User's Manual

Calculating Maximum Wiring Lengths
apC/8X Technical Manual C-7
Calculating Wire Ranges for RM-4E Readers
From Table C-1, the RM-4E Reader draws 1.75 mA (round up to 200 mA or
.2 A).
From Table C-2, the resistance with 18 AWG wire is 0.00879 ohms per foot.
From Figure C.1, the diagram shows that you are going to connect three
RM-4Es to the apC/8X. The RM-4Es are laid out as follows.
 RM A is 50 ft. from the apC/8X
 RM B is 500 ft. from the first
 RM C is 250 ft. from the second
Perform calculations, as follows:
1. Calculate the voltage drop for each reader in the chain.
2. Add the voltage drop for each reader to get the total voltage drop.
3. Subtract the total voltage drop from the original apC/8X supply.
4. Is the remaining voltage sufficient to operate the readers?
1a. Calculate Voltage Drop for RM A
Multiply 50 ft. * .2 A * .00879 = .0879 volts dropped for RM A
1b. Calculate Voltage Drop For RM B
Multiply (50 ft. + 500 ft.) *.2 A * .00879 = .9669 volts dropped
Multiply (550 ft.) *.2 A * .00879 = .9669 volts dropped for RM B
1c. Calculate Voltage Drop For RM C
Multiply (50 ft. + 500 ft. + 250 ft.) *.2 A * .00879 = 1.4064 Volts dropped
Multiply (800 ft.) *.2 A * .00879 = 1.4064 volts dropped for RM C