Medium Voltage Equipment for Data Centers

Data center medium voltage equipment is everything between the utility interconnect and the low voltage unit substations: the on-site substation transformer, the main MV switchgear, the MV distribution loops, and the transformers that step down to 480 V at each building or power block. The key decisions are topology and redundancy, GIS versus metal-clad switchgear, dry type versus liquid-filled transformer placement, and fault current, and all of them have to be made early because lead times drive the schedule.

This guide goes deeper than our data center industry page.

How a data center campus is powered at medium voltage

A large campus takes high or medium voltage service, steps it down on site, and distributes at MV to each building. Schneider Electric notes that data centers above about 5 MW tend to connect to the grid at MV or even at transmission level, and that MV switchgear generally appears once IT load passes about 1 MW.

A typical path looks like this:

Utility service and on-site substation. High voltage lines terminate at a campus substation where power transformers step down to a distribution voltage, commonly in the 13.8 kV to 34.5 kV range.
Main MV switchgear. Breakers receive the transformer secondaries and feed the campus.
MV distribution. Cable feeders, radial or looped, run to each building or power block.
Step-down to 480 V. Pad mount or dry type transformers in unit substations feed the LV switchgear, UPS and PDUs.

Higher distribution voltage pays off. In a DCD analysis, Ormazabal showed that raising distribution from 11 kV to 24 kV cuts current for the same load to about 45% of its original value, and conductor losses can fall by up to 80%, because losses scale with the square of current.

Redundancy at medium voltage: N, N+1 and 2N

Redundancy at MV means losing a utility feed, transformer, bus or feeder does not drop critical load. N is just enough capacity. N+1 adds one spare component, such as a third substation transformer where two carry the load. 2N is two fully independent paths, often called A and B, each able to carry the full load.

At the MV level, those ideas show up as:

Dual utility feeds from separate sources, where the utility can offer them.
Main-tie-main switchgear, with two mains and a normally open tie breaker so one source can pick up both buses.
Double-ended substations, with two transformers feeding a split bus.
Loop distribution, either open loop (a normally open point, switched manually or automatically after a fault) or closed loop (always tied, with differential protection to isolate a faulted section).

More equipment is not automatically more reliable. A Schneider Electric study of MV generator plant architectures found that a simple single-fed design scored higher on reliability than some more complex redundant designs, because the extra distribution equipment adds failure points. Design redundancy around the failures the owner is actually protecting against, and commission every tie and transfer scheme.

For fast restoration on open-loop and dual-source schemes, G&W Electric Automatic Source Transfer covers 5 kV to 38 kV with peer-to-peer high speed transfer and open or closed transition. See distribution automation.

Switchgear selection: GIS vs. metal-clad AIS

GIS saves space and seals live parts away from dust and humidity, while metal-clad AIS is the familiar North American lineup with draw-out breakers. Under IEEE C37.20.2, metal-clad gear puts the breaker, buses and instrumentation in separate metal compartments.

Factor	Gas-insulated (GIS)	Metal-clad air-insulated (AIS)
Footprint	Compact. JST's dry air GIS is up to 75% smaller than AIS	Larger lineups and wider aisles
Voltage range (JST lines we represent)	5 kV to 38 kV, with 69 kV in cubicle GIS	5 kV to 15 kV
Insulating medium	Dry air (J10N, J20N) or SF6 (J10X, J20X)	Air
Live parts	Sealed inside gas-filled enclosures	Draw-out vacuum breakers with integral racking
Arc resistance	J10N and J20N carry IEC and IEEE internal arc classification. J20X is fully arc resistant	J100CLAD is non-arc-resistant
Best fit	Space-limited electrical rooms, 38 kV distribution, harsh sites	15 kV class buildings where teams want familiar draw-out gear

Arc-resistant requirements. Arc resistance is a common data center spec item. IEEE C37.20.7 testing defines accessibility types: Type 1 (front only), Type 2 (full perimeter), Type 2B (maintained with the instrument or control compartment door open) and Type 2C (adds isolation between compartments). The JST J100CLAD metal-clad switchgear covers 5 kV to 15 kV, up to 3000 A and 25 kA to 50 kA with J3MAG magnetically actuated vacuum breakers, but it is not arc resistant. If your spec requires arc-resistant construction, look at the J20X cubicle-type GIS or the dry air lineups. See all metal-clad switchgear and breakers.

SF6-free options. SF6 is a potent greenhouse gas. EPA's summary of state rules notes that California began phasing out SF6 gas-insulated equipment in 2025, and New York's Part 495 sets a voltage-based phaseout starting in 2027. The JST J20N dry air GIS is rated 38 kV, 1200 A and 31.5 kA with 170 kV BIL, and the J10N covers 5 kV lineups at 600 A and 20 kA. Both use dry air in place of SF6. Browse gas-insulated switchgear and our comparison of solid dielectric vs. SF6 switchgear.

Transformers and substations: placement drives the type

Where the transformer sits usually decides between dry type and liquid-filled. Outdoor units are typically liquid-filled, while indoor or close-coupled unit substations usually call for dry type, where fire risk and oil containment matter.

Campus substation: liquid-filled JST power transformers up to 600 MVA, with natural ester coolant available. Specify tap changers and cooling stages with future phases in mind.
Modular blocks: a factory-tested packaged unit substation cuts field integration work.
Outdoor, per building: three-phase liquid-filled pad mounts to 5000 kVA and 34.5 kV. See pad mount transformers.
Indoor, close-coupled: cast resin or VPI units. See dry type transformers.

For the full trade-off, read data center transformers: dry type vs. liquid-filled.

Fault current, sensing and BESS at MV

Current limiting for high fault levels. Fault current climbs as a campus adds transformers, closes bus ties or parallels generation, and can exceed the interrupting rating of installed switchgear. The G&W Electric CLiP Current Limiting Protector is rated 2.8 kV to 38 kV, up to 5000 A continuous and up to 120 kA symmetrical interrupting, with sub-cycle operation. G&W positions it as a way to add sources without upgrading to higher-rated equipment. Power assisted fuses are another option for high fault duty. See current-limiting fuses and protectors.

Sensors and monitoring. Low power instrument transformers (LPITs) feed protection and metering in a smaller package than CTs and PTs. Lindsey LEA/LPIT sensors comply with IEEE C37.92 and IEC 61869-10, -11 and -13, and G&W Accusense voltage sensors cover models to 38 kV. See voltage and current sensors.

BESS at MV. Storage connected at MV supports the whole campus bus. The JST Grid-Scale BESS connects directly at up to 38 kV through an H-bridge cascade topology, scales from 1 MWh to over 1000 MWh and is IEEE 1547 compatible. See battery energy storage.

Planning and procurement

MV procurement starts at schematic design. Market lead times are long: Wood Mackenzie's Q2 2025 survey put average power transformer lead times at 128 weeks and switchgear at 44 weeks (reported by POWER, January 2026). Factory dates for specific ratings differ and change often. Our MV equipment lead times guide goes deeper.

A practical sequence:

Freeze the one-line and fault study early. Ratings for interrupting duty, BIL and continuous current set what can be ordered.
Standardize ratings across power blocks to simplify submittals, spares and future phases.
Decide arc resistance and SF6 policy up front. Both change the product family, so they belong in the basis of design.
Reserve production slots early for long-lead items such as substation transformers.
Schedule factory witness testing, delivery and energization support.

How Ryan Sales helps

Ryan Sales puts data center teams in direct contact with JST and G&W Electric application and production engineers, helps compare gas-insulated and metal-clad switchgear against the spec, and gets current factory lead times for substation transformers and dry type units. We serve Texas and Oklahoma and take data center projects nationwide.

FAQ

What medium voltage level do data centers use?

Most campuses distribute at a utility-standard MV level, commonly in the 13.8 kV to 34.5 kV range, after stepping down from transmission voltage in an on-site substation. Higher distribution voltages reduce current, cable size and losses. The right level depends on the utility service, campus size and the equipment ratings available for the switchgear and transformers you plan to use.

Is the JST J100CLAD arc resistant?

No. The J100CLAD is IEEE-rated metal-clad switchgear for 5 kV to 15 kV, up to 3000 A and 25 kA to 50 kA, but it is non-arc-resistant. If the owner's specification requires IEEE C37.20.7 arc-resistant construction, consider JST's J20X cubicle GIS, which is fully arc resistant, or the J10N and J20N dry air GIS lineups.

What does 2N mean at medium voltage?

2N means two fully independent power paths, each sized to carry the full critical load. At MV that usually means two utility sources or substation transformers, separate switchgear buses and separate feeders to A and B unit substations. N+1 adds one spare component instead of a full second path, which costs less but protects against fewer failure modes.

Can data centers avoid SF6 switchgear?

Yes. Dry air gas-insulated switchgear such as JST's J10N (5 kV) and J20N (38 kV) keeps the compact GIS footprint without SF6, and air-insulated metal-clad gear avoids insulating gas entirely. SF6-free equipment helps owners with emissions targets and reduces exposure to state rules such as California's GIE phaseout and New York's Part 495.

Talk to a data center applications rep

Send us your one-line or equipment list and we will come back with ratings, options and current factory lead times. Call (281) 363-1106 or request a quote.

Medium Voltage Equipment for Data Centers: Switchgear, Transformers and Substations