Three-phase power explained

The line conductors are L1, L2 and L3. A system with an accessible neutral point may also provide N. PE has an independent protective role; it is not an ordinary load-current return.

For an ideal balanced star system, line-to-line voltage is √3 times line-to-neutral voltage. This explains the familiar 230/400 V example: approximately 230 V to N and 400 V between lines. It is a named supply example, not a universal voltage for every system.

Three sine quantities displaced by 120°

In star, three load branches meet at a common point. In delta, each branch lies between two lines. Voltage across each branch therefore differs.

A motor must suit the actual voltage and connection. Rating plate data are essential. An arbitrary six-terminal picture cannot authorise star-delta starting. The contactor guide addresses that separately.

Star and delta: three branches

Balanced sinusoidal line currents sum to zero at the neutral point. That does not establish that an installed neutral is generally unnecessary or harmless.

Unequal single-phase loads produce neutral current. With nonlinear loads, certain harmonic components can also add. Do not assess the neutral solely from an ideal classroom example.

An interrupted neutral with unbalanced star loads can cause dangerous voltage shifts. Actual consequences depend on construction. Never interrupt it for an experiment.

Balance is a specific condition

The phase order matters for many motor applications. A suitable phase-sequence instrument checks the order at its measurement point. Actual mechanical direction additionally depends on the motor and connection.

A clockwise indication is not universal proof of correct machine rotation. Direction changes require an appropriate professional procedure considering standstill, load and protection.

For a balanced sinusoidal load, P = √3 · U_LL · I_L · cos φ. U_LL is line-to-line voltage and I_L is line current. These conditions matter; the expression is not a universal treatment of unbalanced or distorted loads.

An educational example with 400 V, 2 A and cos φ = 1 gives about 1.39 kW. It explains quantities, not conductor, fuse, connector or motor selection.

Does every three-phase load need neutral?

No. Some equipment needs three lines and PE; other equipment also needs N. Markings and documentation determine the connection.

Can PE replace N?

No. They are not interchangeable. PEN is a separately governed concept, not an arbitrary added bridge.

Is 400 V always correct across every motor winding?

No. Winding voltage depends on the connection and motor rating. Use the plate and appropriate manufacturer diagram.

The references support basic principles; they do not replace assessment of the actual installation.