The existing line selection technologies of small current grounding fault are all based on radiating lines. However

the case of bus line loop will appear under certain circumstances

and then the characteristics of the grounding fault will change

which means the existing line selection methods need to be updated. In this paper

a compound network of single-phase grounding fault in distribution network with loop is established. After then

the distribution characteristics of the steady and transient zero-sequence currents at the end of the loop are derived

and the adaptability of the existing line selection methods is analyzed. The results show that

in the case of loop grounding

with the difference of the line parameters and the location of the fault

the electrical quantity at the two ends of the loop does not always appear as the characteristics of the fault line. In the situation

existing steady and transient line selection techniques may cause mistake in line selection. The problem can be solved by increasing the number of alternative lines and using the change of each remaining line's zero-sequence admittance

before and after the resection of an exit line in the loop

to identify the fault line. And it can also be solved by taking the sum of the zero-sequence currents at both ends of the loop into the line selection comparison. Simulation and field data verify the correctness of the fault characteristics and the effectiveness of the line selection methods.