PVC Electrical Tape

[pmbrunelle]

I need to use PVC tape for a wiring harness project, so here I document my observations.

The application is for wire bundling/securing.

What I dislike the most about cheap hardware store PVC tape is that the ends peel off the harness over time, and it turns into a sticky gummy mess. My objective is to find tapes that are less prone to this sort of mess.

I selected two candidate tapes:
Tesa 4173 (because of good experiences with 51036)
3M Super 88 (seems to be a standard)
https://www.waytekwire.com/item/20927/T ... re--Tape-/
https://www.waytekwire.com/item/21008/3 ... cal-Tape-/

2020-12-02

I wrapped four 3" long strips of tape around a piece of welding wire. I did no special prep to the wire (no alcohol wipedown, etc). My hands were clean.

I cut the tape with scissors.

On the inboard tape strips, I was pulling on the tape with quite a lot of tension (tape was being stretched).
On the outboard tape strips, I was pulling on the tape with a small amount of tension.

Toonie for scale:

IMG_5565.JPG (443.25 KiB) Viewed 882 times

3M initial observations:
Glossy black finish
Very stretchy
Pretty thick film thickness
Very sticky/gummy. The roll of tape was stuck to the plastic package, simply with the adhesive that is on the side face of the roll.

Tesa initial observations:
Satin black finish (looks more like Fiero factory tape)
Less stretchy, will break with some amount of (reasonable) elongation
Thinner film thickness
Adequate, but not high stickiness

I left the wire+tape assy on my desk at room temp.

2020-12-05

The assy has been hanging around at room temp.

The highly-tensioned (inboard) 3M pulled back from its initial position.

IMG_5566.JPG (298.98 KiB) Viewed 882 times

The 3M adhesive residue was quite tenacious, though it did wipe off after many (perhaps 20) finger strokes.

The highly-tensioned (inboard) Tesa pulled back too, but less.

IMG_5567.JPG (283.75 KiB) Viewed 882 times

The Tesa adhesive residue wiped off easily.

The low-tension strips are mostly staying in place. Of course, best practice would be to leave the last half-turn or so untensioned, but that would not be a very severe test.

So far, I think I prefer the Tesa as a wire harness bundling tape, since it's less gummy. The thinner film thickness also adds less bulk, and keeps the harness more flexible.

However, if you're bad at planning splices and must seal a splice with tape, I think that 3M will work better.

I will keep the assy at room temp for a few more days before adding some hot/cold.

[ericjon262]

as I was getting close to the end I was going to ask about heat cycles, but I see that's on the to-do list still. Thanks for posting your observations.

[The Dark Side of Will]

What I dislike the most about cheap hardware store PVC tape is that the ends peel off the harness over time, and it turns into a sticky gummy mess. My objective is to find tapes that are less prone to this sort of mess.

So far, I think I prefer the Tesa as a wire harness bundling tape, since it's less gummy. The thinner film thickness also adds less bulk, and keeps the harness more flexible.

However, if you're bad at planning splices and must seal a splice with tape, I think that 3M will work better.

I hate dealing with old electrical tape. That's my least favorite aspect of reworking harnesses... just staying sticky for the entire duration of the job.

Sometimes more is not better.

This may make you cringe, but if I have several points to connect, for grounds or the ECM 5V supply to various sensors around the engine bay, I'll just daisy-chain them and double-stuff the pins (typically using pins for the next larger wire gauge range) instead of making a splice. If convenient, I may even bring the last one back to the first, making a loop to mitigate the extra resistance of the daisy chained circuit.

[pmbrunelle]

I hate dealing with old electrical tape. That's my least favorite aspect of reworking harnesses... just staying sticky for the entire duration of the job.

I always keep some BASF Limco 203 wax and grease remover in stock to wipe down parts before paint.

I decided to try the 203 (poured onto a paper towel) on wires covered in old electrical tape nastiness. It cleaned off the goo easily. I imagine that other solvents could work (aromatic hydrocarbons?), but I haven't tried others.

This may make you cringe, but if I have several points to connect, for grounds or the ECM 5V supply to various sensors around the engine bay, I'll just daisy-chain them and double-stuff the pins (typically using pins for the next larger wire gauge range) instead of making a splice. If convenient, I may even bring the last one back to the first, making a loop to mitigate the extra resistance of the daisy chained circuit.

Splices remain weak points, so if you can avoid doing them in the harness, that's a good thing.

For connectors with cable seals, double-stuffing obviously won't allow for a good seal, but for unsealed connectors, I don't see the harm.

Stock Fiero has two wires going into one terminal at the fuel pump / AC relay socket IIRC. The two wires are placed side-by-side into the crimp terminal. Each side of the strain relief portion of the terminal is curled over one wire. Whatever you do, the important thing is that both wires are secured by the strain relief, and that when the wire is pulled on, you're not pulling on the actual conductor crimp.

As you've figured out with crimps, it's based on the cross-sectional area of the conductors.

Daisy-chaining can be OK, but you have to keep in mind that as device A on the daisy-chain draws more or less current, this will vary the voltage seen by device B. Refer to common-impedance coupling.

I do not really like the idea of "closing the loop" with that last run of wire. What you're doing is creating two parallel paths for the electrical current. In a manner of speaking, this creates a "statically indeterminate" circuit, where the path of the current cannot be determined by simple logic. Instead, the amount of current flowing through each branch depends on their resistances.

It is difficult to study/understand your harness if you don't know where the currents are flowing... I would not complicate my life with a statically indeterminate harness without some good reason to go that way.

[The Dark Side of Will]

Lol... in the case of the 5V devices fed from the ECM, I don't even know how much current each one wants.

What you can say about a loop is that, relative to a daisy chain, two parallel paths to each device means that the resistance and voltage drop between that device and the voltage source is less.

Thanks for the info on solvent.

[pmbrunelle]

They actually did ring circuits in UK house wiring in WW2 to save copper.

The ideal power distribution scheme to prevent common-impedance coupling is to use a star distribution scheme, with one wire per device. However, that will be too bulky. As a reasonable compromise, I suggest splitting the 5V near the ECU into digital (switching crank and cam sensors) and analog (temperature, etc) wires. Likewise for grounds, if you don't already have dedicated pins.

Digital devices changing state can be noisy.

With small current consumers, wire gauge is more determined by connector compatibility and robustness.

Consider a voltage signal that must be transmitted from a sender to a receiver:

Loops.png (18.25 KiB) Viewed 760 times

Any (changing) magnetic field lines that pierce the enclosed area will induce emf, which will be superimposed on the useful signal. Reducing the loop area minimizes the chance of the loop "catching" field lines. For something really important, you can twist the wires together.

The logic also applies to aggressor wires; in general you want to have two wires, each carrying equal currents in opposing directions, laying close to each other. Having a well-defined path for your currents simplifies this task... The closer the wires follow each other, the better the magnetic fields of each conductor will cancel each other. Again, twisting can be applicable.

So as a general guideline, we should seek to minimize loop areas for our circuits, if we want to reduce noise coupling from one circuit to another.

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I will point out that I am a noob in harnesses, as you could see by me not even knowing what tape is good to use. I have mostly worked within a single module, containing multiple PCBs, and on the PCB-level. I figure that the general principles remain applicable to harnesses.

I suggest this book for reading:
"Electromagnetic Compatibility Engineering" by Henry Ott