Hello everyone. I know that a nameplate that reads 208-230V and 60Hz means that the motor is optimal at 230V, with degraded performance at 208V. Just because the motor has 208-230V on the nameplate, does not mean that it is good for 10% below 208V. The 10% above and below rule would apply to the 230V portion of the nameplate, and not the 208V portion. If the nameplate read 208/230 instead of 208-230, then it is an entirely different ballgame. That being said, what if the name plate read 208V-230V and 50/60Hz? Is the optimal motor voltage 230V for 50 and 60Hz? If it were just a 60Hz motor, and I were derating it for 60Hz, then I would think the 208V would be the optimal voltage and it should maintain good performance in a 10% band around 208V. To sum up my question, does the voltage range on a nameplate that reads 208V-230V for a 50/60Hz motor mean that the optimal voltage for 50 and 60Hz operation is 208V (degraded performance) 230V (optimal performance.) Thanks for taking the time to answer this question.
Motor Nameplate Data
- Thread starter fifty60
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kwired
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I am used to seeing nameplates that say something like 208-230/460. Note the - is only part of the low volt rating. In reality this same motor would operate same @ 416 volts if wired for high voltage, as it does when connected to 208 and wired for low voltage.
I don't know that optimal voltage would be 208 when it is marked 208-230. If anything optimal maybe is about 219. What about a supply voltage on same motor that is near 250? Pretty common around here on 240 volt systems.
I don't know for certain if there is an industry standard meaning for "-" vs "/" in the ratings, but it does seem to be common that a "/" usually is separating a value that is different when a major different source criteria is applied, like for dual voltage, dual speed, dual frequency, and a "-" represents a range of values.
A change in frequency is going to change the speed and power rating no matter what happens to voltage.
Thanks for the answer. But what if the motor nameplate reads 208V-230V 50/60Hz. Is it ok to operate this motor at 230V 50 or 60Hz? If the motor were just 60Hz rated, I would derate the voltage to about 195V for 50Hz operation. Obviously I cannot operate it down to 195V at 60Hz. So since it is 50/60Hz rated, can I derate it like a standard 60Hz only rated motor for 50Hz operation? For this 208V-230V motor can I operate it (appropriately) at 195V at 50Hz just as if it were a 60Hz only rated motor? Does the 208V-230V define the operating envelope for both 50 and 60Hz, so I cannot operate at the motor efficiently at 195V 50Hz? Motors are generally rated to operate 10% above and below their nameplate value. I have read that when there is a dash rating, like 208V-230V, then the 10% rule only applies to the 230V and the 208V already implies degraded performance. This makes sense for just a 60Hz rated motor, but when the nameplate reads 208-230V 50/60 Hz...Thanks again for the help.
kwired
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It is not common to see many motors rated 50/60 Hz. Any that have that rating will also have two speed ratings and two HP ratings, because speed of an AC motor is determined in part by the applied frequency. Lower speed means less work will be done and therefore it will also have a lower horsepower rating for the lower speed. If frequency is lowered, usually voltage must also go down in proportion frequency to reduce saturation in windings which will lead to excess heating. So if it is rated 50/60 Hz, it also likely has multiple voltage ratings that correspond to input frequency also.
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I don't know of any secret code regarding - vs. /. If the motor says 208 230 volt I would say that it is rated to run at any of the nominal voltages in that range at either frequency.
What does the amp rating on the nameplate say?
What does the amp rating on the nameplate say?
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double post.
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I think the answer lies in the current draw of the motor. This particular motor says 208-230V 50/60Hz and .9A. I think the nameplate is wrong on the current draw because it only lists one amp value. The motor can be 208-230V but it certainly will draw more current at 50Hz than at 60Hz. The nameplate is incomplete in my opinion. As far as the / vs - goes, the importance there is when you take the + or - 10% around the nameplate voltage for good operation. You cannot use the + or - 10% on either of the number (208-230).
Strathead
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Why would it draw more current at 50 hz? My knowledge of motor theory is thin, self studied and seat of the pants, that said...
The frequency of an AC induction motor determines the speed at which it turns. A motor at 50 hz would turn slower than one at 60 hz. With the same amount of counter force, it would produce less work and therefor, I assume draw LESS current. This is anecdotally (for me) borne up by the fact the Variable frequency drives reduce the frequency to slow the speed and save money with motors.
Strathead
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kwired
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Reduce frequency usually means motor would also like to see reduced voltage also so coils are not over excited. A VFD does this. A (constant torque) motor that normally runs 10 amps @ 60 Hz will still draw 10 amps @ 30 HZ, but will be running at 50% voltage and 50% speed. Will also have reduced total input and output power. Those variables can be tweaked, but that is the general rule and default settings.
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