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Electrical Fire

What causes an electrical fire?

Electrical fires have been at the forefront of the news a lot recently due to several high profile events, but how much do we know about what causes an electrical fire, how can we prevent them happening and what can we put in place to help contain them if they do break out?


Electricity is often overlooked as a potential source of fire as there is no visible flame, yet around 28,000 fires in the home are reported each year to have started from an electrical fault, accident or misuse of equipment. On New Year’s Day 2018, an eco-home that took six years to build and previously featured in the TV programme Grand Designs was burned to the ground. The owner reported that it started in a junction box downstairs. Jasmine Dale, the owner, was quoted in The Telegraph saying: “The fire was caused by a freak electrical fault. I was in the house just a few moments before the fire broke out, and there is a junction box downstairs with many electrical wires.”


Such was the devastation of the fire, the house was completed destroyed and we’re never likely to know the root cause of the fire within the junction box. There are however several possible causes that using good engineering practice and installation methods can be minimised. The phrase “many electrical wires” is worrying. Most standard domestic style junction boxes are designed to take a maximum of 4 cables and have 4 cable entry points. Having too many cables bunched together will affect how the heat dissipates from the cables, increasing the ambient temperature.


Most junction boxes have screw terminals and if these are not fixed correctly, the resistance is increased in the circuit. Where resistance is raised, there will again be more heat given out by the circuit. Loose terminal screws are often a source of electrical fire because of this, and all electrical terminations should be in an area suitable for regular inspection so they can be tightened as required. They are not suitable for mounting behind plasterboard and forgetting about. Special maintenance free connectors and installation methods can be used for areas that cannot be accessed in the future. Many electricians or DIY’ers continue to use junction boxes as they are cheaper.


It is also possible, if the termination was poor within the junction box, that a short circuit could have arisen from two bare cables touching, or being too close, causing an electric arc. An arc has a huge amount of energy which could start a fire if the circuit breaker did not operate as it should (if the circuit has been poorly designed). It is important when adding a new circuit, or modifying a circuit, that you ensure that the maximum amount of resistance in the circuit allowed is not exceeded.


Junction boxes are also not a one size fits all. Some smaller units are only rated at 5 amps. Larger ones tend to be 20 amps. When selecting your materials, ensure that they are suitable for the job at hand. All parts of electrical systems should be to the relevant British Standard, and marked accordingly. Only use reputable suppliers and be cautious as due to the rise of online marketplaces, lots of cheap, sub-standard counterfeit accessories are being sold on a daily basis.


The environment that the box is placed in should also be considered especially with regards to insulation and the box should be of a suitable material for its environment. Since the introduction of Amendment 3 of the wiring regs, all consumer units in domestic settings need to be constructed of a non-combustible materials, usually metal. A metal enclosure with suitable sealed knockout holes will contain a fire within it, stemming the spread. Envirograf manufacture an excellent item called the Envirobust Tube – a plastic tube that bursts open at 70℃ that contains a fire suppression liquid.


Electrical fires are not only caused by DIY installers, faulty equipment or poor install methods. Appliances cause a large amount of fires, most notable the fridge that was the reported cause of the tragic events at Grenfell Tower in 2017 where 71 people lost their lives. Use them in the manner they were intended, protect them from water, and make sure you register them with their manufacturer when you purchase them to be notified of any product recalls. Don’t leave electric heaters unattended and keep them away from curtains. Ensure they are kept in good working order, check cables for fraying and any signs of burning or scorching. If a fuse blows, make sure you replace it with one of the same rating. A 13a fuse in a thin cable won’t protect it, and could cause a fire. If the fuse keeps blowing, it’s because there’s a problem – get it fixed or replace the appliance.


Overloaded extension leads are also a large cause of fires both in the home and at work. Avoid plugging in high powered devices (as a general rule, things that produce heat such as kettles, heaters, cookers use the most power) into extension leads, this useful calculator will help, but is also complicated by the fact lots of extension leads on sale now are not rated at 13a. Some 10a and 5a leads are available, and are cheaper as they use thinner cable, but should only ever be used for low powered equipment such as IT or audio/visual equipment & lamps. It is recommended that extension leads are never used as a permanent fixture, however we all know this isn’t practical, so be careful.


Fires are not only started in the home or office. In January 2018 a fire broke out on the rooftop of Trump Tower in New York, a 58-story skyscraper built in 1983 by the man who went on to become the 45th President of the USA, Donald Trump. It was reported to be caused by an electrical box in a cooling tower and rooftops of large buildings often contain a large amount of plant, most notably air conditioning systems. In this instance, it was actually spotted by the Secret Service who monitor the building for threats and it was dealt with quickly and easily by the FDNY with 3 minor injuries to crew working at the blaze. We’ve not all got the Secret Service monitoring our buildings, but it goes to show that early detection is important in all cases, and this can be done in residential, commercial and industrial environments by the use of fire detection systems, allowing a small fire to be tackled with appropriate extinguishers or the building to be safely evacuated while you wait for Fire & Rescue. Plant rooms and areas are always a risk as they contain lots of equipment, are mostly left unattended and have high ambient temperatures.


Avoiding electrical fires should be something considered at all points of a building or electrical installations life; at the design phase, while being built/installed, during use and maintenance and also, often overlooked, during a change of use that may mean existing systems are no longer suitable.

Misrated Fuse

Common PAT Testing Failures

Here are some examples of common PAT testing failures we find to give you an idea of what is deemed safe or not. It is important that the duty holder and end user have a basic knowledge of these items, so that any appliance that becomes unsafe between test periods gets removed from service and/or suitable repairs are carried out by a competent person.

Misrated Fuse

1. Incorrect Fuse Fitted

While there is an agreed standard for new electrical appliances, incorrect fuse ratings are still the most common issue found when PAT testing. With modern appliances anything that uses less than 700W of power should be fitted with a 3A fuse, anything above 700W a 13A fuse. While this works, and was designed to simplify the process, it’s not always adhered to and can be improved upon.

13A wall sockets are good for anything up to 3000W of power, therefore a general rule of thumb often applied is each 1000W draws approximately 4A of current, therefore needs a fuse rating slightly higher than that to protect the wire. In the event of an appliance entering a fault condition, a surge of current will blow the fuse, break the circuit and stop a too high current flowing down the wire. If the fuse rating is too high, it may not blow, potentially allowing a current too high to pass through the cable, which left over time will cause a fire.

How is it corrected? Your PAT test engineer will replace the fuse with the correct rating and your appliance will be safe to use.

2. Cracked or Damaged Plug

Damaged Plug

Any cracks or damage to the plug, or excessive damage to the appliance itself that may expose it’s electrics will fail. A cracked or damaged plug, could potentially be an electric shock risk when the end user is removing or plugging in the item. A cracked case that exposes the electrics inside, would also be a fail for the same reason.

How is it corrected? A cracked or damaged plug would be replaced by your PAT test engineer. An item with a damaged case will most likely need replacing, insulation tape is not an acceptable repair. If spotted before your PAT testing is due, they should be repaired or removed from service.

3. Non-Insulated Live and Neutral Pins

Non-insulated Live and Neutral Pins Despite not being manufactured in this style for many years, these plugs still crop up from time to time. Newer, modern plugs have the Live and Neutral pins insulated to stop the users fingers making connection with the metal when the plug is partially inserted, during plugging & unplugging of the appliance. Whereas if the plug and socket is the correct size and shape, the user shouldn’t be able to make contact with the pins until they have been disconnected from the source, there have been instances where people have used metal implements to remove a stuck plug and made contact. A common trick amongst school children was to wedge a 1p piece between the pins to create an explosion when plugging in – this is a very unsafe practice, potentially injuring the user, causing a fire and damaging the whole electric circuit. These plugs are very dangerous if used incorrectly and should not be used.

How is it corrected? These will be replaced by your PAT test engineer. If spotted before your PAT testing is due, they should be repaired or removed from service.

4. Earth Pin Insulation

Insulated Earth PinAs a complete opposite to the above problem, the plug attached to the cable to the left has the earth pin partly insulated that it shouldn’t have. We’ve covered this before on our Counterfeit Plugs blog post so have a read of that if you want details, but when this is plugged in, it won’t make the earth connection as required.

How is it corrected? These items are generally counterfeit cables, stamped as meeting the BS1363 when they don’t. The plug cannot be swapped as there is no way in telling if the rest of the cable has been manufactured with sub-standard materials. You should remove them from service, contact the supplier who you purchased them from for a full refund, and inform trading standards.

5. Damaged Flex

Damaged FlexExcessive wear and tear to the cable is also considered dangerous and the item should be removed from service if spotted. If any more damage was to occur to the flex in the image, bare wires would potentially be visible, creating a shock risk if the wire, or a conductive item that made a connection to the wire, was touched.

How is it corrected? In nearly all cases, damaged flex can be disconnected from the appliance and refitted with a direct replacement, or one with a heavier-duty sheath.

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