Destructive Testing - Failure of start / overload relay....

[turbokinetic]

So, today I tested what happens to a motor stator when there is a serious failure of the motor start / overload relay. This is a cotton wound motor winding from a 1930's refrigerator compressor.

 

youtu.be/fMK8WYmO9Vo

 

 

[combo52]

Winding Burn-Out

Neat demonstration David, This is the type of thing my brothers and I did a number of times growing up.

 

It is impressive how long that motor ran with both winding's energized before it got hot enough to melt part of the winding and go open.

 

Because this motor is so over built it had a lot of metal to heat up before it failed.

 

The good thing in the real world is over-load protectors almost never fail, and even if they did the household circuit breaker would almost always trip before a modern motor would ever go up in smoke.

 

John L.

 

[turbokinetic]

Hi John, yeah that motor did take far longer than I had expected to reach the "irreparable damage" point. I was expecting damage by 30 seconds but it made it about 5 minutes.

 

Overload breakers are engineered to fail "open" when they fail, which is usually how it goes. Sometimes, however, they end up with the contact fused together.

 

In this experiment, the current draw never exceeded a normal branch circuit level, until the final short that ended the current flow. It was under 10 amps until the fire was well underway...

 

 

 

[Unimatic1140]

That was really interesting to watch David, it was amazing that the motor ran for as long as it did without the windings going totally open!