Often used in telecoms equipment, gas discharge tubes play a vital role in protecting systems from the damage caused by sudden and intense energy spikes. They can be useful in situations such as a lightning surge to help prevent damage, which can often prove costly or disruptive. These sealed glass tubes contain two or three electrodes and are filled with a special gas. This gas only conducts when a high voltage is applied across the electrodes. When a power surge comes, the gas conducts the energy spike away, dissipating it until it is no longer a risk to the electrical system. Gas discharge tubes are often capable of dissipating substantial amounts of energy.