What's the maximum serial cable length?

The RS-232 standard specifies this as 15 metres (50 feet).

However this is a conservative figure accounting for high serial speeds over high capacitance cabling, for example using a baud rate of 9600 (a common console speed) over typical Cat 5 cabling, the maximum length increases to 100 – 150 meters (328 – 500 feet).

Serial connectors and adapters, such as the 319015, may decrease the maximum length by a few percent.