engineering

Ring circuit

Ring circuit is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ring circuit rather than just read about it. In short: In electricity supply, a ring circuit is an electrical wiring topology in which power is distributed through a continuous cable ring. Each conductor of the ring is connected to the source of the supply at both of its ends.

Key takeaways

Ring circuit belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ring circuit to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ring circuit from memory before moving on to harder problems.

Reference excerpt

In electricity supply, a ring circuit is an electrical wiring topology in which power is distributed through a continuous cable ring. Each conductor of the ring is connected to the source of the supply at both of its ends. The topology contrasts with the typical radial circuit configuration, in which nodes and the distribution point at the protective device are connected in a line or a line with branches or legs off the main line. Ring circuits are used in distribution for power and lighting. Rings at the final consumer current draw off point either for power or lighting are known as a ring final circuit. Ring final circuits are often termed by the historical name ring main in the United Kingdom. Ring circuits are subject to typical cable protection relating for all types of circuit topologies, in which the cable is at a higher amperage loading than the protective device's (breaker) value. In the United Kingdom there is an anomalous ring final circuit with the cable at a lower amperage loading than the protective device. It is under a waiver, 433.1.204 in British Standards 7671. Ring final circuits in the United Kingdom splits ring circuits into two types:

The 433.1.204 ring final having the cable at a lower maximum amperage rating than the protective device; Ring circuits having the cable at a higher maximum amperage rating than the protective device.

433.1.204 ring final in the UK If a circuit designed with the cable at a lower maximum amperage loading than the protective device then 433.1.204 of BS 7671 is triggered. The standard states that such a circuit must only be a ring final - not a radial or star. The 433.1.204 implementation of the ring circuit is predominately used in the United Kingdom where it was developed, and to a lesser extent in countries that adopted the British electrical standards. The 433.1.204 ring final waiver in BS 7671 simply says in layman's terms:

The circuit must be a ring final (the two cable legs into the protective device double the circuits amperage rating over the cable's amperage rating); Protective device must be either 30A or 32A MCB/RCBO/AFDD/fuse; A minimum of 2.5mm2 cable used; The cable must have copper conductors; Minimum current capacity of the cable must be 20A, taking into account derating; If socket-outlets are to be installed on the ring final they must only be the BS 1363 socket-outlet accessory family - the Type G 13A square pin plug and socket. Further guidance for 433.1.204 is in Appendix 15 of BS 7671, recommending such as: a maximum coverage of 100 square metre floor area and that the load must be reasonably distributed around the ring final. A ring final when designed to the 433.1.204 of BS 7671 enables the use of smaller diameter cable than used in a radial circuit of equivalent total current capacity, giving economic installation. The reduced diameter conductors in the flexible cords connecting an appliance to the plug intended for use with sockets on a ring final circuit are individually protected by a fuse in the plug. Its prime advantages over radial circuits are a reduced quantity of cable used, lower voltage drop at the furthest point of the circuit, and greater flexibility of connected appliances and equipment. Because both ends of the ring's cable are connected to the same protective device, current can travel in two directions around the ring to reach any given load. If the load is evenly split across the two directions, the current in each direction is half of the total load, allowing the use of cable with half the total current-carrying capacity. In practice, the load does not always split evenly.

Description

The ring starts at the consumer unit, also known as a Distribution board, visits each load in turn, returning to the consumer unit. The ring is fed from a fuse or circuit breaker in the consumer unit.

Ring circuits to BS 7671, 433.1.204 are commonly used in British wiring specifying only the use of socket-outlets on fused plugs to BS 1363. Because the protective device (breaker) rating is much higher than the cable's maximum amperage rating the ring final circuit can only be used with fused plugs on the socket-outlets, or 13 A fused connection units (FCU) for fixed appliances with flexible cords. 433.1.204 specifies 2.5mm2 cable, or 1.5mm2 mineral-insulated copper-clad cable, as the minimum size used and protected by a maximum of a 30A fuse or 32A circuit breaker.

433.1.204 ring final history The ring circuit and the associated universal BS 1363 plug and socket-outlet system were developed in Britain between 1942 and 1947. Pre-World War II practice was to use various sizes of plugs and sockets to suit the current requirement of the appliance, connected to suitably fused radial circuits. The ratings of the fuses were selected to protect both the fixed wiring and the flexible cord attached to the plug. The Electrical Installations Committee, which was convened in 1942 as part of the Post War Building Studies programme, determined that the ring final circuit offered a greater number of sockets delivering at least 2kW to each socket, and a more efficient and lower cost circuit. Several designs for the socket-outlet system for the ring design were considered, with the new BS1363 13 A flat pin and fused plugs selected, a socket-outlet system developed independently of the final ring circuit. Of the two British Standards socket-outlet systems, the BS546 and the universal BS1363 by the 1960s BS1363 became the single standard for new radial and ring final installations. The committee mandated the ring circuit to increase consumer safety, and estimated that using a ring circuit and single-pole fusing would reduce raw materials requirements by approximately 25% compared with pre-war standards. The ring circuit remains the most common socket-outlet power circuit configuration in the United Kingdom. Ring final circuits are commonly used to a lesser extent in the Republic of Ireland, and were also adopted, for example, in the United Arab Emirates, Singapore, Hong Kong, Beijing, Indonesia, Cyprus, and Uganda, as well as perforce in many countries of the British Empire cum British Commonwealth. It does, however, present more complicated safety concerns than do radial circuits for plug-in solar power.

Installation standards

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Ring circuit

Start with the simplest possible case. Write down what Ring circuit claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ring circuit before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ring circuit ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ring circuit

In research: Ring circuit appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ring circuit in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ring circuit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrical wiring, Electricity supply circuits, so understanding it makes those chapters shorter.
In everyday life: Look for Ring circuit outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Ring circuit in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ring circuit means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ring circuit out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ring circuit in simple terms?

Why does Ring circuit matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ring circuit?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ring circuit.