Electronic – Should neutrals be tied together or left separate

“Persons were charged with stealing electricity by placing a large coil, somehow, near high voltage AC transmission lines.”

Is this feasible or was it perhaps an April fool’s article that I swallowed hook line and sinker in my youthful naivety.

Entirely feasible.
Farmers were occasionally charged with power theft in this country (New zealand) in the past. I haven;'t heard of a case in a decade or few - maybe they are getting cleverer at it :-).

This is the same principle as used for "IPT" / "Inductive Power Transfer as seen in phone chargers, industrial monorail powering, electric vehicle charging and much more.

I started to say that if the pickup coil was symmetrical with respect to two phases that were perfectly balanced that you'd get zero pickup, and then suddenly realised that I've always done IPT with essentially a single phase, and that with a 3 phase system with 120 degrees phase separation you should get the advantage of the full load current even if the two phases were fully balanced.

You are essentially getting fields produced by the current, not the voltage, and the voltage is essentially irrelevant as long as you observe the normal conventions that apply to any other dealing with xxx kV.

Energy Harvesting from Electromagnetic Energy Radiating from AC Power Lines - FAR more energy can be obtained than they achieve.

Worked example - I suspect some of the conclusions are suspect A Solution to the RWP for Exam 1 - Stealing Power

Low technical content - high relevance

Directly relevant but low technical value Electromagnetic Harvesters: Free Lunch or Theft!

Several related stack exchange questions with variably useful content.

• How would an electric company detect wireless theft of electricity?

• https://skeptics.stackexchange.com/questions/3520/is-it-possible-to-obtain-current-indirectly-from-power-lines

• Stealing energy from radio towers or power lines

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Online vehicle transfer - I do not have access to this paper but it is probably at least relevant as it will have examples of dual linear conductors and a pickup coil.

Mythbusters getting it wrong

Related:

Industrial monorail

Maximising transfer

Capacitive - but impressive:

The VERY old solution to this problem uses two resistors and a neon bulb.

I used to use a NE-2 bulb with 2- 100k resistors. One side of the neon bulb goes to Neutral. The other side of the neon bulb goes to one side of both 100k resistors. The other side of each resistor goes to the two switch legs.

The circuit makes use of the relatively high threshold voltage of the NE-2 bulb. This about 65 Volts AC.

When the switches are in a position that does NOT turn the lamp on, one resistor has 120 Vac applied, the other resistor is near 0 Vac. The neon bulb is NOT lit because the voltage across the bulb is less than the threshold voltage.

When the switches are in a position that causes the lamp to be lit, one of the 100k resistors is at 120 Vac, the other resistor is floating (not connected to anything). The neon bulb then lights.

You can place this circuit at each switch location. I used to drill a 1/4" hole in the cover plate and use silicone sealant to glue the neon bulb laying across the rear of the hole.

Note that this circuit also works with 4-way switches.

EDIT BY RYAN: added a schematic... Does this correctly show what you were discussing?

[Dwayne] Yes - exactly. In older houses without a neutral wire in the box, we would use appropriate voltage-rated resistors, then connect the Neutral side of the neon bulb to metal box so as to use Earth ground instead of Neutral. The Electrical Inspectors were okay with that because the current was so low (about 0.5 mA).

^{simulate this circuit – Schematic created using CircuitLab}