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computers / comp.sys.dec / 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
Subject: grounded MMJ cables
From: Phillip Helbig (undr
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Multivax C&R
Date: Sun, 18 Jul 2021 05:22 UTC
Path: i2pn2.org!i2pn.org!aioe.org!VGB9yARrCle+RKwenuC6lg.user.gioia.aioe.org.POSTED!not-for-mail
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)
Organization: Multivax C&R
Lines: 5
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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?



Subject: Re: grounded MMJ cables
From: Grant Taylor
Newsgroups: comp.sys.dec, comp.os.vms
Organization: TNet Consulting
Date: Sun, 18 Jul 2021 08:02 UTC
References: 1
Path: i2pn2.org!i2pn.org!weretis.net!feeder6.news.weretis.net!tncsrv06.tnetconsulting.net!tncsrv09.home.tnetconsulting.net!.POSTED.alpha.home.tnetconsulting.net!not-for-mail
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
Message-ID: <sd0n91$i5o$1@tncsrv09.home.tnetconsulting.net>
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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


Subject: Re: grounded MMJ cables
From: Phillip Helbig (undr
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Multivax C&R
Date: Sun, 18 Jul 2021 08:35 UTC
References: 1 2
Path: i2pn2.org!i2pn.org!aioe.org!VGB9yARrCle+RKwenuC6lg.user.gioia.aioe.org.POSTED!not-for-mail
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)
Organization: Multivax C&R
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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?



Subject: Re: grounded MMJ cables
From: chris
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Aioe.org NNTP Server
Date: Sun, 18 Jul 2021 10:40 UTC
References: 1 2 3
Path: i2pn2.org!i2pn.org!aioe.org!WFgAfjdMCLK7ItoF6n4UQQ.user.gioia.aioe.org.POSTED!not-for-mail
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
Organization: Aioe.org NNTP Server
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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...




Subject: Re: grounded MMJ cables
From: Phillip Helbig (undr
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Multivax C&R
Date: Sun, 18 Jul 2021 11:08 UTC
References: 1 2 3 4
Path: i2pn2.org!i2pn.org!aioe.org!VGB9yARrCle+RKwenuC6lg.user.gioia.aioe.org.POSTED!not-for-mail
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)
Organization: Multivax C&R
Lines: 38
Message-ID: <sd1242$1d2s$1@gioia.aioe.org>
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In article <sd10f5$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.



Subject: Re: grounded MMJ cables
From: chris
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Aioe.org NNTP Server
Date: Sun, 18 Jul 2021 12:50 UTC
References: 1 2 3 4 5
Path: i2pn2.org!i2pn.org!aioe.org!jazQyxryRFiI4FEZ51SAvA.user.46.165.242.75.POSTED!not-for-mail
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
Organization: Aioe.org NNTP Server
Message-ID: <sd182p$eqd$1@gioia.aioe.org>
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On 07/18/21 12:08, Phillip Helbig (undress to reply) wrote:
In article<sd10f5$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.




Subject: Re: grounded MMJ cables
From: Scott Dorsey
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Former users of Netcom shell (1989-2000)
Date: Sun, 18 Jul 2021 13:06 UTC
References: 1 2 3 4
Path: i2pn2.org!i2pn.org!weretis.net!feeder6.news.weretis.net!panix!.POSTED.panix2.panix.com!panix2.panix.com!not-for-mail
From: klu...@panix.com (Scott Dorsey)
Newsgroups: comp.sys.dec,comp.os.vms
Subject: Re: grounded MMJ cables
Date: 18 Jul 2021 13:06:23 -0000
Organization: Former users of Netcom shell (1989-2000)
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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."


Subject: Re: grounded MMJ cables
From: Michael Moroney
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Aioe.org NNTP Server
Date: Sun, 18 Jul 2021 16:34 UTC
References: 1 2 3 4 5 6
Path: i2pn2.org!i2pn.org!aioe.org!Uh3cGLv3BUP05xA/L7flqA.user.46.165.242.75.POSTED!not-for-mail
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
Organization: Aioe.org NNTP Server
Message-ID: <sd1l7j$aq4$1@gioia.aioe.org>
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On 7/18/2021 8:50 AM, chris wrote:
On 07/18/21 12:08, Phillip Helbig (undress to reply) wrote:
In article<sd10f5$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.


Subject: Re: grounded MMJ cables
From: Grant Taylor
Newsgroups: comp.sys.dec, comp.os.vms
Organization: TNet Consulting
Date: Sun, 18 Jul 2021 17:54 UTC
References: 1 2 3
Path: i2pn2.org!i2pn.org!weretis.net!feeder6.news.weretis.net!tncsrv06.tnetconsulting.net!tncsrv09.home.tnetconsulting.net!.POSTED.alpha.home.tnetconsulting.net!not-for-mail
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
Message-ID: <sd1pvr$qld$2@tncsrv09.home.tnetconsulting.net>
References: <sd0dr9$ed3$1@gioia.aioe.org>
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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


Subject: Re: grounded MMJ cables
From: chris
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Aioe.org NNTP Server
Date: Sun, 18 Jul 2021 17:58 UTC
References: 1 2 3 4 5
Path: i2pn2.org!i2pn.org!aioe.org!jazQyxryRFiI4FEZ51SAvA.user.46.165.242.75.POSTED!not-for-mail
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
Message-ID: <sd1q4e$hap$1@gioia.aioe.org>
References: <sd0dr9$ed3$1@gioia.aioe.org> <sd10f5$pd6$1@gioia.aioe.org> <sd1242$1d2s$1@gioia.aioe.org> <sd182p$eqd$1@gioia.aioe.org> <sd190f$3s8$1@panix2.panix.com>
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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...


Subject: Re: grounded MMJ cables
From: Dave Froble
Newsgroups: comp.sys.dec, comp.os.vms
Organization: A noiseless patient Spider
Date: Sun, 18 Jul 2021 17:59 UTC
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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
Organization: A noiseless patient Spider
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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


Subject: Re: grounded MMJ cables
From: Scott Dorsey
Newsgroups: comp.sys.dec, comp.os.vms
Organization: Former users of Netcom shell (1989-2000)
Date: Sun, 18 Jul 2021 18:01 UTC
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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
Organization: Former users of Netcom shell (1989-2000)
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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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