motor wiring

Kevin McGovern

Kevin McGovern

Joined
Jul 31, 2015
Messages
3,118
This is probably a super simple question, but all the searching I do just comes up with 3 phase or VFD wiring. For a 1.5 HP 115v single phase motor, can I add a single pole switch to L1 (hot leg) and connect the white to the other side and grounds to ground of course. my wiring setup is this:

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12345678910 said:
Yes you could, but I like to use two pole switches and switch both hot and neutral.
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^^ I do this too. Single pole switches are also fine according to code/best practice, except that you should CHECK to make sure your power outlet or line is wired correctly and does not have hot switched with neutral, as many accidentally do. If hot and neutral are switched in the outlet/line, then turning the switch off will cut neutral, which turns the machine off but you can still shock yourself when you mess with the wiring on the machine.
 
Obviously a high voltage motor (two hot legs) should never be switched that way. A low voltage motor like you're talking about is less dangerous but remember that neutral does carry current and there will be potential between it and a ground if there is something else running on that circuit.

I'm not sure what code requires, there are lots of examples of switching only hot, but an induction motor with a start capacitor in a shop environment is not the same thing as a ceiling fan. I'd use a two pole.

...honestly, I'd probably use a single pole, but I'm an idiot...
 
I went ahead and exchanged the switch for a stdp toggle. And Christmas is coming a little late, as I just got my first part delivered for my grinder build (the gas shock from McMaster Car).
 
Lieblad said:
To split hairs, does not have to be something else running on that circuit.
Any current flowing on neutral anywhere of the service can produce potential between neutral & a grounded object.
Several variables play into the mix, but several volts is not uncommon.

Code requires switching the 'hot' side at minimum.
Both sides may be switched if both circuits are mechanically linked & simultanious.
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The thing people need to be aware of is the risk of shock from neutral. Even though they're tied together back in the panel there is real potential between neutral and ground if there is much current on a circuit.

To put it another way, you could stand barefoot on a wet concrete floor and stick your tongue on a bare neutral wire and have nothing happen, but then have someone turn on a shop vac on the same circuit and mess up your day...
 
Just to be on the safe side I went with a double pole. If I need to work on it, I would unplug it regardless.
 
Nathan the Machinist said:
The thing people need to be aware of is the risk of shock from neutral. Even though they're tied together back in the panel there is real potential between neutral and ground if there is much current on a circuit.

To put it another way, you could stand barefoot on a wet concrete floor and stick your tongue on a bare neutral wire and have nothing happen, but then have someone turn on a shop vac on the same circuit and mess up your day...
Click to expand...

If it's properly wired, then 15A on a 14AWG wire over 100ft should only have around 8V of potential. I'm not saying you should touch live wires, even the neutral and ground, but the neutral should be safe if wired correctly and properly grounded and there is no need to disconnect it to stop the motor (for sure, you would disconnect the neutral before doing electrical work on the machine).

That's different than saying that the "white wire" is safe - since in some scenarios the white wire is used as a hot wire (e.g., 3 way switches).

I'm not an expert on motors, but I would be worried about disconnecting both the neutral and hot while the motor is running. I don't know what that does to a motor (I know, for example, disconnecting a motor like that from a VFD is very hard on the VFD).
 
Success! Got it hooked up, switch works, I didn't die and it even rotates in the correct direction.
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That toggle looks a little small for switching a 15 amp load. What was the rating in volts and amps on it? The contacts may fry prematurely if it is badly under rated. If the neutral contact fries the motor will still be hot. Yes always unplug before working on the wiring.
 
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