"单芯导线" can be translated into English as "single-core wire" or "single-conductor wire".
"Single-core wire" is a more common and straightforward expression in electrical engineering contexts, directly indicating that the wire has a single core or conductor.
"Single-conductor wire" is also accurate, emphasizing that there is only one conductor within the wire.
Both expressions are acceptable, and the choice between them may depend on the specific context or preference of the user.