Protect yourself and your equipment (using differential protection devices)

Today, it is necessary and technically possible to use electrical installations that are as safe as possible for people, for electrical appliances and the electrical installation itself. The relevance and necessity of using differential protection devices in electrical installations is now recognized in most European countries and the development of international standards forces differential protection to be ubiquitous.

Protecting the life and health of people, their property is a task of primary importance, which predetermines the requirements for the electrical installations of buildings.

Safety in the operation of electrical installations and devices is achieved by using a set of protective measures.

One way to increase Electrical safety is the Residual Current Devices (RCD) application.

The danger of exposure to electric current depends on two factors: the time during which the current passes through the human body and amperage… These two factors are independent of each other and the severity of the electrical injury will be more or less depending on the degree of each of them. The strength of the current dangerous to humans depends on the magnitude of the applied voltage and the resistance of the human body.

Fire hazard

Not only people but also equipment are exposed to electrical hazards. There is a fire hazard for the equipment. For example, a current of 500 mA flowing through combustible materials can ignite them. You should know that in any electrical installation there is a current leakage, which can vary significantly depending on the condition of the equipment, the time of operation, environmental conditions, etc. Leakage currents flow into metal parts (pipes, beams and other structural elements) and heat them up, which can lead to a fire.

Direct contacts

Direct contact occurs due to careless or careless human behavior. Direct contact is human contact with a live conductive part of equipment or installation. Examples: using an extension cord with bare contacts or wires; in a switchboard or cabinet, a person touches a live bus or damages hidden electrical wires with a metal tool, etc.

There are two ways to protect people from direct contact (regardless of neutral mode):

1. Prohibit, if possible, access to live parts of the equipment.

Basic protection. It is ensured by removing or isolating active parts of the equipment. The basic protection must be carried out in such a way that the active parts of the equipment are inaccessible to anyone, even accidental contact.This is achieved with the help of fences, protective enclosures, closed cabinets, exits with covers, insulation, which make the active parts of the equipment dangerous for the user inaccessible.

Additional protection. It is provided by installing differential protection devices with a sensitivity of 10 or 30 mA, such as differential switches Lexica production Legrand... They come into operation only in the event of a violation of the main protection.

Indirect contacts

Indirect contacts occur for reasons independent of human action. They are related to internal malfunctions of the equipment. Indirect contact is human contact with metal parts of equipment that have accidentally turned on due to insulation failure. This type of contact is very dangerous because, unlike direct contact, it cannot be predicted. Example: a person touches the metal casing of an electrical appliance with damaged insulation and, if adequate protection is not provided, receives an electric shock.

There are two ways to avoid this.

1. Block access to potentially dangerous metal parts of the equipment using insulation class II (double insulation: if the first is broken, the second remains effective).

Degree of insulation II - this simple and effective means avoids the danger of current leakage and ensures that people are protected from indirect contact. Class II protection have two main advantages: natural protection against indirect contact with electrical equipment in the circuit section of the input circuit breaker to the differential device;

- transfer of the differential protection function from the input automaton level to the distribution level.This provides the selectivity necessary for the continued and safe operation of the equipment.

2.Automatically turn off the unit in case of power leakage. This requires:

- a good connection between the instrument boxes and their connection to the grounding electrode;

- well-executed grounding device;

-turn off the device.

Whatever the neutral mode, the protection design is based on the fact that the leakage current must be short-circuited to ground: this makes it easy to detect. Therefore, it is necessary to have a well-designed system of earthing electrodes to which all electrical enclosures of consumers must be connected. Added to this is a device for detecting leakage current and automatic shutdown.

RCD — a switching device or a set of elements which, when the differential current reaches (exceeds) the set value under certain operating conditions, should cause the contacts to open.

So in European countries there are about six hundred million RCDs installed in residential and public buildings. Long-term experience in the operation of RCDs has proven their high efficiency as a means of protection against fault currents.

RCDs provide a high degree of protection for people from electric shock with direct and indirect contact, as well as RCDs provide a reduction in the risk of fire in electrical installations.

Residual current circuit breakers, together with overcurrent protection devices, belong to the main types of protection against indirect contact, providing automatic shutdown.

Overcurrent (short circuit) protection provides protection against indirect contact by disconnecting the damaged part of the circuit with a dead short to the box.At low fault currents, reducing the insulation level, as well as in case of opening neutral protective conductor USOs are actually the only means of protection.

The use of overcurrent protection is mandatory for residential buildings and the use of an RCD is recommended. PPE can by no means be the only type of protection against indirect contact.

The main types of protection against direct contact are isolation of live parts and measures to prevent access to them. The installation of an RCD with a rated tripping current of up to 30 mA is considered an additional measure of protection against direct contact in the event of damage or failure of the main types of protection. That is, the use of an RCD cannot replace the main types of protection, but it can supplement them and provide a higher level of protection in case of failure of the main types of protection.

The use of RCDs in electrical installations of buildings is the only way to ensure protection in case of direct contact with live parts.

All devices work as follows: an RCD is included in the circuit of the operating current, and when a leakage current of a certain value (equal to or greater than the setting) occurs, it opens the supply circuit.

There are two types of differential devices: type AC and type A. In the option, devices of both types C (selective) or conventional design can be implemented.

Type AC — sensitive to AC leakage. Usage: standard case.

Type A — sensitive to both AC leakage current and DC leakage current Use: special cases — if the leakage currents are not purely sinusoidal (rectifier, etc.).

Execution C (type AC or A) -delayed tripping to ensure selectivity of operation with other differential devices. Use: to provide selectivity with the introducer.