When the ballast is wet or contains substances such as salt or minerals that conduct
electricity easily, current can flow from one rail to the other rail. This condition is
minimum ballast resistance. With minimum ballast resistance, ballast leakage current is
high. When the ballast resistance decreases significantly, the relay can be robbed of its
current and become de-energized, or fail to pick up after it has been de-energized by a
train and the train has left the track circuit. Because the ballast resistance varies
between a wet day (minimum ballast resistance) and a dry day (maximum ballast
resistance) the flow of current from the battery will vary.