Spikes also often occur when power returns following a blackout. Spikes can permanently damage modems, motherboards and connected peripheral equipment. The power inlet as well as phone lines and networking cables can all introduce a spike to the system. When high power equipment is turned off, the extra power is often dissipated to other power lines. This quick increase in voltage will usually last more than one cycle and can cause component fatigue and burnout.
Frequent surges are especially damaging to systems.
Typically caused by surrounding electrical equipment such as radio transmitters, generators and industrial equipment, noise can cause glitches and errors in programs. Power flow is direct from the power inlet to the UPS output via the inverter until power fails. After a power failure, the power flow is from the battery to the UPS output through the inverter. If the line voltage decreases, the inverter boosts the power without draining the battery. This allows the UPS to work on sites with really bad power without draining the battery.