Knife Disconnects — A Neat Avionics Trick

March 2020 - I learned this nice little technique from an avionics tech who was doing some work on my RV-9A. It's hard to find really great methods of joining wires that don't become a reliability issue. My experience with plastic connectors has been the source of reliability problems that could have been avoided, so let me introduce knife disconnects.

A single knife connector.

Two knife connectors in the half-open position.

Knife connectors in the firmly closed position.

As you can see in the pictures, these connectors are designed to be crimped onto the conductor and snapped together, and they are extremely vibration resistant. The crimping is quick and easy, and the connectors can be disconnected as required. It would be normal to heat-shrink insulation over the joint, but my contact at Shenandoah Avionics, Todd Ott, suggested just tie-wrapping the ends of the shrink tubing, allowing the tie-wraps to be snipped off and the tubing to be slid back for servicing and disconnecting. That's a much easier job, no heat gun required, and the insulating tubing can be reused.

Knife disconnects come in different sizes and are colour coded: red for 16-22 AWG, blue for 14-16 AWG, and yellow for 10-12 AWG. At the time of writing, the red ones, which you are most likely to use in avionics, are 43 U.S. cents each from Aircraft Spruce. Buy some — you'l be glad you did.