Electrical safety devices are devices that interrupt the electrical current if it exceeds what a circuit or appliance can handle. The most common are fuses and circuit breakers. Proper sizing and selection of these devices are essential to prevent accidents such as overloads, fires, shocks, and equipment damage, both in residential and industrial settings.
Because electricity is a powerful yet dangerous substance, there are several standards and certifications that must be considered when assembling your electrical system. Below, we summarize the most commonly used electrical safety devices, as well as the most important standards to observe when purchasing them.
Electrical safety devices and protection systems
Electrical safety devices are part of circuit protection systems in an industrial plant or a residence as a whole. The components of a protection system, in this case, are:
– Instrumentation transformers (current and potential), which regulate the values of voltage and current signals circulating in the system;
– Protection relays, which can be electromechanical, electronic, or intelligent electronic devices (numerical relays or digital relays);
– Communication channels, which facilitate the exchange of information between protection relays and improve the performance of the protection system;
Fuses;
– Circuit breakers, which are capable of cutting off the circuit if it starts operating outside of normal conditions, preventing the formation of an electric arc. In low-voltage installations (quicklagsdevices of the type are used “no fuse”, Circuit breakers, or without a fuse, interrupt the current flow by opening a switch. In this case, the device consists of two elements capable of detecting the presence of overcurrent, which can come from a short circuit or overload: a thermal element, which detects long-duration overload, and a magnetic element, which detects a short circuit. Circuit breakers also have a switch and an arc-extinguishing chamber – which extinguishes the electric arc that is formed when the switch opens.
Therefore, electrical safety devices are part of the circuit protection system. However, there are differences between industrial and residential applications.
Electrical safety devices: which are the most commonly used in industrial and residential installations?
In Brazil, ABNT NBR 5410 is the technical standard that regulates the procedures for installing low-voltage electrical networks (up to 1,000 volts alternating current and 1,500 volts direct current). This standard, based on IEC 60364, covers: residential and commercial buildings, institutional and public use establishments, industrial establishments, agricultural and horticultural establishments, prefabricated buildings, trailers, campsites, marinas, construction sites, and temporary installations.
According to the standard, the main electrical safety devices for residential or industrial building installations are: fuses, surge protection devices (SPDs), residual current devices (RCDs), and circuit breakers (CVMs).
Fuses
These are protective devices composed of a conductive element capable of melting when a specific current occurs within a well-defined time interval. The most common fuses in low-voltage installations are of the screw type, cartridge type (knife or ferrule), diazed and NH, with high disruptive capacity. This is an overcurrent protection device against overload or short circuit and must be replaced after being activated.
DPS device
Surge protectors protect electrical and electronic installations and equipment against the direct and indirect effects of lightning strikes. They are classified as:
Class I: eliminate the direct effects of lightning strikes;
Class II: protects electrical equipment against induced or conducted overvoltages originating from lightning strikes;
– Class III: used to protect equipment located more than 30 meters from the head-up surge protection device (SPD).
DR device
This device protects people from electric shocks. It is necessary because the thermomagnetic circuit breaker does not recognize small currents, which can still cause serious harm to the bodies of mammals. For this reason, NBR 5410 mandates the use of residual current devices (RCDs) in wet or humid locations, such as:
– Points of use in wet areas or areas subject to washing, such as kitchens, garages and laundry rooms;
– Indoor power outlets used to power equipment in outdoor areas;
– Points located where there is a bathtub or shower;
– Electrical outlets in non-residential locations;
– Electrical outlets and lighting in outdoor areas.
DTM device
This is the most common of all. The thermomagnetic circuit breaker is a switching and protection device. That is, it is capable of automatically tripping when it detects atypical heat in the circuit, which may indicate excess current. Such devices are classified according to their type of operation:
– By the number of poles: single-pole, two-phase or three-phase;
– Due to the short-circuit current (of curve B, C or D).
Thus, the most commonly used electrical safety devices are fuses, circuit breakers, surge protectors (SPDs), and residual current devices (RCDs). The difference in choosing between them, however, lies in the type of equipment they will be used with and the building (whether residential or industrial). In any case, correct sizing is essential for these elements to fulfill their function of providing greater safety.
Source: https://loja.br.abb.com/blog/post/dispositivos-de-seguranca-eletrica
See also: https://cswsolucoes.com.br/entenda-a-diferenca-entre-circuito-em-serie-e-paralelo/