Wire Bending Standards / Strain Relief

[Transient1]

Hi,

I'm looking for a standard for instituting strain relief into a wire. I've looked through the NASA workmanship standards and I can't find anything explicit. For example with sheet metal, I've heard a general rule that bend radius must be greater than 1.5 times the thickness.


What is the rule for wire?
What is the general spec for sufficient strain relief?

The situtation is a wire soldered to a pin that goes up through a fixed point in a panel. The panel flexes and so the connection between the panel and the pin must have adequate strain relief.

 

[swall]

What kind of wire? Electrical? Structural?

 

[Transient1]

Sorry, the wire is electrical wire (26 AWG).

 

[IRstuff]

Insulated? or not?

In any case, MIL-STD-454 isn't any help, "prevent undue stress."

If the flex is a LOT, then as much service slack as practical to prevent fatigue. Copper tends to work harden. Oxygen-free copper is supposedly more robust.

TTFN

FAQ731-376

 

[Transient1]

The wire is insulated. The deflection is actually almsot negligible. It is my belief that as long as the connection between the fixed point and the moving panel is not a perfectly straight run (slight C-Shape) that there is adequate strain relief, yet there is an argument about how much is necessary. I may just have to run a set of analyses with wires of different curvature. Thanks for the help.

 

[IRstuff]

The answer to that question depends on the expected life of the cable, i.e., how many cycles of deflection does it need to tolerate?

As a data point, we built a flex cable with a 2" diam service loop for a rotary joint application using standard copper wiring that lasted about 100k cycles. Unfortunately, that represented only about 50 hrs of operating time. So the OFC high-ductility wiring was used in its place and the cycle lifetime was in excess of 10 million, making the system viable.

TTFN

FAQ731-376

 

[Transient1]

It needs to surive 72,000 cycles with 1 mil deflection linear deflection.

 

[IRstuff]

Over what length?

TTFN

FAQ731-376

 

[Transient1]

The linear distance between the solder point and the fixed point on the panel is 0.109.