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Comment by sdfjkl | Hacker News Reader

The problem with these laced harnesses is the same as with zip-tied ones - you can't add or remove anything (without destroying it or making a mess of it, unless you re-tie/lace everything), and that it's difficult to use the simplest and fastest method of wire tracing, which is tugging on it and seeing where it goes.

Therefore the currently best method is IMHO a slotted wire duct. Put the cover on and it's neat and tidy, but easy to pull the cover off, add or remove wires and trace where they go.

That's probably why that method is now industry standard.

Example here, with cover on in the middle and covers removed top and bottom: https://blog.hellermanntyton.de/wp-content/uploads/2017/01/P...

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Another downside to it is EMI. tying all the wires tight together increases the odds of any EMI problems vs letting them be loose in the wire duct.

In a previous CNC machine, I zip tied everything together very carefully, but was getting phantom steps in one of my steppers (even with shielded wires). Unclipping the zip ties caused the problem to go away. (after that, I added plenty of ferrites, too, as a measure of safety, but clipping the zip ties killed the only real symptom)

One other way to solve this is to:

- use EMI sheilded conductors (at greater expense), or

- use twisted pairs where applicable.

I believe the CAN standard is based on twisted pairs, and they work very well for other ground/signal based configurations.

I had actually used EMI shielded wires - but, I think I must have had a faulty connection from shield to ground. Practically speaking, EMI shielding is hard to get right if you're not a pro. I only recently got an Oscilloscope and was able to measure what the EMI noise actually looks like on a wire. That helped a lot in getting rid of it, too. VFDs are pretty awful - the one in my machine nominally outputs 8amp,220v, 500hz power, containing that is a matter of extreme care. My previous CNC (now sold) really just didn't make any attempt and just counted on physical separation of wires and software filtering of signals.

CAN uses a differential pair which is the way to go. EMI will drive the pair in the same direction. Also used in USB, RS-485, pci-e, hdmi, etc.

You don't really have to twist them but it is best practice.

Also heat. Wires bunched up tight can’t cool themselves down as well.

If heat is an concern, you'd probably want to spec a thicker gauge wire.

Yes, but (especially when Cu and Al are pricy) being able to use a thinner gauge can be a big benefit.

Regardless of wire gauge, bundles of wire noticably reduce your heat dissipation ability and therefore reduce your safe current carrying capacity accordingly. That's why electrical code significantly de-rates the current capacity of circuits which run more than just a few conductors in a single conduit or through the same hole.

Had a similar problem on a stepper motor motion control system in a vacuum chamber. The single electrical feedthrough forced motor and signal cables to be in close proximity. The pwm noise from the motors would couple to the opto isolated limit switch signal and force the limit switches on. I solved it by putting 10k pull down resistors with a bypass capacitor to ground on all the inputs. Phantom stuck limits were no more.

I’ve found recently that ferrites really help with this. The electrical noise from large steppers is really erratic, but responds well to ferrite beads with 2-3 wraps. I put one at each end of the cable, since back-EMF is very real in large steppers.

Yes, this technique is not appropriate where wires are added or removed frequently. It's appropriate where you need extreme density, or inside portable equipment where wires not secured to each other may abrade each other.

I learned cable lacing in the aviation world. It is not uncommon to add a certain amount of extra (spare) cable runs to a loom for future use, you can also easily add cables to the outside of a loom.

The tug method of tracing still works, you don't want to tie your looms that tight, your lacing (same with zip ties) will cut into the insulation over time.

Schematics show you where a wire begins and ends. Wire ducts with no covers so people can ‘trace’ wires is a sign that either a) they don’t know how or can’t be bothered to read schematics or b) poor maintenance practices such as making modifications and not updating the schematics.

Wire ducts are popular because they are faster to make a bundle and put it in a duct and not worry about exactly how it looks, but our panel shop is still zip tying wires in bundles that behind and end in the same general vicinity to keep the wire ducts tidy in large panel line ups - say 5 cells each 1m wide.

Yes I use velco ties for that reason.

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