[Info-vax] grounded MMJ cables

[Phillip Helbig undress to reply]

In article <sd10f5$pd6$1 at gioia.aioe.org>, chris
<chris-nospam at tridac.net> writes: 

> On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
> > In article<sd0n91$i5o$1 at tncsrv09.home.tnetconsulting.net>, Grant Taylor
> > <gtaylor at tnetconsulting.net>  writes:
> >
> >> On 7/17/21 11:22 PM, Phillip Helbig (undress to reply) wrote:
> >>> I'm testing out some MMJ cables (useful for console cables) and
> >>> notice that some (all of which are round rather than flat) have an
> >>> additional wire outside of the plug at each end, which looks like it
> >>> might be intended as ground.  What's the purpose of that?
> >>
> >> How long is it?  I'd expect it to be 3-9 inches if it's meant to be a
> >> ground wire that is attached to something else on the chassis.
> >
> > Yes, about 5 inches.  It has an eyelet at the end, so one could connect
> > it to the chassis via a screw.
> >
> >> I would also have significant worries about ground loops and / or sneak
> >> currents.  Both of which can be quite dangerous from an electrical and
> >> safety perspective.  As in more amperage than the wire can safely handle
> >> turning the wire into a heater that can melt insulation and start fires.
> >
> > But is that an issue when using a console cable?
> 
> Not usually from an interference to the cable  point of view and iirc,
> the added wire is at one end only, which would not enable earth loops.

I have seen those, but the two I checked today have it at both ends.

> The answer is more likely to lower any possible emc emissions from the
> cable, not to it. Typical terminal baud rates are not high enough and
> the rise and fall times are usually controlled, but fast edges could
> still be coupled into the cable from the terminal or machine hardware...

OK.