Oil switches are employed for

The correct answer is C. high voltages and large currents circuits.

Oil switches are used in high voltage and large current circuits because they are able to handle the high levels of current and voltage without arcing or overheating. They are also able to provide a clean break when switching off, which is important in high voltage circuits where arcing can cause damage.

Option A is incorrect because oil switches are not typically used in low current circuits. Option B is incorrect because oil switches are not typically used in low voltage circuits. Option D is incorrect because oil switches are not suitable for all circuits.