3. What is the correct safety procedure when switching polarity on a welding machine? A. Switch polarity while welding is in progress B. Change polarity only when the machine is turned off C. Rapidly switch between polarities for better penetration D. Switch polarity whenever the arc becomes unstable

The correct safety procedure when switching polarity on a welding machine is:<br /><br />B. Change polarity only when the machine is turned off.<br /><br />Explanation: It is crucial to turn off the welding machine before changing the polarity to prevent accidental electric shocks or equipment damage. This ensures that the user is not exposed to unexpected electrical hazards and helps maintain the integrity of the welding machine.