What is a ring main circuit, dangers of broken rings

1) What is a Ring Main?

A ring main refers to the installation configuration of a plug socket circuit. These days, the set-up is called a "Ring Final Circuit", although many people still incorrectly refer to this as a RING MAIN. 

The Ring Final Circuit is named so because of its circuit layout. Beginning at the fuse box or consumer unit and ending up back at the consumer unit once again thus forming a continuous loop or "RING" of cable. The method of wiring socket circuits in this manner came around during the second world war when copper was in short supply. Electrical installations from this era typically involved a ring of continuous cable to power every plug socket in the home. This allowed more electrical current to flow through the circuit than if radial circuits had been used with the same thickness of cable and still met the required electrical standards.

(Diagram: Ring Final Circuit / Ring Main Wiring)

2) How does a Ring Final Circuit Work?

As we can see from the diagram above, the wiring for the socket outlets begins at the consumer unit and loops into and out of each socket before continuing onwards around the ring. Finally, the cable leaves the last socket and returns to the consumer unit. Inside the consumer unit, there is a circuit breaker (a type of overcurrent protective device) that prevents overload and short circuits from occurring on the ring final circuit.

3) Which way does current flow in a Ring Circuit?

Current flows throughout the live conductors (that is Neutral and Line Conductors) in a ring final circuit. There is no "one direction" in which current flows as our electrical systems use an alternating current supply. The alternating current supply means that the current changes direction many times per second in accordance with the supply frequency. In the UK and Europe, we have a 50Hz alternating supply and over the pond in the USA the supply is 60Hz. In simple terms this means that 50 to 60 times per second the current changes direction.

(Diagram: Sine Wave)

4) Ring Final Circuits in 2025

Yes, ring final circuits are still used today and will likely continue to be used for the future. Despite the use of ring circuits out of necessity during times of copper shortages, their popularity has remained and many electricians will still use the ring final socket circuit formation when rewiring older properties or installing a new electrical system. These circuits still meet modern safety standards and are particularly popular in kitchens where electrical loading is very high.

5) Ring circuits in older homes and modern homes

50 to 60 years ago it was common the entire house to have only one ring circuit. This was a good idea from a cost standpoint as minimal electrical cable was needed in order to fully supply all the sockets but was a poor idea when it came to electrical faults. When a fault occurred in a “one ring house”, ALL the socket outlets would lose power as the circuit blew its fuse or tripped a breaker.

(Photo: A fuse box with only one Ring Circuit)

These days when we rewire an installation or install a new wiring system, we have to consider what is best practice, meet modern wiring regulations and ensure that there are different circuits installed to supply areas of the property. 

Modern wiring regulations make us consider:

• Inconvenience of circuit failure
• Circuit loading and splitting loads
• Voltage drop considerations
• Load Distribution throughout the ring

and much more. 

It is now common for modern homes to have at least two ring final circuits and in some cases more. Generally speaking, it is a good idea to have a ring final circuit for upstairs and one for downstairs and in homes intended for families, a separate ring final circuit for the kitchen. 

6) Does a house with one ring circuit need rewiring?

A house with only ONE ring circuit will NOT need to be rewired simply because there is only one ring circuit. There are more considerations needed before establishing if a house needs to be rewired. 

We have a separate house rewiring article that discusses when rewiring may be necessary.

7) Ring Circuits vs Radial Circuits

There are a few differences between Ring and Radial circuits that are worth discussing. Firstly, what is a Radial circuit? Well, a radial circuit is one that begins at the consumer unit or fuse box and ends at the last plug socket outlet. Radial circuits are used for lighting, cookers, electric showers, car charging equipment, socket outlets and almost everything else. They have a distinct beginning and an end point.

(Diagram: A Radial Circuit)

A Ring Final Circuit is simply a Radial Circuit which does not end at the last socket outlet. Instead, when the last socket outlet is wired, the electrician takes the cable from that last socket outlet and returns it to the consumer unit or fuse box. That is essentially the main difference. There is no "end of the ring" as it is a continuous loop of cable so to speak.

8) Dangers of Ring Circuits

Despite their popularity, there can be a number of issues with Ring Final Circuits that can present serious danger and for this reason many electricians think carefully before installing them. I tend to install radial circuits for socket outlets these days and either use a Ring Final Circuit for the kitchen only or put a thicker cable in and run a more powerful radial for that room only.

The main issues and typical dangers of ring circuits include:

• Broken Rings / Lack of continuity on circuit conductors
• Overloading one part of the ring
• DIY alterations
• Ring within a Ring faults

A correctly installed and maintained ring final circuit is safe and will cope well with almost any type of electrical load in modern homes and should give no cause for concern. It is important however, that regular inspections are carried out on electrical systems to ensure that continuity of conductors, earthing, cable insulation, protective devices and more are all working as intended. 
A broken ring final circuit can cause a fire, electric shock and damage to your home. Let us look at the typical dangers in more detail below.

(Photo: Overloaded and burnt out wiring)

9) Broken Ring / Lack of Continuity

When a ring circuit suffers a break on one of the conductors (Line, Neutral, Earth/CPC), NOTHING APPEARS TO CHANGE. No fuse will blow, no switch will trip, nothing. What does change though, is the ability of the ring circuit (now broken) to carry the electrical current around the circuit. 

10) Overloading one part of the ring

This is a common issue where spurs are taken from the ring final circuit to feed garages, outbuildings or other electrical equipment where a dedicated electrical circuit should have been installed. This is also the reason that fixed appliances such as an electric oven should be fed with its own dedicated circuit. Appendix 15 of BS7671 wiring regulations has more information regarding acceptable practices on Ring Final Circuits. 

11) DIY Alterations

Where DIY alterations take place in electrical systems there are nearly always problems that occur. Whilst electrical wiring may "seem simple", or "is only 3 wires" things are often more complicated than this and require an understanding of a whole host of technical matters and knowledge of a 500+ page manual of wiring regulations. I regularly see dangerous DIY additions that lead to, premature wear on wiring, electric shock risk, overload risk and potential fires.

(Photo: A DIY junction box installed in a wall incorrectly and against wiring regulations)

12) Ring within a Ring faults

A ring within a ring occurs when a connection is made between two points on a ring forming a new ring internal to the existing. Think, loop within a loop or connecting a socket in the kitchen to one in the living room for example. 

The dangers here are things like:

• Ring breaks / Open Circuit
• Overloading the ring
• Overheating the wiring
• Difficulty tracing faults
• Loose wiring may go unnoticed

13) Cable sizing for a Ring Final Circuit

Typically, we use a 2.5 mm Cross Sectional Area cable for wiring Ring Final Circuits. Under perfect installation circumstances, this cable has the capacity to carry 27 Amps of electrical current and when used in the ring final circuit configuration, the cable can be protected by a 32 amp protective device. Essentially the ring final circuit wired in 2.5 mm cable is actually nearly equivalent to a 5mm radial circuit if such a cable were to exist. This is because each socket is fed independently via 2 x 2.5mm conductors.

(Photo: 2.5mm cable for a ring circuit. Back box too small!)

There are of course, many other factors to consider when sizing cables for electrical installations and it is not safe to always select the same size cable without considering installation factors. Such factors that adversely affect the capability of electrical cables to carry loads include:

• Thermal Insulation Touching Cables
• Grouping of Cables together
• Ambient Temperatures
• Protective Device Characteristics
• Circuit Length

14) Adding new sockets to a ring main (ring final) circuit

Additional points can be added to a ring final circuit but care should be taken to ensure that the new socket, or new electrical loads are balanced and not feeding fixed loads of more than 2kW. Whilst enthusiastic DIYers can assume that electrical additions are simple and straightforward, nothing could be further from the truth. 

The steps that need to be taken when considering adding additional sockets are:

• Is the circuit safe, suitable, and capable to handle the altered circumstances?
• Are the earthing and bonding arrangements suitable?
• Is there RCD protection in place that is tested and functional?
• Would the change in the circuit exceed the maximum floor area for the ring?

​Let’s have a look at these in more detail below,

14.1) Is the circuit safe, suitable, and capable?

The existing circuit should be tested to determine if it is capable of withstanding any additions. Ring Final Continuity should be checked using a calibrated low resistance ohm-meter and the resistance readings compared with expected values, Insulation resistance should be checked to ensure it meets the minimum levels for a healthy circuit as outlined in IET Guidance Note 3 and we should ensure that our additions will not adversely affect the circuit.

(Photo: Poor Insulation Resistance Reading on a Ring Final Circuit)

14.2) ​Are the earthing and bonding arrangements suitable?

We must ensure that the earthing and bonding, where required, is in a suitable condition in accordance with the requirements set out in the IET Safety requirements for electrical installations (Wiring Regulations). Safety connections to extraneous conductive parts must be adequate before altering an electrical installation. 

14.3) Is there RCD protection?

​Pressing an RCD test button is an insufficient way of checking RCD operation when it comes to changing electrical circuits and adding on to electrical systems. RCD devices should be tested in accordance with the wiring regulations and in a suitable manner as outlined in Guidance Note 3. An RCD device is an important, often life-saving, device that must be installed in nearly every electrical circuit. 

14.4) Maximum floor area?

​A ring final circuit cannot supply massive floor areas, the limit is 100m2. In most domestic settings this is not normally exceeded but in the case of older installations, we often see a ring final circuit supplying all the socket outlets in the entire property and any additions may mean that a new circuit is required for additional socket outlets. In any event, one single ring circuit for ALL socket outlets is poor design and likely to lead to serious inconvenience in the event of an electrical fault.

15) Summary

​As we can see from the article, there are a number of considerations that need to be given to ring main or ring final circuits. Whilst a correctly installed ring circuit is often safe, additions over time can lead to potential dangers and electrical faults. In general ring circuits are safe and operate without any problems at all but many electricians are considering the benefits of moving to radial circuits where electrical demand is not as great. Such areas could be upstairs sockets and downstairs sockets. Kitchens and utility rooms should be fed from a Ring Final Circuit or 32 amp Radial Circuit due to expected power requirements.