Induced voltage surges are probably the most common types of power and communication problems. This type of surge is created by the electromagnetic field generated by nearby electrical transients or natural phenomena.

Lightning is an obvious cause of induced voltage surges. During a nearby cloud to cloud lightning stroke the lights inside a building may become bright for a moment, a result of an induced voltage surge. Although the lightning did not actually hit an object on the ground, the electromagnetic field that the lightning produced did. The magnetic field generated by the lightning induced a surge voltage into every conductive material nearby, including all the electrical wiring inside the building.

According to Faraday's Law, the magnitude of the induced surge voltage will be dependent on the length of wire available. So it is possible that a surge protective device attached a distribution panel or service entrance may not provide adequate surge protection to far away rooms during a nearby lightning strike. Plug-in type secondary surge protective devices should be used to protect sensitive electronics from damaging induced voltage surges.

Due to the low voltages normally used in data transmission cables and the sensitivity of the connected electronics, communication cables are extremely susceptible to induced voltage surges. As with power cables, the longer the communication cable the greater the magnitude of induced surge voltages during a nearby transient event. Due to their greater susceptibility to induced voltage transients, many types of communication and data cabling are shielded against electromagnetic fields. However, shielding provides only limited protection and if a significant transient were to occur, then the cable shielding would be compromised causing an induced voltage transient on the cable. The transients produced may cause data loss, corrupted files, unwanted noise, or damage to connected electronics.

Lightning is not the only source of induced voltages. Induced transient voltages are generated any time wiring is exposed to a transient magnetic field. A distribution panel surge protective device diverting a power surge to ground can induce hundreds of volts into a nearby communication wire. Energizing a closing coil of a three-phase contactor may induce ten to one hundred volts onto a nearby data or telephone wire. Starting large electrical loads can induce a significant transient voltage into low voltage control wires running in parallel with the main lines. Routing unshielded communication cables next to power distribution cables can induce significant noise into the communication cable.

Induced voltage surges must be anticipated in any surge protection plan. Effective protection against induced surges can only increase equipment reliability and reduce user stress.