VFD WIRING HELP

[kishore1march]

Dear,

SITE CONDITION - I have a panel with a VFD 90KW and a same capacity of soft starter, where a 75 sqmm cable is being connected to L1,L2,L3 terminals of VFD and another three cables of same size is being looped from VFD input terminals to soft starter input terminals(L1,L2,L3). Now the VFD and Soft starter L1,L2,L3 are looped without any individual MCCB and VFD L1,L2,L3 have two 75sqmm cable connected in each terminal.

QUERY -

1. if the Soft starter L1,L2,L3 got short circuit internally, will it affect the VFD's L1,L2,L3?

2. the rated tightening torque for VFD will differ if 2 cables are terminated in each terminals (L1,L2,L3)?

Pls suggest any problems in the present wiring and any good practice to be followed.

Rough sketch of wiring is attached.

[Werner_JUPPA · Accepted solution]

Hello

These two devices probably never run at the same time, otherwise a common supply of 75mm² would be too small.

1. As soon as the Softstarter fails, the MCCB will trip and the VFD has no power supply anymore (and vice-versa).

2, Two wires of 75mm² each will probably fit in these terminals, but they are not designed for that. The terminals are designed for one wire with a maximum cross section of 120mm².

Basically, we would not recommend this wiring.

Either the two devices are powered individually by two MCCBs, or the two devices are protected locally with two circuit breakers (see attached drawing). These should be dimensioned in such a way that, in the event of a fault, the local CB switches off and not the MCCB. Both architectures are therefore redundant and the VFD remains in operation if the Softstarter should fail.

[kishore1march]

Dear Werner,

This is a well guided answer. Thanks for your info and time.