[Info-vax] grounded MMJ cables

[chris]

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.
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...