The photo shows a commercially available Rogowski coil with the terminating caps removed.
The enamelled wire is wound on a non-magnetic flexible “rod”. The coil is wound as a single layer of winding, and the return connection is passed through the centre of the flexible rod, through the visible soldered end (at the centre of the rod). The outside of Rogowski coil is protected with two layers, both for electrical insulation and mechanical protection.
inside_of_rogowski_coil_magnetica.jpg
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S. Zurek, Encyclopedia Magnetica, CC-BY-4.0
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