Schneider Electric EM3555 manual RS-485 Communications, Daisy-chaining Devices to the Power Meter

RS-485 COMMUNICATIONS

Daisy-chaining Devices to the Power Meter

The RS-485 slave port allows the power meter to be connected in a daisy chain with up to 63 2-wire devices. In this bulletin, communications link refers to a chain of devices that are connected by a communications cable.

Figure 7 Daisy-chaining multiple devices

120 Ω terminator

Belden 1120 A or equivalent (600 V) on the first and last device of the

daisy chain

+–

S

Shield wire

•The terminal’s voltage and current ratings are compliant with the requirements of the EIA RS-485 communications standard.

•The RS-485 transceivers are ¼ unit load or less.

•RS-485+ has a 47 kΩ pull up to +5V, and RS-485- has a 47 kΩ pull down to Shield (RS-485 signal ground).

•Wire the RS-485 bus as a daisy chain from device to device, without any stubs. Use 120 Ω termination resistors at each end of the bus (not included).

•Shield is not internally connected to Earth Ground.

•Connect Shield to Earth Ground somewhere on the RS-485 bus.

•Use 14-24 gauge wire for all connections.

•When tightening terminals, ensure that the correct torque is applied: 3.5 - 4.4 in·lb (0.4-0.5 N·m).

Figure 8 Torque requirements