What is the difference between low voltage and medium voltage switchgear?

Low voltage switchgear operates at or below 1,000 V AC and is built to IEC 61439-2 or ANSI/IEEE C37.20.1, using air circuit breakers and moulded case breakers to feed loads directly. Medium voltage switchgear operates above 1,000 V — typically 3.3 kV to 40.5 kV — and is built to IEC 62271-200 or ANSI/IEEE C37.20.2/20.3, using vacuum circuit breakers to feed transformers, MV motors and distribution feeders. The practical difference is that LV switchgear carries high current at low voltage (up to 6,300 A) while MV switchgear carries low current at high voltage (typically 630-2,500 A), which changes the insulation, clearances, arc control and footprint of the whole assembly.

At what load size should I switch from LV to MV distribution?

The crossover for most industrial projects sits between 1,500 kVA and 2,500 kVA of connected load, or when feeder runs exceed roughly 100-150 metres. Below that, a single LV transformer and an LV lineup is cheaper and simpler. Above it, LV busbar and cable sizing becomes the dominant cost: a 2,000 kVA load draws 2,887 A at 400 V but only 105 A at 11 kV, so the copper cross-section, the number of parallel cables and the I²R losses all collapse when you move the distribution level up.

What does MVSG mean in electrical drawings?

MVSG is the common abbreviation for Medium Voltage SwitchGear on single-line diagrams, equipment schedules and load lists. You will also see LVSG for low voltage switchgear, MCC for motor control centre, RMU for ring main unit and GIS for gas-insulated switchgear. On a single line, MVSG normally denotes the assembly upstream of the distribution transformers, at 6.6 kV, 11 kV, 13.8 kV or 33 kV depending on the region.

How much does medium voltage switchgear cost compared with low voltage switchgear?

Indicative FOB China pricing: a 12 kV metal-enclosed feeder bay with a vacuum circuit breaker at 31.5 kA runs $2,800-$6,500, a 24 kV feeder runs $5,000-$12,000, and a 40.5 kV feeder runs $8,000-$18,000. A comparable Form 4b low voltage section with a 1,600-4,000 A air circuit breaker runs $1,800-$7,000. Per section, MV is roughly 1.5 to 2.5 times the price of LV — but MV replaces many LV sections plus the parallel cable runs they would need, so on projects above about 2 MVA the total installed cost usually favours MV distribution.

Do data centres use low voltage or medium voltage switchgear?

Both, in a defined hierarchy. Utility power arrives at medium voltage — typically 11 kV, 13.8 kV or 33 kV — into an MV lineup that feeds the generators, the unit substation transformers and any MV-connected chillers. Downstream of each transformer, low voltage switchgear at 400 V or 480 V feeds the UPS systems, the power distribution units and mechanical loads. Hyperscale campuses above roughly 10 MW increasingly push MV distribution closer to the hall to cut copper, so the MV lineup grows and the LV lineup per block shrinks.

Is 11 kV medium voltage or high voltage?

Under IEC practice and IEEE Std 1585, 11 kV is medium voltage — that standard puts medium voltage between 1 kV and 35 kV. Confusingly, many utilities and national wiring rules, particularly in the UK, India and Australia, historically call anything above 1 kV "high voltage", so an 11 kV panel may be labelled HV switchgear locally. ANSI C84.1 takes a third position and defines medium voltage as above 1,000 V up to 100 kV. When writing a specification, always quote the voltage in kV rather than relying on the words — that ambiguity is one of the most common sources of quotation mismatch we see.

Can low voltage and medium voltage equipment share the same room?

It is done routinely, but MV and LV assemblies should be in separate defined zones with their own access, and the MV section needs pressure relief venting that does not discharge into the LV working area. IEC 62271-200 internal arc classification is stated per accessible side (for example IAC AFLR 31.5 kA 1 s), and that classification is only valid if the venting path is respected during installation. Where floor area is tight, the usual solution is a packaged unit substation with the MV bay, the transformer and the LV panel in one back-to-back arrangement.

LV vs MV Switchgear: Voltage Classes, Cost & Selection Guide

Quick Answer: LV or MV?

Use low voltage (LV) switchgear — at or below 1,000 V — when you are feeding loads directly and total connected load is under roughly 1,500-2,000 kVA with short cable runs. Use medium voltage (MV) switchgear — above 1,000 V, typically 3.3 kV to 40.5 kV — when you need to move power more than about 100-150 metres, when connected load exceeds roughly 2 MVA, when you have motors above 200 kW, or when the utility connection itself is at MV. Most real projects use both: MV upstream of the transformers, LV downstream of them.

Voltage Classes: Why Three Standards Give Three Answers

Before comparing hardware, settle the vocabulary — because "medium voltage" is defined differently by three authorities, and specifications get written against all three.

Reference	Low Voltage	Medium Voltage	High Voltage
IEC 60038 / IEC 62271 scope	≤ 1,000 V AC	> 1 kV, switchgear standards cover up to 52 kV	> 52 kV (IEC 62271-203 onwards)
IEEE Std 1585	≤ 1,000 V	1 kV - 35 kV	> 35 kV
ANSI C84.1	≤ 1,000 V	> 1,000 V to 100 kV	100 kV - 230 kV
Common utility usage (UK, India, AU)	≤ 1,000 V	Often called "HV"	Transmission only

The practical consequence: an 11 kV panel can legitimately be called medium voltage switchgear in an IEC specification and HV switchgear in the same client's site rules. We receive enquiries every month asking for "HV switchgear" that turn out to be 11 kV metal-enclosed bays. Always write the number. Our guide to what medium voltage actually means works through the regional naming in more detail.

Standard system voltages you will actually meet:

LV: 400/230 V and 690 V (IEC world); 480/277 V, 208/120 V and 600 V (North America)
MV: 3.3, 6.6, 11, 22, 33 kV (IEC world); 4.16, 13.8, 34.5 kV (North America); 10 kV, 20 kV, 35 kV (China and much of Europe)

What Low Voltage Switchgear Actually Is

LV switchgear is a metal assembly containing air circuit breakers (ACBs), moulded case circuit breakers (MCCBs), miniature breakers, contactors, metering and busbars, distributing power at 1,000 V or less directly to loads. The governing standards are IEC 61439-1/-2 for power switchgear and controlgear assemblies, and ANSI/IEEE C37.20.1 for metal-enclosed low-voltage power circuit breaker switchgear in North America.

The defining design constraint is current. Because power equals voltage times current, low voltage means very high amperage: a 2,500 kVA transformer at 400 V delivers 3,608 A on its secondary. That drives everything — busbars are large copper or aluminium bars rated 800 A to 6,300 A, terminations are bolted and torque-controlled, and heat rise becomes the practical limit on how much you can pack into a section.

LV assemblies are graded by form of separation under IEC 61439-2 — Form 1 (no internal separation) through Form 4b (every functional unit and its terminals separated) — which is the LV equivalent of the LSC classification used in MV. Most industrial and data centre specifications call for Form 3b or Form 4b. NAIJI's SLVA grid-standardized low voltage switchgear is built for utility and industrial LV distribution up to 6,300 A. If you are choosing between breaker types inside an LV panel, see our ACB vs MCCB comparison.

What Medium Voltage Switchgear Actually Is

MV switchgear is a compartmented metal assembly containing vacuum circuit breakers, busbars, current and voltage transformers, earthing switches and protection relays, operating above 1 kV. The governing standards are IEC 62271-200 (AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV) and, in North America, ANSI/IEEE C37.20.2 for metal-clad and C37.20.3 for metal-enclosed interrupter switchgear.

Here the defining constraint is insulation and arc control, not current. A 12 kV bay carries a modest 630-1,250 A in most feeders, but it needs phase-to-earth clearances in the order of 125 mm in air, a lightning impulse withstand of 75 kV, an interrupter that clears 25-31.5 kA in under three cycles, and a tested pressure-relief path for an internal arc. That is why an MV bay is typically 800-1,200 mm wide and 2,200-2,500 mm tall for what may be only a few hundred amps.

NAIJI supplies the ASN3-12 at 12 kV, the ASN2-24 at 24 kV and the ASN1-40.5 at 40.5 kV, all with drawout vacuum breakers and full mechanical interlocking. Classification detail — LSC2B, PM partitions, internal arc codes — is covered in our metal-enclosed switchgear guide.

LV vs MV Switchgear: 14-Point Comparison

Dimension	Low Voltage Switchgear	Medium Voltage Switchgear
Rated voltage	≤ 1,000 V AC (typ. 400/480/690 V)	3.3 - 40.5 kV (typ. 11/12/24/33 kV)
Core standards	IEC 61439-1/-2; ANSI C37.20.1	IEC 62271-200; ANSI C37.20.2 / C37.20.3
Typical continuous current	630 - 6,300 A	630 - 2,500 A (4,000 A in generator bays)
Short-circuit withstand	50 - 100 kA, 1 s	20 - 40 kA, 3-4 s
Main switching device	Air circuit breaker, MCCB, contactor	Vacuum circuit breaker, SF6 or vacuum load break switch
Arc interruption medium	Air, with arc chutes and splitter plates	Vacuum (10^-4 Pa sealed interrupter) or SF6
Insulation level (BIL)	Not usually specified; 8 kV impulse typical	75 kV BIL at 12 kV; 125 kV at 24 kV; 185 kV at 40.5 kV
Separation classification	Form 1 to Form 4b (IEC 61439-2)	LSC1 / LSC2A / LSC2B, PM or PI (IEC 62271-200)
Internal arc reference	IEC/TR 61641 guidance	IEC 62271-200 Annex AA, e.g. IAC AFLR 31.5 kA 1 s
Typical section size (W×D×H)	600-1,000 × 800-1,200 × 2,200 mm	800-1,200 × 1,500-2,800 × 2,200-2,650 mm
Protection	Breaker trip units; some relays on incomers	Numerical relays: 50/51, 50N/51N, 27/59, 87, 49
Operator competence	Qualified electrician	Authorized HV/MV person, permit-to-work regime
Maintenance interval	Annual thermographic scan; ACB service ~5 years	Inspection every 5-8 years or 10,000 operations
Indicative FOB China per section	$1,800 - $7,000	$2,800 - $18,000 depending on kV class

Not sure which level your project needs? Send us your single-line diagram and load list — our engineers will size both options and quote them side by side. Contact NAIJI Electric.

The Real Decision: Where the Crossover Sits

Engineers rarely choose LV or MV on preference. The choice is forced by three numbers: load size, distance, and the largest motor.

1. Load size — the current problem

Current for a three-phase load is I = S ÷ (√3 × V). Run that for one 2,000 kVA load at different distribution voltages:

Distribution voltage	Current for 2,000 kVA	Copper needed (indicative)	Relative I²R loss
400 V	2,887 A	6 × 300 mm² per phase, or busduct	Baseline (100%)
3.3 kV	350 A	1 × 120 mm² per phase	≈ 1.5%
11 kV	105 A	1 × 35 mm² per phase	≈ 0.13%
33 kV	35 A	1 × 25 mm² per phase (insulation-driven)	≈ 0.015%

Loss falls with the square of the current, so moving from 400 V to 11 kV cuts conductor losses by a factor of roughly 750 for the same power. That is why the copper bill, not the switchgear bill, usually decides the architecture on large sites.

2. Distance — the voltage drop problem

Voltage drop is proportional to current times length. Commonly applied design limits are 3% on a branch circuit and 5% total in NEC practice, and around 4% under IEC 60364-5-52 Annex G guidance. At 400 V those limits are consumed within roughly 80-150 m on a heavily loaded feeder; at 11 kV the same physical cable can run several kilometres. Rule of thumb from our project work: if a feeder is longer than 150 m and larger than 500 kVA, price the MV option before committing.

3. Largest motor

Motors up to about 200 kW are comfortably fed at 400 V. Between 200 kW and 400 kW it is a genuine trade-off. Above roughly 400-500 kW, MV motors at 3.3 kV or 6.6 kV win on starting current, cable size and motor efficiency — and then you need MV switchgear or a vacuum contactor unit to feed them. See our note on MV motor control with VFDs and soft starters.

Most Projects Are Not LV or MV — They Are Both

The standard architecture on any site above about 1 MVA looks like this:

Utility incomer at MV (11 kV / 13.8 kV / 33 kV) into a ring main unit or an MV incomer bay with metering
MV switchgear lineup — incomer, bus section, and one feeder bay per transformer, generator and MV motor
Distribution transformers, typically 630-2,500 kVA, stepping MV down to 400 V or 480 V
LV switchgear lineup per transformer — main ACB, bus tie, and outgoing MCCB or ACB feeders
Final distribution boards and MCCs at the loads

The engineering question is therefore not "LV or MV" but how far down into the site MV should reach before you transform. Push the transformers closer to the loads and you buy more MV bays but far less LV copper. Our MV power distribution system design guide works through radial, loop, primary selective and secondary selective topologies with cost consequences, and the switchgear lineup design guide covers how many bays a lineup actually needs.

Data Centres: A Worked Example of the Hierarchy

Data centres show the split clearly because the reliability requirement forces redundancy at both levels.

Level	Equipment	Typical rating	Redundancy
Utility / MV	MV switchgear lineup, ring main units	11-33 kV, 1,250-2,500 A, 25-31.5 kA	2N incomers, bus tie
Generation	MV generator breaker bays	11 kV, 2,000-4,000 A	N+1 or 2N gensets
Transformation	Cast resin unit substation transformers	1,000-2,500 kVA	One per block, 2N feeds
LV distribution	LV switchgear, UPS input/output boards	400/480 V, 2,000-6,300 A	2N with static transfer switches
Rack level	PDUs, busway	400 V / 415 V, 100-800 A	Dual corded A/B

The trend on hyperscale campuses above 10 MW is to push MV deeper — feeding MV directly to block-level unit substations rather than running LV busduct across the building. That grows the MV bay count and shrinks LV copper. Detail in our MV switchgear for data centres guide.

Cost, Lead Time and Total Installed Price

Equipment price is only part of the picture, but here are the indicative FOB China numbers we quote in 2026, per section, at 31.5 kA:

Assembly	Typical section	Indicative FOB price	Standard lead time
LV switchgear (Form 3b/4b)	Feeder section, MCCB outgoers	$1,800 - $4,000	20 - 30 days
LV switchgear (Form 4b)	Incomer, 4,000 A ACB + metering	$4,000 - $7,000	25 - 35 days
MV metal-enclosed, 12 kV	Feeder bay with VCB	$2,800 - $6,500	25 - 40 days
MV metal-enclosed, 24 kV	Feeder bay with VCB	$5,000 - $12,000	30 - 45 days
MV metal-enclosed, 40.5 kV	Feeder bay with VCB	$8,000 - $18,000	35 - 50 days
MV gas-insulated (GIS), 12 kV	Feeder bay, compact	$6,000 - $14,000	35 - 50 days

Two things that surprise buyers comparing quotations:

Protection relays can be 20-35% of an MV bay price. A specification that names a European relay brand roughly doubles the relay line item versus a compliant Chinese or Korean numerical relay. Decide deliberately — see our protection relay selection guide.
LV price scales with amperage, MV price scales with kV. Doubling LV current roughly doubles the busbar cost; doubling MV voltage roughly doubles the whole bay because clearances, bushings and insulation all grow.

MOQ is flexible — we ship single bays for retrofits as well as complete lineups. All prices are indicative and confirmed against your single-line diagram and ratings.

Safety and Operating Regime: The Difference Nobody Budgets For

The operational difference between LV and MV is bigger than the hardware difference. LV panels are switched by qualified electricians as routine work. MV switching requires an authorized person, a permit-to-work, documented isolation and earthing, and in most jurisdictions two-person operation.

Arc flash: incident energy is assessed with IEEE 1584-2018 at both levels. LV boards frequently produce the higher incident energy at the working position because arcs at 400-600 V can be sustained in the enclosure, while MV bays are typically protected by tested internal arc containment and venting rather than PPE alone.
Earthing: MV bays carry an integral earthing switch with a making capacity; LV isolation is normally proved with a tester and portable earths. Detail in our earthing and grounding guide.
Interlocking: MV drawout construction enforces the sequence mechanically — you cannot rack in against a closed earth switch. See arc flash protection in switchgear.

10-Point Selection Checklist

Confirm the utility supply voltage and whether the connection point is LV or MV
Total the connected load in kVA and identify the largest single motor
Measure the longest feeder run from the intake to the furthest load centre
Get the utility fault level in kA — this sets the short-circuit rating of everything downstream
Decide the distribution level: if load > 2 MVA or run > 150 m, price MV
Choose the standard system — IEC or ANSI — and do not mix requirements in one specification
State the separation class: Form 3b/4b for LV, LSC2B PM for MV
State the internal arc requirement with duration (e.g. IAC AFLR 31.5 kA 1 s)
Define relay functions and communication protocol (IEC 61850, Modbus, DNP3)
Check the room: door width, floor loading, cable entry direction, arc venting path

Working through a full enquiry document? Our MV switchgear specification and RFQ guide gives a fill-in data sheet, and the short-circuit rating calculation guide covers point 4 in detail.

Why Buyers Source Both Levels From One Factory

NAIJI Electric manufactures medium voltage switchgear from 12 kV to 40.5 kV, gas-insulated switchgear, indoor and outdoor vacuum circuit breakers, and grid-standardized low voltage switchgear in one plant. Sourcing the MV lineup, the transformer-side connections and the LV lineup from a single manufacturer removes the interface problems that cost weeks on site: matching busbar centres, cable entry directions, control voltage, relay protocol and terminal numbering all get resolved on one set of drawings.

Type-tested designs to IEC 62271-200 and IEC 61439 with third-party reports available
12 kV to 40.5 kV MV bays, 6,300 A LV assemblies, single-bay MOQ for retrofits
Standard lead time 25-45 days; factory acceptance test with client witness on request
Export documentation, CE marking and spare parts packages included in quotation

Bottom Line

LV switchgear solves a current problem; MV switchgear solves an insulation problem. Below about 1,500-2,000 kVA with short runs, LV alone is cheaper and simpler to operate. Above that, or beyond about 150 m, MV distribution pays for itself in copper and losses before you count reliability. On almost every industrial site, plant, hospital or data centre above 1 MVA, the correct answer is a properly sized MV lineup feeding transformers that feed properly sized LV lineups — and the engineering value is in deciding where that boundary falls.

Get an LV & MV Switchgear Quotation →