This following is a myth.

“JACK/PLUG – In electronics, a jack is a female part into which one inserts a plug, the male part.”

While often the case, the real definition is the jack is the more fixed of a connector pair and the plug is the less fixed connector of the same pair. Where two connectors are neither less or more fixed with respect to each other, both are a plug.

This was quite sensibly defined most recently in the IEEE-200-1975 standard. This standard was renewed in the 1980s and withdrawn in the 1990s. Even so it and IEEE-315-1975 form the basis on how to create reference designators in and around electrical equipment.

The notion Jack and Plug ever meant anything to do with a male or female contact, seems to have come about in the 1980s and 1990s. Somewhere in that time frame young engineers were not properly mentored by their elders in the way of good engineering practices. Bad habits leaked into the general population and now very few technical folks know how to properly annotate the references in harness designs and other electrical assemblies.

IEEE-200-1975 (also known as ANSI Y32.16-1975) serves as the last collection of knowledge dating all the way back to the 1950s in the MIL-STD-16 specification. UPDATE: See Below

Golden rules for harness reference designation from IEEE-200-1975 include:

  • The movable (less fixed) connector of a mating pair shall be designated P [where P means plug].
  • The stationary (more fixed) connector of a mating pair shall be designated J or X [where J means Jack].
  • If two cables are to be connected to each other, each of the mating cable connectors shall be designated P.

That last item is a mind blower for many. Yes this really means there is no such requirement to have J123 connect to P123. Efforts to try and achieve this are a notorious waste of time and such conventions are very easy to violate and, thus, break. A complete system on how to annotate an entire collection of electrical equipment is well defined in IEEE-200-1975. Despite it being withdrawn from active support in the IEEE, copies are still available from Tech Street and other standards suppliers.

Frequently heard statements:

“The fixed/less fixed distinction doesn’t work when both are unfixed, as is commonly the case when cables are being extended or split.”

This was never a problem since Plugs can connect to Plugs.

“Whatever IEEE may have wanted to establish, that’s not how it worked out…”

The IEEE did not establish anything. They documented what was once common knowledge, at least for technical folks, in the 1970s based on documentation dating back to at least the 1950s. It is clear the lack of mentoring is creating the break from tradition.

“Plugs always have male contacts while Jacks always have female contacts.”

No they don’t. Look at any PC (an older one) with a DB25 parallel and DE9 serial ports – all Jacks. Look at the AC power “Jack” on your PC – male for a very good reason. Still other connectors, aerospace connectors come to mind, have both male and female pins in the same body.

“Our engineers are from MIT so our custom annotation system is better.”

Perhaps, but the chance any super star engineer can outwit the collective knowledge of thousands of engineers and hundreds of thousands of man-hours documented in the standards… is laughable. Sure you may have the smartest team on planet Earth. Good for you. Keep their talents focused on the real engineering problems not engineering methods. Otherwise your A-Team will be in the unemployment lines after you miss your deadlines.

“We mandate each Pxyz to match up to the same Jxyz.”

This instantly breaks if you have two identical sub-assemblies in your assembly since each item will have the exact same series of J numbers on its housing. IEEE-200-1975 provides a very simple and elegant solution for this scenario; Buy a copy and read it.

“We ensure all the Jacks on all duplicate sub-assemblies are unique by writing new J numbers over top the ones printed by the manufacture.”

You just tripled the paperwork to track the “change” you made to an, otherwise simply identified, off the shelf item and must generate a whole new Control Drawing to track this change. Hopelessly ridiculous.

“Do Engineers care about the proper use of reference designators?”

Engineers care. Engineeer wannabees don’t. Harsh, but true.

Other Standards?
I have searched the standards archives in depth to find any current standard that dictates a better approach than IEEE-200-1975. SAE AS50881 “Wiring Aerospace Vehicle” comes close, but really addresses how to identify the wires bundles themselves, not the connectors. UPDATE: See Below

The point is this. How to properly annotate electrical assemblies is nothing new. At some point the knowledge was dropped and chaos erupted causing, among other things, the bizarre concept of a plug meaning a male.

To Young Engineers:
If you are a young electrical engineer, you need to buy your own copies of IEEE-200-1975, IEEE-315-1975 and why not also IEEE-280-1985. Read them. Learn a great way to annotate. Amaze your boss by saying you will take responsibility for annotating your next project using a real standardized approach rather than home-brewing some half-baked method.

To Supervisors:
Supervisors, you need to find a way to pass on the knowledge stored in the above standards. If you don’t you are literally spending your project funding on the equivalent of learning how to read and write. Keep your engineers focused on the real problems to solve. Don’t spend time re-inventing the wheel.

To Contract and Specification Writers:
Make adherance to IEEE-200-1975 and IEEE-315-1975 a requirement. Save money.

If you do nothing else, please find a copy of IEEE-200-1975 and read it through once. It is very short.

Good luck.

UPDATE July 29, 2009

The commenter below discovered ASME, the mechanical engineering standards group, created a new standard to pick up where the withdrawn IEEE-200-1975 left off. It is called ASME Y14.44-2008. Apparently the void left by the removal of IEEE-200-1975 was felt by many so ASME came to the rescue with ASME Y14.44-2008. How embarrassing for the IEEE to have a mechanical engineering association pick up an electrical equipment standard.

I have ordered a copy from ASME and eagerly await its arrival for review and comparison. Stay tuned to this COSJWT post.


  1. Thanks for this post. I’ve got a question for you. Is ASME Y14.44-2008 an equivalent standard? The title is the same.

  2. The foreword of ASME Y14.44-2008 states in part:

    “All information contained in this Standard was documented in IEEE Std 200 (ANSI Y32.16), which was previously withdrawn. Due to the need for this Standard in the industry, it was agreed that it should be reestablished by ASME and a new subcommittee (Subcommittee Y14.44) was formed to carry out the development of a new standard under the ASME Y14 series of engineering drawing and related documentation practices.”

    It goes on to outline the significant changes.

  3. Thanks for the tip about ASME Y14.44-2008. I will check it out promptly. I knew COSJWT readers would provide more details on this topic.

    I have ordered my copy for review.

    Thanks again!!!!
    John (Admin)

  4. !!!UPDATE!!!
    Simpleman, thank you very much for the tip about ASME Y14.44-2008. I just received a copy and it carries forward the ideas expressed in IEEE 200-1975 very well and does so in an actively maintained document. Hurrah.

    The “Golden Rules” in the post above are re-codified in ASME Y14.44-2008 in Section

    This new document also makes reference to the still active IEEE 315-1975 for direction on which reference letter to use where for all your components in your assemblies.

    Thank you ASME. As an EE I am in your debt and will likely join your organization since IEEE let us down.

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