How to wire up 3 phase motor and 3 phase converter?

[ell81Participant @ell81]

So, I have a 3 phase motor, dual voltage. It has come with no cable for it. So I obviously need to wire one in.

It will be powered by single phase power, converted by a single to 3 phase converter.

I am wondering which wires to use for the cable? Is there an amperage rating I need for the wires?

Ideally I want to make the lead on the 3 phase motor have a male socket on it, (will this be 4 or 5 pin?)

and have the 3 phase lead from the converter have a female socket on it.

Will I need just the 4 wires for the 3 phase lead coming from the converter and the lead on the motor?

This way I can unplug the motor and use the converter on a different motor.

Here is a pic of what I mean:

 

Here are the pics of the motor badge, the wiring diagram for it, and the converter connections:

[Robert Atkinson 2Participant @robertatkinson2]

The wire size is set by the VFD output current rating / input fuse rating. While 1mm2 woube adequate I suggest using 1.5mm.
For specific cable types consider “SY”  protected flexible cable. One supplier I’ve used is TLC
https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Multi-Flex/index.html?
But any local electrical supplier should have it. You want 1.5mm2 four core (3 phases and protective earth).
It is generally considered bad practice to put connectors in the output of VFCs. If you must then ideally yo should use a metal bodied connector like a Harting HAN series to reduce interference. A more available choice is a 3P+PE 16A red IEC 60309 “commando” plug and socket e.g.
https://www.tlc-direct.co.uk/Products/MKK9007RED.html

Don’t un-plug with power on, even with motor stopped.

Robert.

[SillyOldDufferModerator @sillyoldduffer]

What Robert said!  I’d go further than “It is generally considered bad practice to put connectors in the output of VFCs.” and positively recommend NOT using connectors and NOT swapping one VFD between several motors.

The VFD isn’t a magic black-box producing a sine wave like wot comes out of a mains socket.  Rather the electronics simulate a sine wave by pulse width modulating a DC signal, and pulses do not behave like sine waves!   No problem with pulses when a VFD is correctly connected to the motor, because the motor windings smooth them out.   But, red-alert, if a VFD phase is disconnected whilst power is applied, the motor winding can behave like a car-ignition coil, and several thousand volts appear on the end.   The operator might get a nasty shock, but more likely the high voltage will punch holes through the motor’s insulation, and/or the VFD’s electronics, turning them into toast.

These days VFDs often come with factory defaults allowing the unit to drive almost any motor out-of-the-box, hurrah!   However, an advanced user might well chose to alter the defaults to suit his a particular motor:  soft-start, frequencies, and a few hundred other tweaks!   And some VFDs automatically tune themselves to suit the motor, and get confused if a different one is plugged in!   Auto tuning used to be reserved for top-end VFDs, but it’s filtering down into cheaper units.   Either way,  not clever to share a tuned VFD between different motors without resetting it first.

Sharing a VFD is a bodge that works perfectly until something goes wrong!  Many ways it can go bad, including the operator absent-mindedly pulling the plug with power on, or the contact pins wearing or corroding, or a wire coming loose.   So best practice is to dedicate a separate VFD to the motor and hardwire it in.   This suits another best practice rule, the 3-phase wiring should be as short as possible, less than a metre, and certainly not running round the workshop.

Another misunderstanding can cause trouble!  Most VFDs are components, meant to be protected inside another box, ideally earthed metal.   Partly to secure the wiring and protect the operator from exposed terminals but also very important to keep swarf, dirt and condensation out of the electronics.

Similarly, though VFDs can be controlled with the supplied keypad, these are only intended for setting up – they aren’t robust!   Normal operation calls for a remote speed control pot, forward/stop/reverse switch and emergency stop.  These controls can be mounted in the box protecting the VFD, but it’s usually more convenient to have the VFD near the motor (short wires are best), with the controls handy for the operator.   Control wiring can be any length.

These problems all relate to cost cutting measures.  Up to the owner to balance the risk, but, as always, “too cheap” is liable to become “unfit for purpose”.

A minor detail next.  The photo shows the motor terminals are currently strapped for STAR aka Y connection, ie 400V  rather than 230.   The straps need to be moved to the delta Δ configuration.  In the pic below, the existing Y connection is high-lighted in red,  you want to move the straps into the green position (delta), as per the diagram inside the lid.

Dave

[noel shelleyParticipant @noelshelley55608]

In this day and age the most common way to run a 3phase motor from single phase is with an INVERTER or VFD, it is NOT the only way, there are CONVERTERS that will raise the voltage to 415V and artificially make the 3rd phase. The OP uses the term CONVERTER, though the picture appears to show an INVERTER, 2 very different types of equipment that require very different methods Etc. The VFD needs in most cases a dual voltage motor set to Delta 220V where as the Converter will use a star connected 415V motor. As for plugs sockets Robert and Dave have covered various points.

If the OP has little knowledge of such things and is dealing with lethal voltages then the best advice is to seek the help of a competent electrician with experience in this field to do the work. Noel.

[OldironParticipant @oldiron]

In the hand drawn layout picture it shows a socket attached to the motor. This should be a plug. Never use a male/male lead for connections.  Although I agree with Robert that its not really good practice to have a connector between units.  Also Noels point that this is really a job for a competent electrician is correct.

[ZanParticipant @zan]

No no no no.  One vdf one motor

for me that’s Myford s7b, Bridgeport, Colchester student and  fobco pillar drill.

4 motors 4 inverters  they all need setting up to match the individual motor  ie current, max and min speed and a plethora of other settings obtainable in the manual ( can’t remember them all, years since I set up the last one )

Far far too dangerous to consider swapping things about, far too much risk of a smoking body laying on the workshop floor………

[Robert Atkinson 2Participant @robertatkinson2]

Well spotted Old Iron. I didn’t look at the sketch. You can easily get male or female 60309 connectors in cable or fixed mounting.
I agree entirely with SOD and Noel but thought I’d just answer the question and not have to get my flame proof overalls on 🙂

[EmgeeParticipant @emgee]

One thing not mentioned so far is connecting the cable screen to the cpc at the VFD, difficult to do if using any type of insulated plug/socket arrangement.

 

Emgee

 

[Robert Atkinson 2Participant @robertatkinson2]

I did mention that ideally a metallic body connector should be used…
The “screen” on SY cable is steel and fairly open so is not a great EMI screen, CY cable is better for that but a waste unless proper 360 degree screened connectors are used. They are expensive https://www.igus.co.uk/connectors/industrial-connectors

In any case the screen should not be directly connected to the CPC (protective earth). It should be connected to the metal plate the VFD is mounted on and close to the VFD output terminals. Ideally by a 360 degree clamp. The plate of case the VFD is mounted on IS directly connected to the Earth/CPC/PE. The screen connection is NOT carried througn if 60309 connectors are used. At the motor end the screen should be terminated to the junction box using a metallic cable gland designed for the purpose.
The screen on a SY cable should NOT be used as the protective earth connection in a circuit. There must ALWAYS be a dedicated, marked (green/yellow) earth conductor (copper) in the cable. This is nomally designated as PE so a cable or connector should be describeds as 3+PE for 3 phase conductors plus earth. Note that SWA cable used underground etc is different as it has more, thicker steel wires.

Robert.

[EmgeeParticipant @emgee]

Robert

Following your link does take you to an illustration of SY cable showing full braided shield, which according to most VFD manufacturers needs to be connected using a suitable gland to the incoming cpc at the VFD for screening purposes.

Check the manufacturer’s advice on connecting the screen.

More importantly it needs to be connected to the cpc in case of cable damage leading to the braid becoming live, if correctly designed the fault current produced would disconnect the power supply by tripping the circuit prrotective device mcb or rupturing the fuse, if a 30ma operating current RCCB is fitted that would most likely trip first.

 

Emgee

[Emgee]

On Emgee Said:

…More importantly it needs to be connected to the cpc in case of cable damage leading to the braid becoming live, if correctly designed the fault current produced would disconnect the power supply by tripping the circuit prrotective device mcb or rupturing the fuse, if a 30ma operating current RCCB is fitted that would most likely trip first.

 

Emgee

Er, not as I understand it!  The steel mesh in an SY cable is intended to protect from physical damage, not to provide a safety earth.  Several reasons against, steel is resistive (gets hot!), the current carrying capacity is dubious, and it might corrode etc.  However, SY cable provides a moderately effective EMC screen.  (CY is better, or cough up serious money for the real McCoy.)

We’re confusing two different types of Earth.

• An Electrical Engineer and his Sparky mates earth for safety reasons.  There are a bunch of guidelines and regulations to follow, all good stuff.  The system operates at 50 or 60Hz.
• Radio Engineers earth to prevent signals entering and leaving a cable system.  The guidelines are quite different because high-frequencies don’t behave like mains power.

If Sparky fits a screened cable to meet safety rules, he’s likely to destroy the screen’s EMC properties.  Even worse, SY cable is unsafe!    Likewise, a radio man misusing the mains earth to ground a vertical transmitting antenna can cause several horrible problems.   And installing a separate signal earth rod next to a PMC system is positively unwise.

Lightning protective earths are different again!

The difference between safety and EMC earthing make it important not to mix different types of earth if it can be avoided.    On a lathe motor safety should be provided by a Green/Yellow earth wire connected in the normal way.

There’s lively debate in the EMC community about whether or not screened cables should be earthed at one or both ends.   Only earth at the hot end gets most votes, but some die in a ditch in support of both ends!   I think it depends on the nature of the EMC problem; there’s a relationship between frequency and cable length, and sometimes both ends of the cable might be ‘hot’.  What’s right for Peter could be wrong for Paul.   And a screened cable grounded at one end for EMC cannot be a safety earth.

Clear as mud!  ell81 may wish to note that earthing is one of several reasons why hardwiring is preferred to plug/socket connecting 3-phase motors to a VFD.   If plug sharing is essential, the cheapest answer is a rotary converter, which have other disadvantages…

Dave

 

 

 

 

[EmgeeParticipant @emgee]

Dave

The link in Robert’s recommended post shows a full braid screen.

Using the correct gland the steel braid is connected to the cpc at point of supply to disconnect the supply if damage occurs causing a short cct between any live conductor in the cable and the braid, if not connected to the cpc at point of supply the braid would remain live.

I have not suggested the braid is used as the cpc to the motor or that it is connected at the motor end.

 

Emgee

[Robert Atkinson 2Participant @robertatkinson2]

Hi,

The link is to examples of screened connectors after the discussion of screened connectors.

I said the braid is not DIRECTLY connected to the CPC. I also said the plate IS connected to the CPC. Thus the braid in the SY cable is grounded. However while this is good practice and highly recomended it is not actually required for safety if the cable end is proppery dressed. This is because ther is already two layers of insulation between the live conductor and the braid.
Connecting the braid directly to the incoming CPC will cause more interference than correctly terminating it. The filter components in the VFC connect to the baseplate the connection between the baseplate and the cable screen needs to be as low an impedance (at the interfering frequencies) as possible. This means short and wide. Round wire is poor at radio frequencies due to skin effect. you need wide, flat conductors or tube either solid or braided in both cases.

Robert.

EDIT:

Crossed with SOD and Emgees posts. Keep getting Honeydos while typing…

SOD is correct.
Even with CY cable the screen braid MUST NOT BE USED as the CPC (safety earth, PE). The CPC must be a dedicated conductor and coloured / marked green-yellow where accesible (even if only to sparkies).
RF earthing is different.
The exact configuration of the connection of the screenng braid depends on many factors and while there is general guidance the only way to be sure on a new design is to test it.
This stuff (and lightning protection) has been part of my day job for 40 years and I’m activily involved in setting the standards for aircraft electrical systems and EMC. I’m a SQEP and prrpoved to sign-off both CE/UKCA marking and UK/EU/USA/Canada ricraft design compliance for EMC and electrical safety  amongst other things. A coule of weeks ago I was trained and qualified for Hydrogen safety because we are working on next generation fuel systems.

Robert.

[EmgeeParticipant @emgee]

Robert

Despite your qualifications it is clearly the case you have not been involved with the repair and maintenance of electrical inatallations in an industrial setting. Claiming a metallic braid, providing a degree of protection to live conductors, doesn’t require connecting to the cpc of the cct power source because there are 2 layers of insulation between the sheath and live conductors is nonsense, manufacturers produce glands especially for that purpose.

Seems to me you are confusing 2 layers of insulation with a Class 2 electrical appliance which doesn’t need a cpc on the supply cable.

Emgee

 

 

 

 

 

[Robert Atkinson 2Participant @robertatkinson2]

I have indeed been involved in industrial electrical installations. I’m not confusing class II insulation either.
CY and CS are not installation cables they are flexes. The insulation layers under the metallic braid meet the same requirements as “normal” flex. Thus the braid is just a bit of metal outside the insulation. It is there for mechanical protection.

While I would always recommend connecting the braid on SY or CY cable to PE / CPC it is not a requirement. It is the same as if you ran a length of 2.5 T&E in a bit of metallic conduit for local protection somewhere in a run. You have to protect the cable from damage by the conduit end, e.g. fit a ferrule of strain relief.

You will often find SY cable used to make up extension leads with 60309 connectors without any connection to the braid. as there is no provision in the connector.

There is also an argument that some sitiuations grounding the braid in SY actually adds a hazerd. this is the case in older industrial installations where there is no differential current protection (RCD). If you had a long length of SY connected to CPC at the source end on a 32A supply and there was a phase to braid short at the far end the high resistance of the braid could cause it to overheat without tripping the overcurrent protection on the 32A circuit.

Connecting the braid “directly” to the CPC/PE inside an enclosure with a VFD is not an installation matter it’s equipment design.

[old martParticipant @oldmart]

When I used shielded cables for both the VFD to motor and for the remote control cables the earth conductors were separate from the shielding. Shielding on its own is not a proper earth connection. Both ends of the shielding were connected to earth connections inside the VFD and in the motor, earth and shielding being common according to the detailed wiring instructions supplied by The inverter Drive Supermarket.

I did all the research on how to do the wiring before buying the motor and VFD.

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