Before you rush out and purchase a 3Phase machine and hope to drive it via a 240V VFD

**BobL** · 7th June 2018, 10:11 AM

I notice a number of people are purchasing 3Phase gear, including DCs, in the "hope" they can drive it from a 240V VFD.

Please note, in no way am I suggesting you connect or disconnect anything inside the motor/mains connection box or motor itself - you are just looking before you buy
Make sure the motor is completely disconnected from mains power before you look inside the connection box and leave all reconnections to a qualified person

Before you buy, there are a couple of things you can do that can save you $$ and a lot of mucking around.

The motor must be made compatible with 240V 3Phase.
Australian 3Phase is normally 415V and this is what most 3Phase motors in Australia will need to operate correctly.
EU and most other places use 380V 3 Phase power
North American 3Phase is 220-240V.
No matter the Voltage, 3Phase motors are normally connected in one of in 2 configurations, STAR or Y , and DELTA or ∆

Int just so happens that if a 3P 415V Y motor is converted to ∆ it automatically becomes a 3P 240V compatible motor.
This helps when moving motors between EU and North America.

Here is a suggested plan of investigation.

1) Check the motor name plate.
A strong indication that a motor can run from a 240V VFD is this information on the name plate.
This photo shows the motor can be configured to run as 415V Y, or as a 240V ∆ motor
It's not 100% guaranteed - I have found a motor that said this but turned out to have the Y only connects inside the motor
Ydeltanameplate.jpg

Heres a motor name pate that clearly says it is wired as a 415V ∆
415V?.jpg
This cannot be run on a 240V VFD or converted internally to run on 240V VFD. You will have to swap the motor out on this machine if you hope to run it on a 240V VFD.
Actually it will run OK on 240V 3P provided there is no load however one a load is applied it won't run for long - maybe long enough to get it home but sooner or later it will start tripping breakers and burn the motor out.

2) Sometimes there is (additional) information under the cover of the motor connection box - like this.
This is a strong indication that the motor can be configured as a either a delta or star.
It also shows how the connections inside the connection box should be arranged - leave that to a sparky, you could burn your shed down.
UndercapofconnectionBox.jpg

When 1) or 2) do not give any indication of what is going on, the connections inside the junction box itself may provide clues.

This motor is connected as ∆, there are 3 wires heading off to the motor at the top and bottom, and there are metal connector strip between the two sets of 3 wires.
IF this motor is already running under 415V 4P then it cannot be used on 240V 3P.
Deltaconnect.jpg

This motor is connected as a Y motor.
If it is running at 415V it can reconverted to ∆ by moving the metal strip to the above and it will become a 240V 3P compatible motor.
I recommend you leave that to a sparky - a wrong connection can at minimum destroy the motor and at max kill you or someone else.
StarCnnect.jpg

Below is a recently posted connection - this is very common.
There is only one set of (red) wires running off to the motor windings on the LHS. The black, brown and blue wires on the RHS are for incoming 3P mains power. plus yellow and green for earth
If there were 3 other wires running off to the motor as shown by the 3 bright red lines it would be a delta, but as is, we haven no idea what the other connections are as it it being done inside the motor.
If it turns out to be a 415V Y connect then it should be possible to convert the motor to ∆ inside the motor
This is a job for a sparky or motor rewinder,.
Unknownmotorconnection.jpg

Here is junction box with 4 connects from a recently acquired machine.
The 4th connect lower RHS circled in red, is the STAR (Y) point brought out to the connection box (more often these star points are inside the motor),
If the circled connection has 3 wires running off to the motor it can be converted to ∆ without opening up the motor. It turns out this motor does indeed have these 3 wires and so was easy to convert but the connects have to be done in a specific sequence, again best left to a sparky.
Ypointinexternal-box.jpg

Clear as mud?

Agan let me reiterate - it's safest if all connects are done by a qualified person. Remember if you burn you house down the insurance company will use the fact you are not qualified to wrangle out of payment. If you kill someone you may be liable.

Swapping out a motor can be easy but it can also be a PITA when physical connections like pulley bore and motor shaft sizes do not match and you could end up needing to spend even more money.

**cjbfisher** · 8th June 2018, 06:51 AM

Thanks for posting this Bob. It will certainly help me when it comes time to upgrade my DC. I've had a quick read through, and most of it makes sense, but when I've got a bit more time I'll digest it properly and more than likely will have a few questions.
The unfortunate back story to this is that I had a 3hp 3 phase machine with pleated filters, and got rid of it when I closed up my other workshop and brought my machines home. If only I knew then, what I know now.

**BobL** · 8th June 2018, 10:02 AM

Originally Posted by cjbfisher

Thanks for posting this Bob. It will certainly help me when it comes time to upgrade my DC. I've had a quick read through, and most of it makes sense, but when I've got a bit more time I'll digest it properly and more than likely will have a few questions.

Yep - no worries

The unfortunate back story to this is that I had a 3hp 3 phase machine with pleated filters, and got rid of it when I closed up my other workshop and brought my machines home. If only I knew then, what I know now.

I've also found myself in the same boat.

I have only seen one DC that had a 3P 415V motor which was readily convertible to 3P 240V plus VFD operation.
OLD School DC issues
This DC was given to our mens shed and would have been at least 50 years old, it was very noisy @50Hz so it was extra noisy at 60Hz (and it did not pull a whole lot more air anyway) probably because of the straight radial fan design. This machine was simply not going to meet the needs of the shed so it was given away. If I had not measured its (poor) performance I would probably have grabbed it.

Flettys 3Phase motor plus VFD install on his DC is one of the neatest but it still required motor replacement
VFD install summaries

My recent DC upgrade from a "single phase 3HP motor" to "3P 4HP motor plus VFD" required significant work.
Upgrading a 3HP Single Phase DC with 4HP 3P motor and VFD
Even though I did the electrical and some of the metal work myself I needed help to convert the 28 mm motor shaft down to the 24mm impeller bore and to cut a new keyway.
My costs were' $35 for the used 3P 4HP motor, a few $ for scrap Al plate, $10 for 3P cable, and I used a Spare VFD I already had in the shed. A replacement VFD would be ~$200. All up ~$250.

I suspect that most DCs will require a motor replacement.
If a new motor is required, the cost of a used DC, VFD, a sparky, plus metal worker will put this out of the $ range for most folks.

**cjbfisher** · 9th June 2018, 03:50 PM

As far as motor plates go, these would all be suitable for running on 240v with a VFD?
3 phase 2.JPG 3 phase 1.JPG 3 phase.JPG

**Pat** · 9th June 2018, 11:41 PM

Or get to know your local sparkie . . .

**BobL** · 9th June 2018, 11:59 PM

The first two look like they would have to be modified inside the motor but the 3rd one looks like its convertible in the motor connection box.
We'd need to see the insides of the connection boxes to be sure..

[EDIT] Actually ALL 3 look like they are convertible - the second one looked like it said <40V for the delta Voltage but it does actually say 240.
The second one got me confused by its orientation - see more details below.

**ericks2** · 10th June 2018, 12:07 AM

Another important thing is not to mix up the "polarity" of the windings

**BobL** · 10th June 2018, 01:00 AM

Originally Posted by ericks2

Another important thing is not to mix up the "polarity" of the windings

That's best left to someone qualified. we're not telling folks how to do the Y to ∆ conversion here, just what what to watch out for before they buy.

**cjbfisher** · 10th June 2018, 09:08 AM

Originally Posted by BobL

The first two look like they would have to be modified inside the motor but the 3rd one looks like its convertible in the motor connection box.
We'd need to see the insides of the connection boxes to be sure..

Bob,
Which part of the motor plate provides that info?

Also, assuming that the motor plate doesn't give the required info and we have to open up to check the connections, will a 415v Y that has been converted to 240v Delta look the same as a 415v Delta connection?

**cjbfisher** · 10th June 2018, 09:10 AM

Originally Posted by ericks2

Another important thing is not to mix up the "polarity" of the windings

As Bob says, we're just trying to make sure we get the right motor. Sparky/rewinder will be doing the work. My heart works fine ATM (I think). Don't need to jump start it just yet.

**BobL** · 10th June 2018, 11:34 AM

Originally Posted by cjbfisher

Bob,Which part of the motor plate provides that info?

The data outlined in red shows what to look for.This one says 220V ∆ but it will work on 240 as well3-phase-1.jpgThis one says the same thing in the ∆V box. When I first saw it I thought it said

**cjbfisher** · 10th June 2018, 12:27 PM

Thanks Bob,
Re the first part of my previous post, I thought you were suggesting that there was something on the motor plate indicating where ( inside motor as opposed to inside connection box) the conversion to 240v Delta could be made.

Where I was getting at with the second part was that if I came across a motor that didn't give any indication of its connection type as per this one:
3 phase 5hp.jpg
If I was to open up the connection box and find a Delta type connection, could I easily identify whether it was 415v Delta, or if it was a 415v Y that has already been converted to run on 240v Delta.
Sorry for the barrage of questions, but when I come to finding something it will most likely be second hand, and I don't want to rely on what someone tells me just so they can make a sale. Just wanting to make sure I'm armed with all the facts.

**BobL** · 10th June 2018, 01:12 PM

Originally Posted by cjbfisher

Thanks Bob,
Re the first part of my previous post, I thought you were suggesting that there was something on the motor plate indicating where ( inside motor as opposed to inside connection box) the conversion to 240v Delta could be made..

Sorry - no there's no hint on that name plate or any other names that tells you what's inside the motor.
If the nameplate says 415 ∆ only then almost certainly it cannot be converted.

Where I was getting at with the second part was that if I came across a motor that didn't give any indication of its connection type as per this one:

That motor could be either.
Does it have 6 wires coming out from inside the motor ?

If I was to open up the connection box and find a Delta type connection, could I easily identify whether it was 415v Delta, or if it was a 415v Y that has already been converted to run on 240v Delta.

It's not possible to tell - even by opening up the motor. Well that's not strictly correct. Most conversions are obvious, few folks use the exact same coloured wires and junction sheathing compared to the original and the restitch of the junctions to the armature are usually obvious. As an alternative to opening the motor, a 415V ∆ motor can be safely run on a 240V VFD so the way I would do it is mount the motor on my HP rig (measures motor HP) and run it with a 240V VFD - if it has been converted it will develop full power, if not it will develop less than half power. Saves opening the motor and guessing at what has gone on. Doesn't help those without an HP rig though,

Sorry for the barrage of questions, but when I come to finding something it will most likely be second hand, and I don't want to rely on what someone tells me just so they can make a sale. Just wanting to make sure I'm armed with all the facts.

No worries - I just hope folks can understand my explanations.

**tomkatoz** · 23rd February 2019, 07:28 PM

Hi all,

I have the chance to be given an old thicknesser and an old jointer, both running 3PH motors.

I've attached photos of both motor plates and wiring boxes and both appear to be star connections.

Any idea if either can be run with a VFD?

Thanks for any advice.

Sent from my SM-G950F using Tapatalk

**NCArcher** · 23rd February 2019, 09:36 PM

You would need to take them to a motor rewinder to bring the star point out to the terminal box so they can be connected in Delta.
Neither of them can be run at 240V delta at the moment.

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