Electrical Fault: What is it & how is it dangerous?

An ELECTRICAL FAULT is any electrical issue that prevents the electrical system from turning on, from staying on or from working safely. Electrical faults can be a whole variety of different things and can range from irritating issues to outright dangerous issues depending upon the nature of the electrical fault. 

We discuss some of the electrical faults that are common to electrical systems below.

1) What Types of Electrical Fault are there?

1.1) Short / Short Circuit

The short circuit is an electrical fault that results in a very low electrical resistance between Line and Neutral. Under normal circumstances there would be electrical loads connected between Line and Neutral such as appliances and lamps that have a reasonable resistance. Low electrical currents would flow through these appliances and their resistances and the electrical system would work. 

When there is a short circuit the amount of electrical current that flows can be very high and can cause immediate damage to the cables in the circuit. As such, electrical systems are designed to disconnect the supply quickly when a short circuit occurs. This is one of the reasons that electrical system design and construction is so vitally important and should be carried out correctly to ensure that disconnection times can be met in accordance with the wiring regulations. 

1.2) What are the common causes of a short circuit?

A short circuit occurs between Line and Neutral so when we think about the causes of a short circuit, we have to consider the circumstances under which this can happen. 

A nail or a screw through an electrical cable is fairly common reason for causing a short circuit. As the nail passes through the cable it often destroys the circuit protective conductor (or earth) and damages the insulation on both the Neutral and Line conductor causing a bridge to occur between them. This ‘shorts out’ the circuit and causing a low resistance path to occur between the two conductors. We can see from the photograph below that floorboards had been nailed through into cables causing multiple short circuits!

Appliances can also develop issues with their internal wiring especially in places where Line and Neutral may be already in close proximity. Circuit boards are a common cause of shorting out. Circuit boards have many different electrical paths in close proximity to each other and something as simple as moisture appearing on a circuit board can cause a short between Line and Neutral. 

2) Earth Fault

This is an issue where either Line or Neutral develops a path to earth of either a high or low resistance. The result of this can cause an MCB to trip if the fault is from Line to Earth and is of a low resistance. An MCB will not trip for a Neutral to Earth fault as the Neutral is not monitored by an MCB device generally. 

The other result we can witness is an RCD type device tripping due to some electrical current disappearing to earth. An RCD device will trip when there is any leakage from Live or Neutral to Earth as it is assumed that there is an electric shock occurring to someone using the electrical installation. 

2.1) What are the common causes of an earth fault?

• Common causes of an Earth Fault could be: 
• Damage to a cable, 
• Damage to an appliance, 
• Poor insulation around the copper conductors of a cable, 
• Water ingress, 
• Rodent infestation affecting the electrical system or almost any other reason.

If a nail or screw hits a cable and causes neutral and earth to touch then an RCD device will trip. If some damage occurs to a cable the internal insulation could become damaged causing current to leak from either Line or Neutral to earth and tripping the circuit off.

Appliances are a common cause of earth faults in electrical systems. Appliances often contain delicate electronics and circuitry with conductors in close proximity to each other. When appliances begin to fail, they can leak electrical current to earth. This will be detected by RCD devices and they will then act to disconnect the supply to the circuit which the appliance is connected to. 
When the insulation around the copper conductors of a cable becomes damaged, aged, or otherwise ineffective there can be electrical current leakage from the circuit to earth. This will be detected by the RCD which will then turn off the circuit(s).

Water ingress is a major cause of earth faults in electrical systems. Water is not a brilliant conductor of electricity but it is good enough to create a sufficient path for electrical current to leak away to earth and for an RCD to detect a problem and turn off the circuit. 

Rodents love electrical cables and will happily chew on these removing the outer sheath and the cable insulation until the cable is damaged enough for the electrical system to detect this and turn off. 

3) Broken conductor

An electrical conductor in an electrical system is usually a copper wire that carries electrical current from one part of a circuit to another. This could be a Line conductor, Neutral conductor, Circuit protective conductor or a switched line conductor. 

Broken conductors are common in electrical systems and they are not always detected by the users of the electrical system an often are only picked up when an electrician performs a periodic electrical inspection or whilst carrying out fault finding on an unrelated electrical fault. The photograph below shows a wall light that require an earth connection but was never connected. This is potentially dangerous but would have gone unnoticed until a fault occurred making the metal work of the light fitting live! 

Broken conductors can result in lights or plug sockets not working correctly or at all. Electric shocks can occur where earth wires are broken or overheating can occur where Ring Final circuit conductors are broken. 

3.1) What are the causes of a broken conductor?

Cause of a broken conductor could be:

• Cable damage
• Damaged electrical accessories
• Loose cables
• Incorrectly wired switches

Cable damage can result in any of the internal wires becoming severed resulting in a broken conductor. This type of fault is likely to also result in an RCD or MCB device tripping as damage to a cable rarely results in a clean break of one single conductor. More likely is that the damage will also result in the broken conductor also touching Earth (circuit protective conductor) which would then operate one of the protective devices at the consumer unit / fuse box. 

Damaged electrical accessories can result in a broken conductor occurring. One example of this would be an electrical plug socket becoming damaged or corroded. On the back of plug sockets there is often an EARTH BAR that runs from one side to the other and carries the earth continuity across the circuit. If this earth bar becomes corroded or broken then it can result in a broken earth to the socket circuit. 

The danger with this is that a broken earth will nearly always go unnoticed until there is a secondary electrical fault that require the earth in place to safely disconnect. ☹ 

Loose cables often occur at the back of electrical accessories such as light switches and plug sockets. They will go unnoticed until there is a secondary issue that pops up. Loose cables are also common in electric panels or consumer units. Electrical systems are generally ignored and not maintained in residential buildings and as a result these types of issue develop over a long time. 

Incorrectly wired switches can result in cross connections or broken conductors as a switch is operated, it breaks the conductor to turn off supply.

4) Insulation Resistance Fault 

An insulation resistance fault is where there is break down in the electrical circuits insulation resistance. Typically, this could be the resistance between Line – Earth – Neutral. This could either be that the insulation around the copper conductors has failed or broken down somehow OR that there is an issue where cables join together or into appliances. 
Insulation resistance should be very high under normal conditions. Typically, millions of Ohms (the ohm is a measurement of electrical resistance) would be expected between Line – Neutral – Earth with no appliances connected in the circuit. 

4.1) What could cause an insulation resistance fault? 

Insulation breakdown in the cable is a common cause of an insulation resistance fault. When cables age, so does the insulation around the copper conductors in the cable. This insulation can develop micro cracks along its length, lowering the resistance of the insulation and causing tiny amounts of electrical current to leak from Neutral or Line onto Earth (no really 😊). 

If the insulation around the cables becomes wet or moist then this can be enough to lower the resistance and cause excessive current leakage. We tend to see more electrical faults in the winter than at other times of the year as winters are typically wetter. 
Water ingress in general can affect the insulation resistance of wiring systems and as water ingresses into various places throughout the electrical system, havoc can ensue!

5) High Resistance

When a high resistance occurs along an electrical conductor, we can see issues with how the electrical system begins to operate. When we think about electrical resistance, envision an impedance to electrical current flow. Similar to a busy motorway or freeway reduced to one lane. All of a sudden there is a massive amount of traffic forced through a tiny gap. Traffic flow is ruined, everything is slowed down and tempers can flare. 

When there is a high electrical resistance the electrical current cannot flow as freely, not enough electrical current can get through the circuit although it still tries to. This causes the circuit to heat up and things to not work properly. Lights can dim, appliance motors can slow down and things may not work at all. 

5.1) What could cause a high resistance fault?

Typically, there are a few things that can introduce a high resistance. When a conductor becomes loose it presents a high resistance to current flow. This can happen where, for example, a screw has not been tightened sufficiently in a plug socket terminal or light switch terminal. We can see from the photograph below that these electrical wires had fallen out of the socket they were so loose!!