Conductors for Inverse Duty Motors

It's inverter duty, not inverse duty. Please try to get the terms correct.

General Purpose vs Inverter Duty - Motors from AutomationDirect

A search revealed millions of answers, given the right information.

Conductors conduct electricity, regardless of the motor type.

I hope this wasn't homework, or an interview question.

Given the spelling correction above is meaningful, then as far as British Standard 7671 is concerned, none whatsoever.

Ask a competent electrician as well. The answer will be the same.

Would converting a motor into a generator be considered an inverse duty motor?

I agree that this is likely about an inverter duty motor and that the conductors will be identical.

Interesting point!

I was considering the conductors between source and motor, not the motor windings. You're quite correct that the OP did not clearly specify which conductors should be considered.

... although the OP does say "between a vfd and an inverse duty motor" which at least suggests he is talking about the conductors between the drive and the motor. Of course, he might also be using the idiomatic "difference between."

I'd say that an inverse duty motor is a motor that becomes less prone to failure the more you abuse it. (The human analogy would be a masochist.) Or perhaps it is a motor that runs cooler with greater load.

I'd say that the OP would be one of less than 63 people on the planet who would ever refer to motor winding as motor conductors.

Not in CE-marked inverters.

To my knowledge, an inverter cannot carry a CE marking.Only an approved motor-inverter pair can be marked CE.

Or has my knowledge data base been obsoleted since my retirement?

CE marking just indicates that the manufacturer claims the product meets European safety standards. CE marking does not come from an independent lab. A Nationally Recognized Testing Laboratory (NRTL) verifies that the whole package design has been safely designed. NRTL certification does not test the overall quality of a design. It only certifies that when this design fails it will likely fail in a safe manner if it is not tampered.

That's correct. Self certification is the cheap way out.

It's smarter to combine CE marking with tests though.

Been through the process before with a noise cancelling headset design. We had Underwriters Lab. test/certify our stuff. Orbital Sciences also did some certification for us. Then we affixed the CE mark.

If one wants to market the product globally, the CE mark is essential. (Unfortunately, as redfred pointed out, testing is not necessarily required)

"Not in CE-marked inverters."

Would you please explain this?

GA

Lyn, thanks for the GA. I wonder if this may be the "root cause" of many of the "Help, my VFD driven motor just failed" postings.

I wonder if motor wiring failures have occurred because of this. I haven't heard of any, but it might not be surprising. Maybe some day codes will require VFD-powered motors to be fed with wire of 2x or 3x the usual voltage rating.

Yes,there is a difference in insulation of the motor and leads,but there are other differences in the design of a VFD motor.You cannot expect good service life from a standard motor used in a VFD mode.The ball bearings and races and retainers in a VFD motor are designed to dissipate induced eddy currents in the rotor due to high frequency harmonics.Without this design, ball bearings will pit and fail prematurely.There are grounding rings made for retrofitting standard motors to properly ground the shafts and bearings, but this is only one facet of the problems encountered.

The harmonics can also induce currents in nearby conductors and equipment if not properly shielded.This can cause havoc in sensitive controllers, like elevators,etc.

So before you retrofit an existing motor to VFD,hire a qualified electrical engineer to review the application and analyse the site for potential problems.

Good Luck!

Friends,

• Valid answers regarding the difference in magnet wire for the motor windings.
• valid point regarding the reflection of the voltage waveform at the point where there is the significant impedance difference between the conductors to the motor and the internal motor winding conductors.
• valid point regarding the creation of induced noise on nearby conductors in a plant.
• My reading and study generally states that the conductor damage from the impedance change is within the first few turns of the motor winding, and not in the conductors leading to the motor.
• My study decades ago on pulse waveforms and standing waves was that the upper limit of the voltage was a doubling, so I am surprised to hear of 2160V on a 480V system. Allowing for 480x2x1.414=1360v. Perhaps someone can double-check this point.
• All the drive manufacturers I have dealt with recommend shielded/screened cables for the conductors going out to the motor and will only certify the installation if the motor's grounding(earthing) conductor is connected to the grounding/earthing terminal in the drive, with the drive then being bonded.
• The voltage spikes and related problems are lower with the most recent drive models, but line and load reactors are usually a good idea and are strongly desired if the motor conductors are near the limits of the recommended lengths.

--John M.