Summary Highlights
- A disconnector provides its specified isolation function; open position alone does not prove absence of voltage.
- Ordinary off-load isolation and specifically rated limited switching duties must be distinguished from load and fault interruption.
- A switch-disconnector combines declared switching and isolation duties; a label or photograph does not establish both.
- An earthing switch has a different function. Fault-making and short-time withstand ratings do not mean fault-breaking capability.
- Qualified personnel need the actual model, assembly manual, supply arrangement and approved work plan.
Article Details
Disconnector, isolator and switch-disconnector: what the names mean
A disconnector provides an isolation function in an electrical installation. In its open position it establishes the isolation arrangement specified for the equipment design. Isolator is also used for this function in English. Confirmation can involve visible contacts or approved position indication, according to the design; neither alone proves absence of voltage.
A switch-disconnector combines an isolating function with the switching duties declared for that product. It is not simply another name for every disconnector or every load break switch. At medium-voltage (MV) and high-voltage (HV) facilities in Turkey, keep the English product name, nameplate, actual model and single-line symbol together so that a translation does not silently change the intended function.
Can a disconnector switch current?
An ordinary off-load disconnector must not be assumed capable of interrupting load or fault current. Where load switching is required, the selected equipment needs the appropriate declared duty, such as a suitable load break switch, switch-disconnector or circuit breaker. A continuous-current rating describes carrying current; it does not establish an interruption duty.
Any limited switching duty must be explicitly declared for the exact device and operating conditions. Such a declaration must not be extrapolated to another disconnector or treated as unrestricted normal-load or fault interruption. An arcing horn, motor mechanism or familiar appearance is not evidence of a switching duty.
The decision must come from the exact manufacturer specification and installation design, not a generic current threshold or a photograph. This explanation is a functional distinction, not an instruction to operate any device.
Compare isolation, load switching, fault clearing and earthing
| Device/function | What to establish | Do not infer |
|---|---|---|
| Disconnector / isolator | The isolation function and any specifically rated limited switching duties | Normal-load or short-circuit interruption from its continuous-current rating. |
| Load break switch | Its declared normal-load making/breaking duties | Fault breaking or an isolating function unless separately specified. |
| Switch-disconnector | Both its declared switching duties and its isolation function | That every device described as a switch or disconnector combines both functions. |
| Circuit breaker | Its declared normal/fault making, carrying and interruption duties and control/protection arrangement | That an open breaker alone establishes all isolation points or absence of voltage. |
| Earthing switch | The designated earthing function and applicable making/withstand ratings | That fault-making capability permits unsafe closing, or that it can interrupt load/fault currents. |
A fused switching combination needs to be evaluated as the specified combination: a fuse’s fault-clearing duty should not be attributed to the disconnector or switch alone. The circuit breaker guide explains the relay-command and interruption chain; the isolation function remains a separate design question.
Open position, voltage indication and earthing have different meanings
When a disconnector is closed, its conducting path is connected; whether it is energized depends on the supply and installation state. When open, it establishes the specified isolation arrangement. Other sources, backfeeds or induced voltages may remain relevant. A position signal and a voltage-presence indicator answer different questions, and a dark indicator is not proof that conductors are dead.
An earthing switch connects the designated circuit section to earth under the installation’s defined conditions. It is related to isolation but does not replace it or establish that every nearby part is safe. A short-time withstand or fault-making rating describes a duty of the device, not permission to close onto an unsafe circuit.
Interlocks help prevent specified incompatible actions; they cannot eliminate every hazard. Work and switching require qualified personnel, the actual manufacturer instructions and an approved installation-specific isolation, absence-of-voltage verification and grounding plan. No generic operating sequence is provided here.
Indoor, outdoor, manual and motor-operated designs
Physical arrangements include centre-break, double-break, vertical-break and other layouts used to suit the installation. Indoor devices may be integrated into a cubicle, while outdoor devices need an appropriate mechanical and environmental design. The number of poles, clearances, mounting orientation and connections belong to the actual arrangement.
Manual and motor-operated describe how the mechanism is driven; remote operation does not add a load- or fault-interruption duty. A visible open blade can assist confirmation in a design that uses a visible gap, while enclosed designs may use approved indication. Neither a drive type nor a blade shape establishes the complete isolation or safe-access condition.
Read complete ratings and assembly interfaces
| Input | Why it matters | Boundary |
|---|---|---|
| Actual device type/model and declared duties | Distinguishes off-load isolation, combined switching and specialist limited duties | Category labels, a photograph or an ampere value are insufficient. |
| Rated voltage/frequency and insulation duties | Matches the system and the required insulation arrangement | Operating voltage alone does not cover all insulation conditions. |
| Rated normal current, A | Describes continuous current-carrying duty | It is not a breaking-current rating. |
| Short-time withstand current plus duration; peak withstand/making where applicable | Separates time-dependent RMS duty from peak duty and earthing making duty | Do not compare a bare kA number without its label, time and basis. |
| Indoor/outdoor environment, pollution, altitude and mechanical conditions | Supports the actual installation and maintenance-access design | One supplier’s range is not a universal Turkey-wide specification. |
| Drive, indication, interlocks and cubicle interfaces | Establishes compatibility with the breaker, earthing function and actual control arrangement | Generic interlock lists are not a complete safe-work plan. |
Request the exact variant’s drawings, manual and declared ratings when documents disagree. The manufacturer’s family brochure may show different load-switching and off-load variants with different duties even where their continuous-current figures look similar. A withstand value or endurance class should not be turned into a fault-breaking rating or guaranteed field life.
Illustrative facility case: identify the missing function
A facility owner asks whether a motor-operated outdoor device can be used for normal-load switching. The available photograph shows an actuator and contact assembly, but no verified model or declared switching duty. The correct next step in the engineering assessment is to identify the actual device and obtain its rated-duty documents; motorization and appearance do not settle the question.
A separate indoor assessment may concern a cubicle with a breaker, disconnector and earthing switch. The information package should show the single-line diagram, all relevant supplies, exact models, manufacturer interlock and position definitions, and the intended work boundary. These examples describe information needs, not a customer case or a switching recipe. Neither can be resolved by copying a generic catalogue current value.
Condition assessment, source scope and further guidance
Condition assessment can consider contacts, transmission links, hinges, drives, fixings, indications, auxiliary feedback and the specified interlocks. Oxidation, looseness, misalignment or inconsistent feedback may require investigation. The selected inspections/tests, outage and access arrangements follow the actual equipment, manufacturer instructions and approved work scope; a visual check alone does not certify complete isolation or future performance.
The disconnector testing and maintenance guide covers assessment separately from this definition. Where the facility needs equipment identification, assembly compatibility or control/interlock evaluation, HV/MV testing, maintenance and repair and LV/MV/HV project design and consultancy can be scoped around the actual installation records. A periodic inspection or HV operation responsibility appointment remains a different scope.
References: the IEC 62271-102 public scope identifies AC disconnectors and earthing switches. The Aktif catalogue provides product-family examples of off-load disconnection, combined arrangements and earthing duties. The Schneider HVL/cc instruction bulletin explains the limits of voltage-presence indication and interlocks. Manufacturer examples remain specific to their product and do not replace the actual installation’s documentation and approved work plan.
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Frequently Asked Questions
What is a disconnector?
A disconnector, also called an isolator in some English usage, provides its specified isolation function in the open position. The design may use visible contacts or approved position indication. It is not automatically a load/fault interrupter, and its open position alone does not prove absence of voltage or authorize access.
What does a disconnector do?
It establishes the isolation arrangement defined for the actual equipment. It can be part of the installation’s maintenance and switching design, alongside a breaker and earthing arrangements. Other supplies, backfeeds and relevant induced voltages must still be considered. Qualified personnel need the approved installation-specific work plan and manufacturer instructions.
Can a disconnector be opened under load?
Do not assume an ordinary off-load disconnector can interrupt load or fault current. Any claimed limited switching duty must be explicitly declared for the exact device and conditions; it must not be extrapolated to another model. Normal-load switching requires appropriately rated equipment. Confirm the actual model and duty under the approved installation-specific plan.
What is the difference between a disconnector and a circuit breaker?
The disconnector provides its specified isolation function. The circuit breaker has declared making, carrying and interruption duties, including the applicable fault duty, and works with its protection/control arrangement. These functions can exist as separate or combined equipment. An open device alone does not prove the whole installation is dead or safe for access.
Are a disconnector and a load break switch the same thing?
No. A load break switch has declared normal-load switching duties; a disconnector has an isolation function. A switch-disconnector combines both where specified. Fault interruption is another duty. Verify the actual manufacturer classification and any fuse-switch combination; appearance, motorization and continuous-current rating do not establish all these functions.
What is an earthing switch?
It connects the designated circuit section to earth under the defined installation conditions. Its earthing function differs from isolation and current interruption. Applicable fault-making and short-time withstand ratings are distinct duties, not permission to close onto an unsafe circuit. The approved work plan must establish the required isolation, absence-of-voltage verification and grounding arrangements.
How is a disconnector's isolation position confirmed?
Use the visible contacts or approved indication specified for the design, with the actual manufacturer instructions and installation plan. Position confirmation does not prove absence of voltage. A voltage-presence indicator is also different from an absence-of-voltage test; a dark lamp alone is insufficient. Qualified personnel must apply the required verification and grounding arrangements.
How is a disconnector used in MV switchgear?
Its function is assessed with the breaker, earthing arrangements, cubicle interfaces and specified interlocks. Exact position definitions and operating/access conditions are product dependent. Interlocks do not eliminate every hazard; qualified personnel must follow the approved installation-specific plan. There is no universal operation order suitable for all assemblies.
What should be considered when selecting a disconnector?
Confirm the exact type and declared duties, voltage/frequency and insulation requirements, normal current, short-time current/duration, applicable peak/making duty, environment, drive, indications, interlocks and assembly interfaces. Use the actual variant’s documents. A bare kA figure, current rating or supplier category range is not a complete selection basis.
Is a disconnector protection equipment?
An ordinary disconnector is not the device that detects and interrupts faults. In a typical MV protection scheme, the relay/control chain and breaker perform that role. Isolation remains essential, but it must not be confused with fault clearing, absence-of-voltage verification or a complete safe-work condition.
What are the types of disconnectors?
Designs vary by indoor/outdoor installation, pole and contact arrangement, mounting and manual or motor drive. Some assemblies combine a disconnector with earthing or load-switching functions. The actual product specification determines those duties; the physical type or actuator does not by itself establish load-breaking capability or safe isolation.