In practical terms with an unknown VSD or CH control system or solar pump speed controller isn't the simplest solution just to adopt supplementary bonding downstream? R <= 50V/Ia. With industrial motors with a lot of bonded metalwork about you're probably not too far away from achieving the required resistances by default. With domestic CH systems etc with an upstream 30mA RCD or even a 3A fuse you'd likely be fine just replying on the c.p.c.s without any additional bonding conductors. Then it almost doesn't matter what the fault current is - less than Ia then it's safe to touch, Ia or above then it disconnects within an acceptable time.
In practical terms with an unknown VSD or CH control system or solar pump speed controller isn't the simplest solution just to adopt supplementary bonding downstream? R <= 50V/Ia. With industrial motors with a lot of bonded metalwork about you're probably not too far away from achieving the required resistances by default. With domestic CH systems etc with an upstream 30mA RCD or even a 3A fuse you'd likely be fine just replying on the c.p.c.s without any additional bonding conductors. Then it almost doesn't matter what the fault current is - less than Ia then it's safe to touch, Ia or above then it disconnects within an acceptable time.
