Industrial applications such as the factory floor are typically electrically noisy environments. Electrical noise, either radiated or conducted as electromagnetic interference (EMI), can seriously disrupt the proper operation of other equipment. Insulation protects a cable mechanically from scraps and abrasion and environmentally from moisture and spills. But insulation is transparent to electromagnetic energy and offers no protection. Shielding is needed to combat the effects of EMI.
Cables can be a main source of transfer for EMI, both as a source and receiver. As a source, the cable can either conduct noise to other equipment or act as an antenna radiating noise. As a receiver, the cable can pick up EMI radiated from other sources. A shield works on both.