What is a Current Transformer (CT Clamp)?

Definition

A current transformer (CT) clamp is a device used to measure the flow of electric current through a conductor without physically disconnecting the circuit. In EV charging, CT clamps provide real-time current data, enabling safe load management, energy monitoring, and integration with renewable energy systems.

Why CT Clamps Matter

CT clamps are critical for ensuring charging does not exceed the available electrical capacity of a site. They allow chargers to intelligently adjust output based on household or facility demand. For solar-integrated systems, CT clamps detect excess solar energy being exported to the grid and redirect it to EV charging, maximizing self-consumption and reducing electricity bills.

How it Works

A CT clamp encircles a conductor, inducing a proportional current in its secondary coil without breaking the main circuit. The charger or energy management system interprets this signal to monitor live load, automatically reducing charging speed or pausing sessions when demand nears the supply limit. Multiple CT clamps can monitor different energy flows such as grid import, solar generation, and EV load.

Key Technologies / Features

CT clamps vary in size and accuracy, from simple analog models to digital sensors integrated into smart meters. Advanced systems use bidirectional CTs to detect both import and export, enabling intelligent energy diversion. Integration with OCPP backends allows CT data to feed into broader energy management and smart grid operations.

Applications

• Residential chargers using CT clamps to prevent fuse overloads.

• Solar homes diverting surplus PV electricity to EVs.

• Commercial depots balancing multiple chargers on limited supply.

• Utility programs monitoring EV load for demand response.

Benefits

By enabling dynamic control of charging current, CT clamps help avoid expensive grid upgrades, improve energy efficiency, and enhance charging safety. They also provide valuable visibility into energy flows for both consumers and operators.

Use Cases

In homes with limited capacity, CT clamps allow 7 kW chargers to operate safely by dynamically reducing current when appliances are in use. In solar-powered homes, CT clamps ensure excess PV is consumed by the EV instead of exported. Fleet depots use CT-based load sharing to distribute available capacity across vehicles.