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luweee 04-05-2008 09:44 PM

Wiring a Switch for a motor

This I know is very simple. But I need your help.

heres what I have. An old Hobart meat grinder (probably made in the 1940's) 110volt AC. It has this funky old switch. There are these contactors in the form of a CROSS. Lets just label them POST A POST B POST C AND POST D. 2 black wires (labeled A and D)from motor tied together are on POST A. POST B has 2 black wires (labeled B and D) from motor also. POST C has black wire (hot wire) from wall. POST D has White wire (neutral) from wall. Ground goes to Frame of motor.

Seems like A and C make Contact and then so will B and D. The switch contacts have seem to all but disintegrated and I want to put in a Modern day switch.

Is this as simple as putting in a Double pole Single Throw switch... Connecting POST A AD (black wires from motor) to POST C Hot wire from wall... .Then connecting POST B BC (black wires from motor) to POST D Neutral wire from wall.. Then of course the ground back to the Frame?


micromind 04-05-2008 11:10 PM

This motor is one of two types; dual voltage, non-reversible or single voltage, reversible. For connecting a switch, it really doesn't matter which one it is.

If you're running it on 120 volts, you can get by just fine with a single pole switch. You can switch both lines if you want to, but you really only need to switch the hot, not the neutral.

If you use a single pole switch, tie the wires on post B to the neutral. Put the wires on post A on one side of the switch. The incoming hot goes on the other side of the switch.

If you use a 2 pole switch, put the wires on post A on one side of pole A. The wires on post B go on one side of pole B. The incoming hot goes on the other side of pole A. The neutral goes on the other side of pole B.

If it is single voltage reversible, a reversing switch can be installed. It's slightly more difficult. If the nameplate states only one voltage (110 for example), it's reversible. If it states two voltages (110/220 for example), then it's not easily reversed.


luweee 04-05-2008 11:38 PM

Thanks rob
yeah i see what you are saying rob. just have to break the black (hot wire) not the neutral.... ive seen so many do that. it works but its dangerous when you break the neutral.
The single pole switch will save me some money too.


luweee 04-05-2008 11:43 PM

also does it matter if post A and post B are swapped? they are actually labled AC and BD.
I dont think this matters though, does it Rob?

Thanks again Sir

micromind 04-05-2008 11:55 PM

Not at all, the motor doesn't care. It only sees voltage across its windings.

If I were doing it, I'd use a single pole switch, and only break the hot. Run the neutral straight through. It's grounded anyway.


elkangorito 04-06-2008 09:39 AM

What size (Wattage) is the motor? This could be important if it is of any substantial size (uses more than 10 Amps).

Will the switch be used to turn the motor on & off or just energise the circuit?

The reason why I ask this is that switches used on inductive loads are usually rated for such a load (Utilisation category). For example, a contactor (IEC) has 4 such ratings;
AC1 - resistive loads.
AC2 - small resistive/inductive/capacitive loads (starting of slip ring motors etc).
AC3 - inductive loads (starts all types of motors).
AC4 - high current inductive loads (inching & plugging of motors).
AC11 - auxiliary or control circuits.

The above does not apply to NEMA contactors but still may apply to switches in the USA. Maybe somebody can shed some light on this with regard to USA switch Utilisation Categories.

micromind 04-06-2008 11:02 AM

In the US, switches, relays, motor starters, etc. are usually rated in volts, amps, and horsepower.

A basic 20 amp light switch will be rated (UL listed) at 20 amps 120/277 volts AC only. They used to have the HP ratings stamped on the switch, but most of them these days only list the HP rating in the catalog. In this case it would be 1HP at 120V, 2HP at 240V.

Relays are pretty much the same. One type I use alot is rated 15 amp 120/240 volts AC, 15 amp 30 Volts DC. 3/4HP at 120AC, 2HP at 240AC. They also have pilot duty ratings, which have to do with maximum current they can make and break.

Motor starters are usually rated in HP at a specific voltage, also a maximum continuous current. They're listed in sizes, 00 through 9. A size 00 starter can handle a 1 1/2HP 3 phase motor at 230 volts, and a 2HP at 480 volts. It's also rated at 9 amps continuous. A size 9 is good for 800HP at 230 volts, and 1600HP at 480 volts. It can handle 2250 amps continuous.

All this applies to 600 volts and lower. Higher voltages are usually rated HP only for motors, and amps only for other loads.


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