I am not sure, how to correctly connect a motor drive to reduce noise as good as possible. The drive runs on 48VDC and the power supply is galvanic isolated, so that GND and Earth are not shorted together. The power supply chassis is on Earth. The motor drive is a PCB without a Earth connector, only Ground points are available.

Everything is in an enclosure, which is pulled to Earth. The motor is also attached to the Earth potential. With this configuration the system works descent so far, but at high motor current, the encoder give more CRC errors, so there might be an EMC problem that should be fixed. The encoder cable itself is shielded with potential to Ground. The motor cable has no shielding, but I will replace the cable with a shielded one and I'm unsure, where I should connect the shield.

Normally, the Motor shield is connected to Earth, but in the end, the distrubances should be flow back into the distrubing source, as low impedant as possible. Since the disturbances need to come from the galvanic isolated motor drive, I think the shield should go to Ground? And if so, I'm not sure if Ground should also connect to Earth, since the motor chassis is already on Earth?

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1 Answer 1


The terms ground and earth are usually used interchangeably. All earth/ground connections should ultimately be connected th an electrode rod that is driven into the ground at a point at or near the location that electrical power inters the building.

The common point of a galvanically isolated circuit can be connected to earth/ground, but that should be done at only one point.

Cable shields, metal enclosures and motor frames should be connected to earth/ground.

Care must be taken to separate power cables from cables that connect signal wiring such as encoder cables. The two classes of cables should not be physically close to each other while running in a parallel direction. Signal cables must be shielded. Power to signaling devices may need to be provided by a separate isolated supply.


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