Electrical – Why does the old table saw power switch cut both hot and neutral

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I am refurbishing an old Craftsman 10" table saw that has been collecting dust in the back of my shop for years.

I don't remember exactly how I acquired it, but to my recollection the one time I tried to start it sparks flew from the on/off switch. The switch controls an integrated 110vt receptacle which the motor plugs into. All is factory original.

I tested the motor by plugging the motor power cord directly into a wall receptacle and it runs fine. I would like to resume using the factory On/Off switch (because it is a safety switch- pull On, push Off) but wanted to check it first.

Opening the switch box I discover that the switch is double-pole, i.e. opens and closes both the hot and neutral wires that lead to the motor receptacle.

  • why did the manufacturer install a switch that opens/closes both the neutral and hot?
  • can I safely use the switch to only open/close the hot (the neutral side is dead/open)? I can wire the neutral to bypass the switch…

Best Answer

The technique is called double-switching. According to this article, on AC equipment the technique is used to avoid dangerous conditions when hot and neutral are reversed, as often happens with outlets that have been improperly wired. It is permitted by this exception in NEC 404.2(B):

404.2(B) Grounded Conductors. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit. Exception: A switch or circuit breaker shall be permitted to disconnect a grounded circuit conductor where all circuit conductors are disconnected simultaneously, or where the device is arranged so that the grounded conductor cannot be disconnected until all the ungrounded conductors of the circuit have been disconnected.

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