Advice for wiring/soldering your own CT cables?


I would like to wire up some solid-core CTs for Iotawatt.

I’m using the Talema AZ-0500 CT (datasheet).

For the TVS diode, I’m using a P6KE6.8CA kindly donated by Bob some time back. (datasheet). It’s all-black, so it’s definitely the bi-directional version.

For the cable, I’m using a 0.5m long 3.5mm to 3.5mm TRS stereo plug cable which I will cut in half, to create two cables.

First question, I wanted to confirm - using a butt connector and crimping onto a component lead (e.g. for the TVS diode) is a big no-no, right? (Context - I don’t trust my soldering skills as it’s been a while).

I saw the NASA wiring standards guide mentions:

Crimping of solid wire, component leads, or stranded wire that has been solder-tinned, is prohibited.

However, I wasn’t sure if this was just NASA being held to higher standards, or if it was completely frowned upon practice for any electronics? (I assume it’s due to mechanical stresses, and the chance of breakage at the joint, right? Because you can’t displace solid wire/component leads like you can with stranded wire? Or is there another reason?)

Second question - does polarity matter here for the 3.5mm cable to the CT?

I assume I wire from the T and R of the 3.5mm cable to the yellow and black cable on the CT - does it matter which one to which?

And does it matter which leg you put the TVS diode on?


This recent post covers most of your questions: YHDC SCT006 Cable Extension - #4 by wwk

Solder or crimp I have no expert advice to offer.

Thank you for the link!

I’ve started trying to make my own - forgive the poor soldering technique:

One issue I have is - many of the 3.5mm leads I’ve purchased have the shielding wrapped around both wires, with no insulation:

For IotaWatt, my understanding is we need tip and sleeve - tip is usually the black (or white) wire, and sleeve is the shielding wrapped around both wires. (I assume there’s a technical reason we use tip and sleeve, as opposed to tip and ring?)

I’ve worried about shorts, when I wire it up to one side. Do you have any advice? (Aside from I guess, just wrapping lots of electrical insulation tape around - which sounds like it would be very messy).

I’ve used heat shrink tubing + tape so it is still messy. :slight_smile:
Now I would use different sizes tubes (small diameter for solder joints and big for the whole tvs+joins bundle).
Happy to learn any other ideas.