Outer conductor (L1,L2,L3)

Outer conductor for transformers

Definition:
A phase conductor (also called phase conductor ) is a current-carrying conductor in an alternating current network which, in contrast to the neutral conductor, carries a voltage to earth. In transformers, the term refers to the lines that carry the current from the primary or secondary side of the transformer to the consumers or to the infeed.

Technical classification

In a three-phase system (e.g. 400 V/230 V), there are usually three phase conductors, which are designated L1, L2 and L3. These each carry an alternating voltage with a phase shift of 120° to each other.

A transformer designed for three-phase current has connections for these three phase conductors on the primary and secondary sides. Depending on the type of connection (star or delta connection), these can be connected differently.

Function in transformer mode

• Primary side: The outer conductors carry the current from the mains to the transformer.
• Secondary side: The outer conductors transport the transformed current to the consumers.
• Voltage level: The voltage between two phase conductors in Europe is typically 400 V, between phase conductor and neutral conductor 230 V.

Typical applications

• Industrial systems: supplying machines with three-phase current via external conductors.
• Households: Even if households usually only use one phase, the electricity comes via one of the phase conductors.
• Grid distribution: External conductors are essential for energy transmission in the medium and low-voltage grid.

Safety and labeling

• Identification color: In Germany and many other countries, the color coding is:
  • L1: Brown
  • L2: Black
  • L3: Gray
• Danger: Outer conductors carry voltage to earth and may only be touched or connected by qualified personnel.
• Protective measures: RCDs, circuit breakers and earthing systems protect against electric shocks and short circuits.