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I am wiring a single to 3 phase VFD to a 3 phase motor (240V delta). The 3/4HP motor powers a lathe in a domestic setting. Supply voltage is 240V 50Hz.

As per the VFD instructions, I am using shielded cable (SY 3 core plus PE) between the VFD and motor and have used the motor cable shield clamp at the VFD. Additionally, I plan to connect the earth wire at the VFD and motor.

VFD datasheet: http://www.elektro-trading.com.pl/pdf/napedyac/601/HA464518.pdf

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My question is should the SY cable shield also be terminated at the motor? Safety is my priority and I would also wish to minimise electrical noise.

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  • \$\begingroup\$ Show your proposed circuit as a diagram. \$\endgroup\$
    – Andy aka
    Aug 29, 2019 at 13:08

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You should thoroughly study the product manual and install the product according to instructions.

Drives 601 Product Manual:

1-5 Product Overview

In order to conform with the specified generic EMC standards the motor cable must be screened and the screen connected to both the motor frame and the motor cable clamp.

4-2 Electrical Installation

Motor Wiring

Motor Cable Clamp

To meet the generic EMC Standards and minimise the electrical interference, connections between the Inverter and the motor must be made using screened cable. The screens must be connected to the motor frame and to the motor cable clamp (PE). The motor protective earth conductor should be connected at the drive end to the motor PE point.

I would interpret that as requiring just one connection to earth at the VFD. The VFD should be connected to earth by using a conductor from the VFD to the earth connection point for the building. That point is probably located at the power distribution panel.

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  • \$\begingroup\$ "1-5 Product Overview In order to conform with the specified generic EMC standards the motor cable must be screened and the screen connected to both the motor frame and the motor cable clamp." -- OK, so that states the screen must be connected to the motor frame and the motor cable clamp (i.e. at the VFD). In other words, connect the screen to PE at both ends. \$\endgroup\$
    – Pzy
    Aug 29, 2019 at 14:45
  • \$\begingroup\$ Yes, that is what is required. \$\endgroup\$
    – user80875
    Aug 29, 2019 at 14:49
  • \$\begingroup\$ But doesn't that add a ground loop? I'm assuming it is correct to connect an earth wire (contained in the SY cable) between the VFD and motor. Or have I misunderstood something? \$\endgroup\$
    – Pzy
    Aug 29, 2019 at 14:53
  • \$\begingroup\$ The earth wire in the cable is the only thing grounding the motor. However, the motor may be mounted to some steel structure that is grounded. That would create a ground loop of unknown impedance, however it would not be considered a hazard and provides the best EMC protection that can be achieved under the circumstances. The VFD manufacturer is instruction what is best for VFD performance and acceptable for EMC standards. \$\endgroup\$
    – user80875
    Aug 29, 2019 at 15:04

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