When, But Mainly How, To Use Shielded Cable

To Start

You have likely heard the term 'shielded' wiring/cable, perhaps you have even used it on your project. What makes it so special and what are the best practices to employ while using it?

Shielded cable comes in a variety of types though we exclusively use and sell either TE Spec 55 or a specific M27500 cable. I say specific because the part numbers can be up to 15 alphanumeric digits long! The wire size, shield coverage and style, base wire specification, internal wire colors, outer insulation material and ratings, and more are determined by this compiled part number.

Shielded cable is most often used on low voltage data signals that are most susceptible to 'noise'. Think of this as wanting to keep noise out of said circuits.

In a standard motorsport application, your most common source of noise will be EMI (electromagnetic interference) which is most often generated by your ignition. In fact, it's been argued that the actual source of the 'noise' is from the spark crossing the spark gap from the central electrode to the 'ground strap' or ground electrode. 

Another use of shielded cable is on high voltage signals, think of a CDI (capacitive discharge ignition), and wanting to keep noise in within these +400V circuits.

The shielded cable we rely on features a round fully woven braid with 85% coverage of tin-coated copper. Quadrax features a dual shield construction, with a 90% wide woven inner braid and a 85% woven braid on top of it.

This cable has an outer jacket made of extruded ETFE that can be very difficult to strip without the proper tool. More importantly, using a freehand blade is dangerous. If you don't cut yourself you could very easily damage the shield and conductors laying underneath. Stripping tools for this use range from $125 to many thousands. Historically, the tried and true Ideal Ringer Tool is hard pressed to be beat for most instances. Repeatable strip lengths can be had with the optional Wire Stop. Important to note, there are (16) different blades specific to the wire type and insulation thickness. What we offer on our site suits 20-26AWG variations of the cable we offer. If you are working with a specific cable, we can even supply the correct blade for the application if you need.

Steps To Follow
Presuming you are using M2279/32 wire and it's M27500 cable or TE Spec 55, M83519/1 or M283519/2 shield terminators, and the Ideal Ringer Tool

1. Use an appropriate stripper such as the linked ringer tool above and set your strip length with the wire stop. Gently squeeze the tool so it compresses over the outer insulation and rotate 4-5 times.
   
   You will see a very light score mark, and that is all there needs to be. Use a slug remover pull off the outer insulation jacket.
   PIC COMING
   
   
2. Dependent on the application and scenario, you have three options from here when doing an end strip. Regardless of the approach you prefer, I recommend putting your shield terminator/solder sleeve on before going forward. I personally prefer the solder sleeve variation with a pre-installed drain wire, but the S01-05-R leaves a lot of room for packing multiple cables if you're crafty.
   PIC COMING
   
   

   Option A

   • Using a flush cutter, trim the shield down to be ~.375"-500" from the outer insulation.
   • Place the sleeve's solder ring center to your exposed shield, insert your drain wire, and heat until fully recovered. 
     PIC COMING
     
   
   Option B

• • Using a flush cutter, trim the shield entirely down to become even with the remaining outer insulation. Focus on cutting away from the wire, working slowly while circling the cable and trim flush.
  • Set the wire stop ~.375" to .500" longer than you had it for the first outer jacket strip and repeat the same process. The result will be a short piece of outer insulation to remove and a perfectly flush cut shield ready for termination, no freehand trimming required.
  • Place the sleeve's solder ring center to your exposed shield, insert your drain wire, and heat until fully recovered.
    PIC COMING
    
    JV Tip:The red dye thermocromic indicator will not always completely disappear, focus on ensuring the solder is fully wetted and no wire strands puncture the blue sealing sleeve after recovery.
    

          Option C

• • Using a flush cutter, trim the shield down to be ~1.50" to 2" from the outer insulation.
    
  • Fold the shield over the outer insulation, and then add another .375" - .500" and trim here. Place the sleeve's solder ring center to your exposed shield, insert your drain wire while favoring the end of the insulation, and heat until fully recovered.
    PIC COMING

What's Next?

The all important part, what are you actually supposed to connect this to? First, do not perform the above steps on both ends of the cable and connect each end to a ground of any type. Doing this will negate any/all benefit of using this material to begin with. 

The shield drain needs to reach a ground plane, and yes there are different types. There is a lot of information to consider here, and many manufacturers have specific, and conflicting...and confusing, ways of doing this. It may even become a forthcoming blog post on it's own, but presuming you are dealing with a manufacturer and device that have a dedicated shield ground pin (as they should), you will need to connect this wire(s) here on it's own. Plural in the event you have multiple shielded cables landing at the same point and shield drain destination.

This should be done as physically close to the device as possible. Consider all of the following variables before approaching this correctly as many manufacturers seem to get a bit careless when compiling pinout assignments. How many different connectors are shielded cables connected to? Are there multiple shield drain pins on each of the connectors I am connecting to? Do I need to provide or run a feeder wire from this termination? Have answers for all of those!

Not planning out the above is the equivalent to end up missing a single wire in your harness. That's because the shield needs to be considered as it's own wire, with just as much purpose as a fuel pressure sensor's signal wire.

Part 2 - Soon?
I'm not a writer, just a guy that likes to build looms. If you have any topic requests, feedback, or this helped you...leave a comment.