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Pigtailing Electrical Cables

I've just read a Festo EMC Checklist guide which recommend the following:

Are cable reserves wound up as coils? If so uncoil, fold in the middle and wind back up doubled over (bifilar winding).

Does this mean that pigtailing cables is bad practice?

0 Simon Barker over 4 years ago
Pigtailing a wire can significantly increase its inductance, and so increase the impedance at high frequencies.

X = 2 π f L

X is impedance, f is frequency and L is inductance.

If you're concerned with EMC, then increasing the impedance may mean that your connection doesn't do what it was intended to - and I'm thinking about grounding connections particularly.
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0 mapj1 over 4 years ago

IF the cable is multicore and the 'flow' and 'return' currents are both in the same cable then the doubling back to create a non-inductive winding is not really a thing,

An enormous pigtail may be a problem, or if very high frequencies are being carried.
you may find the illustrations here of the radiation patterns from varying pigtail shapes interesting.

you should ride through the odd english of the text.

Mike
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0 Former Community Member over 4 years ago

To me “pigtails” aren’t what is in mapj1’s link.

I think of this more as an earth or bonding connection done like that in the picture on the web page in my link below.
https://www.connectixcablingsystems.com/ccs-server-cabinet-spares-supplies/41973-cabinet-earth-bonding-kit.html
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0 prephil over 4 years ago

Paul Skyrme‍ below is what I mean. I cam across the 2nd image in a CE marking book.
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0 Former Community Member over 4 years ago

I see what you mean now.

Very much a combination of the things that have been highlighted.

But yes coiling excess cabling is always a bad idea.
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0 prephil over 4 years ago

Maybe I was using the wrong terminology. Coiling is probably a better term. Thanks.
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0 mapj1 over 4 years ago

I'd treat with caution any electroncis book with mention of 'pig tale' in it.

If they cannot get that right, you wonder about the rest.

Roald Dahl's take on the "three little pigs"tail, or something like that.(*)

* Not a recognised EMC text ...

Mike.
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Pigtailing Electrical Cables

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