High voltage vs low voltage switchgear: low voltage switchgear controls and protects circuits below 1 kV — the boards that feed motors, lighting and building loads — while high (and medium) voltage switchgear handles circuits above 1 kV, such as 6, 10, 12 or 35 kV substation feeders. The higher the voltage, the more the design is driven by insulation, arc interruption, clearances, testing standards and specialist maintenance.
The 6 key differences in brief
- Voltage range – LV is up to 1 kV AC; MV/HV is above 1 kV.
- Insulation and arc interruption – LV uses air-break and moulded-case breakers; MV/HV uses vacuum or SF6 breakers.
- Size and clearances – MV/HV panels are larger, with compartmented, often withdrawable construction.
- Standards – LV assemblies follow IEC 61439; MV/HV follows IEC 62271-200.
- Protection – LV relies mostly on breaker trip units; MV/HV uses separate protection relays with CTs and VTs.
- Cost and maintenance – MV/HV costs more and needs trained, authorised staff and planned outages.
Switchgear is one of those terms that gets used loosely in the industry. Walk through a large power facility and you will find switchgear in the incoming substation, in the motor control room, at the distribution boards feeding individual loads — and the equipment in each location looks and behaves very differently. The fundamental reason is that high voltage switchgear and low voltage switchgear are not simply different sizes of the same thing. They are engineered around different physics, different hazards, different standards, and different operational requirements.
For engineers specifying equipment, procurement teams evaluating suppliers, or project managers trying to understand why two switchgear orders have such different price tags and lead times, this guide covers the six differences that actually matter.
The Voltage Boundary That Defines Everything
Before going into the six differences, it helps to be clear about where high voltage ends and low voltage begins, because the boundary is more specific than most people realise and it is defined by international standards, not industry convention.
Under IEC 62271 — the primary international standard series governing switchgear and controlgear — the boundary sits at 1000V alternating current. Equipment operating above 1kV AC falls under high voltage switchgear standards. Equipment operating at or below 1000V AC is governed by low voltage switchgear standards, primarily IEC 61439 for assemblies and IEC 60947 for individual devices.
In practical terms, the high voltage category covers medium voltage systems from 1kV up to 52kV — which includes the 3.6kV, 6kV, 10kV, 11kV, 12kV, 33kV, and 36kV systems common in utility distribution and industrial facilities — as well as transmission voltages above 52kV. The low voltage category covers the 230V, 400V, 415V, and 690V systems that most people encounter in everyday industrial and commercial settings.
At Danli, we manufacture both categories. Our KYN28-12 metal-clad switchgear operates in the medium voltage range up to 12kV, while our low voltage distribution boards and motor control centres operate within the IEC 61439 framework at 400V and 690V. The six differences below are drawn from real experience building and commissioning equipment across both voltage classes.
Difference 1: Voltage Range and System Architecture
The most fundamental difference is the voltage level each switchgear type is designed to handle, and this shapes everything from cabinet size to safety requirements to where the equipment sits in a power system.
High voltage switchgear handles the transmission and primary distribution of electrical power. In a typical industrial facility, the utility supplies power at 11kV or 33kV, which arrives at the main incoming substation through high voltage switchgear — typically gas-insulated switchgear (GIS) or air-insulated switchgear (AIS) for transmission voltages, or metal-clad switchgear like the KYN28-12 for 6kV to 12kV distribution. This equipment controls the connection between the utility supply and the facility’s internal distribution network.
Low voltage switchgear sits downstream of the power transformer. Once the transformer steps the supply voltage down to 400V or 415V, the outgoing low voltage switchgear — typically a distribution board, motor control centre, or power control centre — distributes the supply to individual loads: motors, lighting circuits, HVAC equipment, process drives, and socket outlets.
In a water treatment plant, for example, the high voltage switchgear controls the 11kV incoming supply and the feeds to large pump motor transformers. The low voltage switchgear distributes 400V power to smaller pumps, instrumentation systems, control panels, and auxiliary equipment throughout the facility.
Difference 2: Insulation Requirements and Arc Interruption Technology
This is where the engineering diverges most sharply between the two voltage classes, and understanding it explains why high voltage switchgear costs significantly more than an equivalent-current-rated low voltage assembly.
At voltages above 1kV, air alone is not a sufficient insulating medium for compact equipment design. Electric arcs in high voltage systems carry enormous energy and do not extinguish naturally when current passes through zero unless special arc interruption technology is used. High voltage switchgear uses one of three main arc interruption methods: vacuum interrupters, sulphur hexafluoride (SF6) gas, or air blast for older or very high voltage equipment.
Vacuum circuit breakers — used in the KYN28-12 and similar medium voltage switchgear — interrupt current by drawing the arc inside a sealed vacuum bottle where the absence of gas molecules means there is nothing to sustain the arc after current zero. This happens within 60 to 80 milliseconds of the trip signal. The vacuum interrupter also requires minimal maintenance over its rated life, which is typically 10,000 mechanical operations and 50 to 100 fault interruption operations.
SF6 gas-insulated switchgear uses sulphur hexafluoride gas at elevated pressure as both the insulating medium and the arc interruption medium. SF6 has dielectric strength approximately three times that of air at atmospheric pressure, allowing GIS equipment to be dramatically more compact than air-insulated alternatives at the same voltage rating. GIS is the dominant technology for transmission voltages above 72.5kV and is increasingly common at 33kV and above in constrained urban substation environments.
Low voltage switchgear interrupts current using moulded case circuit breakers, air circuit breakers, or fuses — devices that operate effectively at 400V to 1000V using thermal-magnetic or electronic trip mechanisms. The arc interruption requirements at low voltage are manageable with arc chute systems that cool and extinguish the arc without exotic insulating media.
Difference 3: Physical Size, Clearances, and Cabinet Design
Stand next to a medium voltage switchgear panel and then stand next to a low voltage distribution board rated for a similar current, and the difference in physical scale is immediately clear.
High voltage switchgear requires substantially larger physical clearances between live conductors and earthed metalwork, between phases, and between the equipment and the operator. At 12kV, the minimum phase-to-earth clearance in air is 125mm and the minimum phase-to-phase clearance is 125mm. These clearances are a direct function of the voltage level and cannot be reduced without either using a superior insulating medium or risking flashover.
The KYN28-12 cabinet, as a reference point, has external dimensions of approximately 800mm to 1000mm wide, 1550mm deep, and 2300mm high for a single standard panel. A low voltage motor control centre panel rated for the same 630A current would typically be 400mm to 600mm wide, 400mm to 600mm deep, and 2000mm high — significantly smaller in all three dimensions.
The internal compartmentalisation of high voltage switchgear also adds physical complexity. Metal-clad switchgear like KYN28-12 must maintain complete metal barriers between the busbar compartment, circuit breaker compartment, cable compartment, and low voltage compartment. This physical segregation is a safety requirement, not a design choice, and it contributes directly to the larger cabinet footprint.
Low voltage switchgear assemblies governed by IEC 61439 have internal form separation requirements that range from Form 1 — no internal separation at all — up to Form 4 Type 7, which provides full separation between busbars, functional units, and external cable connections. Even at the highest form of separation, the physical dimensions remain far more compact than equivalent high voltage equipment.
Difference 4: Governing Standards and Testing Requirements
Every piece of switchgear must comply with standards that govern its design, manufacture, and testing. The standards applicable to high voltage and low voltage equipment are completely different, and the testing regimes they require are significantly more demanding for high voltage equipment.
High voltage switchgear is governed primarily by the IEC 62271 series. IEC 62271-200 covers AC metal-enclosed switchgear for rated voltages above 1kV up to 52kV. IEC 62271-100 covers alternating current circuit breakers. IEC 62271-201, updated in its third edition in July 2026, addresses solid-insulation enclosed switchgear up to 52kV. Type tests under these standards include power frequency withstand voltage tests, lightning impulse withstand voltage tests, short-circuit making and breaking tests, temperature rise tests, and internal arc tests where applicable.
Low voltage switchgear assemblies are governed by IEC 61439. This standard series replaced the older IEC 60439 and introduced more rigorous requirements for verification of temperature rise, dielectric properties, short-circuit withstand, and mechanical strength. The updated IEEE C37.20.1-2026 standard, approved by the IEEE Board in February 2026, governs metal-enclosed low voltage power circuit breaker switchgear for AC voltages up to 1058V and DC voltages up to 3200V — reflecting the growing importance of battery energy storage and DC distribution applications.
The key difference in testing burden is that high voltage switchgear type tests are conducted on complete assemblies at accredited high power testing laboratories, which is expensive and time-consuming. Low voltage switchgear manufacturers can perform more of the required verification testing internally, which reduces the compliance cost but does not reduce the engineering rigour required.
Difference 5: Protection Relays and Metering Equipment
The protection and measurement equipment inside high voltage switchgear is substantially more sophisticated than what you find in low voltage assemblies, and this reflects the higher fault energy levels and the greater consequences of a fault in a high voltage system.
High voltage switchgear panels incorporate numerical protection relays that perform functions like overcurrent protection (ANSI function 50/51), earth fault protection (51N/51G), distance protection (21), differential protection (87), and voltage protection (27/59) depending on the application. These relays receive current signals from high voltage current transformers (CTs) and voltage signals from voltage transformers (VTs) installed in the switchgear. The relays continuously monitor the electrical quantities, compare them against set thresholds, and initiate circuit breaker trip commands within milliseconds when a fault condition is detected.
Modern numerical relays — products from manufacturers like Schneider Electric MiCOM, ABB REF, Siemens SIPROTEC, and SEL — also record fault waveforms, log events, communicate over IEC 61850 GOOSE messaging networks, and provide detailed post-fault analysis data. This level of functionality is standard in high voltage switchgear and is a significant part of the overall panel cost.
Low voltage switchgear uses moulded case circuit breakers with built-in electronic trip units, or separate multifunction power meters for measurement. Protection functions in LV assemblies are simpler — overcurrent, short circuit, earth leakage — and are typically handled by the circuit breaker’s trip unit rather than a separate relay. Motor control centres add overload relays and motor protection devices, but the complexity and cost of LV protection equipment remains a fraction of the HV equivalent.
Difference 6: Cost, Installation Requirements, and Maintenance
The combination of larger physical size, more sophisticated arc interruption technology, higher insulation requirements, and more complex protection systems means that high voltage switchgear carries a substantially higher cost per panel than low voltage equipment — and it demands more from the installation and maintenance teams that work with it.
For a rough order of magnitude, a fully specified medium voltage switchgear panel — incoming feeder or outgoing motor feeder at 12kV with numerical protection relay, current and voltage transformers, vacuum circuit breaker, and metering — will typically cost three to ten times more than an equivalent-current-rated low voltage motor control centre section depending on specification, location, and brand of components.
The installation requirements also differ. High voltage switchgear requires specialised civil works — reinforced substation rooms with restricted access, specific floor load ratings, ventilation to manage heat output, and in the case of SF6 equipment, gas monitoring and handling provisions. The personnel installing and commissioning high voltage equipment must hold appropriate electrical safety competencies and are typically working under a permit-to-work system even during installation and testing.
Maintenance of high voltage switchgear requires coordination with the utility or plant operations team to arrange outages, use of insulating gloves and live line tools where working near energised equipment is unavoidable, and regular scheduled testing of protection relay functions and circuit breaker operation. Most industrial facilities have a three to five year planned maintenance cycle for medium voltage switchgear.
Low voltage switchgear can often be maintained under partial outage conditions because of its compartmentalised construction, and the personnel requirements — while still subject to electrical safety regulations — are less specialised than for high voltage work.
Read More: KYN28-12 switchgear full guide
High Voltage vs Low Voltage Switchgear: Side-by-Side Comparison
| Feature | Low voltage | Medium voltage | High voltage |
|---|---|---|---|
| Voltage range | Up to 1 kV | About 1 kV – 35 kV | Above 35 kV |
| Typical setting | Buildings, light industry, MCCs | Substations, factories, campuses | Transmission networks, power plants |
| Breaker type | ACB, MCCB, MCB | Vacuum (VCB), some SF6 | SF6, vacuum, GIS |
| Cabinet size | Compact | Moderate, compartmented | Large, wide insulation gaps or gas-insulated |
| Maintenance | Simple, routine | Planned inspection and testing | Specialist, higher cost |
| Main IEC standard | IEC 61439 | IEC 62271-200 | IEC 62271 series |
Note: voltage bands vary slightly between countries and standards. Many engineers group everything from 1 kV to 35 kV as medium voltage, which is where most industrial “high voltage” switchgear such as KYN28-12 actually sits.
Choosing the Right Equipment for Your Project
The choice between high voltage and low voltage switchgear is not actually a choice in most projects — both are needed, and the question is where the boundary sits. That boundary is defined by your supply voltage, your transformer configuration, and the load requirements of your facility.
What matters most is that both types are specified correctly, supplied by manufacturers with verified certifications, and installed and commissioned by competent teams following the relevant standards. An undersized low voltage assembly that cannot withstand its prospective fault current is just as dangerous as a high voltage panel installed without proper clearances.
At Danli, we manufacture high voltage KYN28-12 metal-clad switchgear and complete low voltage switchgear assemblies certified to IEC 62271-200, IEC 61439, UL, CE, and ISO standards. Our engineering team supports clients from initial specification through factory acceptance testing to commissioning assistance, ensuring that both ends of the power distribution system are built to the same standard of reliability and safety.
Frequently Asked Questions
The voltage level. Low voltage switchgear works below 1 kV and uses air-break or moulded-case breakers, while high and medium voltage switchgear works above 1 kV and needs vacuum or SF6 breakers, bigger clearances, separate protection relays and stricter testing.
Under IEC conventions, low voltage is up to 1,000 V AC (1,500 V DC). Above that, equipment is medium or high voltage and is covered by the IEC 62271 series.
Usually yes. Power typically arrives at medium voltage, passes through MV switchgear and a transformer, and is then distributed by low voltage switchgear to the loads.
Low voltage assemblies are designed and verified to IEC 61439-1/-2. Metal-enclosed medium voltage switchgear is covered by IEC 62271-200.
