Saturday, September 21, 2013

Why One Can Never Be Too Careful

I'm restoring an elderly 6" bench grinder, and I wanted to confirm the rotation direction of the 1/3 hp motor I have for it. When I switched on the motor, it started up, let out a huge CRACK!! and flash of light and tripped the breaker. Hmmm.

The motor had been checked out long ago by someone of my acquaintance, and should have been ok. I opened up the motor to inspect the internal wiring and found this.

Note the red wire at the centre of the photograph. Its insulation is gone in a spot right down to bare copper. The wire had been getting whacked by the nearby fins of the rotor until its insulation had worn through. I think I know how this came about, and what caused it.

First off, there is no such thing as a limp copper wire -- they all have some 'springiness' to them. When the motor was last opened up and reassembled, the red wire had not been absolutely, positively tucked away where it couldn't possibly come in contact with the rotor's fins. The red wire had been tucked away alright, but not away enough. On first testing the motor, all had seemed well but, in time, the wire's springiness caused the wire to move toward the rotor, eventually contacting it and resulting in the incident I experienced.

Anyway, I cut and spliced and insulated the damaged wire. Here's a view of that.

When I reassemble the motor, I'll make good and sure that that wire is tucked away safely and 'tamed' -- I don't need any repeat performances of the arcing, breaker-tripping incident.

- - -

I ended up adding a ty-wrap, just to be safe. The other wires all lie away from the rotor nicely, but the red wire wants to travel. The ty-wrap takes care of that tendency.

And here's a view of the motor completed and running, happily turning in the direction I need it to.

That was a great illustration of how a tiny oversight can have dire consequences. It pays to pay attention, and leave nothing to chance.

# # #

# # #