{"id":1130,"date":"2026-10-13T07:20:16","date_gmt":"2026-10-13T07:20:16","guid":{"rendered":"https:\/\/liqele.com\/?p=1130"},"modified":"2026-10-14T16:03:22","modified_gmt":"2026-10-14T16:03:22","slug":"medium-voltage-switching-devices-explained","status":"publish","type":"post","link":"https:\/\/liqele.com\/es\/medium-voltage-switching-devices-explained\/","title":{"rendered":"Explicaci\u00f3n de los dispositivos de conmutaci\u00f3n de media tensi\u00f3n: corte, aislamiento y puesta a tierra"},"content":{"rendered":"<style>.liq-prelaunch-article{max-width:900px;margin:0 auto;line-height:1.7}.liq-prelaunch-article h2{margin-top:2.2em}.liq-prelaunch-article h3{margin-top:1.7em}.liq-prelaunch-article figure{margin:2em 0}.liq-prelaunch-article img{display:block;max-width:100%;height:auto;margin:auto}.liq-prelaunch-article figcaption{font-size:.9em;line-height:1.5;color:#555;margin-top:.7em}.liq-prelaunch-article .liq-table-scroll{max-width:100%;overflow-x:auto;margin:1.5em 0}.liq-prelaunch-article table{display:table;width:100%;border-collapse:collapse;margin:0}.liq-prelaunch-article th,.liq-prelaunch-article td{padding:.7em;border:1px solid #ddd;vertical-align:top;min-width:130px;overflow-wrap:normal;word-break:normal;hyphens:none}.liq-prelaunch-article th{background:#f4f4f4}.liq-prelaunch-article a{text-decoration:underline;overflow-wrap:anywhere}@media(max-width:600px){.liq-prelaunch-article{font-size:16px}.liq-prelaunch-article .liq-table-scroll table{min-width:660px}.liq-prelaunch-article .liq-table-scroll[data-columns=\"2\"] table{min-width:600px;table-layout:fixed}.liq-prelaunch-article .liq-table-scroll::before{content:\"Swipe to read all columns\";display:block;position:sticky;left:0;font-size:13px;color:#555;margin-bottom:8px}.liq-prelaunch-article th,.liq-prelaunch-article td{padding:.65em;min-width:180px}}<\/style>\n<style>body.single-post .hero-section[data-type=\"type-1\"]{padding-top:140px;padding-bottom:30px;background:#fff}body.single-post .hero-section[data-type=\"type-1\"] .page-title{color:#151515!important;font-size:clamp(2rem,2.7vw,2.65rem);line-height:1.2}@media(max-width:600px){body.single-post .hero-section[data-type=\"type-1\"]{padding-top:160px;padding-bottom:24px}}<\/style>\n<div class=\"liq-prelaunch-article\" data-liq-article=\"PL15\" lang=\"en\">\n<h2>Quick Takeaway<\/h2>\n<ul>\n<li>Circuit breakers interrupt assigned normal and fault currents; load break switches handle their assigned load duties; disconnectors provide isolation; earthing switches connect a designated section to earth.<\/li>\n<li>A protection relay issues a trip decision, the mechanism moves the contacts, and the interrupter clears the current. An opening command or an open breaker does not establish every function of the assembly.<\/li>\n<li>Allocate the required duties to each feeder first, then compare ratings, installation arrangements and interfaces. Combined switching, isolation or fuse-protection functions belong to the documented device or assembly.<\/li>\n<\/ul>\n<p>Medium-voltage switching equipment performs four separate jobs inside one distribution network. A circuit breaker changes the power connection and interrupts current, including fault current within its assigned capability. A load break switch opens and closes the load currents its documentation assigns to it. A disconnector provides a separation the installation can rely on. An earthing switch connects a designated part of the circuit to earth.<\/p>\n<p>These devices often stand in the same cabinet and are operated from the same panel, but they are not four versions of one thing. A common way to mis-specify MV equipment is to read a device name as a complete description of the device, or to read a function that belongs to the assembly as though it belonged to every component inside it.<\/p>\n<p>The useful starting point is the function: what happens in the power circuit, what the control chain commands, and which responsibilities the installation assigns to each device.<\/p>\n<h2>What medium-voltage switching equipment does<\/h2>\n<p>Medium voltage is the distribution band that sits between the low-voltage equipment at the point of use and the larger supply and transmission levels behind it. Where the band begins and ends is partly a matter of regional and standards practice: some systems count from roughly 1 kV upward, others draw the boundaries differently, and a project&#8217;s working level is fixed by the local network and the equipment applied to it rather than by one universal number. The practical consequence is that &#8220;medium voltage&#8221; tells you the context of a device, not its capability. Suitability comes from the system it is applied to and from the ratings and conditions printed in its own documents.<\/p>\n<p>The context turns up in a few recognisable shapes:<\/p>\n<ul>\n<li><strong>Indoor switchgear<\/strong> \u2014 metal-enclosed cabinets in a substation room, fed from an incoming circuit, distributing energy along an internal busbar to outgoing circuits. The busbar is the energy path inside the cabinet; everything else either connects to it, measures it, interrupts it, or separates it.<\/li>\n<li><strong>Outdoor feeders<\/strong> \u2014 pole, portal or enclosed arrangements in which the switching device, sensing and control equipment are configured for the feeder and its exposure. Their functions may be integrated or housed separately.<\/li>\n<li><strong>Transformer distribution<\/strong> \u2014 a cable drops from the MV busbar to a distribution transformer, and the switching device at the head of that branch must handle the transformer&#8217;s normal switching duty and clear the faults the project assigns to that branch.<\/li>\n<\/ul>\n<p>Across all three, four questions come up repeatedly: which component actually changes the power connection, which one interrupts the current, which one creates the isolation, and which one establishes the earth connection. Answering those four questions first is what keeps the later work \u2014 ratings, installation, control \u2014 on the right track.<\/p>\n<figure class=\"wp-block-image size-full\" data-media-role=\"featured\"><img class=\"wp-image-1294\" src=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10.webp\" alt=\"Reference-based editorial lineup of a vacuum circuit breaker, load break switch, disconnector and earthing switch\" width=\"1672\" height=\"941\" loading=\"eager\" decoding=\"async\" fetchpriority=\"high\" srcset=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10.webp 1672w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10-300x169.webp 300w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10-1024x576.webp 1024w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10-768x432.webp 768w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/featured-final-10-1536x864.webp 1536w\" sizes=\"(max-width: 1672px) 100vw, 1672px\" \/><figcaption>Four distinct switching-device types in an editorial studio arrangement: vacuum circuit breaker, load break switch, disconnector and earthing switch.<\/figcaption><\/figure>\n<h2>Four different jobs in the same network<\/h2>\n<h3>Circuit breaker: interrupting current, not just opening a gap<\/h3>\n<p>A circuit breaker is designed for the assigned normal and fault-current interruption duties. Its role covers the normal switching duty of the circuit it is installed on and the interruption of fault current within its rated capability and stated operating conditions. Those two duties are the same action performed under very different stress. Interrupting a few hundred amperes of load current and interrupting a short-circuit current place different demands on the interrupter, on the mechanism that drives it, and on the structure that has to absorb the resulting forces.<\/p>\n<p>The mechanism does not create the rating; it supplies the movement. Stored energy in a spring or a magnetic actuator is released through a linkage and drives the main contacts apart at a defined speed and travel. The interrupting medium manages the arc as the contacts part and allows the circuit to remain interrupted after current zero. In a vacuum circuit breaker that arc is managed inside the vacuum interrupter, which is why the mechanism and the interrupter can be discussed as two responsibilities: one produces the stroke, the other produces the interruption \u2014 and the breaker&#8217;s electrical design, not its control arrangement, is what sets its breaking capability. The construction of the interrupter itself, its contact geometry and the behaviour of the arc are covered in the separate article on <a href=\"https:\/\/liqele.com\/what-is-a-vacuum-circuit-breaker\/\">what a vacuum circuit breaker is<\/a>; at this level it is enough to note that an open breaker is a circuit that has been switched off by a device designed to interrupt, and that an open breaker on its own is not yet an isolation function.<\/p>\n<h3>Load break switch: the assigned load-switching duty<\/h3>\n<p>A load break switch is rated to break the load currents, and the other currents, that its documentation assigns to it, and to carry the continuous current of the circuit. It opens and closes a circuit that is carrying normal power flow \u2014 including the inductive currents of motors and transformers and the capacitive currents of cables \u2014 within its stated capability. &#8220;Load break&#8221; is not a description of a limited device; it is a precise scope, and the precision matters because the scope does not automatically include fault-current interruption.<\/p>\n<p>The difference between a bare load break switch and a switch-fuse combination is exactly here. In a documented combination, the switch and its current-limiting fuse share the fault work in a defined way: the switch handles the specified load and smaller currents, while the fuse interrupts the larger short-circuit currents, and the two are specified and coordinated as one assembly \u2014 including any specified fuse-to-switch release or striker arrangement. That coordination is what makes the combination an object in its own right. A switch and a fuse taken from two unrelated documents are not that combination, and their separate data sheets do not add up to it.<\/p>\n<p>Some load break switches are described as <strong>switch-disconnectors<\/strong>, which is a functional statement rather than a marketing one: the device both breaks specified load currents and, in its designated position, performs a documented isolation function. That combination is common in modern MV designs, but it is a property of the documented device, not of the words &#8220;load break switch&#8221;. Not every load break switch has an isolation function, an earthing function or short-circuit breaking capability, and the <a href=\"https:\/\/liqele.com\/what-is-a-load-break-switch\/\">load break switch article<\/a> goes into the switching duties and type labels in more detail.<\/p>\n<h3>Disconnector: providing the specified isolation<\/h3>\n<p>A disconnector exists to create separation. In its closed position it carries the rated current of its circuit and withstands the short-circuit stresses assigned to it; in its specified open position it provides the isolation function \u2014 a separation with the dielectric and structural properties the installation requires. The familiar construction is the knife arrangement: parallel blades rotating on a common shaft, opening to a visible gap. The visible gap is convenient, but the function does not rest on visibility; it rests on the open position being the one the device was designed and documented for.<\/p>\n<p>The task a disconnector is not built for is interrupting current. Holding a defined gap in a circuit that has already been de-energised and interrupting a live circuit are different engineering problems with different contact shapes, different operating forces and different test requirements. Isolation is therefore applied after the current has been interrupted by a device designed to do that, and the disconnector is not a general load-breaking or fault-interrupting device. Limited switching duties can be assigned to particular disconnectors under defined conditions, but those come from the device documentation rather than from a general assumption that a knife switch may be operated whenever the current happens to be small. The <a href=\"https:\/\/liqele.com\/what-is-a-disconnector\/\">disconnector article<\/a> covers the isolation function and its application boundaries.<\/p>\n<h3>Earthing switch: connecting the section to earth<\/h3>\n<p>An earthing switch performs a different kind of connection: it links a designated part of the circuit to the earthing system of the installation, short-circuiting it. Its normal task is to establish that connection in a work arrangement, after the section concerned has been de-energised and separated, so that the section has a decided path to earth instead of floating at an undefined potential. It can be a separate unit mounted in the cabinet, or built into one unit with an adjacent isolating or switching device.<\/p>\n<p>The duties associated with an earthing switch reflect a closing action rather than an opening action. A specified version can have a short-circuit making capability \u2014 the ability to establish the assigned short-circuit current when closing onto an energised circuit \u2014 and a defined short-time and peak withstand duty, because once the connection is made the switch must carry the fault current to earth until the upstream protection clears it. Neither of those is a fault-current breaking rating. The earthing switch establishes the designated connection to earth and withstands the assigned stress; another protective device clears any fault current. A making value or a withstand value on an earthing switch sheet should therefore never be read across to another device, nor read as a general permission to close the switch onto an energised circuit. The <a href=\"https:\/\/liqele.com\/what-is-an-earthing-switch\/\">earthing switch article<\/a> sets out the making duty and withstand ratings properly.<\/p>\n<h3>Why one duty cannot substitute for another<\/h3>\n<p>Read together, these four duties are not four degrees of the same skill. Interruption concerns controlling the arc and preventing current from re-establishing under the assigned electrical duty. Isolation is a separation problem: the device has to hold a gap that stands off the system voltage and can be verified as a defined, separated arrangement. Earthing is a connection problem: the device has to establish a path to earth that survives the fault current flowing through it until upstream protection operates. Load switching also requires controlled interruption, but for its assigned normal-load duties rather than a general fault-interruption duty. That division of responsibilities explains why an installation often uses several devices. A device that solves one of these problems well says almost nothing about the others.<\/p>\n<figure class=\"wp-block-image size-full\" data-media-role=\"inline\"><img class=\"wp-image-1295\" src=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10.webp\" alt=\"Circuit breaker, load break switch, disconnector and earthing switch paired with the large duties Interrupt, Switch load, Isolate and Earth\" width=\"1672\" height=\"941\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10.webp 1672w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10-300x169.webp 300w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10-1024x576.webp 1024w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10-768x432.webp 768w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig01-final-10-1536x864.webp 1536w\" sizes=\"auto, (max-width: 1672px) 100vw, 1672px\" \/><figcaption>The four pictured device types do different jobs: interruption, normal-load switching, isolation and earthing.<\/figcaption><\/figure>\n<h2>The protection signal and the power circuit have different roles<\/h2>\n<p>A fault is rarely cleared by the device that first notices it, and understanding which part does what removes a great deal of confusion in MV projects. The chain has five links, and they are genuinely different links.<\/p>\n<p><strong>Measurement.<\/strong> Current and voltage are measured where the arrangement requires it, using instrument transformers or sensors that scale primary values down to information a relay or controller can use. The key word is <em>required<\/em>: not every feeder carries both a current transformer and a voltage transformer, and the set of measuring devices is chosen from the functions the project actually needs, not added by default.<\/p>\n<p><strong>Decision.<\/strong> A protective relay or controller evaluates that information against configured criteria \u2014 thresholds, time delays, curves \u2014 and produces a decision. The decision is configuration, not physics: the same hardware behaves differently depending on how it has been set, which is why protection settings belong to the project rather than to the catalogue.<\/p>\n<p><strong>Command.<\/strong> The decision leaves the relay as a trip order, travelling through the trip circuit to a shunt trip coil or to the electronic control input of the operating mechanism. It is a signal. Nothing has been interrupted yet.<\/p>\n<p><strong>Mechanism.<\/strong> The coil or actuator releases the latch that holds the mechanism, and the energy stored in springs or a magnetic actuator drives the main contacts apart.<\/p>\n<p><strong>Interruption.<\/strong> The interrupter deals with the arc and the current reaches zero. The breaker&#8217;s rating, not the relay&#8217;s capability, governs whether that interruption succeeds at the fault level involved.<\/p>\n<p>Those roles are separate because a failure at any one of them can prevent this protection chain from clearing the fault as intended: an accurate sensor with an unconfigured relay, a correct trip decision with a failed trip coil, or a mechanism that moves contacts the interrupter cannot handle. Issuing a trip command, driving the contacts and completing the interruption of the main circuit are three different responsibilities carried by different parts.<\/p>\n<p>Running alongside this chain is ordinary control, which is easy to confuse with protection because it uses some of the same hardware. Opening and closing a circuit as part of normal operation \u2014 by handle, push button, selector switch, remote command or motor drive \u2014 is operating the circuit, not protecting it. A motor drive provides the charging or operating action assigned to that mechanism; auxiliary contacts report the position of the device; indicator lamps and remote signalling tell the operator what happened. None of those measure current, compare it to a criterion, and decide to trip. An electrically operated switch is therefore not the same thing as a protected feeder, and the presence of a control box on a unit says nothing about its fault duty.<\/p>\n<p>Isolation and earthing sit outside this chain altogether. They serve the work arrangement, not the fault-clearing loop: the breaker interrupts so that the disconnector can separate, and the earthing switch connects to earth a section that has already been separated. The same cabinet holds both groups of functions, and the reasons why they are still needed next to a modern breaker are the subject of the next two sections.<\/p>\n<figure class=\"wp-block-image size-full\" data-media-role=\"inline\"><img class=\"wp-image-1296\" src=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10.webp\" alt=\"Five separate stages labelled Measure, Decide, Command, Move and Interrupt, linked by functional arrows\" width=\"1671\" height=\"941\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10.webp 1671w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10-300x169.webp 300w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10-1024x577.webp 1024w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10-768x432.webp 768w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig02-final-10-1536x865.webp 1536w\" sizes=\"auto, (max-width: 1671px) 100vw, 1671px\" \/><figcaption>Measurement, protection decision, trip command, mechanical movement and current interruption are separate responsibilities. The arrows show functional relationships rather than installation wiring.<\/figcaption><\/figure>\n<p>For the coordination side of this chain \u2014 grading between devices, and how a switch-fuse combination behaves within a feeder \u2014 the <a href=\"https:\/\/liqele.com\/medium-voltage-feeder-switching-protection\/\">feeder switching and protection article<\/a> works through the arrangements in more depth.<\/p>\n<h2>A switching device and a complete switchgear assembly are different scopes<\/h2>\n<p>A cabinet is not a device. It is an assembly that brings together several things which happen to be co-located: the conducting path (busbar, breaker or switch, cable terminations), the sensing, protection and control equipment, the operating interfaces the operators actually touch, and the isolation and earthing provisions the installation needs. When these are built into one enclosure, it becomes tempting to credit the function of the assembly to each individual device inside it, or to assume that a device carrying a familiar name carries the whole package.<\/p>\n<p>Two consequences follow, and they pull in opposite directions. A documented combined device may legitimately perform several functions at once \u2014 a switch-disconnector that breaks specified load currents and also provides an isolation position is a real engineering solution, not a contradiction. And in the other direction, an open breaker is not proof of isolating duty. A breaker that has tripped is a circuit whose current has been interrupted; whether the installation is genuinely separated depends on the assembly and its documented positions.<\/p>\n<p>ABB Uniswitch documentation for fixed and withdrawable assemblies shows both mechanisms. In a withdrawable design, the withdrawable part \u2014 the breaker, its insulated contact arms and contact system, the control plug and the withdrawal assembly \u2014 reaches a test\/disconnected position in which the main current circuit is separated to provide the stated partitioning, while the connections used for testing may remain in place. In that arrangement, isolation comes from the connection position of the assembly rather than from the breaker&#8217;s open state. In one specific fixed breaker cubicle, the same manufacturer fits a three-position switch-disconnector between the busbar and the breaker to give the specified isolation distance, with an earthing switch on the other side of the circuit. Both examples explain why a breaker, an isolating element and an earthing element appear together in one enclosure and are each assigned a different job.<\/p>\n<p>Both are also that manufacturer&#8217;s particular topology. They are not a required arrangement for every fixed cubicle, and they should not be transferred as wiring practice or operating procedure onto another family. A useful boundary to keep in mind is that a device&#8217;s assigned function belongs to a stated position and installation condition: the same component can serve isolation in one arrangement and merely connect in another, and the assignment comes from the design documents of that assembly, not from the component&#8217;s product name. One more practical version of the same point: a switch-disconnector in a fixed cubicle and a withdrawable part in a partitioned compartment may both provide isolation, but a reader comparing them is comparing two installation conditions, not two products.<\/p>\n<h2>Allocate the duties in a 10 kV industrial distribution project<\/h2>\n<p>For an industrial facility supplied at 10 kV through a single incoming feeder, the incoming circuit is normally broken by a circuit breaker feeding the MV busbar in the plant substation. With the required measurement, protection settings and trip path, the incoming breaker interrupts the fault duties assigned to that bay and controls the connection to the site busbar. The documented assembly provides any required isolation and earthing at that boundary. Everything downstream is then allocated according to what each outgoing circuit actually needs.<\/p>\n<p><strong>An outgoing process feeder feeding secondary substations and motor control centres<\/strong>, where the project requires configured protection (overcurrent and earth-fault functions with settings chosen for the process, plus whatever control scope the plant specifies \u2014 remote trip, interlocking, status and metering to the control system), is a natural breaker-based arrangement. The reason is not that breakers are &#8220;better&#8221; but that this circuit needs three things together: a protection decision that can be configured to the process, the ability to interrupt the fault current available at that point on the busbar, and a control interface the plant&#8217;s automation can act on. Where the outgoing feeder is cabled a long distance or feeds a mixture of loads, the fault level and the coordination with downstream protection are the inputs that decide the breaker&#8217;s ratings.<\/p>\n<p><strong>A dedicated transformer branch<\/strong>, where a cable drops to a distribution transformer and the branch exists to serve that transformer, can instead use a documented coordinated load-switch and fuse combination, when that scheme meets the project. Here the division of labour suits the circuit: the switch performs the assigned transformer switching duties, while the specified fuse provides its coordinated fault-clearing duty; transformer inrush and the fuse&#8217;s time-current behaviour must be accounted for in that coordination. This arrangement can suit a single-purpose branch when its documented protection scope matches the project. It is still one specified object: the switch, the fuse type and any specified release arrangement belong to the same combination.<\/p>\n<p><strong>Isolation and earthing<\/strong> are allocated at the sections where they will be used, not at the device that happens to be convenient. A transformer branch can need a documented separation point on the busbar side and an earth connection on the cable side. These functions define the separation and earth connection for the designated cable\/transformer section in the installation&#8217;s work arrangement. An outgoing feeder to a remote substation needs its own arrangement at the far end. Both functions refer to designated circuit sections and to the functions actually built into the assembly; neither is established by an open breaker, and neither is a substitute for the other.<\/p>\n<p>The allocation is stable only as long as its inputs are. If the branch requires protection functions or an adjustable response that the coordinated switch-fuse arrangement cannot provide, a suitable relay-and-breaker arrangement can be the better fit. Communication, remote operation and indication must be reviewed separately: they depend on the specified control and auxiliary equipment and do not, by themselves, rule out a switch-fuse arrangement. Change the load \u2014 if the branch is extended into a busbar serving several motors with frequent switching, or if the fault level at the branch rises beyond what the documented combination covers \u2014 and the combination has to be re-examined against the new duty. Change the installation condition \u2014 an outdoor pole-mounted feeder, a ring-main unit, a compact fixed cubicle or a withdrawable switchgear room \u2014 and the same duties get built into different physical arrangements with different isolation methods. The functional map stays the same; the equipment on it changes.<\/p>\n<figure class=\"wp-block-image size-full\" data-media-role=\"inline\"><img class=\"wp-image-1297\" src=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10.webp\" alt=\"Architectural illustration of an incoming supply, process feeder and transformer branch connected by relationship ribbons\" width=\"1672\" height=\"941\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10.webp 1672w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10-300x169.webp 300w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10-1024x576.webp 1024w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10-768x432.webp 768w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig03-final-10-1536x864.webp 1536w\" sizes=\"auto, (max-width: 1672px) 100vw, 1672px\" \/><figcaption>An industrial distribution project can assign different switching and protection arrangements to the incoming supply, process feeder and transformer branch. The coloured routes show those relationships.<\/figcaption><\/figure>\n<h2>Compare duties before comparing labels<\/h2>\n<p>The useful comparison is not between products but between duties, applied consistently to each family. A circuit breaker carries the rated current of its circuit, breaks and makes the currents within its assigned capability, including fault current, and provides isolation only where a documented arrangement \u2014 a disconnected position, or a separate isolating device \u2014 provides it. A load break switch carries its rated current and performs the load switching assigned to it; a normal-load rating does not establish general short-circuit interruption, and any assigned limited fault-related switching duty must be read separately from the complete switch-fuse rating. It provides isolation only when the device is documented as a switch-disconnector. A disconnector carries its rated current, withstands the short-circuit stresses assigned to it and provides the specified isolation function; it is not a general load-breaking or fault-interrupting device. An earthing switch makes and carries the designated connection to earth, with specified short-circuit making and withstand duties where the version calls for them, and it does not break fault current.<\/p>\n<p>Combined functions belong in the same comparison only when the device documents them. A switch-disconnector legitimately appears with both load switching and isolation against its name. A specified version may combine isolation with an earthing arrangement when its documents assign both functions. Either entry is a statement about that documented device, and it should not be generalised to the type, or to a differently configured variant of the same family.<\/p>\n<p>Behind those rows, four different current duties deserve to be kept apart, because a number confirmed for one of them says nothing about the others.<\/p>\n<p><strong>Carrying<\/strong> concerns the continuous current the device can pass without exceeding its thermal limits \u2014 a steady-state duty, about heat and contact resistance. <strong>Breaking<\/strong> concerns interrupting a current that is already flowing, under stated conditions, which requires arc control and successful interruption under the assigned electrical conditions; it depends on the interrupting technology and the conditions at the moment of operation. <strong>Making<\/strong> concerns closing onto a circuit, including a circuit that is already faulted, which adds electromagnetic forces and pre-strike effects to the mechanical stresses of closing. <strong>Withstand<\/strong> concerns enduring a given current \u2014 a short-time value with its stated duration, or a peak value \u2014 without damage or unacceptable deformation, a duty about the structure and the contact system rather than about arc control.<\/p>\n<p>A disconnector&#8217;s carrying and withstand values do not make it a circuit breaker. An earthing switch&#8217;s making value does not make it a load switch. A breaker&#8217;s breaking value does not make the cabinet isolating. The full field-by-field treatment of these quantities \u2014 what each rating means, which conditions it depends on, and how the fields are written on a product sheet \u2014 belongs to the <a href=\"https:\/\/liqele.com\/medium-voltage-switching-device-ratings\/\">ratings guide<\/a>, which is the natural next step once the duty is settled.<\/p>\n<figure class=\"wp-block-image size-full\" data-media-role=\"inline\"><img class=\"wp-image-1298\" src=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10.webp\" alt=\"Four illustrations labelled Carry, Break, Make and Withstand showing thermal, interruption, closing and structural duties\" width=\"1672\" height=\"941\" loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10.webp 1672w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10-300x169.webp 300w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10-1024x576.webp 1024w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10-768x432.webp 768w, https:\/\/liqele.com\/wp-content\/uploads\/2026\/10\/fig04-final-10-1536x864.webp 1536w\" sizes=\"auto, (max-width: 1672px) 100vw, 1672px\" \/><figcaption>Carrying concerns continuous current and thermal limits; breaking concerns interruption; making concerns closing duty; withstand concerns enduring the assigned current stress. A value for one duty does not establish the others.<\/figcaption><\/figure>\n<h2>Continue from the required function<\/h2>\n<p>The functional map is complete once you can say which duty the circuit needs. The next step is to match that duty to a device family and an installation, then to check the ratings and the interfaces against the project. The technical blog at <a href=\"https:\/\/liqele.com\/blog\/\">liqele.com\/blog<\/a> holds the surrounding articles; a few routes follow directly from the sections above.<\/p>\n<p>For circuits that must interrupt fault current, the breaker families are the starting point: <a href=\"https:\/\/liqele.com\/products\/indoor-vacuum-circuit-breakers\/\">indoor vacuum circuit breakers<\/a> for cubicle-based installations in the VS1-12 family, or <a href=\"https:\/\/liqele.com\/products\/outdoor-vacuum-circuit-breakers\/\">outdoor vacuum circuit breakers<\/a> for pole, portal and feeder-mounted units such as the ZW32-12 family. Both pages lead into the mounting and configuration variants rather than to a single specification, which matters because fixed, withdrawable and side-mounted arrangements reach isolation in different ways.<\/p>\n<p>For assigned load-switching duty, including the documented fuse combinations used on transformer and motor branches, the <a href=\"https:\/\/liqele.com\/products\/load-break-switches\/\">load break switches<\/a> range covers the FKN12 family and the combination variants beside it. For the separate isolation and earthing functions, the <a href=\"https:\/\/liqele.com\/products\/disconnectors-earthing-switches\/\">disconnectors and earthing switches<\/a> range covers the GN19-12 and GN30-12 \/ GN30-12D disconnector families and the JN15-12 earthing switch family.<\/p>\n<p>Two deeper articles pick up where this overview stops. The <a href=\"https:\/\/liqele.com\/medium-voltage-switching-device-ratings\/\">ratings guide<\/a> explains the individual rating fields and the conditions behind them, and the <a href=\"https:\/\/liqele.com\/medium-voltage-feeder-switching-protection\/\">feeder switching and protection<\/a> article works through protection arrangements and coordination between devices in a feeder. When the question becomes the whole project \u2014 duty, ratings, installation, control and the documents a supplier should be asked for \u2014 the <a href=\"https:\/\/liqele.com\/select-medium-voltage-switching-devices\/\">device selection guide<\/a> is the route built for that screening task.<\/p>\n<p>Once a family is identified, <a href=\"https:\/\/liqele.com\/technical-support\/downloads\/\">Downloads<\/a> is the route to available model manuals and to requests for matching outline drawings or wiring information. Review them per model and configuration: matching the voltage level, or recognising a familiar model prefix, does not establish interchangeability, and the isolation position, control interfaces and installation conditions of the selected equipment remain the basis for the final check.<\/p>\n<h2>FAQ<\/h2>\n<h3>Does opening a circuit breaker provide isolation?<\/h3>\n<p>Opening a circuit breaker interrupts current; it does not by itself establish an isolation function. Isolation comes from the documented arrangement, such as a specified disconnected position of a withdrawable assembly or a separate disconnector. The breaker position and the installation&#8217;s isolation position therefore need to be distinguished.<\/p>\n<h3>Can remote operation replace a protection relay?<\/h3>\n<p>Remote operation provides an opening or closing command. Protection also needs measurement, a decision against configured criteria and a functioning trip path to a device with the required interruption capability. A controller may combine these functions, but a motor drive or communications interface alone does not establish them.<\/p>\n<h3>When can a switch-fuse combination serve a transformer branch?<\/h3>\n<p>A coordinated switch-fuse combination can serve a transformer branch when its documented switching and fault-clearing duties match the transformer and circuit. The switch, fuse and any release arrangement need to be specified together, with transformer inrush and coordination considered. If the branch needs protection functions or an adjustable response that the combination cannot provide, a suitable relay-and-breaker arrangement is the alternative to assess.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Una visi\u00f3n general pr\u00e1ctica y funcional de los dispositivos de conmutaci\u00f3n de media tensi\u00f3n: c\u00f3mo interact\u00faan la interrupci\u00f3n, la conmutaci\u00f3n de carga, el aislamiento y la puesta a tierra en una red de distribuci\u00f3n.<\/p>","protected":false},"author":1,"featured_media":1294,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-1130","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-technical-articles"],"_links":{"self":[{"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/posts\/1130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/comments?post=1130"}],"version-history":[{"count":8,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/posts\/1130\/revisions"}],"predecessor-version":[{"id":1299,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/posts\/1130\/revisions\/1299"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/media\/1294"}],"wp:attachment":[{"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/media?parent=1130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/categories?post=1130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/liqele.com\/es\/wp-json\/wp\/v2\/tags?post=1130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}