Simple and idiot-proof at the same time.

My signature used to read,

A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.

 

Simple and idiot-proof at the same time.

Not that well designed IMO, if operated repeatedly it stresses and heats the motor.
Most of the Hoists and Winches I have seen have a centre off position before FWD/REV and at OFF a Magnetic brake is applied.
But of course that cost more to build.!
Max.

 

My signature used to read,

Another quote: "There's nothing so dangerous as a resourceful idiot".

 

Plugging traditionally on a 3 phase motor is instant power reversal.
Max.

a plugging switch is to prevent instant reversal. a lot of equipment here takes very unkindly to trying an instant reverse. so the plugging switch detects the very low speed or stopping of the motor before allowing reversing.

 

The bloke who took it apart and couldn't put it back together was a bit offended when I mentioned how simple the switching arrangement was.

You don't neccessarily need to be an idiot to inadvertently press both buttons at once, the winch was for hauling broken cars onto a recovery truck - vehicle recovery doesn't always go smoothly, particularly in pitch darkness and filthy weather. Just as the car starts to topple sideways off the truck, its an instinctive reaction to press everything at once trying to stop it.

Then there's always meddling kids that sneak up while you're not looking.

there should have been an interlock to prevent foreward and reverse at the same time. sometimes built into the switch, but usually in the reversing contactor.

 

there should have been an interlock to prevent foreward and reverse at the same time. sometimes built into the switch, but usually in the reversing contactor.

The buttons operated directly the high current contacts, You could put a see-saw lever between the buttons so pushing one button down pushes the other one up - but that could lock out the motor braking that was designed in if both buttons are pressed.

 

This is the way I it is used on the equipment I have been involved with http://www.electrical4u.com/induction-motor-braking/
But according to the book considered the motor 'Bible' by Robert Rosenberg this is what he says.
Max.