Motor cable, selection details

Question:

What has to be considered during dimensioning and installation of the motor cables in and outside the control cabinet?

Answer:

For the operation at the frequency or servo inverter for motor cable lengths you should prefer capacity-low, polyethylene-isolated cables (PE) with a capacity per unit length of 110 nF/km (between core and screen) to the PVC cables.

The thermal load of the cable is the maximally permissible operation temperature of the cable. This is dependent e. g. on the cable material. In order not to exceed the thermal capacity of the cable you should attach importance to the ambient temperature and to the way of installation. The capacity depends very much on the actual installation. A cable installed in the cable channel can only be loaded with a lower current as if it would be on an open cable ladder. If the cables are installed in a distance, which corresponds to the sheath diameter, you can expect an important reduction of the capacity with the increasing number of cables. Moreover, cables of other devices installed parallel must be considered.

The dimensioning must be executed exactly according to VDE 0298-4 dated 01.11.1998 with all modifications of the norm. The cables must be installed accordingly to the actual way of installation. Eventually additional heat sources in the environment (e. g. brake resistors) are to be considered.

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