The safety gap is located across the HV leads of the transformer. Its purpose is to break down and conduct when voltages at or above its breakdown voltage appear. This restricts the voltage to a safe value protecting the secondary of the neon transformer from damage due to over voltage or RF kickbacks. During Tesla Coil operation the voltages in the primary tank circuit can sometimes be greater than those of the supply. These high voltage spikes are often referred to as kickbacks. The safety gap is intended as a safety device to avoid damage to the power supply due to kickbacks. It is not typically constructed to handle the similar power as the main gap, as it should only fire intermittently. Adjustment of the safety gap is usually done by setting the gap so that it only fires occasionally, just enough to protect the supply. This gap spacing should be marginally greater than the main spark gap spacing. Tab on picture to enlarge.