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--Edited at Sparky256's suggestion for better clarity--

Background Information

I'm making a power cable for a piece of obscure, surplus military equipment (an AN/UGC-74B teletype, to be precise). I have the manuals that describe the power cable, but the wording doesn't account for part of the schematic, and I can't find a definitive answer that seems to make sense searching online. I'm somewhat familiar with electrical terminology and symbols though not an engineer by any means-- just a hobbyist who still doesn't know much compared to most of the people who will read this. I haven't seen anything like this before. If it's something simple, I apologize.

Power cable schematic taken from the manual

On the right side of the schematic we see the standard three-pronged 120-volt male adapter. BLK and WHT wires connect to pins K and M on the 12-pin Amphenol adapter (not all pins are used) on the other end of the cord, but BRN (or ground) stops at the dashed line that appears to make a circle around the other wires. Then, on the other end of the cord, we see another dashed circle, this time with another wire, also labeled WHT, seemingly coming off it to pin E.

Another schematic of the power input on the device itself shows that pin E appears to have no input from the cable but connects to chassis ground via something called E2-- see here:

Another schematic showing the power input

Also note that there is not only this power input connector (labeled J2 in the schematics) to which my cable will connect, but there is also a ground terminal, and I'm not sure if I should bring the ground wire out of my cable and connect ground there or not, either. If the device isn't grounded via pin E through the power cord's ground wire, I'd assume that I'd need to ground via the GND terminal for safe operation instead.

This is an image of the power input and ground terminal to show you what I mean (additional photos of various parts of the teletype available here-- not my photos but the same model of TTY: http://imgur.com/gallery/FK5nB):

Power input, ground terminal, battery power input, and data connector

At this point, I just am not sure what to do about this. I want to make sure I create the cable properly so I don't break anything; I understand everything else about how to make the cord, but not what to do with ground and pin E.

The manual can be accessed here. It's pretty hefty, so maybe I've just missed something it instructed somewhere-- but I don't think I did: http://www.nj7p.org/Manuals/PDFs/Military/TM%2011-5815-602-24-1%2015-Sep-87%20USAPA.pdf

The full schematics I referenced are on pages 143 (labeled 3-93 in the manual) and 396 (labeled FO-3), as well as additional information describing the power input wiring on page 96 (labeled 3-46).

The Specific Questions I Have

  1. What do the dashed/dotted lines referenced earlier mean?
  2. If the dashed/dotted lines indicate some kind of shielding, does the BRN AKA ground wire connect to the shielding and then the second WHT wire connect from the shielding to pin E, effectively grounding pin E?
  3. If the ground wire does not connect to pin E through the shielding, would it be wise to instead connect my cord's ground wire to the GND terminal instead?
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    \$\begingroup\$ You are asking more than one question, and sometimes you seem to be asking a question. Could you please terminate all actual questions with a question mark (?), and clean up your wall of text a bit so that we know what answers to write. \$\endgroup\$ – Sparky256 May 7 '16 at 22:49
  • \$\begingroup\$ I've altered it slightly to delineate between background information and actual questions and have cut out a paragraph that was definitely unnecessary. \$\endgroup\$ – weildish May 7 '16 at 23:07
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I see several details in your drawings.

1) The top drawing is of a shielded power cable, and the power can be AC or DC.

2) Pin 'E' on the J2 connector is Earth ground for the chassis and power. The J2 connector has a gnd symbol at the bottom to clarify it is earth grounded.

3) J2 also shows built-in capacitors to filter out EMI noise from either direction. I would use pin 'E' as power ground even if you just run a green wire to your power source ground.

4) The dashed lines around J2 refer to the chassis in an abstract way, and show it is grounded to J2 and J3 connector shells directly.

5) There maybe other drawings that tie into these drawings, but for power source and ground these seem to cover the issues.

6) The power cable does not have to be shielded for non-military use. Make sure J2 is wired correctly for the voltage you are using, AC or DC.

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The dotted lines that circle the bundle of signals is often used to delineate a cable bundle (e.g. wrapped together in a sleeve), and when signals are connected to it, that generally means that it represents the (conductive) cable shield.

The second thing you circled (in J2), is a typical representation of Earth ground. I take it to mean that the chassis is bonded to Earth ground.

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  • \$\begingroup\$ Ground is ground is ground ... at some point \$\endgroup\$ – vicatcu May 7 '16 at 23:29
  • \$\begingroup\$ Thank you for your answer, @vicatcu. So you'd say it's pretty safe to assume that the conductive shielding essentially acts as a ground wire, grounding the device via pin E and the ground prong of the plug? \$\endgroup\$ – weildish May 7 '16 at 23:55
  • \$\begingroup\$ @weildish The shield does not ground the device via pin E. The shield is meant to keep unwanted signals out of your cable. So the cable is kept is kept at the same potential as earth ground. \$\endgroup\$ – efox29 May 8 '16 at 0:57
  • \$\begingroup\$ @efox29 I understand that shielding is meant to keep unwanted signals out of the cable, but if it's conductive shielding and the ground prong of the plug connects to pin E through the shielding as the schematic seems to indicate (essentially using the metal shielding as a third wire), then I'd think it'd act as both shielding and a wire for ground. In my case, I don't have a shielded cable-- just a regular 16/3 cable. My idea is to ground pin E through the power cable using the standard third/ground wire as Sparky256 indicates would work in point three of his answer. \$\endgroup\$ – weildish May 8 '16 at 1:56
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I would agree, this appears to be a conductive shield around the the 2 leads in the power cable, the clue here is the military spec on this device, this is done generally to try and prevent Emf interference on the operating device

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The dashed oval outline designates a conductive overall shield. Typically a braid of small, bare copper (or tinned copper) wires. However ordinary power cables just have the safety ground as a third, insulated internal wire just like hot and neutral.

Note that back in vintage days (as when those diagrams were drawn) the color standard in North America was white for neutral, black for hot, and green (or some other color) for safety ground (if there even was one).

Today the European Community standard along with the international marketplace have de-facto standardized on power cords with light blue for neutral, brown for hot, and green with a yellow stripe as safety ground.

For something like an antique teletype, I can't see that you actually NEED a SHIELDED power cord. An ordinary cord capable of the voltage and current rating would be completely sufficient.

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  • \$\begingroup\$ Yeah, I would like to know WHY a power cable would need to be shielded. The only thing I can think of would be if the power cable was very long and the source resistance was relatively high like a few ohms because it was a battery and it's used right next to a radio transmitter. Even then I'm not sure I see how it could make a lick of a difference if the power supply has the usual filtering. \$\endgroup\$ – squarewav May 8 '16 at 4:33
  • \$\begingroup\$ It seems quite possible that it was "overengineered" for government or even military use. \$\endgroup\$ – Richard Crowley May 8 '16 at 5:38

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