Electrical installations have a very important role in buildings, since they provide an energy source for many appliances and building systems. In modern society, electric current is the fastest and most efficient method to deliver energy. However, the power of electricity also makes it dangerous when not used property, and electrical systems must be safe and reliable.

Buildings use plenty of equipment and devices that run with electricity. There are many types of electrical installations, but they must all meet two common requirements:

• Being able to deliver enough power for all the electrical devices connected, while keeping a stable voltage.
• Operating safely without exposing occupants to electric shock, and without creating fire hazards.

The NFPA 70 National Electrical Code (NEC) is one of the most widely used references for electrical design, not only in the USA but also internationally. The NEC was developed by the National Fire Protection Association, and the first edition was published more than a century ago in 1897. The code is reviewed and updated every three years to keep up with the latest technologies, and the most recent edition was published in 2020. Cities, states and even entire countries have created their local electrical codes based on the NEC. Delivering enough power and operating safely are basic requirements for all electrical installations. However, electrical engineers also recommend the use of energy efficiency measures. While these measures may increase the initial cost of your electrical systems, every dollar invested is recovered several times during the service life of your building. If the local power grid is dependent on fossil fuels, energy efficiency will also reduce the carbon emissions produced by your building. Generating electricity on site is now viable, and solar panels in particular can adapt to buildings of all sizes and occupancies. However, a safe and reliable electrical installation is important even when clean energy sources are used. Also, energy efficiency maximizes the value of every kilowatt-hour produced.

Electrical protections have a very important function in buildings: when an electrical fault occurs, they disconnect the affected circuits immediately. If an electrical circuit is left connected with an active fault, the consequences can include major component damage, fire, or electric shock. Most electrical protection devices use thermal or magnetic mechanisms to disconnect faults, and many protection devices use both types.

• Thermal protections use the heat released by the high electrical current that occurs during a fault. The heat expands a contact inside the protection device, opening the circuit and interrupting the fault current.
• Magnetic protections respond to the magnetic fields caused by fault currents, opening the circuit in response. Since there is no heating involved, magnetic protections act faster than thermal protections.

Magnetic protections may seem like a better option because they are faster, but this is not the case - each protection mechanism is suited for different applications. Devices like electric motors and lamps with ballasts have a brief inrush current when they activate, and the magnetic protection must not trip with this current. Instead, the magnetic protection must be calibrated for much higher currents, such as those found in short circuits and ground faults.

There are cases where a high current lasts longer than normal, indicating a fault. For example, an inrush current is normal when a motor starts, but an operating current above the motor’s nameplate value indicates an overload. In this case, a thermal protection device heats up and trips with the overload current. There are many types of protection devices, each designed for different applications. The following are some of the most common types found in residential and commercial buildings: Some appliances and equipment need more than one type of protection to achieve full safety. For example, power outlets in bathrooms are protected by a circuit breaker at the distribution board, but they also use an integrated GFCI. Circuit breakers are arranged in distribution boards, which have special contacts and terminal blocks to simplify connections. Each distribution board must be specified with enough spaces for all the circuits that will be connected. Note that circuits with two live conductors use 2-pole breakers, while three-phase circuits use 3-pole breakers. These circuit breakers with more than one pole use several spaces in the distribution board.

Circuit breakers and other electrical protections are only reliable if they are suited for the application at hand. Using high-quality products is important, but their capacity can only be specified after a detailed electrical load calculation.

Building codes normally require an emergency power system, to ensure that key equipment can stay operational during an electric service interruption. This includes fire protection systems, since they must be capable of responding to fire 24/7, even during blackouts. Diesel generators are the most common option to supply emergency power in buildings, but natural gas generators and battery arrays are emerging as viable alternatives. Emergency power systems are subject to stringent specifications and building code requirements, due to their critical function.