Wiring connector keying / clocking assignments 1

[kontiki99]

Does anyone know of any rule of thumb conventions or systems airframe OEMs use for picking or tracking wiring connector clocking in areas where large arrays of same size connectors are installed?

 

[FieldTeam]

SAE-AS 50881C
Connectors used to provide separation of or connections to multiple electric circuits in the same location shall be installed so that it will be impossible to mate the wrong connector in another mating unit. It is preferred that wiring be routed and supported such that an improper connection cannot be made. The order of precedence for making the connector selection for a multiple connector location shall be as follows:
a. First, the connectors shall be different sizes or have different insert arrangements.
b. Second, the connectors with the same insert arrangements shall have alternate insert positions or keying positions.
c. Third, if none of the above requirements can be met, identical connectors shall have color coded sleeves attached to the wiring near the connector which identifies the associated connector mating half. In cases where one of the connectors is mounted, the connector shall be coded by a color identifier on the adjacent structure.

 

[kontiki99]

Thanks FieldTeam,

I don't get enough exposure to design specs in the airline world.

 

[IRstuff]

Weird, though, since the basic requirement for not being able to incorrectly connect connectors is in most military/aerospace contracts.

The other thing that you need to make sure is that your array of connectors are not so tightly packed to make mating difficult or slow, since any time delay may cause the maintainer to hurry and not pay attention to the color coding and stuff...

TTFN

FAQ731-376

 

[kontiki99]

This topic comes up for us because we're making extensive modifications to aircraft that have been out there for a while. On a mod to standardize a system, it makes sense to install new harnesses & connectors in unused locations. The plate on the back of a 757 electronics shelf is typically three rows of maybe 20 connectors. Boeing probably used a system for tracking their connector choice, but we have no real way of fitting in or even detecting a pattern without doing a prohibitive amount of research.

On the other hand multiple connectors usually wouldn’t be removed unless you were removing the shelf. Any time I disturb a connection, I call out a Return To Service check to verify everything’s gone back together properly anyway.

 

[MikeHalloran]

I got a quiet laugh out of FieldTeam's mention of SAE-AS 50881C. One time I worked for an outfit that went all the way to paragraph 'd'... or maybe it should be 'z'.

We were only making four (complex) systems, with units coming from two locations. What could possibly go wrong?

In order to save money, we only used white wire. With heat-shrink sleeves, nicely stamped with each wire's designation. Okay, not so bad.

Also in order to save money, 'we' ordered the five big, many-hole, system harness connectors with identical keys. Color coded sleeves, right? Nope. Hot-stamped reference designators, black on white, easy enough to read.

This is where we went off the track. Remember, the major units came from different companies at different locations. Clearly documented, somewhere, was the fact that the connector on the harness from Unit 1, marked P1, was supposed to be plugged into the socket on Unit 2 marked J3, and conversely, or something like that, because of some design change or early screwup that would have been expensive to fix otherwise. All the EEs knew about it, and their managers had signed off.

At System Integration time, however, they were short of bodies, and enlisted one of my ME friends, who logically put P1 in J1 and conversely. ... which connected a really stiff +5 supply to ground, in a loop that ran through >every< harness.

Yep, saved a bunch of money there...


Mike Halloran
Pembroke Pines, FL, USA

 

[kontiki99]

That's interesting Mike.

The vast majority of the wire I see is white with stamped numbers. There are all sorts of special cases and exceptions where standard colors are used, but given all the wires in a large aircraft, proportionally it's not many.

One thing we do now after all the connections are made and the continuity checks complete are power/ground checks (with no LRUs installed.

Only after we know that grounds are in fact grounded and power is only where it belongs (this is on the connector at the back of an equipment tray) do we install black boxes (LRUs in our world) and attempt to power up the system.

So far we haven't let the smoke out. We're installing glass cockpits in a fleet of 757s with about 20 or so supporting system standardization mods.