480V-3ph Motor connections to VFD Inverter

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Rob2025

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Location
Toronto, Canada
Occupation
Electrician
Hi

I would like to learn more on 400V-3ph Motor connections to VFD driver.

In general, I found there are only 3 connections U, V, W available on VFD Inverter terminals for the motor. If there are only 3 wires connected from VFD to the motor and as there is no Neutral terminal available from VFD, then does it mean Motor is always connected in a Delta configuration?
Is there any way we connect the motor in Wye or Star configuration to VFD?
 
You connect the motor for the voltage output of the VFD. You show a 400 volt motor. That is an IEC voltage. They often have 6 leads are are connected in delta for a 230 volt supply, and in wye for a 400 volt supply.
 
The two answers above are correct.

The motor itself is a balanced 3 phase load, and may internally be connected wye or delta.

But that local neutral connection doesn't get connected to anything outside of the motor. The motor is a 3 phase load that doesn't require a supply neutral.
 
Reason a Nuetral is never required on three phase VFD'S is the three phase feeds a rectifier that on 480 volts produces approximately 665 DC Buss voltage that supplies power to IGBT'S.
 
garbo said:
Reason a Nuetral is never required on three phase VFD'S is the three phase feeds a rectifier that on 480 volts produces approximately 665 DC Buss voltage that supplies power to IGBT'S.
Click to expand...

That is correct, but I believe the OP is asking about the connection between the VFD and the motor, not the circuit supplying the VFD.

The OP was asking how they could connect a motor, internally wired in the wye configuration to a VFD.
 
To bring more clarity on my question, please see below the picture of the label on the motor that is currently connected to the VFD. The VFD output I measured is 400Vac-3Ph.

Motor label plate.JPG

Looking at this, what is motor configured as Delta or Wye?
If I say 400V, then it's not Y-connection and for 230/265V it's not a Delta connection!
 
The motor is wired in the wye connection, supplied by 3 phases from the inverter. The motor star point isn't connected to anything outside of the motor.
 
Rob2025 said:
Looking at this, what is motor configured as Delta or Wye?
Click to expand...
Motors are always supplied as delta loads, using three lines only, and no neutral.

You're looking at the internal wiring configuration, wye vs delta, not the supply.

In Tom's diagram above, the dotted line is not brought out of the motor wiring.
 
LarryFine said:
Motors are always supplied as delta loads, using three lines only, and no neutral.
Click to expand...
Well, I think you mean that for 3 phase motors you only supply 3 wires (leaving out Y-D starting and 2 speed motors for this discussion). The INTERNAL connections in the motor windings can be configured as wye or delta as the case may be.

With dual voltage IEC motors like what is shown, the internal motor connections are ALWAYS configured as delta for the low voltage, wye for the higher voltage. A memory trick is the D for delta is “lower” in the alphabet and Y for wye (or S for star) is “higher” in the alphabet.
 
Good question — this trips up a lot of people when working with VFDs.


The three output terminals on the VFD (U, V, W) are just the three phases for the motor. VFDs don’t provide a neutral, and you don’t actually need one to run a three-phase motor. How the motor is wired (Star/Wye or Delta) is decided at the motor’s own terminal box, not at the VFD.


  • If the motor has six terminals, you can link them to run in either Star or Delta, depending on the voltage rating.
  • If it only has three terminals, then it’s already internally wired in one configuration, and you don’t get a choice.
  • The VFD doesn’t “force” Delta; it simply feeds three-phase power to whatever configuration the motor is set up for.

For example: a motor nameplate might say 400/690V. On a 400V supply (or 400V VFD), you’d connect it in Delta. On a 690V supply, you’d use Star. Always check the motor nameplate first to be sure.
 
MichaelDavis said:
Good question — this trips up a lot of people when working with VFDs.


The three output terminals on the VFD (U, V, W) are just the three phases for the motor. VFDs don’t provide a neutral, and you don’t actually need one to run a three-phase motor. How the motor is wired (Star/Wye or Delta) is decided at the motor’s own terminal box, not at the VFD.


  • If the motor has six terminals, you can link them to run in either Star or Delta, depending on the voltage rating.
  • If it only has three terminals, then it’s already internally wired in one configuration, and you don’t get a choice.
  • The VFD doesn’t “force” Delta; it simply feeds three-phase power to whatever configuration the motor is set up for.

For example: a motor nameplate might say 400/690V. On a 400V supply (or 400V VFD), you’d connect it in Delta. On a 690V supply, you’d use Star. Always check the motor nameplate first to be sure.
Click to expand...
IMHO... The VFD itself is just that a VFD not a transformer. The nameplate on the VFD is indicating that it can be used on either voltage level "low" or "hi". The motor itself is then connected in either a delta connection or a wye connection by the manufacturer. Six or twelve lead motors can be connected in either delta or wye configurations by installers. Just my $.02. :)
 
Deltaforce said:
May used for fault monitoring purpose with vfd IF neutral terminal provide not in op case though
Click to expand...
In the over 500 VFD'S from 2 to 250 HP from Danfoss, ABB, Allen Bradley, and many mother brands drives that I PM'ed, installed ,replaced or troubleshoot never came across a three phase one that had any p!ace to connect a neutral. All the ones in at least the last thirty years have ground fault built into drive.
 
garbo said:
In the over 500 VFD'S from 2 to 250 HP from Danfoss, ABB, Allen Bradley, and many mother brands drives that I PM'ed, installed ,replaced or troubleshoot never came across a three phase one that had any p!ace to connect a neutral. All the ones in at least the last thirty years have ground fault built into drive.
Click to expand...
VFD digital input use for neutral voltage fault monitoring, vfd ground fault not effective in HRG systems
 
garbo said:
In the over 500 VFD'S from 2 to 250 HP from Danfoss, ABB, Allen Bradley, and many mother brands drives that I PM'ed, installed ,replaced or troubleshoot never came across a three phase one that had any p!ace to connect a neutral. All the ones in at least the last thirty years have ground fault built into drive.
Click to expand...
I too, have never seen a neutral terminal on any of the VFDs I have worked with.
 
Rob2025 said:
To bring more clarity on my question, please see below the picture of the label on the motor that is currently connected to the VFD. The VFD output I measured is 400Vac-3Ph.

View attachment 2578721

Looking at this, what is motor configured as Delta or Wye?
Click to expand...
Since the OP is in Toronto where he measured 400V
and in Toronto 416/240Y is a common service voltage provided by the utility there, the VFD is likely on a 416/240 60 hz system.
The Line to line voltage going to the motor is then 416V 60 Hz and the motor connections are wye.
While I am not aware of any 416V delta systems if there was one the motor could run off it, however the VFD may not like that.

That motor can also be run on common in the US three phase 240V system if you connect the motor 'delta'.
That could be any three phase 240 system where you have 240V line to line such as 240 delta or the newer 240/139Y for VFD's.

Jraef said:
Well, I think you mean that for 3 phase motors you only supply 3 wires (leaving out Y-D starting and 2 speed motors for this discussion). The INTERNAL connections in the motor windings can be configured as wye or delta as the case may be.

With dual voltage IEC motors like what is shown, the internal motor connections are ALWAYS configured as delta for the low voltage, wye for the higher voltage. A memory trick is the D for delta is “lower” in the alphabet and Y for wye (or S for star) is “higher” in the alphabet.
Click to expand...
Good advise ^^
 
A Wye is delta pier to VFD'S will all work. The three phase input connects to a rectifier that creates a two wire DC Buss voltage that feeds IGBT'S.
 
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