If a cable has a fire rating, does this mean that it won’t burn?
Fire rated cables are designed to continue functioning during the course of a fire for a specific period of time which allows for safe evacuation of a building by maintaining smoke handling systems, emergency lighting etc. The cable will burn however in a manner that ensures circuit integrity during the fire. The tests to determine the fire rating of a cable system are documented in AS/NZS 3013:2005.
Can a cable with a fire rating operate continuously in hot environments, for example, very close to a furnace?
No, a cable with a fire rating does not necessarily mean that is it suitable for use in a hot environment. It is necessary to design cables using special materials such as silicone or glass fibre to withstand relatively high temperatures (in excess of 110°C on a continuous basis.)
What does a two hour fire rating mean?
The fire test for determining the fire rating of a cable consists of exposing a cable and fittings to extreme temperature in a furnace over a period of two hours. The temperature builds throughout the period to a final temperature of around 1030°C. The cables are subjected to their round operating voltage and a current flows through the conductors. If the insulation fails, ie shorts to ground, or if the current stops flowing, the test has failed. This test permits comparisons between different manufacturer’s products and provides a benchmark on which installation standards can be based.
How is the resistance to mechanical impact measured?
A length of cable is energised and the impacted with a device, loaded with a predetermined weight. The impact point will consist of two different points, a blunt crushing type of point and a sharp cutting type of point. If the cable maintains circuit integrity through this test, it attains a mechanical rating. Different loads can be applied to attain different levels of rating.
What does the cable system consist of?
The AS/NZS 3013:2005 fire test requires that all of the items that comprise a cabling system operating in the fire rated zone must be tested and pass as a system. In other words, it is no longer possible to test the cable in isolation. Other components that may comprise a system include fasteners, saddlers, ladders, cable trays, clamping systems, etc. Joints only need to be tested if they are installed in the fire rated zone. Alsecure® is available in lengths to suit the contractor, hence this requirement should not be necessary.