ddawg16
Well-known member
Some of you sparky's will know this.....especially those who do commercial work.
For you residential guys.....you may have never seen this....
So...add this to your 'So What' file.
The more 'modern' motor control centers for motor starters typically use electronic overloads. Smaller and adjustable.
In the old days before the wazu electronic stuff, they used motor heaters. These are devices that open up a starter if one or more legs of a 3ph motor starter pulls too much amperage. This is not to be confused with the fuses or circuit breakers which have a different function....protection for high current/fault conditions.
The thermal overloads are what protects the motor when it's running slightly over it's max current....a condition that fuses would not protect.
It's rare I see one like this....99.9% of the time....the proper over loads are installed and I never have to mess with them.....today I had to install some on a system I'm starting up....so I figured it was a good time to take pics.
This is the actual overload. The strip of metal between the two tabs (holes) is a resistive that gets warmer as the current goes up. The part in the middle that looks like a small gear on a shaft is the protective part. That 'gear' is connected to a shaft that goes inside the tube. The whole mess is put together with a low temp solder...similar to what was used in the old school fire sprinklers. Melts at a much lower temp than regular solder....like around 125-150 deg.
When the current across the unit goes up...it gets hot....when it gets hot enough, the solder melts and the wheel (gear) can turn.
This is the starter with the thermal over loads installed. If you look closely you will see what looks like a metal paddle sitting on top of the wheel. In this pic the overloads are in the 'tripped' position....all the paddles are out and the over load is open (no power to the motor)
In this pic the over load has been reset. See the red handle? You push that in....it pushes the paddles back and they park on the serrated edge of the wheel. Because the solder is not melted...the wheel can't turn and the paddle stays locked in the on position (power to the motor).
If the over load see's too much current, solder melts, the paddle can now turn the wheel...and it pops out....opening the power to the motor.
When it comes to simplicity are reliability....thermal over loads are the way to go....but.....if you need to change the current setting, you have to buy new over loads. Hence, the electronic stuff is taking over.
That includes your lesson for the day.
For you residential guys.....you may have never seen this....
So...add this to your 'So What' file.
The more 'modern' motor control centers for motor starters typically use electronic overloads. Smaller and adjustable.
In the old days before the wazu electronic stuff, they used motor heaters. These are devices that open up a starter if one or more legs of a 3ph motor starter pulls too much amperage. This is not to be confused with the fuses or circuit breakers which have a different function....protection for high current/fault conditions.
The thermal overloads are what protects the motor when it's running slightly over it's max current....a condition that fuses would not protect.
It's rare I see one like this....99.9% of the time....the proper over loads are installed and I never have to mess with them.....today I had to install some on a system I'm starting up....so I figured it was a good time to take pics.
This is the actual overload. The strip of metal between the two tabs (holes) is a resistive that gets warmer as the current goes up. The part in the middle that looks like a small gear on a shaft is the protective part. That 'gear' is connected to a shaft that goes inside the tube. The whole mess is put together with a low temp solder...similar to what was used in the old school fire sprinklers. Melts at a much lower temp than regular solder....like around 125-150 deg.
When the current across the unit goes up...it gets hot....when it gets hot enough, the solder melts and the wheel (gear) can turn.
This is the starter with the thermal over loads installed. If you look closely you will see what looks like a metal paddle sitting on top of the wheel. In this pic the overloads are in the 'tripped' position....all the paddles are out and the over load is open (no power to the motor)
In this pic the over load has been reset. See the red handle? You push that in....it pushes the paddles back and they park on the serrated edge of the wheel. Because the solder is not melted...the wheel can't turn and the paddle stays locked in the on position (power to the motor).
If the over load see's too much current, solder melts, the paddle can now turn the wheel...and it pops out....opening the power to the motor.
When it comes to simplicity are reliability....thermal over loads are the way to go....but.....if you need to change the current setting, you have to buy new over loads. Hence, the electronic stuff is taking over.
That includes your lesson for the day.
