- Joined
- Feb 13, 2017
- Messages
- 2,138
Wow, I haven't seen one of those motors in years. You will want to run it on 220 (240) volts if at all possible. And get a couple of furnace filters to wrap it in. If swarf gets in the motor, you're in for a world of hurt. The rotor is an armature and is electrically active from the line. Unlike an induction motor, where the rotor acts on induced power, hence "induction motor". A repulsion start motor does have the advantage of higher starting torque and is well worth keeping in place.
Now, and this is important! The NEC code book is confusing. There's no nice way to put it. But then, electricity is dangerous, and unlike gunpowder or gasoline, the danger cannot be seen. It usually is just a puff of smoke and the "thing" doesn't work any more. If you push it, that smoke becomes a fire. Like the guy said above, a circuit breaker protects the wiring, not the load. Then there are the wiring tables, all dozen (more or less) of therm. It all comes back to smoke. How much current a wire can handle is determined by its' insulation class. That insulation class determines how much temperature rise the wire can handle before the magic smoke gets out.
Motors are usually wound with class "H" or better. However, class H is very brittle and once the wire is moved or flexed, its' protection is broken. But it can run much hotter than wire in a conduit. That's why motors get so warm. If a wire in conduit gets that hot, there's trouble around the corner. From a non technical (layman's) perspective, the safest approach is to use the wiring tables for residential construction.
As an aside, wire insulation classes are befuddling to an extent. Type NM, non-metallic, what we think of as Romex, is a 300 volt class. Then there is THHN, very common in industrial installations. THHN is water proof, oil resistant, higher voltage (600 V) and more wear resistant. I have actually seen Romex (NM), when stripped back lettered for THHN on each wire. Yeah, right, tell me another one. . .
Then there are circuit breakers. As a general rule, a circuit breaker should never be loaded beyond 80% of its' rating. Breakers break down a little each time they are switched. Not much, but cumulatively can fail just from being used as a switch. That's the basis for "known" current ratings and their limits. Take a 15 amp circuit, that's AWG 14 wire on a 15 amp breaker. But for continuous running, the current should be limited to 12 amps. Likewise for a 20 amp "branch" circuit. That's AWG 12 wire, but should be limited to 16 amps continuously. That's why most of my shop is wired with 30 amp wire, AWG 10. But then I tend toward having a fuzz higher safety factor built in. As an example, when I wired my residence, some 40 odd years back, I used AWG 10 wire on most of the branch circuits. But have only 20 amp breakers to protect the circuits. Paranoid, yeah that's me, but with a very old (1886) wood structure I'm comfortable that there will not be an electrical fire. Cheap insurance. . . A hundred plus years of books, many of which would be impossible, not difficult but impossible, to replace.
Now all this techno-speak aside, if you even got this far, what is needed for that motor? Well, it can be run on 120 volts, but. . . A 120 volt circuit would need 25 amps capacity, plus the 20% breaker factor. So we are looking at a minimum 32 amps. Thats a 35 amp breaker, with the appropriate wire size. You could use AWG 10, THHN in metal conduit. But to keep costs (and labor) down, I would call for a 40 amp circuit with AWG 8 wire. That way you could use NM (Romex), which should be a regular item at the home supply house. But this places an enormous load on one side of the incoming line. Many of the household 120 volt loads should be moved to the other side of the line. But only when the motor is running. Arrggghhhh. . .
All in all, it would be far better to feed the motor with 240 volts. Even if it required pulling new wire from the entrance panel to the sub-main. If that ends up the answer, go a little oversized so future loads can be accomodated. I won't specify a specific size because most residential entrance panels have varying load demands. My submain feeder is about 40%(80 of 225) of the main capacity. But that's mine, and was planned for when the service was installed, 40 odd years back. Whatever you end up doing, plan for a little extra above the immediate demands.
And lastly, to answer the very specific question about motors, when they are in "locked rotor" or stalled condition, the current is essentially a short circuit. What ever the supply will provide, that's what the motor will pull. It all has to do with the 60 Hz (50 overseas) reactance of the windings. That gets deep into electrical theory and is one of those things that must be taken as "the way things are" by a layman. It just is. . .
.
Now, and this is important! The NEC code book is confusing. There's no nice way to put it. But then, electricity is dangerous, and unlike gunpowder or gasoline, the danger cannot be seen. It usually is just a puff of smoke and the "thing" doesn't work any more. If you push it, that smoke becomes a fire. Like the guy said above, a circuit breaker protects the wiring, not the load. Then there are the wiring tables, all dozen (more or less) of therm. It all comes back to smoke. How much current a wire can handle is determined by its' insulation class. That insulation class determines how much temperature rise the wire can handle before the magic smoke gets out.
Motors are usually wound with class "H" or better. However, class H is very brittle and once the wire is moved or flexed, its' protection is broken. But it can run much hotter than wire in a conduit. That's why motors get so warm. If a wire in conduit gets that hot, there's trouble around the corner. From a non technical (layman's) perspective, the safest approach is to use the wiring tables for residential construction.
As an aside, wire insulation classes are befuddling to an extent. Type NM, non-metallic, what we think of as Romex, is a 300 volt class. Then there is THHN, very common in industrial installations. THHN is water proof, oil resistant, higher voltage (600 V) and more wear resistant. I have actually seen Romex (NM), when stripped back lettered for THHN on each wire. Yeah, right, tell me another one. . .
Then there are circuit breakers. As a general rule, a circuit breaker should never be loaded beyond 80% of its' rating. Breakers break down a little each time they are switched. Not much, but cumulatively can fail just from being used as a switch. That's the basis for "known" current ratings and their limits. Take a 15 amp circuit, that's AWG 14 wire on a 15 amp breaker. But for continuous running, the current should be limited to 12 amps. Likewise for a 20 amp "branch" circuit. That's AWG 12 wire, but should be limited to 16 amps continuously. That's why most of my shop is wired with 30 amp wire, AWG 10. But then I tend toward having a fuzz higher safety factor built in. As an example, when I wired my residence, some 40 odd years back, I used AWG 10 wire on most of the branch circuits. But have only 20 amp breakers to protect the circuits. Paranoid, yeah that's me, but with a very old (1886) wood structure I'm comfortable that there will not be an electrical fire. Cheap insurance. . . A hundred plus years of books, many of which would be impossible, not difficult but impossible, to replace.
Now all this techno-speak aside, if you even got this far, what is needed for that motor? Well, it can be run on 120 volts, but. . . A 120 volt circuit would need 25 amps capacity, plus the 20% breaker factor. So we are looking at a minimum 32 amps. Thats a 35 amp breaker, with the appropriate wire size. You could use AWG 10, THHN in metal conduit. But to keep costs (and labor) down, I would call for a 40 amp circuit with AWG 8 wire. That way you could use NM (Romex), which should be a regular item at the home supply house. But this places an enormous load on one side of the incoming line. Many of the household 120 volt loads should be moved to the other side of the line. But only when the motor is running. Arrggghhhh. . .
All in all, it would be far better to feed the motor with 240 volts. Even if it required pulling new wire from the entrance panel to the sub-main. If that ends up the answer, go a little oversized so future loads can be accomodated. I won't specify a specific size because most residential entrance panels have varying load demands. My submain feeder is about 40%(80 of 225) of the main capacity. But that's mine, and was planned for when the service was installed, 40 odd years back. Whatever you end up doing, plan for a little extra above the immediate demands.
And lastly, to answer the very specific question about motors, when they are in "locked rotor" or stalled condition, the current is essentially a short circuit. What ever the supply will provide, that's what the motor will pull. It all has to do with the 60 Hz (50 overseas) reactance of the windings. That gets deep into electrical theory and is one of those things that must be taken as "the way things are" by a layman. It just is. . .
.
