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If using a contactor for three- phase motors with a single-phase motor, can just the hot (120 V) line be passed through the contactor, with the neutral and ground bypassing it? I believed the concept for circuit breakers is applicable in this case too.

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    \$\begingroup\$ I don't see why not. \$\endgroup\$
    – DKNguyen
    Jul 21, 2020 at 19:07
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    \$\begingroup\$ You can switch neutral with it too but never switch the ground / earth wire. \$\endgroup\$
    – Transistor
    Jul 21, 2020 at 20:25
  • \$\begingroup\$ For clarification, with a device using a hot, neutral, and ground wire, there is no danger in leaving the neutral wire unbroken? My conclusion was that this only poses a risk if two devices share a common neutral. \$\endgroup\$
    – coolro
    Jul 21, 2020 at 21:40
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    \$\begingroup\$ Current UL regulations require that neutral be disconnected from AC line power as well as each phase. Ground is NEVER disconnected. \$\endgroup\$
    – user105652
    Jul 21, 2020 at 22:45
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    \$\begingroup\$ When a single phase motor is to be controlled using a three phase contactor and bimetal overload relay, the line is to be wired through 2 contacts in series and the neutral through the third. This is covered in detail at electronics.stackexchange.com/questions/463051/… \$\endgroup\$
    – vu2nan
    Jul 22, 2020 at 5:57

1 Answer 1

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When a single-phase motor is to be controlled using a three-phase contactor and a bimetal overload relay, the line is wired through two contacts in series and the neutral through the third.

This is covered in detail at Does only wiring 2 poles of a 3 pole overload relay have any effect?

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