Cable tray is often supported by using Channel as the base connected by threaded rod - (As per photo)
This is a secure method of fixing and gives total flexibility to positioning of upright supports.
Simply cut the slotted channel to length and connect either side with threaded rod. This can be then fixed to the ceiling or supported from girders. The cable tray then simply sits on the channel and fixes into place using a channel nut & bolt.
This method can be used or all cable sizes and especially useful when covering large spans and cable of supporting heavy loads.