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Network isolators are installed as part of a wired Ethernet system as galvanic isolators to reduce the potential for electrical injury and limit the extent of damage due to lightning strikes.
Through the applied principle of electromagnetic induction, network data is transmitted across an electrically non-conducting barrier. High frequency AC voltages conveying data are induced across an isolating gap.
The network isolator is a passive device, and functions without any requirement of an external power supply. A functional equivalent to network isolators is Ethernet over a small stretch of optical fibre, using media converters or Ethernet switches/network cards with fiber connections on each end.
Network isolators have many other applications in overcoming the problems of differing ground potentials across networks, or between network components. For example:
Network isolators are used in medical devices to protect patients against leakage currents.
Network connections between medical devices and Ethernet networks (and other non-medical devices, such as personal computers) must be in accordance with the IEC 60601-1 standard. This standard specifically deals with medical electronic and electrical equipment and systems, and classifies non-medical devices as potential hazard sources. A specific hazard stems from possible differences in ground potentials between network components, which, when not properly isolated, can result in a leakage current that can flow through the patient, which is dangerous, and potentially lethal. Such voltage differences can also arise through incorrect installation and wiring of network systems, electrical shorting within damaged cables and cabling, or shorting between damaged network cables and other voltage sources.
Network isolators work to remove this hazard, by electrically disconnecting medical devices from a network. Isolators may be used as network accessories, built into medical devices, or installed within a medical network system. Networks isolators should be installed as close as possible to the medical device in question. As they serve no therapeutic or diagnostic purpose, network isolators themselves are not classed as medical electronic equipment according to the IEC 60601-1 standard, nor do they fall within the scope of the Medical Devices Directive 93/42/EEC. They are often installed in the medical field in conjunction with isolation transformers, which serve to protect the patient from other electrical faults.
The international standard IEC 60601-1 Medical Electrical Equipment (3rd edition) specifies stringent criteria on the safety and isolation of medical devices. These requirements are of course much more stringent than those of a typical consumer product standard (i.e. IEC 60950 Safety of Information Technology Equipment), as the patient may be unconscious, anaesthetised, or otherwise unable to move, and the need for patient protection is therefore paramount.
The IEC 60601-1 standard requires that two independent precautionary measures (Means of Patient Protection, or MOPPs) are set in place, to protect the patient from electrical shock in the medical system. A network isolator can be constructed to provide one or both required MOPPs. In the case where only a single MOPP is present in a system, a second measure of protection for the medical device must be made. This can be achieved, for example, by installing a fixed, low-resistance earthing cable, bar, or strap, referred to as a potential equalisation conductor. Conformation to the requirements of applicable standards and guidelines, in particular the IEC 60601-1 standard, involves manufacturers themselves declaring CE compliance and/or gaining certification from an approved independent testing laboratory.
The number of MOPPs a network isolator provides will be stated in the certification of the device. These are achieved by a combination of clearance and creepage distances, and the breakdown voltage of the insulating materials. Although requirements on breakdown voltage levels are 1.5 kilovolts for one MOPP, and 4 kilovolts for two MOPPs, the number of MOPPs actually provided cannot be derived from the breakdown voltage alone.
Network connections made with unshielded cables are occasionally used as a form of isolation, in that no shield connection exists between the device and the network. However, this fails to provide sufficient protection in the scope of IEC 60601-1, as the data lines themselves are not isolated, and may be floating at dangerous voltage potentials.
Network cards and other active network components which are designed to meet IEC 60950 (Safety of Information Technology Equipment), will usually not comply with the more demanding isolation requirements of IEC 60601-1 (Medical Electrical Equipment), and therefore require additional isolation before being used in medical applications.
The transmission quality of a network isolator can be determined by measuring the industry standard parameters or characteristics, for example, insertion loss, return loss, and near-end crosstalk.
By definition, a network isolator completely eliminates each and every direct electrical connection between devices connected through a network connection - specifically all the data lines, and the cable shield.
Network isolators are commercially available in various designs, to suit customers’ requirements:
Voltage ratings (rated in kilovolts) and maximum transmission speeds (e.g. 1000BASE-T) vary between models.
In electrical engineering, ground or earth is a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.
A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.
An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons or to reduce transients and harmonics. Isolation transformers provide galvanic isolation; no conductive path is present between source and load. This isolation is used to protect against electric shock, to suppress electrical noise in sensitive devices, or to transfer power between two circuits which must not be connected. A transformer sold for isolation is often built with special insulation between primary and secondary, and is specified to withstand a high voltage between windings.
Power over Ethernet, or PoE, describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. This allows a single cable to provide both data connection and electrical power to devices such as wireless access points (WAPs), Internet Protocol (IP) cameras, and voice over Internet Protocol (VoIP) phones.
In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them. This is typically caused when enough current is flowing in the connection between the two ground points to produce a voltage drop and cause two points to be at different potentials. Current may be produced in a circular ground connection by electromagnetic induction.
Ground and neutral are circuit conductors used in alternating current electrical systems. The ground circuit is connected to earth, and neutral circuit is usually connected to ground. As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.
Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure.
Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks. It does not normally cover the transmission or distribution of electricity to them.
A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
An earthing system or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary considerably among countries, though most follow the recommendations of the International Electrotechnical Commission (IEC). Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.
Extra-low voltage (ELV) is an electricity supply voltage and is a part of the Low voltage band in a range which carries a low risk of dangerous electrical shock. There are various standards that define extra-low voltage. The International Electrotechnical Commission (IEC) and the UK IET define an ELV device or circuit as one in which the electrical potential between conductor or electrical conductor and earth (ground) does not exceed 50 V AC or 120 V DC.
Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted. Energy or information can still be exchanged between the sections by other means, such as capacitive, inductive, radiative, optical, acoustic or mechanical.
A power entry module(PEM) is an electromechanical component used in electrical appliances, integrating the appliance inlet with other components such as:
In electrical engineering, earth potential rise (EPR) also called ground potential rise (GPR) occurs when a large current flows to earth through an earth grid impedance. The potential relative to a distant point on the Earth is highest at the point where current enters the ground, and declines with distance from the source. Ground potential rise is a concern in the design of electrical substations because the high potential may be a hazard to people or equipment.
The Comparative Tracking Index (CTI) is used to measure the electrical breakdown (tracking) properties of an insulating material. Tracking is an electrical breakdown on the surface of an insulating material wherein an initial exposure to electrical arcing heat carbonizes the material. The carbonized areas are more conductive than the pristine insulator, increasing current flow, resulting in increased heat generation, and eventually the insulation becomes completely conductive.
Electrical safety testing is essential to make sure electrical products and electrical installations are safe. To meet this goal, governments and various technical bodies have developed electrical safety standards. All countries have their own electrical safety standards that must be complied with. To meet to these standards, electrical products and electrical installations must pass electrical safety tests.
IEC 60601 is a series of technical standards for the safety and essential performance of medical electrical equipment, published by the International Electrotechnical Commission. First published in 1977 and regularly updated and restructured, as of 2011 it consists of a general standard, about 10 collateral standards, and about 80 particular standards.
The train communication network (TCN) is a hierarchical combination of two fieldbus for data transmission within trains. It consists of the Multifunction Vehicle Bus (MVB) inside each vehicle and of the Wire Train Bus (WTB) to connect the different vehicles. The TCN components have been standardized in IEC 61375.
CEBEC is a private Belgian rating label for the quality assurance of electrical appliances. Use of this label indicates that a piece of equipment conforms to European safety standards. The label is issued by SGS-CEBEC, now part of the SGS group. CEBEC has its own electrical testing laboratory located in Brussels. It is an approved laboratory for the purpose of certifications granted by SGS.