Split-Phase Energy Monitoring for North American 120/240V and 120/208V Systems

Monitor 120/240V and 120/208V Split-Phase Systems with IAMMETER Understanding 120/240V and 120/208V Systems The Challenge: Monitoring Both Grid and Solar New Feature: CTCratio How to Set CTCratio Installation Example Why Use IAMMETER's Three-Phase Energy Meter for Split-Phase Monitoring Conclusion About IAMMETER Solutions Products System

Monitor 120/240V and 120/208V Split-Phase Systems with IAMMETER

Monitor Split-Phase 120/240V and 120/208V Systems with three-phase Wi-Fi energy meter from IAMMETER can be easily adapted to monitor North American split-phase systems, including both 120/240V and 120/208V configurations. With the introduction of the CTCratio parameter, users now have an efficient way to monitor solar inverters and grid connections with minimal wiring.

Understanding 120/240V and 120/208V Systems

These two common North American systems are:

120/240V split-phase: A single-phase 3-wire system with two hot wires (L1 and L2) and a neutral. The voltage between L1 and L2 is 240V, while each hot wire to neutral is 120V. The two hot wires are 180° out of phase.
120/208V configuration: A two-phase section of a 3-phase system, where the two hot wires are 120° out of phase.

Both systems are widely used in residential and light commercial buildings.

The Challenge: Monitoring Both Grid and Solar

To fully monitor the bidirectional flow of energy between grid and solar in a split-phase system, ideally four current channels would be required. However, in most practical cases, the output of a solar inverter is nearly symmetrical between both legs, making it possible to estimate the total output by measuring just one leg and doubling the reading.

New Feature: CTCratio

The CTCratio setting allows you to automatically double the readings from Phase C of the IAMMETER's three-phase energy meter.

This method works because most split-phase inverters output balanced power across the two hot wires. In a typical 120/240V or 120/208V split-phase system, the inverter produces equal current and power in both legs (L1 and L2). Therefore, by monitoring just one leg and doubling the reading, you can accurately estimate the inverter’s total generation output. This is especially useful when Phase A and B are used to monitor the grid legs, and Phase C is connected to one leg of the solar inverter output.

By setting CTCratio = 2, you effectively double the current, active power, and energy (kWh) readings of Phase C, giving you an accurate estimate of the total solar production.

How to Set CTCratio

Default value: CTCratio = 1
To double Phase C readings: http://<meter_ip>/api/ctcratio?x=2
To reset: set x=1

📘 More on CTCratio in our documentation

Installation Example

Use Phase A and B of IAMMETER's three-phase energy meter to monitor the two grid lines (L1 and L2).
Connect Phase C to one leg of the solar inverter output.
Set CTCratio to 2.

This setup allows full bidirectional monitoring in 120/240V or 120/208V systems with just one IAMMETER's three-phase energy meter energy meter.

Why Use IAMMETER's Three-Phase Energy Meter for Split-Phase Monitoring

✅ Compact DIN-rail design for easy installation
✅ Works in 3-phase, split-phase, or three single-phase mode
✅ Built-in Wi-Fi with Modbus/TCP, MQTT, and RESTful API
✅ Open API and support for local or cloud-based integration
✅ Cost-effective and flexible monitoring solution

Conclusion

With the new CTCratio feature, IAMMETER's three-phase energy meter becomes an even more powerful tool for monitoring split-phase systems in North America. Whether you're tracking grid usage or solar generation, this setup simplifies wiring and provides accurate real-time data.