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3.2. Installation: RS-485 peripherals (CT clamp/E-meter)
The charger series 3SLC/3TLC support peripheral devices on an RS-485 bus (wired twisted pair
connection extending up to 30m). Currently supported devices are CT clamps and Eastron MID
meters ("Modbus V2" series, #230 for single-phase and #630 for three-phase). The charger
supports one device on the RS-485 bus per unit.
CT clamps are intended to be installed on the current-carrying live conductors ahead of the
MCB. They monitor the total installation power (e.g., of an entire house or parking lot) and
relay the values to the charger unit, which can then regulate its output power to prevent the
MCB from tripping.
CT clamp kits consist of a split-core current transformer hard-wired to a CT transmitter hub,
which measures and converts the reading of the transformer into digital signals for the charger.
Ensure that the CT clamps are secured to their designated phase in three-phase installations.
Failure to do so may result in incorrect current readings and charging malfunction. If a charger
is configured as a single-phase charger, it may use a single-phase CT clamp kit or a 3-phase kit
where only the L1 current transformer is connected to the feeder line supplying the charger.
When an external MID energy meter is used on the RS-485 bus, the EVSE will obtain the
voltage, current, and power measurements from the device and store them in its internal
memory. The MID meter is intended to be installed immediately upstream of the charger, so
that it will only monitor and measure the power for charging EVs. As noted, the charger series
is guaranteed to work with Eastron Modbus DIN rail meters. Other meters that use the
Modbus RTU protocol can be used, provided that the following required parameters are met:
- Baud rate: 9600bps.
- Start bit: 1
- Data bits: 8
- Parity: None
- Stop bits: 1
- MDBUS device address: 0x01
The following table provides the register set that must be implemented in a compatible MID
meter (parameters marked with an asterix * are required for three-phase measurements):
Modbus Input Register
Parameter
Phase 1 line to neutral volts
Phase 2 line to neutral volts*
Phase 3 line to neutral volts *
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