Posted 15 October 2012
There have been high profile cases recently of substantially undersized conductors being sold, mainly in products such as conduit wire, T&E or flexes, showing total disregard to safety.
In the good old days when copper was relatively cheap, conductors were primarily sized by their cross sectional area. This was all set out in IEC 60228 and BS 6360 with different classes for solid, stranded and flexible conductors. While these standards dictate the number of strands and maximum strand size, the overiding element is the maximum resistance figure.
Originally this was to combat impure copper conductors. Now however, due to the high price of copper, many manufacturers are working entirely to the resistance figure and conductors are bearing little resemblance to the correct mm² size.
This can cause major problems from crimping on lugs and terminations. Although a conductor may pass the resistance test prior to manufacture, by the time it has passed through the unavoidable tensions and stresses of the production process, reeling and eventually installation, the conductors can easily become elongated to a point where the resistance figure is below the acceptable standard.
With copper likely to remain high for the foreseeable future it is important to look beyond just cost when comparing quotes. Suggested weights of copper for any popular conductor size are shown in the back of ‘The Little Red Book’ and you can always get up to date copper prices from www.lme.com.
As ever, if a price looks too good to be true it probably is.