Solar consumption monitoring and CTs

Most solar inverters report how much they generate, but that only tells half the story. Consumption monitoring — powered by current transformers, or CTs — reveals what the home actually uses and how much of the solar is self-consumed versus exported. Here is how CTs work and what the data shows.

What a current transformer is

A current transformer (CT) is a sensor that measures the current in a conductor without any direct electrical connection to it:

• It clamps around a wire (it does not cut into it).
• The magnetic field from the conductor's current induces a proportional small signal in the CT.
• A monitor reads that signal and calculates power and energy.

Because CTs are non-invasive, an electrician can add them inside an existing panel without rewiring the circuits they measure.

Production vs consumption monitoring

The two kinds of monitoring answer different questions:

• Production monitoring — how much the array generated. Inverters report this natively; a dedicated production meter can too (see solar meters — production vs net).
• Consumption monitoring — how much the home used. This needs CTs on the main service conductors to capture total household load.

With both, the monitor can derive the full energy balance: generation, consumption, self-consumption, and grid import/export.

What the data reveals

Whole-home consumption data helps homeowners and designers:

• Self-consumption rate — how much solar is used directly versus exported, which drives the economics under many rate structures.
• Load shape — when the home uses the most energy, useful for battery and time-of-use planning.
• Verification — confirming the system performs as designed.
• Troubleshooting — spotting phantom loads or a failing appliance.

This granularity is a lighter-weight alternative to a full smart electrical panel, which provides circuit-by-circuit data plus control.

Where CTs go in the panel

CT placement determines what gets measured:

• Around the main service conductors (both legs of a split-phase service) for total consumption.
• Around the solar output conductors for production, when the inverter's own reporting is not used.
• Orientation matters — CTs are directional, so an installer follows the arrow toward the load to get the sign right.

Because CTs are installed inside the load center around energized conductors, this is work for a qualified electrician.

A note on accuracy

CT accuracy depends on correct sizing (the CT's amp rating should suit the conductor), proper seating around the wire, and correct phase association. A miswired CT shows negative or swapped readings — usually a quick fix by checking orientation and phase.

CTs turn a one-way generation report into a full picture of how a home makes and uses energy. Confirm CT ratings and placement against the monitor's instructions, and have a licensed electrician handle work inside the panel. Ready to plan a system? Try the DIY workflow or start at the home page.

Educational reference, reviewed 2026-07. A design aid, not a substitute for a licensed electrician or PE. Confirm the enforced NEC edition and local amendments with your AHJ.