Your application may specify the cable configuration required for connecting a peripheral device to your computer. You should follow those specifications. If you build or purchase your own cables, Digi recommends shielded cables (15 pF or less capacitance per foot) for all installations.
The FCC requires the use of shielded cables to comply with EMI/RFI emission limits. In addition, cables that run long distances or through electrically noisy areas are subject to voltage surges that can cause data errors or equipment damage. EIA-232 specifies a maximum cable length of 50 feet. If you run cables farther than 50 feet, you increase the risk of surge damage and data loss. (However, using shielded cable of 10-15 pF capacitance per foot somewhat lessens the risk of data errors.)
When routing your cables, do not run them parallel to AC wiring or on top of fluorescent light ballasts. Bundling several EIA-232 cables is acceptable