Fires in the home – Electrical consumer units

  According to Electrical Safety First (Electrical Safety Experts), in the UK alone, there are approximately 19,300 accidental fires a year where electricity has been determined as the potential cause1. It is my experience that many electrical fires occur in and around domestic consumer units (‘fuse boxes’). The majority of fires in consumer units occur due to poor installation, poor or no maintenance, or the mis-use of electrical systems and devices. For many years’ consumer units have been made of plastic. A fire breaking out within a plastic consumer unit can cause a fast spreading fire and the release of harmful toxic gases.  

     The hazards associated with such fires are only heightened if the consumer unit is installed at or near exit routes (such as hallways or under staircases)2. In January 2016, the IET Wiring Regulations introduced the requirement that all consumer units in domestic properties are to be manufactured from non-combustible materials. In my view this is an excellent step forward which has no doubt reduced the risk of serious fires and therefore decreased likely repair costs and thus expenditure on insurance premiums. However, following on from Colin Walkers excellent article3, could we not go one step forward and eradicate the fire threat in the first place?

     The amendments in the (IET Wiring Regulations)4 are welcome. However, such regulatory changes may only benefit a select few newer properties or refurbishments, as existing plastic consumer units may not be replaced for many years. This means there will continue to be a large number of combustible consumer units in service for many years to come. With this in mind, I believe it is important that tenants, homeowners and their appointed insurance companies are aware of the potential fire threat from their consumer units.

When a fire occurs in a consumer unit, the offending connection, outlet or circuit protective device (CPD) will begin to combust. If this process continues undisturbed, the consumer unit casing may catch alight and any combustible materials stored near the consumer unit can also be ignited. During this fire growth stage, molten materials and droplets of burning thermoplastic combustibles are ejected, causing secondary fire damage elsewhere. At this stage, the fire can develop further and spread throughout the property. This may result in severe fire damage to the property and occupants suffering injury or even death. Now, what would happen if this fire occurred in the middle of the night? After all, consumer unit fires can occur at any time. The release of blackened toxic smoke can put the sleeping occupants into a deep asphyxiant stupor, which reduces their chances of waking up to the smoke alarm.

     To protect yourself, your family and property against fire within the consumer unit, make sure you know the signs of an electrical fire. If you become aware of a persistent burning smell from an unknown origin, breakers continuing to trip, or charred or discoloured outlets and switches, call a specialist for help. For more information on signs to look out for, see EnvionUP’s informative article5.

Main Causes of Consumer Unit Fires

Localised Resistive Heating

     Probably the most common cause of consumer unit fires is the unwanted generation of heat within the consumer unit. Localised resistive heating is caused when an electrical load passes through a termination or connection, which is not able to properly conduct the current (normally due to the connection not having been properly tightened). This imperfect contact between connections increases resistance to current flow, in turn generating heat. Over time the contact resistance increases and eventually the heat generated is sufficient to start a fire.

     I attended a fire investigation at a property where the fire originated at the consumer unit. The tenant advised that while watching the television, it unexpectedly turned off. When going to check the MCB, fire and smoke were observed coming from the consumer unit. The fire was caused by a resistive heating fault on a neutral bar in the electrical circuit. The electric shower was in use at the time of fire. The heavy current feeding the shower provided enough heat build-up at an already loose connection to start a fire which resulted in considerable fire damage to the property.

Overloading of the circuit

     Overloading can occur when the circuit carries a heavier load than it is designed for. On a 20-Amp circuit, all the electrical devices connected to that circuit should add up to no more than 20 amps. If excess current flows through the circuit then excess heat will be developed in the wires and at electrical connections, which could result in overheating and eventually start a fire. Fuses and circuit breakers normally prevent this by “blowing” or “tripping” thus breaking the circuit when such overload occurs.

Faulty circuit protective devices

    Circuit protective devices (CPDs) such as fuses and miniature circuit breakers are designed to disconnect the supply should the current exceed a set value.However, fires have been known to originate at these devices. This can be due to a poor connection i.e. faulty installation. Also, there have been issues with some devices being defective. For instance, in July 2011, Electrium released a second safety recall notice that outlined a product recall of MCBs which were sold under the brand names of Crabtree, Volex and Wylex6. The recall related to a fire risk associated with MCBs supplied between April 2009 and February 2010. The issues related to localised melting and erosion between the static and moving contacts in the MCB. With the average success rate of an electrical product recall in the UK standing at just 10-20%7, this means that there are potentially recalled faulty CPDs still in use today.

Prevention of Fires in our Consumer Units

     There are several steps that can decrease your chances of injury if a fire were to occur within your consumer unit. Make sure any new electrical installation work is done by a fully qualified and certified electrician in accordance with the IET Wiring Regulations. If you are the owner of an older house, get the wiring and consumer unit checked by a fully qualified and certified electrician. If you are a tenant in a rented property, make sure your landlord is adhering to annual testing of the electrical installation. If practicable, make sure your consumer unit is installed in a place that will not inhibit exit during a fire. Ideally, follow the current IET Wiring Regulations and install a non-combustible consumer unit enclosure as this will contain the fire spread, significantly decreasing the likely level of damage to your property and give you a greater chance to escape.

     There are new devices on the market that are designed to detect excess heat within the consumer unit before an ignition can occur. Thermal Monitoring Systems (TMS) are designed to be installed inside the consumer unit. These thermal switches operate at a temperature below that at which there is a risk of ignition, but above that of normal circuit running conditions. So, they stop current before it becomes dangerous. Another device currently on the market is automatic fire suppression systems that comprise a combustible tube (containing a fire suppression liquid) that bursts open when the enclosure reaches a temperature of 70֯c 8.

     So, as you can see, although the threat of consumer unit fires is real, there are ways in which we can minimise the risk of such fires occurring in our home. If you think you have an issue with the electrical installation in your property then please get the problem rectified before it is too late.

References and Further Reading

  1. Electrical Safety First, 2020. Electrical Safety-First Core Data Set – England. Online at [].
  2. Electrical Safety First, 2011. Electrical Safety in Commercial areas of Residential properties. Online at [].
  3. Colin Walker, 2016. Technology Transferring Electrical Fire Safety. Online at [].
  4. The Institute of Engineering and Technology, 2015. New non-combustible enclosure requirement for consumer units. Online at [].
  5. EnvisionUP, 2020. What are the signs of an electrical fire? Online at [].
  6. Ministry of Defence, 2011. Electrical Miniature Circuit Breakers – Product Recall Notice. Online at []
  7. Electrical Safety First, 2020. Product Recalls & Safety Notices. Accessed online at []
  8. Envirograf 2020. EnviroBurst Automatic Fire Suppression System. Online at [].

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