WIRING
ADVICE - NAPIT
Fig 1
Fig 2
Fig 3
Cable ladders are used for supporting high volume or heavy cabling at long support spans. With the spaced out rungs they offer plenty of air flow which prevents cables from overheating
Cable trays are typically used for light weight cables, instrumentation and tubing
Cable baskets are a popular choice of cable containment systems available
FRANK BERTIE, CHIEF TECHNICAL OFFICER AT NAPIT, LOOKS AT DIFFERENT INSTALLATION METHODS AND MECHANICAL PROTECTION… It’s not all twin and sling
Installation or wiring methods?
a wiring system, and in most cases, it can be used for, or with, many different wiring systems. One such example of a containment system is the cable basket, as shown above in Fig 1, where the open metal frame design offers less surface area so increases air circulation and prevents both heat and dust build-up. Another cable containment system is the cable tray, as displayed in Fig 2, which is commonly used to support a multitude of light-weight cables. In the same way, we may choose to use cable clips or cleats. These can be used for many differing wiring systems; the clips or cleats themselves vary by design, but the principle behind their use is basically the same. For heavy duty and high-volume cables, cable ladders are typically used as a containment system, as shown in Fig 3. When we use singles, 6491X and similar, these are only half of the system. As 6491X cable only possesses basic insulation and no mechanical protection, we have to install them inside suitable mechanical protection. We can’t call 6491X cable a system, unless we also
refer to its mechanical protection part at the same time. There are two basic principles for mechanical protection of 6491X single cables, which are conduit and trunking. These again are split into two types of material construction, leading to four distinct types in total. For 6491X to be called a system, it needs to be referenced with one of these four mechanical protection parts. These two mechanical protection parts of a system, conduit or trunking, although they serve the same purpose, have very different properties and skill sets needed to install them. We generally wouldn’t use a separate containment for 6491X/conduit systems, as the system itself is the containment. A conduit system, whether metallic or plastic, will use saddles to secure it, but is considered to be integral to the wiring system and not optional. We wouldn’t lay conduit or trunking onto a cable tray or basket, for example, as this is not a proper use of either piece of equipment. Flexible metallic conduit is often utilised for connections to equipment, although there has been an increase
Whenever we speak to contractors or they ask our advice on an installation or wiring type, there is often some confusion over the different installation methods and how they can be used. Let’s be clear, wiring methods are different ways of saying installation methods, so they are generally taken as being the same principle. What’s a wiring system? These differ slightly from installation methods and refer to a cable or system containing both basic and mechanical protection when installed and commissioned correctly. PVC/PVC flat twin and earth cables are classed as a wiring system as they possess all of these properties and also include a cpc, as do SWA, MICC, soft skin fire cables (FP200 and similar) and many other similar cable types. The systems we use to support these cables are referred to as containment because they contain the cable wiring system. A containment system or method is not
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