The saw has a simple pushbutton start switch and a latching off / emergency stop switch fitted in a box below the table.
The originals were in sound condition so were cleaned up and reused.
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The advantage of fitting controls in a sealed enclosure is dust resistance. Cable glands and a rubber seal around the box combine with industrial style switches which have rubber O rings around their mounting holes.
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The industrial switches are typical of the type. Made in three parts there is a button or switch up front, a mid section that secures the switch to the panel, and clip on blocks at the back that do the electrical switching. The contact blocks on these switches screw firmly to the metal section rather than using spring clips.
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Notice in the bottom image the contact blocks are labelled NO (normally open) green, and NC (normally closed) red. In most typical setups, the green contact block is clipped onto a green start button or rotary start switch. The red block onto a momentary stop switch or emergency stop button.
An important point to note. These switches operate a control circuit only. Power goes to the motor through a large 3 phase relay aka "contactor" that sits in a box on the back of the saw. The pushbuttons and the safety relay in the next post work at 3 phase mains voltage but carry only the small current that flows through the operating coil of the contactor.
FOOTNOTE: One small detail nagged at me and had to be put right after the event.
You may notice that the industrial switches in this control box have metal frames and bezels around the buttons. That is a nice quality detail, but used here in a plastic enclosure, an unlikely but hazardous fault could arise. IF a live wire were to come loose from one of the switches because of vibration, fatigue or a mistake in tightening the terminal screws, AND IF that loose wire happened to touch part of the metal clamp / frame on one of the switches, then that part and the metal bezel around the switch on the outside could become live at 240V.
Normally this would never happen because the enclosure would be metal and grounded. The frame and bezels of the switches make a good electrical contact with the box and are also grounded. In a plastic enclosure this can't happen. We needed to go back and explicitly earth the bodies of the switches as a safety measure against 3 pieces of bad luck coinciding.
If this machine were being run off a variable frequency drive, the pushbutton control circuitry typically works at just 10 or 12 volts, or at max 24V. Had that been the case, I wouldn't have worried because the number of simultaneous faults needed to put 240V on the switch bezels would make the odds too small to worry about.
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