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computers / comp.os.vms / Re: grounded MMJ cables

SubjectAuthor
* grounded MMJ cablesPhillip Helbig (undress to reply
`* Re: grounded MMJ cablesGrant Taylor
 `* Re: grounded MMJ cablesPhillip Helbig (undress to reply
  +* Re: grounded MMJ cableschris
  |`* Re: grounded MMJ cablesPhillip Helbig (undress to reply
  | `* Re: grounded MMJ cableschris
  |  +* Re: grounded MMJ cablesScott Dorsey
  |  |`* Re: grounded MMJ cableschris
  |  | `- Re: grounded MMJ cablesScott Dorsey
  |  `* Re: grounded MMJ cablesMichael Moroney
  |   `- Re: grounded MMJ cablesDave Froble
  `- Re: grounded MMJ cablesGrant Taylor

1
grounded MMJ cables

<sd0dr9$ed3$1@gioia.aioe.org>

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From: hel...@asclothestro.multivax.de (Phillip Helbig (undress to reply)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: grounded MMJ cables
Date: Sun, 18 Jul 2021 05:22:49 +0000 (UTC)
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 by: Phillip Helbig (undr - Sun, 18 Jul 2021 05:22 UTC

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?

Re: grounded MMJ cables

<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>

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From: gtay...@tnetconsulting.net (Grant Taylor)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 02:02:20 -0600
Organization: TNet Consulting
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 by: Grant Taylor - Sun, 18 Jul 2021 08:02 UTC

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.

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.

--
Grant. . . .
unix || die

Re: grounded MMJ cables

<sd0p53$1v7k$1@gioia.aioe.org>

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From: hel...@asclothestro.multivax.de (Phillip Helbig (undress to reply)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 08:35:47 +0000 (UTC)
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 by: Phillip Helbig (undr - Sun, 18 Jul 2021 08:35 UTC

In article <sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant Taylor
<gtaylor@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?

Re: grounded MMJ cables

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From: chris-no...@tridac.net (chris)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 11:40:38 +0100
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 by: chris - Sun, 18 Jul 2021 10:40 UTC

On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
> In article<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant Taylor
> <gtaylor@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...

Re: grounded MMJ cables

<sd1242$1d2s$1@gioia.aioe.org>

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From: hel...@asclothestro.multivax.de (Phillip Helbig (undress to reply)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 11:08:50 +0000 (UTC)
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 by: Phillip Helbig (undr - Sun, 18 Jul 2021 11:08 UTC

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

> On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
> > In article<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant Taylor
> > <gtaylor@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.

Re: grounded MMJ cables

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From: chris-no...@tridac.net (chris)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 13:50:33 +0100
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 by: chris - Sun, 18 Jul 2021 12:50 UTC

On 07/18/21 12:08, Phillip Helbig (undress to reply) wrote:
> In article<sd10f5$pd6$1@gioia.aioe.org>, chris
> <chris-nospam@tridac.net> writes:
>
>> On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
>>> In article<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant Taylor
>>> <gtaylor@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.

Ok, but the one I have has just one, but maybe that was third party
item.

The frame or chassis ground and signal grounds are separate pins
on a 25 pin RS232 layout, even though they may be joined inside the
equipment. If they joined, it's often with a low value resistor, say
100 ohms, to prevent excessive earth loop currents. Don't know the
circuitry for a VT220, for example, but DEC would have done the job
right, both from an emc and safety points of view. They were obsessive
about standards...

>
>> 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.
>

Re: grounded MMJ cables

<sd190f$3s8$1@panix2.panix.com>

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Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
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 by: Scott Dorsey - Sun, 18 Jul 2021 13:06 UTC

chris <chris-nospam@tridac.net> wrote:
>The frame or chassis ground and signal grounds are separate pins
>on a 25 pin RS232 layout, even though they may be joined inside the
>equipment. If they joined, it's often with a low value resistor, say
>100 ohms, to prevent excessive earth loop currents. Don't know the
>circuitry for a VT220, for example, but DEC would have done the job
>right, both from an emc and safety points of view. They were obsessive
>about standards...

Correct. There is no equivalent to pin 1 on an MMJ connector, only to
pin 7. Therefore pin 1 on the DB-25 side is brought out to a lead
that can be connected to chassis shield.

Whether or not you need it depends on your installation and what you are
doing. Everything should have one and only one connection to anything
else through the ground net. The manual for the device may discuss it.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Re: grounded MMJ cables

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From: moro...@world.std.spaamtrap.com (Michael Moroney)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 12:34:58 -0400
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 by: Michael Moroney - Sun, 18 Jul 2021 16:34 UTC

On 7/18/2021 8:50 AM, chris wrote:
> On 07/18/21 12:08, Phillip Helbig (undress to reply) wrote:
>> In article<sd10f5$pd6$1@gioia.aioe.org>, chris
>> <chris-nospam@tridac.net>  writes:
>>
>>> On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
>>>> In article<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant Taylor
>>>> <gtaylor@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.
>
> Ok, but the one I have has just one, but maybe that was third party
> item.
>

I have never seen anything like that on a DEC MMJ cable.

Re: grounded MMJ cables

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From: gtay...@tnetconsulting.net (Grant Taylor)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 11:54:45 -0600
Organization: TNet Consulting
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 by: Grant Taylor - Sun, 18 Jul 2021 17:54 UTC

On 7/18/21 2:35 AM, Phillip Helbig (undress to reply) wrote:
> Yes, about 5 inches. It has an eyelet at the end, so one could
> connect it to the chassis via a screw.

ACK

> But is that an issue when using a console cable?

I don't think so.

I would assume that the actual data lines on a console cable have some
sort of isolation to thwart things like current loops. Or at the very
least fuses to protect the rest of the system.

I know that I'm used to electro-optical isolation like that on Cisco
equipment. Specifically for this very problem.

--
Grant. . . .
unix || die

Re: grounded MMJ cables

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From: chris-no...@tridac.net (chris)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 18:58:37 +0100
Organization: Aioe.org NNTP Server
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 by: chris - Sun, 18 Jul 2021 17:58 UTC

On 07/18/21 14:06, Scott Dorsey wrote:
> chris<chris-nospam@tridac.net> wrote:
>> The frame or chassis ground and signal grounds are separate pins
>> on a 25 pin RS232 layout, even though they may be joined inside the
>> equipment. If they joined, it's often with a low value resistor, say
>> 100 ohms, to prevent excessive earth loop currents. Don't know the
>> circuitry for a VT220, for example, but DEC would have done the job
>> right, both from an emc and safety points of view. They were obsessive
>> about standards...
>
> Correct. There is no equivalent to pin 1 on an MMJ connector, only to
> pin 7. Therefore pin 1 on the DB-25 side is brought out to a lead
> that can be connected to chassis shield.
>
> Whether or not you need it depends on your installation and what you are
> doing. Everything should have one and only one connection to anything
> else through the ground net. The manual for the device may discuss it.
> --scott
>

The only reason I can think of for the separate screen wire, apart
for emc reasons, is to ensure that both ends chassis are at the same
potential. The careless may use a 2 wire outlet at one end or the
other and switchers always have leakage, so a good safety feature...

Re: grounded MMJ cables

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From: dav...@tsoft-inc.com (Dave Froble)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: Sun, 18 Jul 2021 13:59:49 -0400
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 by: Dave Froble - Sun, 18 Jul 2021 17:59 UTC

On 7/18/2021 12:34 PM, Michael Moroney wrote:
> On 7/18/2021 8:50 AM, chris wrote:
>> On 07/18/21 12:08, Phillip Helbig (undress to reply) wrote:
>>> In article<sd10f5$pd6$1@gioia.aioe.org>, chris
>>> <chris-nospam@tridac.net> writes:
>>>
>>>> On 07/18/21 09:35, Phillip Helbig (undress to reply) wrote:
>>>>> In article<sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>, Grant
>>>>> Taylor
>>>>> <gtaylor@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.
>>
>> Ok, but the one I have has just one, but maybe that was third party
>> item.
>>
>
> I have never seen anything like that on a DEC MMJ cable.

Any MMJ cables from DEC that I saw were 6 conductor flat cables. Not
that I've seen everything on the planet.

Anybody can make cables with MMJ connectors. I've done many. Anybody
can add anything they want.

--
David Froble Tel: 724-529-0450
Dave Froble Enterprises, Inc. E-Mail: davef@tsoft-inc.com
DFE Ultralights, Inc.
170 Grimplin Road
Vanderbilt, PA 15486

Re: grounded MMJ cables

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From: klu...@panix.com (Scott Dorsey)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: 18 Jul 2021 18:01:52 -0000
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 by: Scott Dorsey - Sun, 18 Jul 2021 18:01 UTC

chris <chris-nospam@tridac.net> wrote:
>
>The only reason I can think of for the separate screen wire, apart
>for emc reasons, is to ensure that both ends chassis are at the same
>potential. The careless may use a 2 wire outlet at one end or the
>other and switchers always have leakage, so a good safety feature...

Precisely. Check the original RS-232C standard, it is very intelligently
designed. Many implementations have not been so well done.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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