A green-yellow wire is essential to connect touchable conductive parts to the safety Earth. It behaves as an inductor at higher frequencies, rendering it useless as equipotential connection. When you select a bad wire length, the wire can work as transmitting or receiving antenna. Equipotentiality only exists with respect to a frequency range (e.g. DC to low frequencies for the safety Earth connection). The type and length of the connection defines in which frequency range the systems can be considered as equipotential.
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