Would twisting 3 wires together be as effective (or close) to a twisted pair?

Question

Would twisting 3 wires together like a twisted pair would be as effective as an ordinary twisted pair? Or at least a definite improvement to not twisting them at all?

^{simulate this circuit – Schematic created using CircuitLab}

I need to measure the current of each load and I can only do it near the voltage source. Although I plan to use an ethernet UTP cable of which I can just use another wire for a second ground. I am curious if a 3 wire twisted cable is as effective as the twisted pair or it might be not as effective but close.

Intuitively speaking it should still work because the EMI would still cancel out assuming the wires are twisted properly.

Answer 1

The effectiveness of a good twisted pair cable relies on these things to largely eradicate differential-mode induction: -

• What source feeds it and
• What receive circuit it connects to

So, if the send and return wires (and their associated transmit and receive circuits) don't present a balanced impedance to ground, then twisting is not effective at countering magnetic interference.

Intuitively speaking it should still work because the EMI would still cancel out assuming the wires are twisted properly.

1. The return wire will have less capacitance to ground hence it won't be balanced
2. The receive circuit input impedance is not balanced
3. The transmit circuit may not be very well balanced
4. Twisting by itself isn't a solution to electric field interference

You are probably wasting time twisting them under these circumstances.

Answer 2

For the cancellation of magnetic fields, you want to use machine_twisted wires, not human_twisted wires.

And dense twists --- many twists per inch --- are required, otherwise the field variations will not be cancelled.

And the imperfect alignment of the wires inside the field will not be uniform, so cancellation will not be perfect.

Again, use machine_twisted pairs, that have many twists per inch.