Comments on: Coiled mains cable heating and inductance

By: Tomi Engdahl

Tomi Engdahl — Sat, 06 Sep 2025 06:08:07 +0000

Do figure 8 actually works?

Figure 8 is like two coils that create opposite direction magnetic fields. On distance those will cancel significant part magnetic field. On the neat field not so much, because quite weak magnetic field connection between coils.

let’s analyze figure 8 and single coil. Figure 8 is like two coils. Let’s think the diameter of single coil and one side of figure eight are the same. If there is N winds in figure 8, there would be 2×N turns in single coil. If the inductance of one half of figure 8 is X, then inductance of whole figure 8 would be around 2X. The inductance of all in single coil would be about 4X. The figure 8 would have more surface area and less winding layers on most parts (in the center when cables cross more space for air) so resistive heating can escape better. Yes figure 8 can offer some help.

By: Tomi Engdahl

Tomi Engdahl — Sat, 06 Sep 2025 05:41:17 +0000

In typical speaker cables have signal going and coming back on wires inside same cable. The magnetic fields of both wires cancel each other pretty completely, meaning coiling does not create much inductance for speaker signal. The resistive heating at high with lots of cable in tight space does not allow enough cooling still applies. If you want low pass coil, wire just + side through your coiled cable and connect the – side through short wire outside the coil. Now you have inductance and magnetic fields.

By: Tomi Engdahl

Tomi Engdahl — Sat, 06 Sep 2025 05:10:03 +0000

They also say to uncoil your audio cables to avoid picking up interference. Antennas are made by wrapping wire into loops similar to electromagnets. A messy pile will perform better than a neat coil.

Depends on the cable. That is why some cables are twisted and shielded to cancel that effect.

Shielding and twisted (balanced) cables are better at high frequency noice.
But any cable will pick up noice and/or degrade signal of improperly handled.

By: Tomi Engdahl

Tomi Engdahl — Sat, 06 Sep 2025 05:04:20 +0000

AC with the nuetral and hot in the same cable , cancel each other as they are exactly out of phase , the issue is when the cable is coiled , it cant dissipate normal heat buildup . If you want a magnetic field , you need the single conductor in a coil .

By: Tomi Engdahl

Tomi Engdahl — Mon, 04 Nov 2024 05:01:39 +0000

Looping cable does not create extra resistance that causes wire heating to begin with. The small inductance added by coiling cable does not increase cable heating.
Tightly coiled cable just prevents the resistive heat from the cable to escape efficiently – cable heats up – heating up causes the copper wire resistance to increase slightly.

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By: Tomi Engdahl

Tomi Engdahl — Mon, 08 Aug 2022 13:35:10 +0000

Tomi Engdahl Good write up. Except one point about the 20W lightbulb – that energy density in W/m2 is a lot higher then the actual cable itself so the temp rise on tehinsulation is not much. And cable ratings in free air are usually fairly generous. Heating effects from regular coiling and or fig 8 coiling doesn’t matter much unless the whole cable is ennclosed /under a carpet etc etc.. PVC cable is the real risk as the cores start to migrate once the cable temp gets to about 60 to 70 deg C especially on tight bends. Rubber cable not so much. That is a real thing and have seen it happen.

By: Tomi Engdahl

Tomi Engdahl — Tue, 07 Dec 2021 10:11:01 +0000

How to Correctly Fig 8 Wind a Cable and it is not a Straight Figure 8
https://www.youtube.com/watch?v=jgq8-4m133o

It can desirable to wind a cable in a figure 8 to reduce inductance related heat in power cables, to fit a large cable in a case, or to reduce inductance related signal degradation in audio cables to name a few.

Turns out that winding a straight figure 8 is not optimal and does little to nothing in altering the inductance build up compared to a coiled cable. In this video you can hear the effects of inductance build up of coiled and Fig 8 cable as well as see it on an analyzer. I will also show you how to wind a cable figure 8 (perhaps better called a figure 80) such that there is little to no inductance build up.