Re: 18/4 or similar stranded wire cable

www.mcmaster.com sells shielded 4 conductor wire specifically for use
on CNC machines (flexible and with tougher oil resistant jacket) and
the good news is you can buy it by the foot. Search their online
catalog and you'll find it. Ground the end of the shield on the driver
end to the driver ground, leave the other end of the shield unattached
and you'll knock out most of your motor EFI noise. Going by memory I
think its available in both 18 and 16 gauge.

Paul T.