The SONEL ERP-1 adapter, in combination with meters that can generate measurement current of 200 mA, serves for measuring of resistance of multiple groundings without disconnecting control connection clamps. The flexible, big diameter coil allows to measure earth resistance of e.g. transmission towers - including lattice poles - without shutting down the power line. Ergonomic design of the adapter, its convenient housing and simple operation make earth resistance measurements on transmission towers and pylons quick and problem-free. The protection degree of the adapter is IP67, which makes it suitable for operation in muddy and rain conditions.