Main Breaker Switch Burnt Out. Why? How? What to do?

May 2024

1) Power Problems and the Main Switch

A MAIN SWITCH BURNT OUT will normally mean that you have a complete and total power loss to your home. The main switch or linked main switch as it is also known, is a key component to the consumer unit, electrical panel or fuse box. 

The main switch takes the incoming power supply from the mains and sends it to the various components inside the electrical panel. When the main switch is turned off or burnt out, none of the panel will have any power supply but could still be live!

With an RCD or GFCI Main Switch, there may be some power cuts before it burns out. You may find that the main switch trips before it actually burns out. This is likely because of loose connections occurring where the mains cables meet the terminals on the main switch OR where the outgoing cables and busbar are connected to. 

2) Main Causes

Whilst there are several possibilities for your electrical fault the most likely causes of a MAIN SWITCH BURNT OUT are:

• Loose connections at switch
• Internal wear and tear
• Excessive electrical loads
• Over torqued terminals
• Short Circuit

We will discuss each of these situations and their effect on the switch, the power supply and any other risks associated with them. 

3) Loose Connections at the Switch

The incoming side of the Main Switch receives the power cables from the mains supply equipment. These cables are usually much thicker than the rest of the electrical cables in your home as they are intended to carry the total electrical load for your property. 

As a result, they can be difficult to install, subject to heating and cooling and may work loose over time. If the connections become loose or are not tight enough in the first place then the joint will heat up and start to cause problems.

When copper heats up to a certain point, it oxidizes creating a situation where electricity struggles to pass. Oxidized copper is less conductive than shiny bright copper and poses a resistance to electrical current flow. This increase in resistance along with the resistance created by poor electrical contact of loose connections can really start to heat things up. Just like tempers can flare in bottleneck traffic jams, electrical current is very similar. 

All the current wants to continue flowing but it is difficult for it! Resistance brings more heat; more heat increases resistance and very quickly we develop a situation where electrical fires can start. 

4) Internal Wear and Tear

Components of the electrical system all have a life span. It’s easy to think electrical problems occur randomly but in reality, many electrical problems are years in the making. Over time components, cables and electrical accessories can wear out creating heat, resistance and electrical burnout. 

It is much more common to have electrical problems in older homes as the electrical circuits are likely to have seen extended and prolonged use. Modern electrical wiring and systems are incredibly efficient, good value and fit for use for many decades if properly looked after and maintained by a professional electrician. 

The main switch does not have an easy life, it has to handle the total electrical demand for the electrical system and this can eventually create oxidized internal metal parts, tarnishing and poor internal connections. The location of installation can also contribute to a premature main switch failure. Where electrical components like this are installed in damp areas, they are more prone to internal metal tarnishing than in other locations. 

5) Excessive Electrical Loads

Each main switch will have a maximum voltage rating and a maximum electrical current rating. The current rating is the most important aspect to focus on when it comes to considering excessive electrical load. 

Most main switches are rated to allow for any electrical equipment that will be installed but occasionally they can become overloaded. This is becoming more common with the dawn of electrical vehicle charging equipment, older main switches are now being put under additional load which will make an aging switch fail far more quickly than it would otherwise have done. 

If you think that you may be overloading your main switch look for the current rating. This is denoted by a number followed by ‘A’. We can see from the picture below that this main switch is rated for 100 ‘A’ or AMPS (electrical current measurement unit).

If we were to regularly exceed 100 amps of current demand from our system this would result in a MAIN SWITCH BURNT OUT along with the associated damage to the incoming power cables and other components within the electrical panel or consumer unit. 

6) Over Torqued Terminals

When electrical work is carried out on a consumer unit or electrical panel, many electricians will check the existing connections inside as good practice to ensure that nothing is too loose. There are specific torque requirements set by the manufacturer of the switches and consumer unit. 

These torque requirements should be followed as too little torque will result in loose connections and too much will result in sheared, screws, stress fractures to the internal metals and a higher probability that the main switch will fail sooner. 

Bad connections can also be caused by using tools such as an impact driver to tighten switch terminal screws. These are particularly savage to electrical components as they hammer whilst driving the screw tighter causing metal stress fractures and even splitting the switch open.

7) Short Circuit

On rarer occasions, a main switch can fail internally and short out. When this happens, it is likely that the main supply cut out fuse will blow and you will be plunged into darkness without any power at all. The electricity network will need to be notified at this point and attend once your main switch has been replaced. 

8) How does a Main Switch Work?

The main switch is normally contained in the circuit breaker panel and its responsibility is to break the electrical connections from the main supply to the electrical system, isolating the supply.

The main switch for your electrical installation is sometimes a TRIP SWITCH as well as an isolation switch. Where the main switch is also a trip switch then it will perform other functions besides just isolation. 

The linked main switch is a mechanically linked switch that will disconnect BOTH line (hot) and neutral conductors at the same time. 

The trip switch will detect various issues including earth or ground fault, possibly overload and short circuit issues. The simple main switch will not trip for any reason as it is present ONLY as an isolation device. In the face of excessive electrical demand, it will simply result in a MAIN SWITCH BURN OUT.

9) Can a faulty switch cause a fire?

If your main switch is faulty then it potentially could cause a fire. Its important to remember though, there are other devices in places for when this kind of situation happens. The electricity suppliers’ main fuse in your home should blow as it is designed to. This would prevent a fire in this type of shorting out situation.

(Rusted switch creating poor resistance and electrical burning)

If there were other faulty switches in your electrical panel or consumer unit then these could also be a fire risk. Electrical fire is very common where the switches are incorrectly rated. Say for example the cable for an electrical circuit was undersized, then the cables could theoretically catch fire before a trip switch or main switch were to trip. This would appear as if the switch was faulty when in reality, the electrical installation had been poorly designed and installed.

10) How do I know if my Main Switch is Faulty?

If you are experiencing power outages intermittently especially when you use electrical equipment like an electric shower, electrical outlets, power hungry electrical appliances or vehicle charging equipment then it could be a sign that your main switch is faulty or potentially burning out. 

Flickering lights is also sometimes an indicator that things may not be right with the main switch.

If your electrical system is behaving strangely then ask a qualified electrician to come and check it for you for your peace of mind. 

11) What steps can I take to prevent a Main Switch Burnt out situation?

A periodic electrical inspection is a great way to check on the condition of the electrical system in your home. A periodic electrical inspection is where an electrician visits to check the fuse box/electrical panel, and faulty wiring, the light switches, plug sockets and electrical outlets. 

The electrician SHOULD take several hours to complete this process. There are many different checks that the electrician will perform such as:

• Checking the lighting circuits for correct earthing and cable quality
• Checking the electrical box and the wire connections
• Looking in the back of the switch on light switches
• Checking the electrical supply and its condition
• Looking for signs of damage in the electrical system
• Checking the circuit overload devices are correct
• Ensuring that electric shock protection is adequate
• Looking for faulty wiring

12) Summary

Where you suspect that you have a MAIN SWITCH BURNT OUT its always best to engage the services of a licensed electrician. There are multiple q&a communities online that may offer advice but beware, an online community may have no qualified persons that really know what advice to give. Seeking advice from these places is often no different than asking around in a bar. 

Whilst there can be many different symptoms that may indicate a burn out main switch, if you have any suspicions that your electrical system has issues, if you have a strange burning smell or see any smoke from any equipment, shut off the power supply immediately and obtain the services of a reliable electrician to check things out for you. 

A problem found quickly and not ignored is often a less expensive problem to fix.