Electrical Fault Finding

Electrical Fault Finding

Types of Electrical Faults

Electrical faults can come in various forms. Some can be just a bit annoying, whilst others could actually be quite dangerous as they present a shock risk.

Here are some examples:

Short circuit caused by moisture or damage

A damaged cable is quite commonly caused by the hanging of pictures or putting up shelves. When drilling into a wall with cables hidden beneath the surface, there is always the risk that you could drill into the cable, or subsequently screw into it.

If that screw penetrates the cable, it is highly likely that it will create a contact between some of the conductors, causing a short circuit. There are prescribed zones where cabling in walls is allowed, not all electrician have adhered to those rules, and of course many DIY enthusiasts may not be aware of such zones, and this can unfortunately catch people out with unpleasant consequences.

If the circuit has been set up correctly, it will have a protective device which should automatically disconnect the circuit from the supply, and will continue to trip each time you reset it until the fault has been rectified.

Moisture can also be a problem. Appliances such as irons and sandwich makers can suffer from the steam they generate seeping into the body of the appliance and causing a short circuit between the conductors. Steam generated by a kettle could have the same effect if the steam is allowed to get into mains sockets.

Outside lighting and sockets can also be a problem due to an ingress of moisture. Always choose lighting and sockets for use outdoors with appropriate IP Ratings, but in reality these don't always last forever. Water seepage or condensation can cause a short circuit, as can a poorly thought out installation.

The photos below show outdoor garden lamps. One had been mounted on a tree stump, which subsequently succumbed to fungus growth over the connector block, and the moisture caused a short circuit to occur, frequently tripping an RCD which disconnected several circuits in the house. The other lamp suffered due to ants having caused a build up of moist soil inside a six feet tall garden lamp post. The connector block was close to the top of the lamp post, yet the ants still managed to cause a short circuit and trip the protective circuit breaker.

Short circuit due to moisture on outside lighting
Lamp post in garden with short circuit due to ants
Lamp post in garden with short circuit moistureg
Some causes of short circuits on garden lighting

Overloaded circuit

Any circuit can only cope with so much electrical current before it fails.

To avoid a circuit failing due to overload, electricians need to ensure that the circuits are designed and installed correctly for their intended use. This means that the appropriate cable thickness is installed relative to the installation method, location and length, and also that the protective circuit breaker (an MCB for example) is of the appropriate value.

So what could happen if we plug in too many high powered appliances at the same time, such as a convector heater, hair dryer, kettle, toaster, etc? Or what could happen if a more powerful electric shower is installed in place of a lower powered shower?

Well in the case of the shower, if the original shower was adequately supplied by a 6mm2 cable protected by a 32 Amp circuit breaker, but the new more powerful shower exceeds the current carrying capacity of the 6mm2, the cable could get hot and possible fail and catch fire. To prevent that happening the 32 Amp circuit breaker should trip before the cable fails.

At least we could say that the circuit breaker is doing its job correctly, but the solution to the problem would be to have the cable size increased (most likely by replacing it with a 10mm2 cable), and only then have the circuit breaker changed to one with a higher breaking capacity.

In the case of there being too many high powered appliances in use at the same time, given that increasing the size of the electric cables and the circuit breaker is going to involve a fair amount of work and cost, the simplest solution would be to reduce that number of appliances.

The possible consequences of overloading mains extension leads is clear to see here...

Electric extension lead overheating
Coiled electric extension lead hazards
Electrical extension lead on fire

Breaks in a ring circuit

A break in a ring circuit might not be something you notice easily, but it could lead to potential problems. Here's why...

Ring circuits consist of a number of mains sockets which are linked together in a ring. This ring starts at the consumer unit and ends back there too. Therefore every point connected to that ring circuit is fed by electric cables from two directions. That means that each socket has a live wires (L and N) going to and from the socket, as well as an earth wire which is also connected in a continuous loop.

It therefore follows that if, at one socket, one of the connections comes away, that socket and all of the others would still work because the power could be coming from the wire from the other direction which might still be connected. So where's the problem?

Ring circuits are designed so that each point on that circuit gets an equal share of the supply. In relation to the consumer unit, there is no nearest and furthest point like there would be on a radial circuit (see below), as the path for each of the Line, Neutral and Earth conductors is continuous.

* A radial circuit consists of an electric cable which leaves the consumer unit to provide power to one or more sockets or connection points, but does not have a cable returning to the consumer unit like a ring circuit does. Therefore a radial circuit has a start and end. Lighting circuits, cooker circuits, shower circuits and immersion heater circuits are all examples of radial circuits. Radials are also used for socket circuits too, often wired in 4mm2 cable compared the more common 2.5mm2 cable used in ring circuits.

As stated previously, if one of the connections at one of the circuits came loose or disconnected, the sockets are still likely to work, but instead of that circuit being a ring, the break in the ring circuit has caused this to become two radial circuits. Depending on the length of each of these "accidental radials" and the electrical load placed on them, there is the potential for overload to occur, and this could mean that excessive heat and cable failure (including fire) could occur.

So what can be done?

Your electrician could run a continuity test on each on the conductors in the circuit. The expected results would be that the ring circuit is continuous and a resistance reading is obtained. But no continuity (otherwise known as an open circuit) would indicate that there is a break somewhere. The electrician would then follow steps to identify where that break is, and rectify the fault.

One thing the electrician ought to consider is the value of the circuit breaker in the consumer unit. A domestic ring circuit is usually protected by a 32 amp MCB, but if we find that the ring has been broken and had left us with two radial circuits using 2.5mm2 cable, consideration should be given to reducing the value of the circuit breaker to 20 Amps instead.

Note that is not unusual for a ring circuit to have a break in Line, Neutral AND Earth conductors, and not all at the same place. Despite this, the ring circuit could still work, but with the potential of an electrical overload occurring.

Electrical Fault Finding in Spalding

We are based near Spalding in south Lincolnshire, and offer electrical fault finding as part of our service. So if you're in the Spalding area and need some help with diagnosing an electrical fault, please contact us for a free quotation without obligation.

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Electrical Fault Finding
Electrical Fault Finding