Why all core should be shielded for VFD cable?

What will happen to motor if we connect normal 3 Core wire armoured XLPE cable without individual screen for each phase to 3 pole of Motor? Why all core should be shielded for variable frequency drive (VFD) cable?

A: If you're not doing anything exotic like running especially high carrier frequency, extreme cable distances (>100m), or operating at 690V, standard tray cable works just fine.

I've been applying variable frequency drives to industrial applications since 1986, and that was LONG before specialized VFD-rated cables came along. I have yet to personally see an application where the cable failed before the motor, though I have read about such failures in trade magazines. However, if I recall correctly these failures were all in unusual applications, not standard pump, fan, conveyor or machine applications. My one concession to the late 1980's switch to IGBTs is to recommend 1000V rated cable rather than 600V.

As always, due attention MUST be paid to keeping motor leads separate from instrumentation and other low-voltage cables, and keeping high voltage (2,400V and higher) cables away from low-voltage (<1000V) VFD motor leads to minimize the possibility of interference.

Of course, if you're wiring a commercial building with all high carrier frequency VFD on chilled-water circulation pumps and air-handlers, by all means invest in VFD-specific motor leads, but in industrial applications I firmly believe such cable is an unnecessary expense except in easily identifiable special cases.