Power quality considerations for CNC machines: grounding

Power quality considerations for CNC machines: grounding

“…When lightning strikes a facility, the lightning current flows into the earth at the main service switch (grounding electrode system) and also travels along the conduitlequipment grounding conductor through the CNC machine and into the ground rod driven in the earth [4]. Fig.…”

“…shows how utility fault current flowing through the earth can flow up the CNC machine's ground rod, travels along the conduitlequipment grounding conductor, onto the utility neutral and back to the source (the utility substation). The presence of these large currents can result in malfunction, degradation, and damage to the electronic components within the CNC machine [4]. Drawing a comparison with other electronic equipment, like computers, electronic motor drives, programmable logic controllers, none subscribe to such a local grounding practice.…”

“…This technique is believed to help eliminate related operating problems while maintaining the safety requirements of electrical codes. Even if the following recommended practice is not followed, it is important to point out that a ground rod must never be driven at and connected directly to the CNC machine's ground plate [4]. Fig.…”

“…The new signal reference is created by the connection of the neutral of the transformer's secondary to the equipment grounding system via the bonding jumper and to the grounding electrode system via the GEC. The bonding jumper also provides a path for fault current, which allows the proper operation of overcurrent devices [4]. Fig.…”

“…Furthermore, an equipment grounding conductor should supplement the conduithceway where practical. This will help maintain a continuous, low impedance equipment grounding path [4].…”