Contactor
Motor Starter
[OP]
Member
So I'm reviewing the options available at the discount electronics stores for the components to assemble my own mag switch for my new-to-me cyclone. The design is a combination of my own work and Alan Schaffter design. One of the first components in line is the contactor. What are the opinions here of using a contactor versus using a motor starter? The later is a contactor with addition current limiting functionality built in.
Member
It depends...is the motor thermally protected? I've added magnetic controls to several machines. In each case the motor just had an on/off switch so I didn't bother with overloads.
Member
I have a 5 hp motor on my cyclone wired direct through a 2 pole 30 A switch - 10 gauge wire. right wrong indifferent ?? It works. The main reason magnetic starters are used is to isolate the user from potentially hazrdous voltages and to provide thermal overload (thats the way I understand it) and in the event power is lost the machine cant just start up when power is re-applied (again, a safety issue) I went through the whole mess of re-building / repairing, etc. the starter on my Uni-saw and finally just got a new switch off e-bay for like 25 bucks or so. You just need to pay attention to the Amperage the unit is rated for and if it has thermal protection - hey it works for me
Elvis isn't dead, he just went home Yes, I am a joker - Take it with a grain of salt
Contributor
Anthony, as Matt indicated we can't choose because you haven't indicated whether the motor has built in thermal protection.
If it does, you can use a horsepower rated contactor, if not you need a starter with overload protection.
Regards, Rod.
[OP]
Member
I don't believe that it does have protection and protection is not required. My question is what would you choose. I have found a contactor for $11 and a motor starter for $49 for a 20A 220VAC.
Contributor
Anthony, motor overload protection is required by the electrical code for motors that large.Originally Posted by Anthony Whitesell
Why do you believe protection isn't required?
Regards, Rod.
[OP]
Member
I guess I should clarify. Additional protection is not required. Of course we don't want to direct wire the motor to the main without a circuit breaker in between. According to a random 2HP motor installation manual from marathon motors, the connection to the branch circuit requires "short circuit protection (circuit breaker or fuse) and a power disconnect properly sized for the motor selected and installed per applicable electrical codes and local codes and practices". The only other information provided reminds you not to electrocute yourself and to verify the frequency, voltage, and current capacity to be within the limits listed.
How would you tell if a motor had built-in overload protection? My first two thoughts were 1) listed on the name plate or 2) had a little red button. A review of the motors in my shop revealed only one with built-in protection and it fell into both categories 1 and 2. It was listed on the nameplate and had the little red button. This motor is on my tablesaw, it is not the original motor but is a older craftsman 1HP motor.
Last edited by Anthony Whitesell; 02-07-2011 at 9:31 PM.
Contributor
Anthony, yes the motor will be marked "thermally protected" or words to that effect, or it will obviously have a reset button on the motor.
If it doesn't have either, it needs overload protection per the NEC and local codes.
The installation manual for the motor isn't what is required to be followed for installation, although it may have specific information regarding maintenance etc. for that motor.
Regards, Rod.
[OP]
Member
I'm finding this very very interesting. My 2002 Craftsman contractor "2HP" table saw (which is opposed to my 1954 Craftsman TS with upgraded motor) the 2003 1.5HP Ryobi Dust Collector very obviously do not have any protection as I can follow the wires from the motor to the switch to the wall plug. The G0490 jointer does not list protection, but the manual indicates that it is included in the switch/mag starter. The Jet 16-32 drum sander and G0513X2 bandsawmotors do not list having thermal protection, but they do have control boxes that may be more than the simple on/off switches of the table saw and dust collector. I cannot see a rhyme or reason to the protection. Do we know what designates as requiring the additional protection versus what does not? Could the protection be as simple as an onboard circuit breaker?
Last edited by Anthony Whitesell; 02-08-2011 at 9:00 AM.
Contributor
To protect a motor from catching fire, the manufacturer can either provide built in thermal protection inside the motor, or provide it externally via a thermal overload.
If a motor is only sold as part of a machine, and not for general use then it could be built in and not marked as it's approved as an assembly.
If the motor is a general use one (such as you would see on a cyclone) it will be marked if it has built in thermal protection.
Thermal protection can be built into a manual motor starter (these are switch type starters or push button starters where the push button mechanically closes and opens the contacts).
Thermal protection can also be built into magnetic starters.
Your Craftsman saw and Ryobi dust collector would probably have built in thermal protection inside the motor since they have a manual motor starter without overload protection.
A thermal breaker could also be incorporated into the system as overload protection, it would be sized very close to the motor rated current.
Regards, Rod.
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