EST EST3X - Calculating Maximum Wire Capacitance Per Foot; Signature Data Loop Wire Length

Appendix A: System calculations
234 EST3X Technical Reference Manual
Calculating maximum wire capacitance per foot
The capacitive property of twisted-pair cable varies and the cost of cable
generally increases as the capacitance per foot decreases. Following is a sample
calculation for determining the maximum capacitance per foot that a cable can
have for a given network length.
The maximum capacitance per foot equals the maximum cumulative capacitance
divided by the total network length. In equation form:
MCPF = MCC / TNL
Where,
MCC = Maximum cumulative capacitance, from the table given in this topic
TNL = Total network length, the sum of the lengths of individual copper runs in
the network
For example, the total copper distance of a network is 26,000 feet. Calculate the
maximum capacitance per foot that can be used for 18 AWG twisted-pair cable at
38.4K baud.
MCPF = MCC / TNL
MCPF = 1.4 µF / 26,000 ft
MCPF = 53.8 pF/ft
Signature data loop wire length
Signaling line circuit resistance and capacitance determines the maximum length
of a Signature data loop. Circuit resistance affects the wire length of the longest
loop branch. Circuit capacitance affects the total amount of wire that can be used
on the loop.
Notes
• The design of the Signature data loop must not exceed either of the two
measurements.
• There are no restrictions placed on the wiring used for the Signature data
loop. Longer wire runs may be obtained using standard (non-twisted,
non-shielded) wire pairs.