Motor control · lesson 10 of 12
Hand-Off-Auto
A Hand-Off-Auto selector lets someone run a motor by hand, stop it, or leave it to an automatic device. In Auto the float switch is in the circuit; in Hand it is bypassed; in Off there is no path at all.
Hand-Off-Auto with a float switch
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Hand runs it now; Auto lets the float decide; Off is off.
How the selector is drawn
A selector has contacts that are closed only in certain positions. On a print you will see each contact labelled with the positions where it is closed (the lab writes "HOA (Hand)" and "HOA (Auto)"), or a small truth table beside the switch with an X under each position where a contact is made. Here one contact is closed in Hand and feeds the coil directly; another is closed in Auto and feeds the coil through the float.
The classic HOA trouble call: "the pump runs all the time". Nine times out of ten someone left it in Hand after testing. The pilot light in rung 2 only proves the switch is in Auto — which is exactly why it is there.
Questions people ask
What does Hand-Off-Auto mean?
A three-position selector. Hand runs the motor now, regardless of the automatic control. Off stops it. Auto hands control to a pilot device such as a float switch, pressure switch or controller.
Is the overload still active in Hand?
In a properly drawn circuit, yes — the overload contact is in series after the selector, so it protects the motor in both Hand and Auto. What Hand bypasses is the automatic control, not the protection.
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