Information about the types of failures we find 

This series is designed to pass on  some of what we have learned from doing Electrical Safety Testing over several years. The information is probably not available elsewhere as is is presented from our particular perspective as safety testers. It is not intended to cover all aspects of the safe use of electrical products, only to highlight issues we have become aware of through safety testing. As such, it should be read in conjunction with and in addition to warnings and recommendations from the manufacturers, regulatory bodies and electrical authorities. 

Supply Leads - Care and feeding of

These are the leads (fixed and detachable) that connect the mains supply from the wall socket to an electrical appliance and includes extension leads.

Supply leads are our highest failure rate category. As can probably be expected, the faults we find are mostly due to physical damage. There is not much we can say about that other than to be careful and get damages fixed before the lead is reused.   

Most people would know to protect supply leads from the risk of cutting and burning. What seems to be less well appreciated is the damage caused to a lead that gets crushed. The insulation often splits at a crush point and the break can be very difficult to see. Also, the cores of the lead may be squeezed out of their position within the outer insulation, creating a weak point that can flex beyond what the lead was designed for. Crushing damage should be avoided just as much as cutting and burning.

IEC leads need a special mention. These are the detachable power leads that typically come with computer equipment. They have a problem where the earth connection in the appliance end of the lead weakens and possibly fails to earth the appliance. We use a gauge to test for this weakness and failure rates can be as high as 10%. We recommend annual testing of these leads because of this problem.

IEC leads that are often plugged in and out at the appliance end or used on different appliances seem to be the worst affected. We suggest that old leads don't get used on new equipment. Dispose of the old leads with the old equipment. When unplugging the appliance end of the lead, avoid twisting (rotating) it. Only move the plug up and down in line with the pins to loosen it.