Grounding of Motor

You may very well "bond" the motor frame to the nearest steel structure (with two seperate and distinct connections) but please ensure that the steel structure is connected solidly to the plant earth grid at all times.

Is the cable your proposing SWA? If yes, and the armour is used as the CPC then yes, bond to the local steelwork as well.

But please don't use the steel structure as your only earth return path.

and please don't use the armor of the cable as a grounding conductor . . .

@TonyS:

It's not an SWA Cable but PVC Cable.

If I use 3C + E, means that I have to provide 300 m copper that 'bonds' MCC and motor together. Or I can use 3C cable + 4 m of ground cable that 'bonds' the motor and steel structure together?

Would the two give the same result?

Thanks in advance..

Safety costs money unfortunately.

....while a lack of safety costs considerably more. Like, lives, for instance.

As mentioned many many times in this forum, you need to check the local rules in force where this is located.

If this was in Canada, a seperate bonding conductor would be required.

Your two conditions still satisfy the requirement that motor should be grounded. The difference between the two is the flow of effective ground fault return to facilitate the operation of your protective device. I prefer additional E copper wire than steel structure because copper wire is more conductive than steel.

Dear all,

In NEC, 3core without EGC (Equipment grounding conductor) is prohibited. So, in USA, you must use 3 core + EGC.

In IEC, you have more freedom, you may have 3 core + PE cable.

If you do not want to spend for the additional PE core, you may bond your motor body to the nearby earthed steel structure. To keep your system TN-S, the bonded steel structure must have metal connection with your substation or your neutral of the transformer. If you are not sure of this metal connection, you may select TT system, where your motor can be earthed with local earthing electrode, in your case, nearby steel structure. However, you must ensure the protection circuit will trip in case of an earth fault at the motor, this may require earth fault protection at the motor starter.

Regards