rs232 maximum length
Words from the standard, ANSI/TIA/EIA-232-F-1997:
3.2 Cable Length
The maximum length of the cable is not defined; it is determined by the electrical requirement in 2.1.4 (see Annex A for guidance).
2.1.4 The load impedance of the receiver side of an interchange circuit is defined for an applied voltage range of 3 volts to 15 volts magnitude. It shall have a dc resistance of not less than 3000 ohms, nor more than 7000 ohms, measured with an applied voltage of 3 to 15 volts in magnitude. The effective shunt capacitance (CL) of the receiver side of an interchange circuit, including the capacitance of cable, measured at the interface point, shall not exceed 2500 picofarads. The reactive component of the load impedance shall not be inductive. The open circuit receiver voltage shall not exceed 2 volts in magnitude. (see 6.3, 6.4, and 6.5).
1.3 Data Signaling Rates
This standard is applicable for use at data signaling rates up to a nominal limit of 20,000 bits per second.