Friday, June 17, 2011

Motor Wire Repair – Part 2

So what is an Underwriter’s Knot?  According to

“An Underwriter's knot is a simple and effect way to support the cord within the plug and give the connection some durability”

In this case, the knot is between the coil and the grommet in the motor case to prevent strain on the coil.  Here’s how to tie it as described on one of many websites.

Bend the left wire to the left into a loop, passing the end behind the body of the cord. Make a loop to the right with the other wire, passing the end in front of the body of the cord. Pass the end of each wire through the opposite loop and pull tight. Ta-da; an underwriters’ knot.

Here are a few pictures of what my knot looked like after I tied it.  I have to admit, practicing on spare wire helps quite a bit.

Underwriters Knot     Underwriters knot -view 2

The next step was putting a new grommet in the motor case and then putting a larger piece of heat-shrink over both the red and black wires to connect them together and make it more aesthetically pleasing.  One problem I ran into was that I couldn’t get the red wire brass ring through the heat-shrink after the black wire had gone through (all this before shrinking of course).  So, my solution was to remove the brass ring from the red wire.  Here is what it looked like when I was done.  Not too bad, eh?

Completed motor wire repair

Well, I couldn’t get brass ring crimped back on to the red wire, so I decided to experiment with creating a “home-made” ring, which in the end worked out pretty well.  Here’s how I did it.

  1. Strip your wire about 1-inch from the end  Exposed wire
  2. Twist the exposed strands tightly  Twisted wire
  3. Wrap the twisted strands around the tip of a pencil to form a ring.  The ring should be large enough, to fit around the post of the 3-pin terminal, yet not so large that it won’t touch the pin or fit in the pin cavity.
  4. Apply solder to the ring so it has some rigidity and won’t come apart
    (front view) Coiled & soldered (back view) Coiled & soldered (2)

I did several practice rings on scrap wire and and tested them on my 3-prong terminal to make sure the size was right before making the “real thing” on the end of the red motor wire. 

DISCLAIMER:  I don’t know know if this is the most appropriate way to finish off your wire, but it is aesthetically pleasing and does not harm the conducting properties of the wire.  I won’t be able to confirm how well it works until Ms. Rusty is back together again, so I guess we’ll find out together. 

In any case, it was fun making all the pretty rings and helped hone my soldering skillsSmile

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