Proper Earthing

→ British Standard 7671.

As our British friend has replied (succinctly)...use your local code authority.

I would refer to:
NEC (NFPA 70)

IEEE Std 100

IEEE Std 142

Usually its would be considered very recommended to grounding the motor directly to the steel structural ,but you still need to connect the motor to the grounding conductor along with the power cable to provide the motor with particular protection required.

I bet if some motors located at the higher floors of the building with power supply 440V, 3 phase leaks, and some of the structures gets wet by the rain and get into the cold water line, then the water gets, a really a nutty and refreshing flavor. The last time you would see yourself into, is looking in the mirror at the lavatory and getting attracted with the faucet.

Hi MegaThink, you are part of the way right, the electrical earth should be connected directly to the supply distribution board, but bonding of other metallic structures may be bonded directly to the main motor earth. This is for earthing the metallic structure that is connected to the motor, bonding of all metal is important in an electrical installation. It is also required that an additional earth wire is used to earth structures that are metal, but sometimes installation teams do not follow this rule, due to them being lazy.

Cheers

Joe

Joe you said..bonding of all metal is important in an electrical installation. It is also required that an additional earth wire is used to earth structures that are metal, but sometimes installation teams do not follow this rule, due to them being lazy.

Very true, but that's where the inspectors and commissioning people play their part in identifying this failing, and getting it rectified to ensure the installation complies with local codes, BEFORE the installation is signed off.

to the OP...

Yes in the UK we have BS 7671 plus other on site guides etc, etc... Yes, use your local electrical guides and standards, but common sense together with a high degree of experience will tell you if and when something is right or wrong. It's simple really, if it doesn't have an earth, then put one in.

you have asked a good question, but cannot be answered fully as we don't know where you are in the world and we don't know your local electrical codes.

Hi Brich, I have to agree with what you have said, but sometimes inspectors can be a bit to casual in their testing, they only on some occasions check that there is continuity on the earth connections, and not investigate where this earth connection comes from.

You also said: That I had asked a good question, I don't think that I have asked any questions in this forum, I only made a statement. I think that you may be referring to the AP.

Anyway Very Best Regards

Joe

the "good question" comment was to the OP...