Medium Voltage vs Low Voltage Switchgear: Scope and Pricing Differences for Estimators

Voltage Class Definitions: Where LV Ends and MV Begins

The boundary between low voltage and medium voltage is not universally defined, but in North American practice, the conventional boundary is at 1000V AC:

• Low voltage (LV): Up to 600V AC in the US NEC context; up to 1000V AC in IEC terminology
• Medium voltage (MV): 1kV to 36kV (US practice); IEC defines medium voltage as 1kV to 52kV
• High voltage (HV): Above 36kV or 52kV depending on the classification system used

Common MV distribution voltages in North American commercial and industrial applications are 4.16kV, 12.47kV, 13.8kV, and 15kV. Large industrial installations may use 25kV or 34.5kV. The specific voltage class affects the choice of switchgear, the insulation design, and the arc flash energy levels — all of which affect scope and pricing.

Where MV Switchgear Appears on Projects

Medium voltage switchgear is used on projects where power is distributed at voltages above 600V before being stepped down via transformers to LV for end-use equipment. Typical applications:

• Large commercial buildings: High-rise office towers and large retail centres often receive utility service at 13.8kV or 15kV, with MV switchgear at the building's main substation feeding transformers to 480V LV distribution
• Industrial plants: Large motor loads (above ~200kW) are often fed directly at 4.16kV or 13.8kV, avoiding the large cable sizes that would be required at 480V
• Data centres: Large data centres increasingly receive utility service at 13.8kV and use MV switchgear and unit substations (transformer + LV switchgear in a single enclosure) for distribution
• Hospitals and campuses: Campus distribution systems often use 15kV underground distribution between buildings, with each building having its own MV/LV substation
• Renewable energy projects: Solar and wind generation is typically collected at MV before connection to the grid via a step-up transformer

MV Equipment Types: What You Are Pricing

The main MV switchgear types differ in construction, cost, and application:

Metal-Clad Switchgear (ANSI C37.20.2)

The standard specification for commercial and industrial MV switchgear in North America. Key features: draw-out vacuum circuit breakers, individual compartmentalisation of bus, circuit breakers, and cable connections, automatic safety shutters on the bus stabs when the breaker is withdrawn, and multiple mechanical interlocks. Per-section pricing for 15kV metal-clad with a 1200A VCB and microprocessor protection relay typically ranges from $35,000 to $75,000 depending on options, metering, and communications.

Metal-Enclosed Interrupter Switchgear (ANSI C37.20.3)

Less expensive than metal-clad — uses load interrupter switches (not full circuit breakers) for switching, combined with current-limiting fuses for overcurrent protection. Used on distribution feeders and transformer primary protection where full circuit breaker interrupting capacity is not required. Per-section pricing for 15kV interrupter switchgear typically ranges from $8,000 to $20,000 per section — significantly less than metal-clad, but limited to switching and fuse protection, not adjustable overcurrent tripping.

Pad-Mount Switchgear

Outdoor, tamper-resistant metal-enclosed switching equipment for underground distribution systems. Used for loop feeds in underground distribution — the utility feeds into one side of the pad-mount, the load is taken from the same section, and the loop continues to the next pad-mount. Priced per unit rather than per section, typically $15,000–$40,000 depending on ratings and switching configuration.

Ring Main Units (RMU)

Compact, gas-insulated (SF6 or vacuum) MV switching units commonly used on IEC-standard projects and increasingly available on ANSI projects. Used for loop switching and transformer protection in compact switchrooms. Per-unit pricing typically $5,000–$18,000 depending on configuration (number of switching points, type of protection).

Protection Relays: The Scope Item That Changes Everything

Low voltage panelboard protection is essentially handled by the circuit breaker itself — a thermal-magnetic or electronic trip unit that trips on overcurrent. Medium voltage protection is a separate engineering discipline. MV circuit breakers are dumb switching devices without built-in protection logic — protection is provided by separate microprocessor-based protection relays that monitor current, voltage, and power factor, calculate the protective function, and issue a trip signal to the circuit breaker when required.

For estimators, MV protection relay scope includes:

• The relay hardware (microprocessor relay, current transformers, voltage transformers) — typically $3,000–$10,000 per relay position depending on the relay type and functions required
• Relay setting and coordination study: a protection engineer must calculate and set the overcurrent, time-overcurrent, instantaneous, and ground fault elements of each relay to achieve selectivity (the right relay trips for the right fault). This is a professional engineering service that should be priced as a separate line item or confirmed as the client's responsibility.
• Factory acceptance testing of the relay settings: the protection relay settings are typically verified at the factory before shipment, either by the manufacturer or by the client's protection engineer.
• Site commissioning of the relay settings: primary injection or secondary injection testing at site to verify relay calibration and correct tripping of the associated circuit breaker.

Switchroom Requirements: More Space, More Civil Scope

Medium voltage switchgear requires a dedicated switchroom with specific civil and services requirements that significantly exceed LV requirements:

• Arc flash venting: ANSI C37.20.2 metal-clad switchgear must have adequate arc flash pressure relief. Switchrooms must have arc flash venting panels or duct arrangements to direct arc flash pressure away from personnel and equipment. This is a civil scope item often overlooked when estimating the complete MV installation.
• Access and maintenance clearances: IEEE C37.23 specifies minimum working clearances around MV switchgear — typically 36 inches (915mm) at the front for breaker withdrawal, and adequate overhead clearance for breaker removal using an overhead beam and hoist.
• Overhead beam and hoist: Draw-out MV breakers are heavy — a 15kV vacuum circuit breaker weighs 150–250kg. The switchroom must have an overhead beam or monorail and chain hoist for breaker handling. This is a separate scope item that is frequently omitted from MV switchgear estimates.
• HVAC: MV switchgear generates significant heat from copper losses in busbars and transformers. Switchroom HVAC sizing must account for the total heat rejection from the switchgear, which is higher per unit floor area than LV switchgear.
• Access doors: Switchrooms housing MV equipment must have outward-opening doors in the direction away from the switchgear, to allow emergency egress when the switchgear is at the front.

Lead Times: The MV Premium

Medium voltage switchgear has significantly longer lead times than LV panelboards. Standard lead time expectations in 2026:

• LV distribution panelboards (standard configurations): 4–12 weeks
• Custom LV switchboards: 10–20 weeks
• MV metal-enclosed interrupter switchgear: 16–28 weeks
• MV metal-clad switchgear with microprocessor protection relays: 24–40 weeks
• MV switchgear with SCADA integration or special bus configurations: 30–52 weeks

On projects where MV switchgear is on the critical path to energisation, the lead time must be confirmed with the manufacturer at bid stage — and the project program should be assessed against the realistic delivery schedule. Discovering a 40-week lead time after contract award on a 12-month project is a significant program risk.

Commissioning: The Extra Discipline

MV switchgear commissioning is a specialist activity. It requires high-voltage testing equipment (typically a HV test set rated for the switchgear voltage class), qualified high-voltage personnel (typically requiring specific training and certification per NFPA 70E and IEEE 1584 for arc flash assessment), and the protection relay commissioning expertise described above.

Standard commissioning tests for MV switchgear:

• Insulation resistance (megger) testing of buses, cable terminations, and transformer windings
• High potential (hi-pot) testing at 2.5 × rated voltage to verify cable and equipment insulation integrity
• Contact resistance testing on circuit breaker main contacts
• Circuit breaker operating mechanism tests (trip time, close time, spring charging)
• Protection relay secondary injection testing (verifying relay calibration and trip outputs)
• Primary injection testing (optional, but recommended) — injecting actual primary current to verify current transformer ratios and relay operation
• Interlocking function tests — verifying all mechanical and electrical interlocks operate correctly
• Utility witness inspection — for utility-connected switchgear, the utility authority typically requires a witnessed commissioning test before energisation approval

Conclusion

Medium voltage switchgear estimation requires a fundamentally different scope framework than LV panelboard work. The equipment itself is 5–15x more expensive per circuit, the protection relay coordination is a professional engineering service in its own right, the switchroom civil requirements add significant associated scope, and the commissioning regime is substantially more intensive. Estimators moving into MV work for the first time should build up their MV scope template carefully — and review it with an experienced MV commissioning engineer before releasing it on a live bid.