NEC with (50Hz, 380V)motors
- Thread starter Manal
- Start date
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- Location
- Bremerton, Washington
- Occupation
- Master Electrician
This forum is based on the NEC, we may not be able to answer your question, but there may be some who know, be patient.
What electrical standard do you use?
What electrical standard do you use?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
My experience is only with 60 hz motors, can you contact motor mfg and ask them? NEC can't be used in your case as the motor tables don't apply
Where are the motors located?
Then wouldn't you be better to use IEC Affiliate Country Programmes rather than the NEC standards?
Just my thoughts.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
It interesting how the Code Forum is found worldwide, guess its the power of Google.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
While I agree that you should be sizing your motors with consideration to the local codes that apply, you can get an approximate idea of what the NEC would require as follows:
1) Take the motor kW rating and multiply by 1.34 to get an approximate horsepower rating. (1hp = 746W, but this is a nominal rating and IEC motors are rated differently than NEMA motors, so the simple kW to hp conversion is only a rough approximation)
2) Take this hp rating and multiply by 6/5 because at 60Hz the motor will run at about 6/5 the 50Hz speed.
A 380V 50Hz motor has essentially the same V/Hz as a 460V 60Hz motor. So at the same torque load you will have approximately the same current load. (Note that many loads change torque with speed, so in a machine the actual current used will likely change.)
So if you take the above hp estimate and put it into the NEC tables for 460V motors, you will get an idea of what the NEC would require for such a motor operated at 60Hz.
Again: lots of approximations in the above. I would not simply do this without significant data from the manufacturer. But for study purposes it will give you an idea of what you would be dealing with.
-Jon
1) Take the motor kW rating and multiply by 1.34 to get an approximate horsepower rating. (1hp = 746W, but this is a nominal rating and IEC motors are rated differently than NEMA motors, so the simple kW to hp conversion is only a rough approximation)
2) Take this hp rating and multiply by 6/5 because at 60Hz the motor will run at about 6/5 the 50Hz speed.
A 380V 50Hz motor has essentially the same V/Hz as a 460V 60Hz motor. So at the same torque load you will have approximately the same current load. (Note that many loads change torque with speed, so in a machine the actual current used will likely change.)
So if you take the above hp estimate and put it into the NEC tables for 460V motors, you will get an idea of what the NEC would require for such a motor operated at 60Hz.
Again: lots of approximations in the above. I would not simply do this without significant data from the manufacturer. But for study purposes it will give you an idea of what you would be dealing with.
-Jon
Carultch
Senior Member
- Location
- Massachusetts
There are two terms that apply when talking about the current of a motor in the NEC. They are the FLC value, and the FLA value. These terms really stand for "full load current" and "full load amperes" which sound like interchangeable synonyms. But the NEC makes an important distinction.
A good way to remember it, is pretend the terms stand for the following:
FLC = "full load code"
FLA = "full load actual"
FLC are tabulated values of current in the NEC to correspond to typical motors with a given horsepower rating of the mechanical output power. Usually this is an upper limit to the current of the motor, so it allows you to design your motor branch circuit in a brand-agnostic manner. In other words, it doesn't matter what specific motor you put in that position in the circuit, as long as it is a motor with the horsepower and other specs as specified.
FLA values by contrast come from the motor's own nameplate or manufacturer's datasheet, and reflect the efficiency and other details of the specific make/model of inverter, at the voltage rating selected. This is the current that it draws according to the way the product test results.
If you have a motor that isn't built for grids governed by the NEC, there is no table of FLC values for motors built for foreign grids. You can get a general trend from the theory that Winnie provided. You will still have the FLA value from the specific motor datasheet, which is what you should ultimately consult for planning the circuit. Some motors allow you to adjust taps on the windings, to adapt it one of several different grid voltage/frequency combinations. There may be a change in the rating of the mechanical output power/torque/speed, due to a change in the voltage and/or frequency
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