this may cause the cables to be saturated with water. Persistent water satura- tion can lead to insulation resistance damage and even rotting of cables causing short circuits and earth leakages. Cables which can be subjected to such conditions must be care- fully selected in accordance with the acceptable standards. The cable selection must ensure that the cable used is for outdoor use and can be used in wet conditions. In order to prevent or protect cables from water damage due to constant water logging, shading and elevating of PV cables in sealed channels and conduits. For PV cables underground the same princi- ple of sealing exposed ends of conduits or sleeves will alleviate the saturation of cables with water. To protect the PV cables from water in general they shall not be fixed (if possible) where they will be exposed to the accumulation of water which might damage the conductor or its protective covering

Cable standards for PV cables Standards by definition are ‘a quality that is consid- ered acceptable or desirable’. Two agencies which have approvals for solar

cables in the USA are the Underwriters Laboratory (UL) and the National Electric Code (NEC). The two types of approvals for Photo-Voltaic cables are USE-2 and type PV. The Technischer Uberwachung- Verein (TUV) – Germany and this has approvals based on the ISO 4892 [1], EN50395 [2] and EN50396 [3] all being tested according to IEC 60811 [4]. Only PV cables of a quality that is considered acceptable or desir- able in accordance with the recognised standards can therefore be used in solar installations as a mere baseline requirement. Concept of cable protection against external influ- ences For the purposes of this article, the external influences that affect the protection of PV cables are considered. The life of PV cables is generally twenty five (25) years or more, but being exposed to harsh environmental conditions can subsequently damage unprotected cables. The concept of cable protection starts with the cable selec- tion in accordance with acceptable standards and the progress to the installation process in accordance with a recommended cable management standard. Protection of cables from sunlight and heat Cables that are used in PV installations are rated as Ultra Violet (UV) resistant or simply that they can withstand high temperature ranges fromas low as -60°C up to as high as 90°C. Although the insulation and jacket materials that surround the conductors are extremely resistant to UV radiation, the underlying fact is that they must be kept from direct sunlight exposure as much as possible. With continuous direct sunlight exposure the cables suffer degradation causing damage. By also selecting the correct colour for the PV outdoor cable which is ‘Black’ (containing carbon black in its insulation), the cable will be provided with additional UV resistance. Unprotected PV cables from direct sunlight or high ambient temperature results in the cable becoming brittle or breakable.

October ‘16 Electricity+Control

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