Power tool protection classes: design features, operating conditions and electrical safety

Work with any electrical installation is fraught with the danger of electric shock. This is especially true when handling a hand-held electric tool, since the body of the device is always in the hands during operation. The degree of safety is determined by a special classification. The protection class of a power tool reflects the design features and conditions of use, aimed at preventing electrical injury.

Safety degree

The safety of a power tool is determined by its protective characteristics. Depending on them, requirements are established for the place of work, device connection and additional protection measures.

Device classification

Classification according to the degree of protection against electric shock is essential when using an electric tool. The lower classes represent the greatest danger in the process of work, with an increase in the indicator, the protection against the effects of current on a person increases. The list of protection classes is as follows:

• Class 0. Zero-class instruments are provided with working insulation of live parts only. Other non-current-carrying metal elements of the device, including the case, are not insulated, therefore, temporary or permanent contact of a person to areas with high electrical conductivity is possible. The devices are not designed for protective grounding. The unit does not have a special indication of abnormal operation of the device if there is a voltage hazardous to humans on the case or other elements. Zero class includes many relatively old devices with a metal case that do not have grounding, electric hotplates and other open coil heating devices, lighting devices. Most of the Soviet-made electrical appliances belong to this group.
• Class 00. All characteristics, with the exception of the indication that the case is energized, correspond to zero class. Class 00 is not marked in the official classification, but this designation is widely used. Examples of these devices include individual models of portable electrical generators.
• Class 000. The designation is also not standardized. Such devices have the same characteristics as in the zero class, but are equipped with an integrated residual current device. Protection parameters may differ, but usually the RCD provides automatic shutdown of the device at a leakage current of 30 mA, acting for several hundredths of a second.
• Class 0I. The devices are provided with working insulation only. All other metal elements are not insulated. Protection against the effects of electric current on a person is provided by grounding. The design assumes the presence of a separate grounding contact on the body. It is denoted by the traditional symbol in the form of a stylized arrow, consisting of one vertical and three horizontal lines. With this method, it is required to select a wire of the required section, connect one end of it to the contact grounding on the unit body, and the second - to fix it in the grounding loop connector located in the electrical shield. Today it is already quite difficult to find a tool that uses this grounding method. However, old appliances, as well as massive machine tools and large electrical units, often use an independent connection to the ground loop.
• Class I. All characteristics correspond to class 0I, however, the grounding of the case and other metal non-current-carrying parts is carried out more than common way: the power cable is equipped with an additional grounding conductor, which is connected to a separate pin of the plug forks. Such appliances should only be connected to a socket outlet equipped with an earthing connection. Otherwise, the operation of the device will pose a significant danger, and the tool itself in all respects will become similar to the zero class. Examples include a washing machine, microwave oven, desktop computer system unit. For modern power tools, first class protection is usually not used.
• Class I +. The parameters of the devices are similar to the first class, however, as an additional safety measure, a residual current device is included in the design of the device. This modification is rarely used, so its designation is not standardized.
• Class II. The devices are reinforced or double insulated. By definition, grounding of the device case is not required. The plug is not equipped with a grounding terminal. There is a generally accepted graphic designation of such devices in the form of two squares, one of which is embedded in the other. It is to this class that most mains power tools belong: drills, saws, wrenches. Examples of devices of this class are also TVs, vacuum cleaners, household hair dryers.
• Class II +. All parameters are similar to the second class, however, a residual current device is introduced into the design of the device. This type is quite rare, therefore, it is also not noted in the standardized classification. The graphic markings are similar to the second class, but the + sign is placed in the small square.
• Class III. This group includes all devices that do not have circuits in the design, the voltage of which exceeds 42 V DC or 36 V AC. Devices of this type can be graphically marked on the body in the form of the number III, enclosed inside a rhombus. Examples include any cordless tool without high-voltage circuits: screwdrivers, drills, scissors. Among household appliances, this group includes lanterns, radios powered by batteries or accumulators. The third class also includes all devices powered by an external power supply connected to a wall outlet.

The use of devices with the highest possible degrees of protection allows you to best protect the worker from abnormal situations that may arise in the event of a tool malfunction. In the presence of improved insulation and the absence of housing elements made of electrically conductive materials, the lack of grounding should not be confused, since there is no need for it.

Features of operation

The protection class of the device dictates certain requirements for the operating conditions. Compliance with these recommendations allows you to protect a person from the possibility of receiving electrical injuries. Before starting work, you must make sure that the available tool is suitable for use in the existing environment. Here are the basic requirements:

• Devices of the zero protection class may only be used in rooms that do not pose an increased electrical hazard. This means that the interior must be dry and the floor and walls must be made of non-conductive materials. Before carrying out work, access to the premises of unauthorized persons who are not involved in the production process should be excluded.
• In exceptional cases, it is allowed to operate class 00 devices in conditions of high humidity and outdoors. Only specially trained personnel are allowed to perform such work. All operations can be carried out only with the use of dielectric personal protective equipment.
• Class 000 products are also permitted in exceptional cases to operate in conditions of increased electrical hazard. However, their characteristics already allow for work not only by specially trained personnel, but also by any other person. The use of personal protective equipment against electric shock is also mandatory.
• Class 01 devices allow only minor movements during operation, limited by the length of the ground wire. Operation of such devices without connection to the ground loop is strictly prohibited.
• First class devices can be operated without restrictions. Exceptions to this rule may be specially stipulated in the instruction manual for the device. It is allowed to connect such devices to the network without protective grounding, but only in rooms with low electrical hazard. It should be remembered that in this case all the restrictions imposed on the zero class apply.
• Devices of class I + are used without any restrictions, but only with a ground connection. Operation without connection to the ground loop is allowed, while the employee must use personal protective dielectric equipment.
• Devices of the second class do not require special operating conditions. The only exception can be the prohibition on the use of devices with enclosure protection less than IP65 in conditions of high humidity, when it exceeds 85%.
• Devices of classes II + and III have no restrictions on operating conditions.

Currently, there is a trend towards a complete rejection of the use of zero-class devices. A growing number of countries have identified such devices as unsafe.

Case characteristics

The safe performance of work is influenced not only by the electrical safety class of the power tool. To the same extent, to prevent electrical injuries, the degree of protection of the device case from access and touching current-carrying elements, ingress of foreign objects and moisture is important. The degree of protection is marked on the devices with the IP designation followed by two numbers. The first characterizes the protection against the penetration of solid objects, and the second - moisture.

Foreign objects

Protection against foreign objects involves not only limiting the penetration of external foreign objects, but also preventing a person from touching the internal elements. Thus, protection is designed not only to protect a person from electrical injury, but also to prevent damage to the device. The value of the indicator is deciphered as follows:

• A zero value indicates a complete lack of protection.
• The unit assumes protection against objects larger than 50 mm, that is, it cannot protect against touching with fingers.
• Number 2 indicates the inability to touch the mechanism. The housing prevents the penetration of objects over 12.5 mm.
• The triple eliminates the possibility of contact with live elements of some tools, the thickness of which is more than 2.5 mm.
• Number 4 indicates that a tool thicker than 1 mm will not penetrate inside.
• The five indicates the dustproofness of the case. Penetration of small amounts of finely dispersed dust is allowed, which does not affect the operation of the device.
• The number 6 indicates complete dustproofness.

The numbers 5 and 6 indicate complete protection against touching the internal elements of the device, directly or with a tool.

Water penetration

Moisture protection is aimed at preventing damage to the tool itself. However, this characteristic also indirectly affects electrical safety, since water is a good conductor. Protection levels indicate the following parameters:

• Zero indicates no protection.
• The unit shows protection against vertical drops of water.
• Deuce - from drops falling on the body at an angle of up to 15 degrees.
• Digit 3 demonstrates splash protection. This includes exposure to rain at an angle of up to 60 degrees.
• Number 4 indicates protection against splashes from any direction.
• The five indicates protection against water jets.
• Number 6 indicates resistance to strong water currents.
• Seven allows short-term immersion of the device in water to a depth of no more than one meter.
• The figure eight allows the device to be immersed deeper than one meter and for a period of more than thirty minutes.
• The nine indicates complete protection against the impact on the body of powerful jets of high temperature water.

For maximum safety when using your power tool, familiarize yourself with the level of protection before starting work and provide the necessary conditions in accordance with the specified class. It is necessary to strictly adhere to the requirements for grounding and the use of personal protective equipment. If you need regular use, it is recommended to purchase the most secure devices, their cost will certainly pay off with reliability and safety.