Electrical Safety: Theory and Tests

Electrical safety, ES — a system of organizational measures and technical means that prevent the harmful and dangerous effects of electric current, electric arc, electromagnetic field and static electricity on workers.

Electrical safety comprises legal, socio-economic, organizational-technical, sanitary-hygienic, medical-preventive, rehabilitation and other measures.

Electrical safety rules are governed by legal and technical documents and by the normative-technical framework. Knowledge of the fundamentals of electrical safety is mandatory for personnel servicing electrical installations and electrical equipment.

Protection methods

Protection methods are a set of measures aimed at reducing to zero the probability of injuries and/or damage when using electrical equipment.

Design

Design is carried out by a person holding the documentation (competence) required for designing electrical systems, or by a qualified person under the supervision of a competent person. During design, all possible risks arising from the use of electric energy are taken into account and methods of avoiding hazards are applied. Design always proceeds from the worst-case operating conditions, taking into account a 100% probability of all risks. Before a project is commissioned, depending on the degree of hazard of the facility being designed, it must be approved by the relevant authorities.

Reducing touch voltage.

Values of up to 50 volts, with galvanic isolation of the circuits, allow the distance between a living organism and the given live part to be reduced all the way to actual contact.

Grounding

A protective, deliberate electrical connection of electrical installations and consumers to a grounding device in accordance with the manufacturer's instructions or the design.

Ability to quickly remove voltage

Disconnector (load-break switch)

In the event of a hazardous situation, it must always be possible to remove the voltage as quickly as possible, thereby freeing people who have come into contact with live parts. For this purpose, a load-break switch — a disconnector — is used at the entrance to the electrical panel. If people come into contact with live parts, switching off the incoming disconnector immediately de-energizes all circuits, freeing the affected people — the voltage is removed much faster this way than by searching for the branch fuse, greatly increasing the chances of saving the victims. The disconnector is selected according to the number of phases and the rated current. The rated current of the disconnector can be chosen based on one of three criteria:

• matching the rated current of the fuse protecting the supply line of the given electrical panel
• the sum of the rated currents of all the branch fuses (not recommended)
• if the supply cable is a trunk cable feeding several electrical panels at once, a fuse is installed as the input switching device

Motor circuits

Emergency stop button

To prevent mechanical injuries in equipment fitted with electric motors, an emergency stop button is used — the so-called mushroom-head button. As a rule, it is a button with normally closed contacts that locks in a fixed position and is wired into the motor control circuit in series with the contactor. When this button is pressed, the mechanism locks in the "depressed" position, keeping the control circuit open; and since the contactor coil no longer receives power, the contactor opens its contact pairs, breaking the circuit and cutting off the supply to the motor. Once power to the motor is cut off, it stops, freeing the person from the mechanical action of the motor's rotating parts.

Fire safety[

Fuse

One of the aims of design is to prevent hazardous operating modes in which wiring could overheat and cause a fire. The electrical system must be designed so as to rule out operation under fault conditions that lead to damage from excessive temperature or to fire. In other words, all the heat energy released during operation must be dissipated into the environment without damaging any part of the electrical equipment.

Electrical separation of networks

An extensive, branched electrical network has significant capacitance and low phase-to-ground resistance. In this case, even touching a single phase is very dangerous. If a single network is divided into a number of smaller networks of the same voltage, the risk of electric shock is sharply reduced. Network separation is usually carried out by connecting individual electrical installations through isolating transformers. Protective network separation is permitted only for networks up to 1000 V.

When carrying out electrical work

When carrying out electrical work, ensuring that live parts are inaccessible (both during and after the work) is considered, in order to minimize risks or eliminate entirely the danger of touching live parts of the electrical equipment. This is achieved by guarding and positioning live parts at an inaccessible height or in an inaccessible place. Both solid and mesh guards are used, with a mesh cell size of 25×25 mm. Solid guards in the form of enclosures and covers are used in electrical installations up to 1000 V.

Responsibility

• the presence of a person legally responsible for the electrical work (the person in charge of the electrical work) who holds the documentation (competence) required to carry out this type of electrical work;
• the personnel carrying out the electrical work having sufficient qualification for its safe performance;
• possession of the necessary tools and other equipment for safely carrying out the electrical work.

Site of the electrical work[

Before starting electrical work, the site is prepared:

• to eliminate hazards, the site of the electrical work is fenced off from outsiders;
• for the safety of the workers themselves, any sources of danger that pose a risk to the workers and/or threaten the safe conduct of the work are eliminated;
• in a damp environment, unsuitable equipment can become faulty, so it is necessary to make sure there is no excess water in the surrounding environment.

Removing the voltage

Single-side supply diagram. During electrical work, the consumer side must always be short-circuited to ground.

To avoid creating hazardous situations, the voltage is removed from the relevant section of the electrical circuit before work begins, and the switching device is marked with the appropriate warning signs. In industrial electrical installations, grounding blades are used to short-circuit the phase conductors on the consumer side when the voltage is removed to ground: if the voltage is mistakenly restored, a short circuit will occur and the fuse will blow, so people working in the installation will not be harmed. In domestic electrical work, it is usually sufficient to switch off the fuse — in this case, an accidental return of voltage would endanger the lives of people working in the installation. Portable grounding is used for overhead lines.

Checking for the absence of voltage

A technical measure. Checking for the absence of voltage on bare conductors is carried out exclusively with a two-pole voltage indicator, the UNN-1. Before use, the UNN-1 itself is checked for correct operation at a point where the corresponding voltage is present. The device must be operated and stored properly. In networks above 1000 volts, a high-voltage indicator, the UVN, is used.

Tools

Screwdriver with an insulated handle.

When working in an electrical installation, only insulated tools with a handle insulated for the relevant voltage may be used. To avoid electric shock or burns from a short circuit, it is strictly forbidden to work in an electrical installation with ordinary metal hand tools.

Live working

Live working carries the following risks:

• electric shock due to the large area of exposed conductors;
• burns due to the possibility of an accidental short circuit.

Up to 400 volts

When it is not possible to remove the voltage, workers use special equipment: dielectric gloves and face protection against burns. Before starting work, the possible risks are carefully weighed and sources of potential danger to the workers themselves are eliminated.

Remote work without removing the voltage

Diagram: current-carrying conductor — a tested insulating rod — rubber gloves — lineman on the ground.

Working at potential without removing the voltage and without breaking the line, at permissible safe distances between lines and to ground

Diagram: a tested basket on insulating supports — lineman in shielded protective clothing — a rod for attaching the equalizing conductor on the basket to the line conductor.

Another arrangement: a helicopter with an equalizer suspended in the air — rod attachment of the equalizer to the line — landing on the line.

Installation

The main aim of the installation is to minimize the risks associated with the use of electric energy. For example, all control and monitoring devices must be enclosed in a panel, access to conducting parts carrying dangerous voltage must be reliably shielded against accidental contact, and the protection rating of the electrical equipment must correspond to the operating environment.

Completion of work

Upon completion of the work, the work site is tidied up, waste is disposed of, and before the voltage is restored, the work is accepted by the person responsible for the electrical work (the person in charge of the electrical work) or by an inspector of the technical supervisory authorities holding the appropriate powers. At the moment the voltage is restored, the electrical installation must be fully fit for use: all workers must have left the site of the electrical work (as it is complete) and the conducting parts must be carefully closed off from outsiders.

In domestic use of electric energy

• Timely maintenance.
• Timely monitoring of insulation and grounding.
• Refraining from deliberately creating hazardous situations as a domestic user.

Electrical insulation

This symbol marks electrical installations with double insulation

A layer of dielectric that covers the surface of live parts, or a structure made of non-conducting material that separates live parts from the other parts of the electrical equipment. The following types of insulation are distinguished:

• basic — the electrical insulation of the live parts of an electrical installation that ensures its normal operation and protection against electric shock;
• supplementary — electrical insulation provided in addition to the basic insulation to protect against electric shock in the event that the basic insulation fails;
• double — insulation consisting of basic insulation plus supplementary insulation;
• reinforced — improved basic insulation that provides the same protection against electric shock as double insulation;
• the insulation resistance must be no less than 0.5 MOhm.

Every electrical appliance used in the home has a certain protection class. Each protection class corresponds to a certain degree of insulation:

• Class 0 — the appliance has only basic insulation (no longer manufactured today);
• Class 1 — the appliance has only basic insulation, but also has a terminal for connecting a protective conductor;
• Class 2 — the appliance has basic and supplementary insulation, or reinforced insulation, and therefore does not require grounding;
• Class 3 — the appliance is supplied by a voltage that is safe for humans and does not require enhanced precautions

Electrical safety qualification groups

In Russia, in accordance with the PTEEP (Rules for the Technical Operation of Consumer Electrical Installations) and the PTB (Labor Safety Rules), personnel servicing (working with) electrical installations are assigned 5 electrical safety qualification groups:

• Qualification group I is assigned to non-electrotechnical production personnel: PC operators, staff servicing electric furnaces, and the like.
• Qualification group II is assigned by a qualification commission to non-electrotechnical personnel servicing installations and equipment with electric drives, electric welders (without the right to connect equipment), heat-treatment operators of HF induction units, crane operators of lifting machinery, mobile machines and mechanisms with electric drives, personnel working with hand-held electric machines and other portable electric receivers, and so on.
• Qualification group III is assigned to electrotechnical personnel. Electrotechnological personnel are equated in rights and duties to electrotechnical personnel. This group grants the right to independently service, inspect, connect and disconnect electrical installations from the network. It is assigned only upon reaching the age of 18.
• Qualification group IV is assigned only to persons who are electrotechnical personnel. Persons with qualification group IV have the right to service electrical installations with a voltage above 1000 V. For a labor-safety engineer, at least 3 years of work experience in production (regardless of position) is required.
• Qualification group V is assigned to persons responsible for the electrical facility and to other engineering and technical personnel at installations with a voltage above 1000 V. For a labor-safety engineer to obtain this group, at least 5 years of work experience is required.

Persons with qualification group V have the right to issue instructions and direct work in electrical installations with voltages both up to 1000 V and above.

Electrical safety tests

Electrical safety tests with four answer options, one of which is correct:

1. Which organizational measures help prevent the harmful effects of electric current on workers?

• a) Organizing days off
• b) Carrying out fire evacuation
• c) Conducting electrical safety briefings *
• d) Participating in sports events

2. Which legislative acts regulate electrical safety issues?

• a) The Consumer Protection Law
• b) The Constitution of my country
• c) The Technical Regulation "On the Safety of Equipment"*
• d) The Transport Law

3. What measures are provided for protection against an electric arc?

• a) Use of remote control
• b) Use of genuine leather gloves
• c) Installation of protective screens*
• d) Practicing meditation

4. What technical means are used to prevent the hazardous effects of static electricity?

• a) Special antistatic suits*
• b) Use of antistatic creams
• c) Use of antistatic floor mats
• d) Frequent technical prayers

5. What kinds of electric fields can have a harmful effect on the human body?

• a) High-intensity electric fields *
• b) Electric fields of light
• c) Electric fields generated by closed microwave ovens
• d) The Earth's magnetic fields

6. Which medical-preventive measures are recommended when the body is exposed to electric current?

• a) Taking hot baths
• b) Consulting a doctor*
• c) Applying heating pads to the affected area
• d) Drinking sweet beverages

7. What basic principles of electrical safety should be observed when working with electrical equipment?

• a) Absence of safety instructions
• b) Use of non-standard outlets
• c) Checking that the equipment is in working order before starting work*
• d) Neglecting personal protective equipment

8. What is remote control and how is it related to electrical safety?

• a) Controlling remote objects using a computer or mobile device*
• b) Controlling a machine at school
• c) Remote control of a vacuum cleaner
• d) Controlling a TV from the couch

9. What requirements are placed on personnel within the framework of electrical safety?

• a) A mandatory higher-level education
• b) Possession of an electrical safety certificate*
• c) Ability to play musical instruments
• d) Work experience in the culinary field

10. What safety measures are recommended when carrying out electrical installation work?

• a) wearing safety glasses*
• b) Use of certified materials*
• c) Working with the power disconnected*
• d) Following safety instructions*

11. What are the basic principles of organizing a safe workplace when working with electrical installations?

• a) The presence of a large number of unsecured cables
• b) Cleanliness and order in the workplace
• c) Use of ungrounded devices
• d) Absence of safety instructions

12. What technical protective means are used to prevent electric shock?

• a) Use of wooden tools
• b) Use of insulating gloves*
• c) Ignoring grounding
• d) Working alone

13. What grounding principles are applied to ensure electrical safety?

• a) The presence of many insulated wires
• b) Grounding the current-carrying parts of electrical installations*
• c) Coating the equipment with colored paint
• d) Using metal tools

14. What measures should be taken in the event of an emergency situation involving electrical equipment?

• a) Observe the situation without taking any action
• b) Urgently call friends
• c) Take measures for safe evacuation and call the emergency services*
• d) Continue working regardless of the situation

15. What hazards are associated with the improper operation of electrical installations?

• a) The appearance of colored paint on the walls
• b) Damage to equipment*
• c) The possibility of rain appearing indoors
• d) Increased equipment productivity

16. What preventive measures help prevent fires associated with electrical equipment?

• a) Regular cleaning of dust and debris*
• b) Lighting bonfires near the equipment
• c) Increasing the number of electrical appliances in the workplace
• d) Using open flame in production

17. What safety measures are recommended when working near power lines?

• a) Ignoring warning signs
• b) Using tools with metal handles
• c) Working without the necessary clothing
• d) Maintaining a safe distance and using insulating equipment*

18. What special considerations are associated with the rehabilitation of workers after an electrical injury?

• a) Absence of medical care
• b) Returning to work regardless of health condition
• c) Undergoing rehabilitation courses and medical supervision*
• d) Isolation from society

19. What are the basic requirements for personal protective equipment when working with electrical equipment?

• a) Use of unreliable protective equipment
• b) Possession of certified protective equipment*
• c) Not using protective equipment at all
• d) Buying the cheapest protective equipment

20. What safety measures should be observed when operating power tools?

• a) Using tools without regular inspection
• b) Working without protective clothing
• c) Regularly checking the tool's condition and grounding it*
• d) Using a power tool during a thunderstorm

See also

• Protection class against electric shock
• IP (Degrees of protection provided by enclosures)