VFD motor leads

[weressl]

If you have a 230/460 volt rated motor and connect it to a 460 volt drive the peaks of the output voltage can be in the 750 volt range. Connect the same motor to 230 volt drive and it will be half of that. Winding insulation is what the issue is here. Line reactors will smooth out the peaks but now the reactor first in line subject to the peaks. They are probably better designed to take it than some motor windings are.

For smaller motors, if you have a choice for voltage readily available it may be worth consideration.

As I understand the switching spike reflected wave can reach up to 1600V in the case of 480VAC line supply.

 

[JWCELECTRIC]

Would NOT install a new application with ordinary cable and other than IEE841 motor.

If your have project with tight budget would you use single RHW cable instead of THHN for each phase, and is there a difference between the two?

 

[don_resqcapt19]

Dual voltage motors will take more of a hit from the voltage spikes if connected to the lower rated voltage.

Can you expand on that?

If you have a 230/460 volt rated motor and connect it to a 460 volt drive the peaks of the output voltage can be in the 750 volt range. Connect the same motor to 230 volt drive and it will be half of that. Winding insulation is what the issue is here. Line reactors will smooth out the peaks but now the reactor first in line subject to the peaks. They are probably better designed to take it than some motor windings are.

For smaller motors, if you have a choice for voltage readily available it may be worth consideration.

The windings in that dual voltage motor are all designed to operate at 230 volts, if the spikes from the VFD, when operating at 230 volts, are half of what they would be when operating at 460 volts, how does the motor take a bigger hit when connected for the lower voltage?

 

[weressl]

If your have project with tight budget would you use single RHW cable instead of THHN for each phase, and is there a difference between the two?

The budget is ALWAYS tight, but can you afford the downtime?! You may noticed that I have not used the word 'never'. Everything always open to scrutiny.

My standard installation approach is three conductor cable with three groound conductors in the interscises. We just don't use conduit for motor wiring, everything is in CT/TC and use CLX for ASD aplications, hence single conductor installation just never comes up. SO I would need to think long and hard how I would implement a conduit installation and spend perhaps more time than the cost tradeoff worth.

 

[kwired]

The windings in that dual voltage motor are all designed to operate at 230 volts, if the spikes from the VFD, when operating at 230 volts, are half of what they would be when operating at 460 volts, how does the motor take a bigger hit when connected for the lower voltage?

I see your problem with my statement. I did not write what I was thinking. Motor takes bigger hit from spikes when operating at the high voltage. Mind was thinking one thing and fingers were thinking another.

 

[GeorgeB]

My standard installation approach is three conductor cable with three ground conductors in the interstices.

Sounds like the Bus Drop one of my ex-employers used for all 3 phase wiring on their machines ... but if I recall correctly, the chief electrical engineer knew it wasn't technically rated as ok, even if always in the machine confines. We WERE UL qualified, and the evaluation was that it was satisfactory for the intended use. What do you specify that NEC accepts?

 

[weressl]

I specified that we use THWN in rigid conduit and that in most cases there are also 120 volt conductors for the HOA in the same raceway as the motor conductors. I understand the manufacturers position and why they says what they say. I just stated that in my experience we have not seen those issues. And, yes in general the smaller drives are installed without any more than what we would use for a FVNR starter.

I will say that most of the drives are 25 hp or less and that drives for motors over 100 hp do have load side reactors. However even with the large motors the conductors are, with a couple of exceptions, THWN in rigid conduit. For the larger motors there are no control conductors in the raceway with the motor leads as the plant standard does not permit #14 conductors in the same raceway with conductors larger than #4.

IME the load side reactors are only needed on very long lengths of cables and it also depends on the drive. AFAIK Danfoss nearly doubles the lengths compared to others. MTC had delivered a reactor for a 130A service that nearly doubled the size of what they show in the catalog and takes up 4 times the space of the drive it serves.:rant:

 

[jdsmith]

Sounds like the Bus Drop one of my ex-employers used for all 3 phase wiring on their machines ... but if I recall correctly, the chief electrical engineer knew it wasn't technically rated as ok, even if always in the machine confines. We WERE UL qualified, and the evaluation was that it was satisfactory for the intended use. What do you specify that NEC accepts?

The cable Weressl is referring to is likely Okonite CLX (Section 4 Sheet 1) or similar, which is UL listed as type MC-HL. This is a continuously armored cable that is common in the petrochemical industries.