Users manual

25-3
Chapter 25: Relay Output Module
Communications Wiring
The Relay Output Module communicates with the SCADA 3000 using a high-speed serial
communications bus. This 4-wire bus is used to connect up to 15 modules to the main unit
to provide additional inputs and/or outputs. The communications cable must be 4-Conductor
Twisted Pair. You may use unshielded cable in electrically quiet environments, but be sure to
use shielded cable if your cabling must navigate around electrical machinery or equipment.
Modules may be located a maximum of 2000' away from the main unit and should be connect-
ed in a daisy-chain fashion from one module to the next. Each module connects to the next via
a 4-wire communications cable connected to the terminals labeled A,B, Y&Z. The cable must
be 4-Conductor Twisted Pair (shielded or unshielded) with a nominal impedance of 120W
(forexample,Belden#8132or9842cable).UseonepairforA&BandtheotherpairforY&
Z.Notehowthewiringisreversedbetweenthefirstmoduleandthemainunitbutbetween
modules the wiring is straight-thru. Correct wiring setup is shown in Figure 3.
Figure 3: Correct daisy chain setup: Main unit on the end.
Figure 4: Incorrect daisy chain setup: Main unit in the middle of the chain.
The Main Unit should always be on one end of the chain, never in the middle.
Cabling Notes
Follow these guidelines to protect the communications cable from electrical interference.
• Keepthecommunicationscableatleastfivefeetfromanyelectricmotors,trans-
formers, rectifiers, generators, arc welders, induction furnaces, or sources of
microwave radiation.
• Ifyoumustrunthecableacrosspowerlines,runthematrightanglestothelines.
• Keepthecommunicationscableatleast6inchesfromACpowerlinescarrying
less than 20A, at least 1 foot from lines greater than 20A, and 2 feet from lines
greater than 100KVA.
• Ifyourunthecableinametallicwirewayorconduit,keepthecommunications
cable at least 3 inches from AC power lines carrying less than 20A, at least 6
inches from lines greater than 20A, and 1 foot from lines greater than 100KVA.
Running the communications cable through conduit provides extra protection from physical
damage and electrical interference. If you route the cable through conduit be sure to ground