Hi Oxford

The neatest way of configuring the power input wiring to your multiple VFDs is to create a common bus bar (Terminal strip) for each phase + neutral + earth. You may or may not need the neutral. The type of wire needs to be suitable for the intended purpose both in terms of current carrying capacity and insulation and mechanical protection. The leads from the VFD to the motor should be both short and screened as these carry high frequency currents and can create a lot of radio interference. Suggest you use flexible screened wire or metal conduit to carry these wires. The appropriate wire would be SY multicore cable. This cable is flexible and is available in current ratings as well as multicore and termination is made using special glands available in both 20 and 25 mm conduit sizes. (Three, four, five and seven core are commonly available.) The SY cable could be used to wire the power input side of each VFD back to the power distribution box that contains the contactor/s and the supply fuse or RCD and isolator following the local regulations governing both the electricity supply and the health and safety regulations.

The easiest way of achieving the power distribution is to use a three phase distribution box (often known as a TP+N with isolator - this will provide a three phase isolator switch and the necessary bus bars and if the DIN rail type is procured there will be one or more rails to which the appropriate current breakers (MCBs) or fuse carriers can be fitted along with the DIN mount four pole contactor.

Suggest you procure a catalogue from your local electricians supply house. The three phase distribution boards are arround £100 in the UK for the box and isolator with DIN rail. A four pole contactor is arround £30 to £50 depending on current capacity - don't forget the VFD looks like a capacitive load and it is the in-rush current that is important not the running current. If you are using over current breakers (MCBs) then these need to also be rated for the in-rush current and I would suggest type 'C' not the more usual usual type 'B' which has a lower in rush capability.

The use of twisted wires can cause problems as the insulation can easily flow particularly if the wires are not de rated for such use. Normally the wire has to be of higher gauge if run in close proximity to other current carrying conductors - hence my recomendation to use type 'SY' cable.

Hope this helps you achieve a neat and safe installation - regards Pat.