Engineering Documentation

Chapter 3 – Field Panels
TX-I/O Product Range
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TX-I/O Island Bus Extension Cable Options
The maximum TX-I/O island bus cable length is 164 ft (50 m). This length is based on
54 picofarads per foot (pF/ft) capacitance, which is typical of shielded PVC tray cable.
● When the TX-I/O island bus is inside an electrically quiet enclosure, use 2 Twisted
Pair (TP) with 24V~/ home run to the transformer and CS/CD run between the
Power Supply or Bus Connection Module. System Neutral ( ) is not required to run
with CS/CD.
● For use between enclosures or in an electronically noisy enclosure where AC and
DC power require the same size cable, use 1 Twisted Shielded 4C for CS/CD/
/24V~.
● For use between enclosures or in an electronically noisy enclosure where AC and
DC power require different size cable, use 1 TSP for 24V~/ and 1 Twisted
Shielded 3C (Triad) for CS/CD/ .
Operating the TX-I/O Bus in an Electrically Noisy Enclosure
Electrically noisy enclosures include motor control cabinets with VFD or motor power
greater than 100 kVA, such as direct online (DOL) starters for motors greater than 25
HP.
The TX-I/O island bus cable must be shielded and separated from high voltage wire
as described in Chapter 1 [➙ 14].
Calculating the Maximum TX-I/O Island Bus Cable Length
The following factors are used to determine the maximum TX-I/O island bus cable
length or power transfer:
● Total capacitance
● Vdc drop
● Vac drop
Total capacitance includes all branches. Total TX-I/O island bus cable capacitance
must be less than 9 nanofarads (nF). Exceeding this limit causes communication
errors.
Maximum power delivered to each branch is determined by TX-I/O island bus length
for the branch, cable resistance and allowable voltage drop factor (12 for DC or 48 for
AC).
R = 2 × branch length in feet × Ω/ft cable, or
R = 2 × branch length in meters × Ω/m cable
Where:
R is determined using maximum ambient temperature of wire at 75°C not mean 25°C.
14 AWG = 0.006 Ω/ft 2.0mm
2
= 0.0104 Ω/m
16 AWG = 0.009 Ω/ft 1.25mm
2
= 0.0168 Ω/m
Maximum DC Power (CS, CD, ) = Vdrop × Vdc / R = 0.5 Vdc × 24 Vdc / R = 12 V2 /
R
Maximum AC Power (24V~, ) = Vdrop × Vac / R = 2 Vac × 24 Vac / R = 48 V2 / R