Hello, I am looking for an experienced opinion which I am sure I will find in here. The boss bought a 240V 3 phase belt sander. Problem is that we have a 208V service. Should I buy a step up auto transformer or try the motor on 208V. I am thinking that the motor will run hotter and may have a problem with nucence tripping of the breaker if I apply 208 to it.

From my experience, it would be better off running proper voltage to the sander. We've had way too many issues in the past running 240V @ 208. Some of the equipment wouldn't even start at 208V, never mind run hotter.

Unless the equipment nameplate tells you it is suitable for 208 volt, then I would also suggest you stick to the 240 volt supply. If you assume at least 5% voltage drop to the piece of equipment at 208 volt then you are getting 198 volts to the equipment designed for 240 volt.

You will probably be replacing that motor often if you run it at low voltage.
A few years ago, I had a situation where I was called for problem at a school that was maybe 1-year old, which had 3-phase 208V service, and a large well water pump wired by the original EC that was designed for 240V.
The well pump was shot and the well company told the school they wouldn’t replace the pump under warranty because it was constantly being run at low voltage. The original EC never checked the nameplate voltage before connecting the pump.
The well company installed a new pump and at the same time I installed a boost transformer to bring the voltage up to spec and all has been fine for several years now.

If the motor is rated 208-230V then its fine but if not, I wouldnt try it, especially if the line voltage is known to run on the low side of 208.. My former highschool had this problem with a few window shaker A/C units, they wound up installing "buck / boost" transformers for them

A.D

I had a similar thing with a 7.5HP air compressor. I called the manufacturer. I didn't want to risk anything. Last thing I need is to be on the hook for a burnt-up compressor.

They said NO - and suggested the customer take it back their dealer and exchange it for the 208V version.

The main concern with a motor is heat. If it fails to start quickly, runs too slow for the fan to keep it cool, or is overloaded for a period of time, it will overheat. The overload protection may not act quickly enough to protect the motor, but, I've seen many 240 volt motors running on 208 volts.

If your boss insists that the motor be connected, he could very well be telling you "I told you so", in a couple years.

As long as you stay within 10% an EE with tell you it's ok.I have seen them trip and weaken the winding thermals and crack klixon o/l when ran at rated load.Ive also seen them have a long happy life.Check current draw for a few cycles and you should have your answer.
cheers

A 10% drop in voltage is still 226 volts which is still a higher voltage than 208 would deliver. A motor run undervoltage will in fact run at the rated speed as motor speed is related to the number of poles and frequency of the supply. Universal motors are voltage sensitive for speed but not a squirrel cage.
Your problem is going to be reduced torque and horse power. If the motor was oversized and the torque requirements over sized then maybe the motor will hum along just fine. How much the motor needs to be oversized is unknown to me.
Another issues is going to be efficiency. So if your belt sander runs 1000 grit on balsa you might be ok but if there is any 120 grit or courser and anyone pushes hard on the belt the motor will run hotter because it will run higher than rated current and will not meet your production or performance requirements. The cost of this motor might be very much higher than the cost of getting the right motor installled. Add it up. reduced efficiency, lower Hp = slower sanding. More electrons to pay for too. Cost of replacement before amortizing the purchase cost. Down time when the motor smokes at a high demand moment in production, etc.
Get a new motor. A boost transformer would work but you are again adding to the complexity and cost of what is probably not that expensive a motor to begin with.

seems a little strange for it to be 240v three phase that would be delta which is very rare to findive only seen 208/347 hydro can give you 240 three phase but virtually unheard of

My thoughts exactly, maybe its a single phase 240V sander? If it is 3 phase I would go for a boost transformer, or new motor.

Sorry guys, it is actually a 220V motor 3 phase. It is on a belt sander. I built a new starter for it as it was not CSA approved. It is European. I was getting nuisance tripping on start up so I just increased the value a bit. Seems to work great now.

I would take some sample temperature readings during typical/hard use periods.

208V rated motor on a 208V supply has always bugged me - there's no allowance for voltage drop as when you connect 220/230V motors to a 240V supply.

The same windings are getting less voltage and more current... it's going to equate to more heat.

Anyone compared 208-230V rated motor's life expectancy when compared to 208V and 240V supplies?

220V 3-phase would be pretty unusual in Europe.

Normally you would only find equipment designed to operate at either:

230V 50Hz Single Phase
or
400V 50Hz Three Phase

or, in the UK and Ireland for construction site equipment :
110V 50Hz delivered as split-phase i.e. 55V on each leg, this is designed to prevent dangerous electric shock in the event of cable damage, even without relying on GFCIs/RCDs. Such equipment is supplied via a local step-down transformer.

Previously these were :

220 V and 380V in Continental Europe and Ireland
and
240V and 415V in the UK

EU/CENELEC Harmonisation moved Europe to 230V/400V

Usually the motors are 230-460V. Taking the valid points everyone else has said into consideration,there is one other thing to consider.

This motor will underperform to a certain degree because of low voltage but what level of performance do you require? If you need the full horse power from this machine then you will need a 3ph autotransformer and 230V. You won't find an autotransformer for 208 - 240V as readily.

If the machine is more capable than your requirements then you will not overheat anything. A 240V motor will run fine on lower voltage as long as there is a light work load.
You can run a 460V motor on 240V but with very little available torque and no overheating under no load.

If the machine is overkill in size you will probably be ok but watch the startup current. It will also stall easier when you load it up and or trip the O/L relay.

I have a customer that has a large 230V 3ph belt sander for sanding doors and it works acceptable on 204V - 208V but he has to be careful to moderate the rate of feed into the machine. Since it has an automated feed this is not a big deal. Your milage may vary of course. You could always try it on 208V before committing to a transformer purchase.
If the motor is 220V then even better.

Just my opinion.