Innotech Genesis V4 System - Manual (Page 83)

Installation Instructions for Innotech Genesis Systems
Edition 011100
A-2
A-2.3. GENII RS485I ISOLATED RS485 COMMS. The GENII RS485I Isolated
RS485 Comms Card is an optional daughter board that can be plugged onto the bottom board
of a Genesis II Digital Controller to isolate the Digital Controller from the RS485
communications cable.
A-3. GENESIS I AND GENESIS II CABLE SPECIFICATIONS.
The cable should be designated as suitable for use in RS485 serial communications. It is
recommended that the cable to be used for Net Comms and Global Points with the Genesis I and
Genesis II controllers be a dual twisted pair cable with each pair preferably having their own
shielding. A single shielded twisted pair cable can be used if only the Net Comms or the Global
Points are connected. If the Comms cable is to be run in contact with power cabling, the voltage
rating of the sheathing must comply with the ratings for a power cable. The cable characteristics
as specified by the manufacturer should be as follows:
•
Shielded, dual-twisted-pair (Two shielded, single-twisted-pair cables can be used if
necessary)
•
7 x 0.2mm
2
conductors
•
120 Ohms characteristic impedance
•
Sheath thickness 0 to 3mm.
•
36 to 42 picoFarads per metre capacitance between conductors
•
65 to 76 picoFarads per metre capacitance between one conductor and all other conductors
and shield
•
Sheathing to meet the necessary voltage rating, if required.
A-4. INSTALLATIONS.
It is not possible to cover all the situations that may be encountered in the wide range of
installations found in the field. The following examples are provided as a guide to assist in
deciding the best method of connection and layout and to illustrate the differences between the
Genesis I and Genesis II products.
Some situations require additional care to avoid hazardous situations. These may be covered by
legislation or regulations such as those set by Telecommunications Authorities, Electrical Wiring
Rules and Local Authorities. Much of the Genesis product line is designed to comply with the
extra low voltage standards and, therefore, any wiring connected to these products should also
comply with these standards if the product compliance is to be maintained.
Communication links between equipment supplied from different electrical switchboards should
be electrically isolated from one another. The voltages at the earth connections at the
switchboards will usually have a small difference under normal conditions but, if a fault occurs
on equipment connected to one switchboard, the voltage difference can increase dangerously. If a
non-isolated communications link is used, this voltage difference can cause a large current to flow
through the communications cable and the integrated circuits (ICs) connected to it. An isolated
connection will block the current, but it would have to withstand the full supply voltage for up to
several seconds.
The Genesis I Digital Controller cannot be isolated from the RS485 communications cable. This
places some restrictions on its application. If isolation is required, it must be provided by a
GENII RPTR Repeater Module.