Contemporary Control Systems BASrouterLX Installation Guide - Manual (Page 6)

TD120100-0IC
6
POWER
The BASrouterLX requires 24 VAC or 24 VDC and draws a commensurate
amount of current. The recommended conductor size is 16–18 AWG. COM is
directly connected to zero volts and the chassis is DC isolated from zero volts.
Input connections are reverse-polarity protected.
Figure 5 — Power Options
WARNING: Powering devices can present hazards. Read the following carefully.
Since the product incorporates a half-wave rectifier circuit, it can share the same
24 VAC power with other half-wave rectified devices. It can also be powered
from a 24 VDC source. A redundant power connection exists for back-up power
schemes.
The product incorporates a 3-wire optically-isolated EIA-485 interface for the
serial connection, allowing better circuit protection and noise immunity. To
connect to other 3-wire devices simply make a one-to-one connection to the other
devices. But when connecting to 2-wire non-isolated devices, the signal common
(SC) on the product must share the reference used by the 2-wire devices. This is
accomplished by tying the SC pin to COM on the product and by grounding the
low-side of each power supply on all connected devices. In this way all EIA-485
transceivers share the same earth reference. Notice that the SC pin is signal
common and not a shield pin. For shield connections, use the SH pin. Far-end
external termination is required as shown. Near-end bias and termination are
internally supplied within the product.