The authors study the threshold sensitivity of detecting ice accretion by location probing and stability of amplitude and transmission delay of reflected signals in the normal operation mode in the absence of ice. Due to long-term investigations of the active power lines annual and daily variations were discovered in amplitude and transmission delay of reflected signals. It was shown that these variations as well as sporadic fluctuations in the normal operation mode are far less than the changes in signal amplitude and transmission delay at the early stage of ice accumulation. Guidelines to set operation threshold for detecting early ice accretion on electric power lines and wire breakage by amplitude and transmission delay are given.