🔍 Key Concepts
• Difference between low voltage release and low voltage protection in motor control circuits
• How a 2‑wire control circuit (maintained contact, like a pressure switch) behaves after a power failure vs. a 3‑wire control circuit (Start/Stop pushbuttons with a holding contact)
• In the EL‑0042 diagram, how the Hand/Auto selector changes which device actually controls the CR (control relay) coil
💭 Think About
• In HAND mode, trace the path that energizes the CR coil: does it go through the Start/Stop pushbuttons and a holding contact, or only through a maintained switch? What must the operator do after a total loss of control power?
• In AUTO mode, trace the path to the CR coil: which contacts of the Hand/Auto switch are closed, and what device (pressure switch PS or Start button) is now in control? After a power failure, if that device remains in the "demand" position, what happens when voltage comes back?
• Compare your findings with the formal definitions: which condition means the motor will not restart automatically on power return (protection), and which condition allows it to restart automatically (release)?
✅ Before You Answer
• Carefully check which contacts (A or B) of the Hand/Auto selector are closed in each position, using the small contact-position table in figure A.
• Verify whether the CR coil has a sealing (holding) contact in series with the Start button in HAND mode, which would require a manual restart after power loss.
• Verify whether, in AUTO mode, the CR coil is controlled only by the pressure switch (PS) acting as a maintained 2‑wire control, which would allow automatic restarting when voltage is restored.