A particular type of wiring system will influence but doesn't usually dictate the choice of containment used. The containment system is chosen by the budget available and practical considerations of operating in the building where it is being installed.
Fixings Used for Cable Management Systems
As cable management options available range from lightweight cable trays to heavy-duty trunking, your choice of fixings needs to consider both the cable management solution's weight and the cables it will carry. It would help if you took specialist advice from fixings manufacturers themselves or structural engineers on site regarding the weight the fixings can carry. In cases of heavy loads, You may secure things safely with anchor bolts or brackets.
What types of cable management systems are available?
Cable basket tray is lightweight. Components are easily connected, as they usually clip together, making them very quick to install. It is often used for Category 5e, Category 6 and Category 6a TCP/IP data cabling but can be used for many cable types with more than basic insulation, including electrical cables.
Cable tray and ladder racking is mostly used in industrial installations, mineral insulated and other small diameter, soft jacketed cables. Cable tray is a set of fittings that make a rigid structure to support and secure low voltage and electrical cables, allowing the safe installation of cables across open spaces. It is in effect the skeleton, of a building's HV and LV electrical system. Ladder racking is mainly for heavier cables, especially armoured cables, because it is strong enough to withstand more weight than a cable basket.
Cable trunking is available in both metal and plastic or PVC, suitable for surface mounting. Larger sizes of plastic cable trunking are also often called Maxi-Trunking. It is used for single insulated cable in electrical installations and most low voltage systems, trunking can be fitted with bends and jointed into complicated routes, so it is a versatile way to manage different cable types. Trunking is available in an extensive range of manufactured shapes and sizes so in most circumstances you can easily install it. Metal cable trunking is almost always galvanized, or powder coated by the manufacturer. Both metal conduit and cable trunking systems act as parallel conductors, so standard earth fault loop-impedance in these systems often ends up being less than calculated before install.
Mini-trunking is used for installations of smaller amounts of cable, like small offices. Mini-trunking, is sometimes called miniature trunking, and is used instead of larger PVC maxi-trunking. It is also available with a self-adhesive backing for fitting exceptionally quickly to a ceiling, wall or floor.
Dado trunking is fitted similarly to a "dado rail" though usually about a metre above floor level and is usually used in commercial offices or buildings that are fitted with many power and data outlets. It usually has multiple compartments, allowing power and communications cables to be routed together but kept separate. It also allows the position of those outlets to be altered easily after initial installation when necessary.
Rigid Conduit System is available in both metal and plastic or PVC. Conduits are the tubes and connecting fittings that are used to protect and route cables. They come in various materials, which you choose depending on the installation conditions. Plastic (PVC) or galvanised metal are both standard. Conduits can be used for complete wiring systems or single cables to reduce the risk of faults by protecting them from damage. Conduits are fitted to walls and ceiling using saddles. There are several saddle types;
Spacer bar saddles -the usual fitting in most circumstances
Distance saddles - to fix conduit to uneven surfaces
Hospital saddles - have a thicker base and allow cleaning more easily around the conduit if fitted where hygiene is essential.
Conduit systemsenable wiring system 'drops' to yet-to-be-installed equipment, meaning you can complete building work and the cables pulled into place later. Conduit Couplers connect lengths of conduit. Where a conduit needs to enter a box with no thread entry, use a coupler and a brass bush to fix.
Flexible Conduits are used for short and complicated routing of cables to enclosures. They are available made in bare or plastic coated galvanised metal, or made entirely from plastic (Polypropylene). Glands are fitted to cut lengths of flexible conduit to provide a secure mating to trunking, transit boxes or equipment enclosures. If protection is required in harsher environments Liquid Tight fittings are available to prevent water ingress into the conduit. Glands can either be fixed to the flexible conduit, or swivel glands that allow the conduit to turn inside the gland, which is important when working with longer lengths.
What colours are available for cable trunking?
A limited number of trunking systems, including Algar (minitrunking and maxitrunking) and D-Line (decorative TV trunking), are available pre-coloured in Black, Red or Brown to blend in with decorative finishes.
You can also paint both plastic or metal trunking or conduits, when following good practice guidelines to ensure the paint finish takes to the trunking properly, and so remains a durable finish.
What regulations does trunking need to comply with?
The regulations that relate to the use of trunking in electrical installations is contained in BS 7671. They include:
Non-sheathed cables may be installed in a trunking system if the trunking provides at least IPXXD or IP4X protection, and if the cover can only be removed using of a tool or with a deliberate, rather than accidental action.
In trunking systems that use joints fabricated onsite, the installer must ensure that these also meet at least the level of IPXXD protection.
To comply with NICECI 18th edition regulations for fire safety, trunking fitted at high level should secured with metal fixings, and cables retained within them using metal clips.
To comply with good practice, all cable containment systems using trunking, conduit or wire basket tray should follow “fill ratio” and space factor guide lines to ensure both long term cable integrity and avoid heat buildup.
What does an IP rating indicate?
An Internal Protection (IP) rating denotes the degree of protection any enclosure will provide against external elements. The IP code is shown in a format giving four digits:
First number: ranges from 0 to 6, or the letter X – gives the protection level of people against access to hazardous parts on the inside of the enclosure.
Second number: ranges from 0 to 8, or the letter X – shows the level of protection of the equipment against the ingress by solid objects.
occasionally there is an additional letter(s)
First additional letter: either A, B, C or D – which shows the level of protection of the equipment against water penetration.
Second, supplementary letter: either H, M, S or W – which shows the protection level against access to any hazardous internal parts.
Note that the additional letter is only ever used if the protection level provided against access to any hazardous parts is greater than the protection level of the first digit.