My 12 year old Unisaw cuts off without warning, and then can be restarted several minutes later. When I went to the Delta service center to buy a new switch (to replace the thermal overload), the technician suggested that I first have an electrician verify that sufficient current is getting to the saw.
Since I am electrically challenged, I’d appreciate some advice. Is having an electrician test the service a reasonable first step? If so, what am I asking him to measure? What are sufficient minimal levels of current/volts/amps for a Unisaw? Are there any other potential culprits besides the thermal overload switch or the electrical service?
I should add that the saw has run fine for 11 years, and only started cutting out about a year ago. All assistance is greatfully appreciated.
Chuck
Replies
You don't state the motor horsepower or the power supply voltage, so some guesswork is required. I'll assume you are running the motor on 220 volt single phase and it is a 1-3 hp motor, which I'd consider appropriate for a unisaw.
It is much easier to think in terms of voltage rather than amperage, and much easier to measure voltage than amperage in an ac circuit. An electrician will check the voltage at the service entrance (the fuse or breaker box).
The power company is supplying you the specified voltage at the service entrance. That is the last thing you need to worry about.
If you have a long run of thin wire between the service entranceand the motor, the thin wire will constrict the current flow to the motor like tryng to run too much water through too small a hose. This will cause a voltage drop at the motor since part of the supply voltage is disapated in the wire.
Motors draw a lot of current when they start up and much less current when they are running at speed. If the wire is too thin, you will have problems starting the motor, not running it. You will usually throw the breaker, not the thermal overload on the motor during start up if this is the case.
A 15 amp circuit normally takes 14 gauge wire. A 20 amp circuit takes 12 gauge wire. Either of these will start and run a motor up to 3 hp at 220 volts in a small shop where the wire runs are not long. In large factories where wire runs are longer, heavier wire may be used.
If the problem shows up starting the motor, it will show up in the breaker. If the problem shows up in a running motor, look for the problem in the starter.
Also, after 12 years you might check the motor and saw arbor bearings. Spinning bad bearings is a lot of work.
Thanks!
Thanks, OWG, for taking the time to post your lengthy and informative reply. Your assumptions regarding my saw were correct, and I appreciate your advice.
Just to add to what (almost everything) was already said by OWG, you didn't say whether or not you have a magnetic or IEC starter. Magnetic starters have heaters in them (overload relays), which start to melt after a being 'overcooked' after either 10, 20, or 30 seconds, depending on the type. In woodworking tools, it's usually 20 seconds. In addition to solving your load problem, you may need to install new heaters (it's pretty straight forward), if you have a magnetic starter.
Bearings that are worn out can certainly have a lot to say in a situation like you describe.
Jeff
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