ATA 24-20, Shorted Power Feeder Wire

Found during engine change, shorted IDG power feeder wire. Approximately 20 inches away from IDG connection terminal. How this thing didn't cause a differential fault is beyond me.



A 1/0 cable splice and terminal were needed for repair. Some part number references.




This job required the use of a special hydraulic crimper.



The proper dies have to be used.



Just for reference, we found a oil soaked sheet in the manual for the crimper. This thing mentioned Eastern Airlines on it.



From the manual....

In our SPWM it states all engine wiring with damage must be replaced in it's entirety. I noticed you had 14 FT of cable. I watched the repair of an IDG cable using that hydraulic machine- pretty impressive.

New repair....

Splice of wire at top of pylon with hydraulic crimper.
  
     
  
Proper die for our wire (1/0).
  
     
  
Completed splice.
  
     
  
Reference for splices and tools.
  
     
 

We rejected the splice shown above.

The start of the crimp should have been at the serrated markings. We were about 1/8" of an inch off.
  
     
 

25+ years of aircraft avionics/electrical work..... "0" power feeder wire issues. Last 8 years..... 10+ power feeder wires.

Another one. PW 4000 on a 767. BPCU (Bus Power Control Unit) showing left DP (Differential Protection) Fault and Overlap Fault.

This particular problem reacted differently than most. Instead of just a generator disconnect, it dumped the whole left bus also. "THIS IS NOT NORMAL". The system should dump the generator feed and then the Left Bus Tie Breaker should have closed to feed power from the right to the left.

To isolate the issue we disconnected the three main feeds (and the smaller connections) from the generator breaker (upper left wires).
    
       
  
We disconnected the feed wires from the IDG and fed 1000V from the megger into each lead. As a note: when using the megger, all wires have to be isolated. If we megged forward from the IDG without disconnecting on the other end, we could fry some downstream components. Not so much the breaker itself, but the sense wires going to the BPCU and GCU (Generator Control Unit).

Anyway.....
  
      
  
This was at the pylon disconnect box at the top of the engine. What sucks here is that I was originally shaking the wires and my co-worker on the ground is hearing a buzz. I'm right there and I'm not (it sucks when your hearing is dropping off). After swapping positions, he saw the spark.
  
  
At the forward feed-through of the box is a flange with a short tube. Inside that tube there is supposed to be a thick rubber grommet to center the wires. Where's the grommet???
  
     
  
All items underlined are part of the grommet assembly. The nut and bolt on either end are tightened to squish the assembly inside the tube. With the rubber sealed against the inside diameter of the tube, all the wires are isolated from the edges.
  
     
  
We had one wire shorting on the tube. You can see a pile of molten metal below.
  
     
  
Flange replacement, new wire, and properly positioned grommet.
  
     
  
Removed wire and flange.