Thread: Three phase motor grounding. The official way to ground all things electric on machine tools is a bonded ground from the ground buss in the breaker panel through continuous green insulated conductors to the ground connection of the electrical control panel branching on to each of the connected motors and other electrical loads and devices. Only a single wire is permitted from buss to ground, that is you can't run the ground conductors in a loop. Make the circuit look like a tree not a lasso.

Now this is electrical advice from me, a perfect stranger. Maybe I know what I'm talking about, maybe not.

That's that hazard of electrical advice on message boards. As it happens I know a fair amount about electrical jazz but my electrical code knowledge is a long ways from complete. I have no formal electrical training and I certainly have no electrician's license.

The best source for electrical advice is from a local licensed industrial electrician knowledgeable in local electrical code and familiar with the requirements of electric motors. You frequently find good advice in the electrical departmens of the big box stores where they hire a diabled or disillusioned electrican or two to keep the DIY guys on the paths of electrical righteousness.

Ask them about their credentials before following their advice. Article 2. 50 in the NEC addresses grounding conductors.

Article 4. 30 addresses motor circuits and controllers. Look in the NEC index under appropiate topics. My NEC is dated 1.

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Your mileage may vary if you have access to a current edition. Your local library has the latest and greatest NEC and a copy machine. Regardless of all my caveats and cautions the grounding requirements for your project is simple. You did mention using the metallic electrical conduit as a gounding conductor. Local code may prohibit this for good reason. Mechanical onduit connections can be unreliable as conductors. A ground fault may cause an arc to develop in a high resistance connection and fail to trip the circuit protective device.

If the conduit fails to an open circuit condition, this leaves the machine and part of the conduit energized at line voltage for some time before a cascade of event least to personal injury or possibly fire. Some local codes permit using conduit as a ground but it's bad economy and a worse shortcut. Tia Portal V11 Download Rapidshare Link there. The possible consequences aren't worth saving a little time and wire. For that reason you want a low resistance high current capacity bonded ground conductor from motor to enclosure to panel to earth ground. This is so any fault to ground causes a heavy current to flow tripping the protective devices in the control enclosure and/or the branch circut MCCB in the distribution panel.