Glossary

Ring circuit

What is Ring circuit?

A cable routing in which a run is led back to its starting point so that loads are fed from two sides. On board it is unusual in the DC system.

What matters about Ring circuit in practice?

The apparent advantage — halved voltage drop, redundancy — is outweighed by a serious drawback: the current splits over two paths, and in the event of a fault it is no longer clear which section is affected. Protection and troubleshooting become much more difficult.

The usual layout on board is therefore the star: a central distribution from which each circuit branches off separately — on the positive side as on the negative side.

Why is power distributed in a star on board?

In star distribution, every circuit leaves a central distribution point on its own: positive through its own fuse, negative back to a common negative busbar. Each conductor carries only the current of its load, and cross-section and fuse match it exactly. If a circuit fails, it is clear where to look.

What speaks against a ring main?

  • If one leg of the ring is broken, nobody notices: the current silently takes the other path, and the remaining conductor can be overloaded.
  • The current divides according to the resistance of the sections. How much flows through which part cannot be said without measuring.
  • A ring on the negative side causes equalising currents that distort shunt and tank sender readings.

Where is a ring main common?

In the household wiring of some countries, the United Kingdom for example, ring circuits are used in the AC system. They have no place in the DC system of boats and vehicles. The cable configurator calculates the cross-section of each conductor in the star.

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