An arrester disconnector is a device connected in series with an arrester that separates the ground lead from the bottom of the arrester if the arrester has overloaded and failed. It is also known as a ground lead disconnector (GLD) or isolator.
The normal failure mode of these arresters is a short circuit to ground, causing ground fault current to flow. This current will cause the arrester body to fail if it is not stopped quickly. The first function of the ground lead disconnector is to disconnect the ground lead of the surge arrester in case of an internal failure of the arrester, preventing explosive failure of the arrester body. The ground lead disconnector contains a cartridge in series with a gap. The gap is shunted by a resistor. As the current rises, the voltage across the gap increases until the gap flashes over, creating an arc which ignites the cartridge, blowing the ground lead free.

The second function of the ground lead is to give a visible indication of arrester failure for arresters mounted on overhead distribution lines. If a lineman sees an arrester with its ground lead hanging in midair, he knows that he has a failure which must be replaced.