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Star Discuss Watch

Acquiring the Hardware

Table of Contents

Here’s a quick summary of everything you’ll need:

Some of the links below are Amazon Affiliate links, and purchasing the items through these links help support this project.

Purchasing items directly from my shop in the links above allows me to continuously maintain this open source project, work on improvements, and provide user support. I am very thankful for your support!

Selecting CTs

With the list that you’ve written down from the previous step, you should know the ratings of the circuits you intend to monitor.

When choosing a CT, select a CT with a rating that is at or slightly above the rating of the breaker. The diameter of the CT opening increases as the rating of the sensor goes up. Here is a quick summary:

  • 20A - 60A: 10mm
  • 100A - 120A: 16mm
  • 150A - 250A: 24mm

It is possible that a conductor is too large for the sensor according to the breaker rating, so you should also have the electrician double check the diameter of each wire that you want to order and make sure the selected sensor will fit.

Continuing the example from the planning section… I would purchase the following to meet the requirements, after ensuring the conductors will fit the diameter of the CT sensors:

Mains: 2x 200A sensors

Solar: 1x 100A sensor

AC Unit: 1x 30A sensor

Master Bedroom: 1x 20A sensor

EV Charger: 1x 60A sensor

Using a third-party CT

The CTs in my shop are manufactured specifically for my project. It is possible to use other sensors, but it’s not always ideal. If using a sensor you have on hand, it should be of the “current-output” type with a maximum output of ~50mA. If your sensor is the “voltage-output” type, the ideal (and absolute maximum) output is 1.65V. Do not use a sensor that puts out 5V as this will likely cause damage to the ADC.

9V AC Supply

The 9V AC to AC transformer provides the grid voltage reading to the power monitor. It does not power the Raspberry Pi. I only stock North American compatible AC transformers, so if you have a different grid, you’ll need to source one yourself. The required specs are:

Output: 9V AC, at least 100mA.
Plug type: 2.1 x 5.5mm, center positive


Once you have your Pi and microSD card, you can move onto the software.