Proper size of capacitors for transient suppression?

I've decided to "beef up" the transient suppresion on my cabling.
I'm trying to pick the proper size capacitor to use between the "hot"
leg and ground. I've seen people use .1 mf and Gecko uses 470 mf
across their terminals. Thats a hell of a range. Also Gecko
recommends using if the cable is longer than 18 inches (.5 meter).
They show the cactior next to the active equipment. My original NC
controller had capacitors in series with resistors for this funcion
on many of the longer lines.

ANY RECOMMENDATIONS OF HOW TO SORT THIS OUT WOULD BE APPRECIATED

Jeff