VFD to motor cable

[David Brown 9Participant @davidbrown9]

[David Brown 9Participant @davidbrown9]

I am thinking of getting a VFD and a 3 phase motor, it will be a 1 hp motor. I have bought 3 of the Workshop Practice series about motors and VFDs and am reading through them

There is also a Youtube video of someone setting up a VFD and 3 phase motor for a Myford ML7 lathe which is quite informative. For the motor to VFD connection the man in the video states that he used the cable from a 16 amp 3 phase extension lead, as this was cheaper than buying lengths of wire.

As far as I can make out from my reading the power going from the VFD to the motor will be 240 volt 3 phase. Can I buy a 16 amp 3 phase extension lead from Machine Mart and use the cable from this, even though it is 400 volt?

Does the cable need to be shielded? Should it be 4 core 2.5 mm? The length of the cable will be 1-2 metres at most.

If possible could someone give links to where I can buy appropriate wire. Screwfix has some armoured wire but it is hard to tell if it is shielded and it is 25 meters long and over £60!

For the cable from the mains to the VFD I am planning to use a 13 amp plug and the same heavy duty cable I used for my existing first phase 1/2 hp motor-or should this cable be shielded as well?

The motor I am going to get is-TEC IE2 0.75kW Aluminium Three Phase Motor 230V/400V 4 Pole 80 Frame B5

David

[EmgeeParticipant @emgee]

David

For such a short length 1.5mm 4 core screened flexible cable, connect the screen to cpc (E) at inverter but not at motor.

Emgee

[SteviegtrParticipant @steviegtr]

As above , even 1.0mm will do the trick. 1.0mm rated at 10A & that's for a 50metre run by the Regs. You will probably have no more than 3 or 4 Amps flowing through the 3 conductors.

Steve.

[Peter Simpson 1Participant @petersimpson1]

Use 4 core SY cable, I would use 1.5 sq mm. You can use the fourth core for earth, you can solder a tag onto screen and use this to earth the screen to stop RF interference. Loads for sale on the bay.

[Paul BarterParticipant @paulbarter66156]

Hi the cable you need is usually referred to as SY as emgee says use four core three for the phases one for earth connection on the motor case to earth connection on the vfd, the braided sleeve should then be connected to earth at on end only to provide shielding, you will need to buy this from an electrical wholesaler rather than one of the sheds. eBay has some at enhanced rates! Eg Rexel, city electrical factors etc uh

Paul

[SillyOldDufferModerator @sillyoldduffer]

I got mine from TLC. Shielded is best because it semi-armours the cable and reduces radio interference, which gets worse as the cable gets longer. TLC list glands on the same page. Any size from 1mm up will work, but I've a notion there's a slight advantage in using bigger diameters rather than small due to the RF component in VFD outputs.

Depending on how the motor is earthed, may be better to get 4-way rather than 3-way. The extra wire can be used to earth the motor back to the earth in the terminal box. Do not use the shield as a safety earth.

No point in shielding the mains input back to the 13A plug.

Dave

[SteviegtrParticipant @steviegtr]

Where in the country are you Dave. If anywhere near Leeds I have quite a bit of the SY cable. Probably got some 20mm stuffing glands/locknuts in the drawer too.

Steve.

[Pete RimmerParticipant @peterimmer30576]

SOD is correct you mustn't use the SY braid as a current carrying earth. Even many site temporary electricians don't understand this and I'm forever getting 'picked up' for it when it's not required. We were even recently sent some new SY cables at work fully assembled with the shielding tailed to the earth pins both ends.

Earthing it one end for shielding is ok.

https://www.voltimum.co.uk/content/earthing-cable

Edited By Pete Rimmer on 28/02/2020 20:21:26

Edited By Pete Rimmer on 28/02/2020 20:22:46

[David Brown 9Participant @davidbrown9]

Thanks for all the advice.

I am in London/Essex. I have ordered some cable from TLC-1.5mm² 4 Core SY Protected Cable Flex. They have a branch not far from me so I will collect if from the branch

David

[Robert Atkinson 2Participant @robertatkinson2]

+1 for the 1.5mm 4 core SY

https://www.tlc-direct.co.uk/Products/MF1dot5slash4.html

SOD and Pete are also correct about the braid. The braid in SY is not to be used as a protective earth conductor. It's main purpose is physical protection, but it will add some screening t reduce radio interference. The braid should be connected to ground at the VFD end only. At the motor end it should be cut flush to the sheath and insulated with sleeving or tape.
This stuff is part of my day job.

Robert G8RPI

[SteviegtrParticipant @steviegtr]

Posted by Robert Atkinson 2 on 28/02/2020 21:04:10:

+1 for the 1.5mm 4 core SY

https://www.tlc-direct.co.uk/Products/MF1dot5slash4.html

SOD and Pete are also correct about the braid. The braid in SY is not to be used as a protective earth conductor. It's main purpose is physical protection, but it will add some screening t reduce radio interference. The braid should be connected to ground at the VFD end only. At the motor end it should be cut flush to the sheath and insulated with sleeving or tape.
This stuff is part of my day job.

Robert G8RPI

Yup mine too for 50 some years. Regards.

Steve.

[mgnbukParticipant @mgnbuk]

connect the screen to cpc (E) at inverter but not at motor.

Can't take that for granted with a VFD – read the specific drive manual & comply with the manufacturer's recommendations for that particular drive, which are frequently to connect the shield at both ends.

Nigel B.

[Mike PooleParticipant @mikepoole82104]

CY cable should be used for screening applications, SY is for mechanical protection.

Mike

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