Cable Lengths And Cross Section; Line Stubs; Central Power Supply By The Acs-8; In The System - Honeywell ACS-8 Installation Instructions Manual

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6.2.3.3 Power supply of the modules via a separate power supply unit
Since the power supply through a bus is very limited, a separate power supply unit located near the modules
(door) must be used where larger distances or increased current consumption is required.
Each communication module has two RS 485 drivers with a separate supply.
An internal or external power supply can be used for each RS 485 driver. The supplies of the two drivers
must not be inter-connected.
External power supply units supply the potential separation module (POT) with 12V DC. Details of these can
be found in the product list.
6.2.3.4 Cable lengths and line cross-section
A maximum length of 1200m is possible for the RS 485 bus (without power supply).
Whether the +12V/0V lines are included in the bus or on a separate cable, the required cable cross-section
must be calculated.
Modules with higher current demands, require a separate line or a cable with a larger cross-section.
6.3

Line stubs

Stubs are not appropriate for use with buses and lead to data reflections (the signals bounce back) from high
impedance blind end terminations and should be avoided during installation.
If stubs cannot be avoided, they must not be greater than 3m in length and the terminating
resistor should not be connected.
6.4 Potential Isolation
The communication module has two floating RS 485 interfaces.
The 4I, 4O, 4I/2O modules are each fitted with a floating RS 485 interface.
The reader, keypad and door modules are not floating.
If potential isolation is required, up to 4 of these modules can be connected to the RS 485 bus with the
potential isolator. Each of the 4 modules can be located up to 10m from the potential isolator (POT).
6.4.1 Central power supply from the ACS-8
No potential isolation is required.
6.4.2 Decentralized power supply using several external power supply units distributed

in the system

If problems should appear with the data transmission to the ACS-8, a potential isolator (POT) should be
used.
(Blind spurs)
Installation Instructions / ACS-8