Electric equipment protection classes
Electric equipment protection classesDate of publication: 23-11-2022 Update date: 24-04-2024 🕒 6 min read
- Electric shock protection rules
- Direct and indirect contact protection
- Protection classes – general
- Protection class 0
- Protection class I – protective conductor
- Protection class II – double or enhanced insulation
- Protection class III – low-voltage protection
- Other safety-relevant classifications – IP degrees of protection
- Are you keen on electronics? Visit Tech Master Event
In electric engineering, a protection class indication is used to classify and identify electric equipment (e.g. devices and system components) depending on the existing general and electric shock protection measures. Each class is identified by an individual symbol placed on devices you buy or operate.
Electric shock protection rules
Protection against electric shock is aimed at reducing (to a maximum possible degree) the possibility of injury or death caused directly or indirectly by electric current impact.
Here, the danger comes from the fact that we do not detect the voltage presence until we come into direct contact with it. Unlike in the case of e.g. fire, which manifests itself with light or smoke, nothing warns us of electricity. The voltage presence can only be detected by an induced current, however, it is often too late to react at that point.
General principles of electric shock protection applying to electric systems, networks and equipment stipulate that dangerous live parts must not be easily accessible, while those conductive parts which are or must be accessible should be safeguarded:
- under standard conditions (operating as designed, with no faults present);
- in the case of a single fault.
While providing electric shock protection, the following significant electric shock-related hazards must be taken into account:
- voltage values in relation to the earth potential, which depend on the system voltage rating;
- environmental conditions related to electric equipment operation.
Direct and indirect contact protection
In order to prevent electric shock, hazardous to humans, the following protection measures are implemented simultaneously:
- direct contact protection (also referred to as “basic protection”) performing its function under normal conditions;
- indirect contact protection (often referred to as “secondary protection”, or “fault protection”) triggered when a single fault (e.g. insulation damage) occurs.
Usually, each of the above-mentioned protection methods is implemented separately and differently, but there are also enhanced protection measures that fulfil both above-mentioned tasks. Such a system ensures simultaneous protection against direct and indirect contact.
Protection classes – general
Protection classes for all electric devices are defined in DIN EN 61140 and PN-EN 61140:2005 standards.
There are four protection classes for electric equipment, however, only protection classes I, II and III are approved in the EU and other industrialised countries. Protection class symbols provided to identify equipment are defined in the IEC 60417 standard. Protective measures to be implemented for electric equipment of various classes are described in the PN-EN 61140:2005 standard.
Protection class I label
Protection class II label
Protection class III label
It must be noted here that a protection class is a notion different from a protection type. A protection class rating describes the means of protection against hazardous voltages on touchable, non-live parts of the equipment, while a protection type specifies safeguards protecting active parts against contact, ingress of foreign bodies and water, as well as shock resistance (i.e. enclosure protection).
Protection class 0
Class 0 equipment does not provide any special protection against electric shock, apart from basic insulation. There is no connection to a protective conductor system, and protection is provided only by the equipment surroundings. Protection class 0 is not designated with its own symbol, as no labels are applied to it. In numerous countries, including Germany, operation of such unprotected equipment or systems is not permitted.
Protection class I – protective conductor
As far as equipment with this protection class is concerned, all electric-conductive enclosure components are connected to a system of protective conductors of a fixed electric installation with the earth potential. Mobile equipment rated as protection class I is equipped with a plug-in connector with a protective contact or a cable fitted with an additional protective conductor and a plug equipped with a protective contact. The protective conductor connection is designed as a leading contact, so that it is the first to be activated when a plug is inserted, and is the last to be disconnected when it is removed. In addition to the mechanical strain relief feature, a connection cable inserted into a device must be designed in such a way that, in case the cable is pulled out, the protective earth conductor gets pulled out last. If a live cable accidentally touches the enclosure connected to the protective conductor, a short-circuit occurs. The protective conductor enclosure connection is dimensioned in such a way that there is no permanently hazardous touch voltage on the enclosure, and a line breaker, fuse or residual current switch-off device is triggered momentarily and disconnects the circuit power supply.
Classic neutral earthing with PEN conductors that can still be encountered in building systems goes against the protection class I concept. A PEN conductor combines a protective (PE) and neutral (N) conductor. To connect sockets, a neutral conductor is connected to socket protective conductor contacts, which results in neutralising the required protective measure. PEN conductor interruptions may also result in hazardous voltage transfer onto enclosures of all protection class I equipment connected to a corresponding circuit.
Protection class II – double or enhanced insulation
Protection class II equipment comes with enhanced or double insulation at the rated insulation voltage between live parts and elements that can be touched. They are usually not connected to a protective conductor. If they come with an electrically conductive surface or conductive elements that can be touched, they are separated from the live parts with enhanced or double insulation, and their touch current value does not exceed 0.5 mA.
Mobile class II equipment usually comes with plugs that are not fitted with a protective conductor connection or a protective conductor itself. It includes primarily small-sized white goods or tools, such as electric drills, or certain electronic appliances.
Note that if a cable with a protective conductor is used, it must not be connected to an enclosure and must be treated as an active cable.
Protection class III – low-voltage protection
Protection class III equipment operates at safety extra-low voltages (SELV) or protected extra-low voltages (PELV). Such devices can only be connected to SELV or PELV power supplies. They include:
- safety transformers as per the applicable standard;
- electro-chemical power supplies (batteries and rechargeable batteries);
- solar cells, generators, crank generators and similar equipment supplying low voltage.
Protected extra-low voltage (PELV) equipment comes with enhanced or double insulation between a mains connection and low-voltage carrying components, but the low-voltage circuits or enclosure can be earthed. The earthing is not provided for safety reasons, but in order to ensure electromagnetic compatibility (interference emissions, earthing loops, ESD protection). Such solutions are treated as functional earthing. Laptop or audio equipment power supplies are perfect examples of such devices.
Other safety-relevant classifications – IP degrees of protection
The IP degree of protection is an international standard (EN 60529) that defines the resistance of electric equipment to environmental conditions and its protection against access to hazardous (e.g. live) parts. In addition to the degree of spill or splash resistance, which is important in numerous applications, IP codes designate the degree of user’s protection against access to unprotected equipment components or other safety features.
Read more about IP degrees of protection
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