I can understand keeping cables away from sharp metal, but any metal? That one's new to me.
With any large sort of cable running next to or through metallic surfaces, you end up with induced and eddy currents, respectively, especially over long runs.
This is why things like cable trays/ladders are equi-potentially bonded together and earthed.
With respect to cables making entry to equipment, these days, especially where high frequency drives are concerned, you must use an EMC type cable gland, not just the normal nylon one.
I've investigated numerous stray voltage problems, where this has been put down to Eddy currents flowing in metallic parts of the installation, caused by the lack of bad screening/wrong gland used.
