Help with 3 phase motor

i have an oldish 3 phase 2hp motor i want to use for a project, i want to use a vfd inverter so i can both run it from 240v ac and also vary the speed
I have a few questions perhaps someone could help with;

The plate on the motor doesn’t mention if it’s delta or star, a look at the connections shows that there are 3 wires plus earth so i am pretty sure its delta as believe although it’s not absolutely necessary there
is nearly always a 4th wire for neutral in a star config. it has a starter control that i think probably starts it in star and runs it in delta. The resistances between terminals are comparable at about 7 ohms. Is it a fair assumption that it is a delta?

it’s rated for 415 volts. do you think this refers to the phase to phase voltage and therefore 240 would be sufficient? image this diagram refers to both 415 and 230, although its a star configured motor.

Does anyone have a recommendations for a cheap, reasonable VFDs? i think i am leaning towards a huanfang chinese vfd, not the cheapest but lots seem to be used for home made cnc machines to control the spindle speeds, there is lots of online support and they are remotely controllable via rs485 which might be useful for future use.

see below for pictures of the motor plate, wiring and starter controls.

any help is very much appreciated


The starter looks like a DOL or NVR starter so nothing to do with running the motor in start or delta configuration, just prevent it restating after a power failure.

The winding are 415 phase to phase and 230 to neutral in the diagram which is standard and I would agree that it appears to be in a delta configuration, star is used to reduce the current during start up typically.

Starting a motor in star connection reduces voltage and therefore current in each phase. Starting torque is thus lower, but enough to start the motor. When a preset speed is reached, or after a preset time, connection of winding is changed to delta.

Going straight to delta is also fine depending on the load on the motor, the required speed of the motor and power supply available for the motor.

For a VFD anything on ebay is fine.

What is your application for the motor.

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Hi Dean
thanks for your input.

I am making something similar to this Which should be a fairly low torque startup application and something I can deal with using a speed ramp up setting on the VFD.

I.e A brush backed rotary sanding head.

I am correcting in thinking that I have a 415v 3 phase motor, I wont be able to run it with a standard cheapy VFD running from single phase 240v that outputs 240v 3 phase?



PS. I think I am in situation 2 in the table on this page ( ) I had hoped that I was in situation 1, ie the plate on the motor was referring to 415v only when it was used it in star config but as it appears it is wired for delta I would be OK with using a 240v.

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It is common for a VFD to take 240v single phase in and output 415v 3 phase

You also get them in 240v 3 phase out i.e you are often able to set the voltage out on the VFD or tell it the motor config [ 230V / 400V (delta/star) ]

I’ve edited this a few times to try and make it clearer but think I should add a backgrounder here :slight_smile:
When you split the single phase into three phase it becomes both 230 and 415 (in the UK context) depending on where you measure it and how you wire it up (and in the VFD almost everything is configurable)

Voltages - there are standards and tolerances the 240 which is what I am used to calling it can be 220 or 230 I think the standard is now 230 -10/+15 % and what this is affects whether you get 415 420 or 440 it is 99.99% of cases not material

It is best practice to stop interference going back up the line by using a filter ( it can cause problem with computers etc) check EMI/Filter rating requirement etc / eg C1 C2 C3|230Vac+3ph


WEG CFW300 Series AC Inverter for 2.2kW (3HP) 230V three phase motor. Converts fixed frequency single phase (or three phase) 230V input to variable frequency three phase 230V to control the speed of a standard AC Induction motor. Operates in standard VxF and Sensorless Vector control mode.

Hi Dean
again, many thanks for the effort and your input…

I think I am 75% of the way there in understanding but either I am missing something or I struggle with the inconsistencies when I read stuff on the internet as not everybody is clued up.

From the beginning I thought I could use one the of the VFDs you linked to ONLY if the 3-phase 220/230/240 that it output was used to run a 3phase motor that was wired in Delta, I was under the impression that would work but one of those cheap VFDs would not work if I tried to drive a 3phase motor that requires to be wired in star config because that requires 415v and often, but not always used a 4th wire for neutral. I have seen plenty of modern motors that are dual voltage when wired either star/Delta which makes me think the config dictates the supply voltage, is that a wrong assumption?

This morning I became further confuddled, I was first in the building this morning and the communal spaces had no power, they were on emergency lighting, the electrician was sent to check the building, we got talking as I reported it and afterwards I asked him to look at the photos I posted here, he thought my motor was probably 415v and wired in Star! he said a neutral return is not needed as the centre of the star will be connected internally in the motor and because its balanced in theory it is not needed. He said 240V to 415 VFDs were available but I read that the extra step of stepping up the voltage before its chopped into 3 phases in the VFDs make them more expensive…




voltage is potential difference and this can be seen if you connect a motor to 3 phase and run it … then test between phases you will get 415 volts ac or so and then test to earth or neutral and you will get 230 volts ac or so … potential difference

I would be wary of domestic electricians they are great with lights and plugs but

I would not worry if it was in star or delta

the only thing I would worry about is that the inverter is single phase in and three phase out and not having it undersized in terms of watts ie the equivalent of 2hp

call the support team at they will help you choose

I have bitten the bullet. I have ordered a 2HP inverter and will get a modern (smaller, lighter and less HP) AC motor ordered. My troubles will now shift from electrical issues to mechanical as I think I will use a pillow block bench arbor setup similar to this…

I might hang the motor underneath, out of the way. I am probably going to need to use a lathe to make the arbor to take the sanding head.

thanks again

you should be all right using off the shelf pulleys and taper locking bushes

And for the various choices