[ Industry view: Technology ]
Using busbar trunking instead of traditional cables
contained by trays can also save on weight and resources. In an electrical installation, the weight of the cabling accounts for approximately half the total mass of materials used. This is because each outgoing load from the switchboard has to have its own cable. However, with busbar trunking there is one feed out
from the switchboard and each load can be locally fed off the system at any point using a tap-off unit. Also the amount of raw material in busbar trunking is less than an equivalent cable run, so it’s a more environmentally friendly solution. For example, returning to the previous installation scenario, a traditional electrical distribution system would weigh around 737kg for the cabling alone. However, the equivalent installation using busbar trunking would weigh only 451kg.
Cutting out the errors
In addition to helping businesses save energy, using busbar trunking prevents mounting errors and reduces fitting time. The work can be carried out safely without exposure to live connections because, for example, live parts in the busbar trunking tap-off units are not accessible. They can also be safely added and removed with the trunking energised, and eliminate installation errors as they provide a reliable connection. Installation times can be planned precisely in advance and, if plans must be changed, a fast and effective solution
is always available with an adaptable and upgradeable system. Modifications can be made easily, whereas with traditional cable systems, the same changes could take longer than a day. Busbar trunking allows changes of direction in a smaller
space than with cable. It can be designed with 180-degree bends that can reverse direction in an area just over twice the width of a trunking length, whereas a cable may need to be formed into a large loop to do the same, particularly a large diameter armoured cable designed to carry heavy current. Busbar trunking also gives a true 90-degree bend,
making best use of often restricted space. Contractors can easily replace straight runs with T-pieces, bends and other components, without disturbing the rest of the network. Once the installation has taken place, busbar trunking
can be amended if the business changes its layout or increases its power rating. The electrical installation can easily be upgraded as part of future investment projects and it is possible to add or remove loads without cutting off power to the rest of the installation. The advantages of busbar trunking have led to it being recognised as a viable alternative to cable and it is frequently specified by architects, contractors and consultants over cable. It provides numerous benefits for the contractor and
the end user – amp for amp it is smaller, more compact than cables installed on trays, weighs less, reduces raw materials, simplifies the installation and offers flexibility.
Busbar trunking at Derby City Hospital
The new 47-acre Derby ‘Super’ hospital site accommodates facilities for both Derby City General Hospital and the Derbyshire Royal Infirmary. Skanska, a leading PFI service provider in the UK, selected Schneider Electric to provide the electrical distribution equipment. One objective was to implement a modular system. For this installation, trunking was chosen over cable, as significant cost savings are realised through its easier installation, greater flexibility and superior lifecycle. Canalis KTC trunking was used as it is designed to feed high power into industrial and commercial buildings. The compact trunking can be mounted edgewise, flat or vertically without any de-rating of the current. This also cuts out the need for fire barriers where the trunking passes through building slab floors or firewalls, and offers a two- hour fire resistance rating as defined by ISO 834. A total of 1,154 metres of busbar trunking was used, ranging from 1600A to 5000A. In addition, 480 distribution boards from Schneider Electric’s Isobar 4c range of modular distribution boards was chosen because it allows for hundreds of combinations to be assembled from just a few standard modules.
The main LV switchboard contains air circuit breakers, which are both electrically and mechanically interlocked to perform automatic changeover. In the event of loss of the main supply, the generators will start and the changeover will operate automatically to enable the generator supply to feed the outgoing loads. Since time was a major factor, the design of the installation meant it could be speedily connected. The distribution board cabling was completed off site to save time, making installation very simple and quick. Moreover, factory testing eliminated any possible site errors. The distribution boards were simply connected, reducing the number of skilled electricians required on site.
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Using busbar trunking instead of traditional cables contained by trays can also save on weight and resources... there is one feed out from the switchboard and each load can be locally fed off the system at any point
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Summer 2010 ECA Today 61
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