If two conductors are not touching but are close to each other, a large enough voltage will cause an to occur between the conductors.

Electrical breakdown.

Explanation:

When two conductors are relatively close enough, and have a very large voltage between them, it can lead to a Dielectric breakdown. A dielectric breakdown occurs when an insulator is subjected to a high enough voltage, suddenly becomes an electrical conductor and electric current flows through it. The air between the conductors is the insulator that breaks down, leading to an electrical discharge arc to flow between the two conductors. This electrical breakdown can cause catastrophic failure of electrical equipment, and fire hazards.