Why is insulation monitoring needed in DC charging?

First define the DC circuit being monitored

In DC charging, insulation monitoring tracks the insulation resistance between the live conductors of the unearthed DC circuit and earth. Deteriorating insulation produces an alarm for the charging control system to evaluate. However, the station's DC output, charging cable and vehicle high-voltage system do not form the same electrical boundary in every operating state. Contactor positions and galvanic separation change which section is included in the measurement. Rather than considering voltage range alone, the precharging, connection and energy transfer states must be defined together.

This is different from AC residual current monitoring

Residual current sensors in AC charging assess the sum of currents through the monitored conductors and are used with suitable protection and switching arrangements. A DC-sensitive sensor still performs this current measurement. An IMD, by contrast, determines the insulation resistance of the unearthed DC system using an active measuring method. An AC-side residual current sensor therefore does not automatically provide the required insulation monitoring at the DC output. Nor does an IMD alone fulfil every protection and disconnection function in the installation.

DC in RDC-DD refers to the DC residual current component detected during Mode 3 AC charging. This differs from the IMD function that monitors insulation resistance at a DC fast-charging output.

isoCHA425HV and iso175 serve different locations

The isoCHA425HV is specified for CCS/CHAdeMO DC charging stations with a suitable AGH420-1 or AGH421-1 coupling device. Measuring profiles and alarm settings are adapted to the application; information can be sent to the charging controller via interfaces such as Modbus RTU over RS-485. The iso175 is intended for unearthed high-voltage vehicle drive systems; depending on the variant, it communicates via Bender CAN or SAE J1939 and can measure before the HV system is energised. These models are not general-purpose substitutes for one another. System voltage, system leakage capacitance, measuring profile, control sequence and interface must be considered together. As Bender's distributor in Türkiye, ADEO Teknik supports the selection of suitable models and technical sources.