This is the second of three posts focusing on addressing electrical safety non-compliance in many older residential dwellings. In the first post, we looked at the risks and documented incidents this situation is causing for people, infrastructure, equipment, and buildings. Before we talk about the steps needed to improve the situation, let’s do a brief review of how today’s safety standards help reduce risks in residential electrical installations.
Protection against electric shocks
Installation standards define several protective measures. This includes protection against direct contact with live parts, as well as fault protection. For dwellings, this commonly requires the presence of a protective earthing conductor, and automatic disconnection in case of a fault. Depending on the type of earthing system, the disconnecting device can be a circuit-breaker, or a residual current device (RCD). The IEC 60364 standard also requires additional protection by means of a 30 mA RCD on circuits supplying socket outlets up to 32 A, and circuits supplying mobile equipment for outdoor use, and – as per a recent revision – for lighting circuits in dwellings.
These protective devices shall be installed in an electrical switchboard or enclosure, to avoid any direct contact with the live parts and this switchboard shall comply to a safety standard to guarantee safe behaviour.
Protection against overcurrents and arcs
Protection against overload and short-circuit currents is primarily intended to avoid thermal damage or destruction that can result in fire. These protections limit the continuous and short-circuit current that may circulate in the cable and, in turn, the potential degradation of the cable’s insulation. The devices used to protect against overcurrent conditions are circuit breakers and fuses, each complying with their specific product standards; they are selected according to the conductors characteristics (cross section, type of insulation) of the circuit to be protected
Arc-faults are another serious hazard. They can be especially dangerous in premises with sleeping accommodation or where there may irreplaceable goods stored. Locations that have specific kinds of combustible materials or fire propagating structures can also be at high risk. In these situations, arc fault protection devices that comply with relevant standards are recommended.
Protection against overvoltages
An overvoltage condition can be extremely damaging to electrical equipment and installation. It can occur because of an atmospheric event, such as lightning, or from switching of a high-power load somewhere in the electrical system, either inside a building or on the external utility network. Such overvoltages may severely damage the electrical equipment of the installation. Protection against overvoltage requires the presence of a connection to the earth and a surge protective device (SPD), complying to safety standard. According to latest installation standard, overvoltage protection is mandatory where the consequence of overvoltages affects: human life, medical services, public services, commercial and industrial activities.
Safety of components – Compliance to standards
All the above mentioned safety measures need to be achieved by safe electrical accessories and protective devices. What it your circuit-breaker is not able to trip in a few milliseconds in case of short-circuit ? Or if your socket-outlet shows visible damage like broken parts or shows wear and tear ? All these aspects are covered by standards.
Conductors, circuit-breakers, socket-outlets, switches and all components of an electrical installation must comply to their relevant safety standards.
In addition, some countries forbid some types of devices (e.g. socket outlets with claw fixing) or require additional safety measures like devices for connecting luminaries (DCL) or socket-outlets with shutters.
Verification – the key to preserving safety
The electrical standards and technologies mentioned here ensure that new residential electrical installations are safe. Standards also make sure installations remain safe over their entire lifetime. IEC 60364-6 defines both initial verification of an installation to the standard, as well as recommending verification of residential dwellings every 10 years. This periodic verification checks that fundamental protective measures remain active and reliable.
A similar program of periodic audits can be applied to older existing residential dwellings to reveal non-compliances and set a path toward gradually raising safety levels. We’ll discuss this approach in the next post in this series.
To learn more about the subject of this blog series, refer to the Schneider Electric white paper ‘Raising the electrical safety of existing residential buildings’.