3 Phase Motor

A1a) because the motor is running in delta?

A1b) because it doesn't need to be?

A1c) because it is properly connected to neutral instead?

A2) In anything other than an IT system, the circuit protective device(s) will operate, disconnecting the supply from the fault. So the voltage and current will drop to zero.

Ask any competent electrician and they can tell you.

I hope you don't claim to be an electrician!

Incompetence can kill you!

The star point might not be earthed but motor frame would be I assume.

But where is your earth fault and how did it occur? If in the motor, say a winding burns out and shorts to the frame, the frame will become live (and a safety hazard) at a voltage depending on the resistance of the now unbalanced load of the earth fault circuit and the current flowing until the protective gear trips out.

The star point, if earthed, would have some affect the distribution of the line and phase currents - but somewhat complex to calculate - even with additional data.

Either way, the motor tries to run on two phases, until it catches fire or the cables burn out. Maybe taking the building with it and electrocuting a few people in the process.

A spectacle best viewed from a distance.

Article 430.1 in the NEC. gives you a one line diagram for the proper wiring for a 3 phase motor

I'm assuming that you have a 3 wire "Y" or "Star" system as opposed to a 4 wire Wye and not a 3 wire Delta system. Follow this thread and you may answer your own question http://www.allaboutcircuits.com/vol_2/chpt_10/5.html

There is no need, in fact it would draw vast currents, causing major problems, though I have never felt the need to try it out either, to earth a three phase motor at the star connection point.

Only earth the motor frame of course, which will be linked to neutral for single phase loads only, not 3 phase loads.

The neutral/earth link is usually at the local substation in my experience. It may be only made once....it has been extensively discussed on CR4 for many years.

This question crops up at least once a year.....a proper education as an EE will explain the reasons more fully than I have.....