An electrical installation is an essential part of any room, office, or building. Every such installation requires maintenance, upgrading, or repair from time to time, which involves a certain amount of risk taken by the electrician (electrical installer) involved.
key safety rules and most common mistakes when making an electrical installation
Working with electrical installations always carries a degree of risk, however, it can be effectively minimized. The prerequisite is to follow safety rules, use the right tools and avoid basic mistakes that can lead to a failure or an accident.
Principles of safe electrical installation
Electricity in typical single-phase or three-phase installations can pose a serious danger to health and life. Therefore, for your own safety, you should wear appropriate personal protective equipment (goggles, gloves, clothing, footwear, insulating matting) and use safe tools and equipment (certified meters, testers, probes, insulated hand tools such as pliers, screwdrivers, combination pliers, open-ended or socket spanners). When working with an electrical installation in your home, you can increase safety by ensuring that the installation is properly designed and protected using the TN-S system, i.e. with a separate protective conductor for the entire system, which is only used to protect the connected appliances. Here, there are a few basic rules, the most important of which is to have a three-wire single-phase system (phase wire, neutral wire, and a protective wire) or a five-wire three-phase system (phase wires L1, L2, L3, a neutral wire, and a protective wire). The obvious conclusion is that in all rooms, sockets with a protective contact, to which a protective wire is connected, must be installed. The situation is similar with luminaires, which must be compliant with protection Class II: they also must be connected to a protective conductor.
Residual current circuit breakers and safe electrical cable routing
One of the key safety rules is to protect installation circuits with residual current circuit breakers and to use equipotential bonding that connects protective conductors with conductive parts of other installations in order to equalize the electric potential of conductive components. It is also necessary to route electrical cables in straight lines and always parallel or perpendicular to the edges of walls and ceilings: this is an absolutely fundamental principle and must be followed. Obviously, all cables should be concealed in special cable ducts, tubes, or trays, with the exception of multi-conductor cables covered with plasticized PVC sheath (the so-called polyvinyl), which can be freely laid directly on the surface or under the plaster. When installing sockets in bathrooms and other rooms where there is a risk of splashing or dusting of such sockets (garages, sanitary facilities, etc.), it is necessary to use appliances with at least an IP44 protection rating.
To ensure further safety at work with electrical installations in the building, it is advisable to run separate circuits for lighting, general-purpose plug sockets, plug sockets with a higher risk of splashing (bathroom, kitchen), and for some appliances that require individual protection (computers, server, etc.).
Making an electrical installation – the most common mistakes
Safety at work with electrical installations can be increased by avoiding some common mistakes:
- Mistake 1: use of protections that are not appropriate to the load– the consequences include installation overload, which can lead to damage to appliances or cause a fire;
- Mistake 2: choosing conductors with insufficient cross-section– the consequences are the same as in the case of overloading the installation;
- Mistake 3: inconsistent use of colored conductors– the effect, particularly in the case of three-phase appliances, may be the occurrence of voltage on the appliance casings, which may result in an electric shock;
- Mistake 4: discontinuity of insulation, incorrect insulation of contacts, or twisting of contacts within the electric switchboard– this may lead to current leak (idle power consumption), short-circuits, and triggering of residual current circuit breakers;
- Mistake 5: missing or careless labeling of fuses and wires in the switchboard (fuse box)– such omissions make it difficult to locate the part of the installation that needs to be temporarily disconnected;
- Mistake 6: excessive loads on individual electrical circuits and sockets– this common consequence of limiting the number of circuits results in the overload, which has already been discussed earlier.
Until as recently as 25 years ago, a typical electrical installation in detached houses consisted of 4 to 6 electrical circuits, including constant and recurring elements such as a lighting circuit, a socket circuit, and a circuit for devices with high power consumption, i.e. the so-called “kitchen & bathroom circuit”, which powered cookers, ovens, kettles or washing machines. Over time, another, fairly obvious circuit appeared among those designed to power the property, i.e. the circuit to which yard lighting, an electric gate, an intercom, or garden tools such as a lawnmower and sprinklers are connected. Today, the number of systems and devices (which are often very sensitive to changes in or loss of power supply) that require separate circuits is significantly higher. It can also be concluded, based on practical experience, that it is not worth overloading each circuit. It is, therefore, better to make more of them, taking into account possible future needs. Nowadays, the number of circuits that are worth considering when designing electrical installations for detached houses is often more than two or even three times as many as what was recommended 2 decades ago. Suggested optimized division of the installation into individual circuits is presented in the list below.
- Lighting circuit: in the era of LED lighting, which is gradually replacing old-fashioned incandescent bulbs, it is safe and functional to create a separate circuit for the kitchen, bathroom, outdoor lighting, as well as a separate circuit for the rooms on each floor of the building.
- Plug sockets in rooms: sockets should be connected to a separate circuit or several circuits – depending on how many of them are being connected and the size of the building. A separate circuit for each room is an optimal solution.
- IT equipment – AV – TV: a separate electrical circuit for the computer, printer, scanner, music system, and home cinema is highly recommended. For safety reasons, it is advisable to support such equipment with an uninterruptible power supply (UPS).
- Passageways (evacuation routes): all corridors, passageways connecting structures between the house and the garage, etc. should be connected to a separate circuit. This increases the safety of residents.
- Appliances with a power output greater than 1500W: all such appliances should be supplied by a separate circuit. As there are now many appliances in our kitchens and bathrooms with a power consumption of at least 2000W, experts recommend setting up several circuits – an individual one for the induction hob, the dishwasher, the fridge, and the kettle, the washing machine, the oven, the kitchen lighting, and the extractor hood. As a rule, kitchen and bathroom sockets for small domestic appliances should always be connected to a separate circuit. The same applies to underfloor heating, which has recently become very popular in bathrooms (heating mats or cables).
Backyard, surroundings of the property: backyard (garden) lighting, pool pump, electrically operated gate, driveway heating, pond, yard maintenance equipment all require a separate circuit or two, depending on your needs and the electrical load
choosing the right fuse for the circuit – how to match the fuse to the power?
Automatic overcurrent circuit breakers, commonly called fuses, protect individual circuits and the equipment connected to them. Their purpose is to immediately cut off the electrical energy in the event of a short-circuit or overload. This can happen immediately or with a delay, e.g. in the case of C-type fuses, which have a high inrush current capability. They are connected in the distribution box to the phase wire on one side and to a socket or a switch on the other end.
What are the characteristics of an automatic fuse?
Automatic fuses are quite a diverse group of products that can be divided according to several parameters. It is worth mentioning here the time-current characteristics, which specify the time after which the breaker will trip. In this case, proper choice of a fuse is extremely important, because a circuit to which sensitive electronic devices are connected must be protected in a different way than, for example, the one to which motors that require higher inrush current are connected. While discussing solutions for the protection of a home installation, we can skip some of the characteristics that are related to industrial applications and focus only on the first three of them.
- Type-A time-current characteristics– These are the most sensitive fuses and they will trip immediately when overload is detected. They are used to protect delicate electronic equipment.
- Type-B time-current characteristics – These fuses are the most commonly found in homes and they protect, for example, lighting circuits or circuits connected to electrical sockets. Their overload trip current is 1.13 – 1.45 times greater, while the short-circuit trip current is 3 – 5 times greater than the rated current.
- Type-C time-current characteristics– Circuit breakers with this characteristic are used for the protection of devices with increased inrush currents. They can protect circuits in a garage or a workshop. The overload trip current is the same as for the B-type fuses, while the short-circuit trip current is 5 – 10 times the rated current.
How to choose the right overcurrent circuit breaker?
Choosing the right overcurrent circuit breaker for a specific circuit depends primarily on the type, or rather the degree of load in the circuit generated by the equipment connected to it. Here, calculations are necessary to correctly choose parameters such as: short-circuit breaking capacity, number of poles, tripping curve or rated current. In practice, for a circuit in a typical household installation, B-type DIN rail-mounted overcurrent circuit breakers should be used, with short-circuit capacity of 6kA and 10kA, as they are fully effective in protecting cables against overloads and short-circuits. For circuits operating under greater loads – such as kitchen or bathroom circuits – breakers with the rating of 16-20A are recommended. For standard “socket circuits”, 10A-16A fuses should be sufficient, and for a circuit connected to luminaires, a 10A fuse will be more than enough.
RCD – why is it important to install a residual current device?
Since quite recently, residual current devices – (RCD for short) – have become mandatory components installed in every household switchboard and in every new installation. They are often confused with overcurrent circuit breakers, but their operation and functions are completely different. In a nutshell, professionals distinguish three types of RCDs based on the differential current they can handle. These are, respectively:
- High-sensitivity residual current devices(up to 30 mA), which are used in kitchens, bathrooms, workshops, studios, etc. – where the risk of fire caused by a faulty installation or appliance is quite high;
- Medium-sensitivity residual current devices(from 30 to 500 mA), which are ideal for protecting general-purpose circuits in residential buildings or on construction sites;
- Low-sensitivity residual current devices(from 500 mA up), which are used for circuits with high leak current and as main circuit breakers for the entire home electrical installation.
How to install RCDs?
The method of installation of the RCD clearly reveals its mode of operation, as it is mounted in the distribution box in such a way that the phase and neutral conductors pass through it. When the situation is stable and safe, the current flowing in the circuit is the same as the current flowing in the neutral conductor. As soon as there is a fault in the installation, the current “leaks” and is present, for example, on the housing of an electrical appliance – as a result, the values of the phase and neutral currents start to differ. It is this difference between the two parameters that gave the name to RCDs, and its occurrence triggers a mechanism that disconnects the installation from the power supply.
The above description of the operation and use of RCDs largely answers the question posed in the title of the chapter. This equipment primarily protects users of the installation and connected devices against electric shock resulting from direct or indirect contact. This function may save not only health but also life. At the same time, RCDs minimize the risk of fire caused by a possible failure of the installation or appliances connected to one of the circuits.
The distribution box, commonly known as the fuse box, is a built-in space in which all the circuits of the local electrical installation are grouped – both those routed inside the house and those leading outside, i.e. to the garden, yard, or driveway. This is where all the protections are located, thanks to which the installation functions properly and which protects the circuits, connected devices, and us – the users – in case of unusual and dangerous events or situations.
As a standard, every such box – often also called a switchboard or junction box – contains overcurrent circuit breakers, which protect the circuit and its users from the effects of a short-circuit or overload by interrupting the flow of current. Apart from them, the presence of at least one RCD is required. In the switchboard, you can also find a so-called isolating switch, which cuts off the power supply from the entire installation. This main emergency stop switch allows – for example in the event of a flood or fire – to immediately switch off the power in the entire facility.
In addition to the abovementioned basic components, there are often additional modules and accessories installed in the distribution box. Much depends on the age of the building and the electrical installation, and on whether the building manager has equipped the building with additional automation, which, along with the development of the ”Smart Home” concept, is becoming more and more popular in our households. The following list presents most of the possible additional modules and accessories available on the market that can be installed in a typical distribution box:
- Surge protectors often called surge arrestors: protect the electrical installation and the equipment connected to it from damage that may occur due to the flow of high amperage current. This is a typical situation during a thunderstorm when lightning strikes a nearby transmission line.
- Priority relays: they monitor power distribution and load. When too many electrical appliances connected to the installation or circuit are switched on, these relays allow the appliances identified as a priority to operate. Other, less important ones are switched off.
- Control programmers: they are a part of a simple home automation system and allow selected circuits to be powered at specific times according to a pre-set program. Typical applications include switching on lights before entering the house or starting the water heater.
- Electricity meter: this is a compulsory component of any electrical installation and very often it is installed in a fuse box, although this is not the rule.
- Indicator lights, also known as indicators: are used to inform users of the installation of the presence of voltage in a given circuit or connection point.
- Socket outlets: these are most often associated with typical construction switchboards, but for some time now they are also installed in household distribution boxes, both in single-phase and three-phase installations.
- Data transmission modules: these can be grouped together in separate multimedia switchboards, but can also function in a single common fuse box. They include devices such as routers, converters (fiber optic internet), TV and Wi-Fi repeaters, switches, controllers, or power strips with 230V and USB sockets.
Three-phase installations: how do they differ from single-phase installations?
Three-phase installations are becoming an essential piece of equipment, not only in a home workshop or studio but also in any modern kitchen is detached or multi-residential houses. The three-phase power supply is a 230/400V installation, which consists of five conductors. Three of these are phase conductors and the other two are the neutral N and the protective PE conductor, which is rather uncommon in older three-\phase systems. Such an installation is used in houses equipped with devices and machines with considerable power consumption. These include electric cookers, hobs, electric boilers, instantaneous water heaters, boilers, washer-dryers, and underfloor heating systems.
Supplying power to high-power appliances is not the only benefit of a three-phase installation. Another one is safety and comfort: three separate phases allow you to use the abovementioned appliances at the same time without any worries.
Necessary components of a 3-phase installation (equipment, accessories).
Three-phase installations basically consist of the same components as single-phase installations. However, their individual circuits, which supply particularly important appliances with high power consumption (kitchen and workshop equipment), should be well planned. A recommended addition to such installations is three-phase sockets outside the house, in the workshop, or garage. They will supply power to construction equipment when needed, e.g. when the users decide to expand their house.
When it comes to protecting home electrical installations, it is worth making sure that tripping the residual current device will not turn off the power in too many places at the same time. Therefore, the optimal solution is to use at least 2-3 RCDs, including a separate one for three-phase devices. However, when choosing the right RCDs, it should be remembered that in this case, the key parameters are the cross-section of conductors and their load capacity. These parameters are particularly important for three-phase installations, hence the need to reach for B-type 20A circuit breakers.