A TALE OF MICE

Evening Star, Issue 19775, 27 January 1928, Page 2

A TALE OF MICE

FAILURE Sf ELECTRIC PLANT It is not altogether uncommon for failure of electric plant to occur as a result of damage done by rats and mice (reports the ‘Electrician’). In one of the above-mentioned cases, a periodical inspection of thirty-five horse power slip-ring induction motor showed that the terminal box was entirely filled by a rat’s nest. The only means of ingress was by way of the air vents in the end shield at the slipring end, tbence through the passagering way between the stator core stampings and the frame, and finally, through the holes for the leads at the top of the frame. The nest was removed. and it was decided to fix expanded metal over the vents in the shield. Before this could be done, the rat paid a further visit and was electrocuted on coming into contact with the terminals, no longer protected by the insulating material of the nest. In another case—a ten horse power squirrel-cage induction motor of the ventilated type—it was noticed that the joints between the rotor end-rings and the bars wore in poor condition, and that solder was being thrown out. On opening out the machine it was also found that the insulation of the stator winding was damaged at the overhanging parts, and was exceedingly dirty. , , After cleaning sixty-four dead mice, all mutilated, were found in the space between the rotor core plates and the shaft. It was usual for the motor to be stopped for several consecutive days each week, and it appears that the mice had entered the carcase during one or more of these stoppages, and nibbled at the insulation of the stator winding, damaging it. They had then crept through the holes in the end plates into the recessed part of the rotor core, where they were killed when the machine was restarted. Thus we see once again a forcible illustration of the truth of the saying that the best laid schemes of mice gang aft agley.