> On Feb 2, 2018, at 7:26 PM, Paul Berger via cctalk <email@example.com> > wrote: > > > > On 2018-02-02 7:13 PM, Fred Cisin via cctalk wrote: >>> they might have different ground systems. If so, grounding both ends might >>> produce a LARGE current through the cable, possibly enough to be hazardous. >> >> OB_Ignorant_Question: Is that the reason why RS232 DB25 has both pin 1 and >> pin 7? > Pin 1 is supposed to be protective (shield) ground and pin 7 is signal > ground. > > Paul.
Similar to safety ground (green) and neutral (white, in the USA) on power wiring. paul