I was inspecting and testing some of 110v extension leads earlier this week. I was not really surprised that all seven had defects that were found during the visual inspection. To be honest in a workshop environment extension leads have a hard time and it is perhaps a wonder that they survive as long as they do. Cables will get crushed and melted and plugs and sockets damaged.
Electricity was invented way back in the nineteen century since then safety standards have improved and the materials and machinery used to make cables, plugs and sockets have changed out of all recognition. So other than in a heritage scenario you would not expect to find, within touching distance, a knife switch fixed to a nicely varnished piece of hard wood along with some brass terminals and a couple of meters; one registering 125 volts and the other 220 amps.
So why in the twenty-first century should it be possible to come a cross a mass produced, factory assembled, extension lead where one of the screws that hold the two parts of the plug body together has cut through the insulation on both the protective earth and one of the live conductors ?
In this example at least four things have gone awry. Firstly the plug design is poor with the fixing screws passing through the space that is going to be occupied by wires. Then a cable has been prepared, the ends stripped and a cylindrical crimp fitted to each one, but, the length of insulation covered wire between the yellow outer sheath and the crimp is far too long. Next up the cable has been terminated in the plug by someone with no interest in their work otherwise they would have flagged this up to a supervisor. Last but not least this cable must have been assembled in a factory where the terms Quality Management, Batch Inspection and Final Inspection are alien concepts.
Note in a UK 110v industrial wiring system the secondary winding of the step transformer has the centre tap that is connected to Earth to that both current carrying conductors are “live”. e.g. 55v – 0v – 55v If you are unfortunate enough to get an electric shock in most cases it will only by 55v. For most healthy adults this will probably only cause them to feel a “bit of a tingle”.