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What do I need to know before attempting to hook up a strong motor ( for example 1/4 hp AC)? Answered

The intended use is for a miniature lathe, but I don't know the first thing about hooking up a motor! Can I just solder the connections to a plug and plug it in?


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Best Answer 9 years ago

Guessing from your info of 1/4hp AC, I presume it's either 120 or 240V AC for the purpose of this answer;

What I recommend any time you're working with power is safety first. Always work with your circuit unplugged, switched off, de-energized, grounded, and anything else you can think to make it no kill you. :)

Since this will be a power-tool with the capability to kill you, you want it to have switcheS to turn in on and off, not just a 'plug it in to turn it on'. What switchs? I'd recommend a safety switch that is 'pull to turn on, push to turn off' and big. They can be had for cheap from ebay or local if you know where to look. Also, you want an everyday 'operation' switch in series that you use to operate the tool, something heavy duty enough to handle the motor, that you won't accidentally turn on.
Kill switches
Power switches

You want your wiring to be heavy duty enough to handle the current the motor will draw - 1/4 HP is easy because it's so small. 

All wiring junctions must be enclosed in a junction box
Plastic is fine, but you may want to use metal depending on your application.  If it's in an environment where the wires may be damaged by 'abuse'...then consider running the cabling through electrical Conduit to protect it.  In a commercial setting, all wire MUST be run in a conduit.

To wire it up the motor will have 2 or 3 wires coming from it.  Hopefully they're labelled or just Black, White, and Green.  (per north american convention) ymmv
Green (optional) = Safety ground.  It's hooked up to the chassis of the motor and if anything short circuits inside, it will have a safe path to ground that doesn't involve the user of the tool.
White = Neutral.  This wire stays at 0v.  It's electrically active, but it should never show a voltage when the circuit is off.  This sounds complex, but it's not.
Black = Hot.  This wire is the one that changes voltage in AC terms, it is a sine wave that goes from -120v to +120v.  (or 240 if that's your juice).  This wire will kill you.  It's the narrower blade on a north american 'polarized' socket because it carries the power.

If you have a green (or bare copper) wire from your motor, that will be hooked electrically to the ground - so you need a grounded plug (3 prong).  The ground connection will be attached to everything in the circuit that supports it. 
The white will connect directly to the motor from the wall plug - no switch. 
The BLACK will run through BOTH switches, such that if either of them trips, the tool will turn off.  (see diagram)

The wire enters the first box and the black is hooked to a terminal of the switch, where the white connects to the next box.  In between the boxes will be a short length of wire, hence you likely need a junction here.  The green wire may or may not be connected to the switch also, but will be screwed to the box. Note how killing either switch will kill the motor? 

Talk to your local hardware store and they'll explain the EXACT parts you should use, but this should get you started!  Any questions feel free to ask!

motor safety switch.png

9 years ago

Well if it's compatible with your power source (120v mains, 12v battery, whatever), then yes, you can just solder the connections and plug it in. And of course, be careful with motors like that. they can hurt you if you're not careful.


9 years ago

Can you give more details from the I.D. plate on the motor or just by looking at it? Voltage, current, power, RPM, horsepower (1/4?), AC/DC (AC ?), single/multi phase, how many wires or terminals does it have?