MGM Transformer K-Factor rated dry-type transformers (K-4 / K-9 / K-13)
MGM K-Factor dry-type transformers, 15 to 1,000 kVA harmonic-rated units from a stocked California line
This model is part of SecondWatt’s transformer research catalogue. Specifications and price observations are included where supported by sources. Equipment availability and commercial terms require confirmation.
MGM Transformer K-Factor dossier: K-4 to K-13 dry-types, 15-1,000 kVA, DOE 2016 compliance, harmonic-load guidance, inspection checklist, failures.
MGM Transformer Company of Commerce, California builds low- and medium-voltage dry-type (VPI and cast coil) and liquid-filled lines, and its K-Factor series addresses non-linear loads. Catalog coverage confirms K-4, K-9, and K-13 ratings at 15-1,000 kVA with 480 and 600 V delta primaries into 208Y/120 and 480Y/277 secondaries at 150 C rise, DOE 2016 compliant under 10 CFR 431, UL and CSA listed, designed and tested to NEMA, ANSI, and IEEE practice. A K-20 tier does not appear in the catalog.
K-factor matters because harmonic-rich loads (UPS front ends, VFDs, LED and server power supplies) drive eddy losses that overheat standard transformers; a K-13 unit carries the same nameplate kVA at full non-linear duty. MGM backs the line with a stocked general-purpose program that ships fast from California inventory, a 2025 Inc. 5000 listing signaling growth.
Secondary supply is thin and mostly unpriced: a used 75 kVA MGM dry-type sat live at a dealer without a published price, and the LV dry class generally trades price-on-request outside commodity general-purpose sizes.
Why it matters
Every modern data hall load is non-linear, and under-K-rated transformers fail early from harmonic heating, a failure mode invisible until thermal scans catch it. K-rated supply protects nameplate capacity at real duty. MGM is one of the few independents publishing a full K-Factor catalog with DOE 2016 compliance, making it the reference spec for the class.
Who buys it
Electrical contractors and engineers serving data centers, broadcast, medical imaging, and industrial automation specify K-rated units wherever measured load profiles show harmonic content. West Coast buyers value MGM's stocked program against 20-32 week class leads; used buyers accept unpriced dealer stock because testing costs stay small at this scale.
Role in the data center
K-13 step-down units feeding PDU and mechanical loads with harmonic-rich current profiles, sitting in the electrical room between the 480 V switchboard and the 208Y/120 panels. The K-rating is what keeps the unit at nameplate capacity where a standard dry-type would have to be derated for eddy-current heating.
Key specifications
| K-factor tiers | K-4 / K-9 / K-13 |
|---|---|
| kVA range | 15-1,000 kVA |
| Primary voltages | 480 / 600 V delta |
| Secondary voltages | 208Y/120, 480Y/277 |
| Temperature rise | 150 C |
| Efficiency | DOE 2016 (10 CFR 431) |
| Listings | UL, CSA |
| Stocked program | general purpose LV dry, fast ship |
| Growth signal | 2025 Inc. 5000 honoree |
| Companion MV lines | VPI and cast-coil dry-type; liquid-filled pad-mount and substation |
| Design and test practice | NEMA, ANSI, IEEE |
| Location | Commerce, California |
| Class comp, GE 10 kVA mini unit substation, new | 1,598 USD |
| Class comp, Hammond 45-225 kVA step-up dry-type, new | 2,595-9,495 USD |
Technical summary
K-factor tiers: K-4, K-9, K-13 (no K-20 in catalog). Range: 15-1,000 kVA. Primaries: 480 delta, 600 delta. Secondaries: 208Y/120, 480Y/277. Temperature rise: 150 C standard. Efficiency: DOE 2016 per 10 CFR 431. Listings: UL, CSA. Design/test: NEMA, ANSI, IEEE practice. Stocked program: general-purpose LV dry, fast ship from California. Company: Commerce CA; 2025 Inc. 5000 honoree. Companion lines: VPI and cast coil MV dry-type, liquid pad-mount.
Major variations
Three K-factor tiers are published in the catalog, K-4, K-9 and K-13, and the choice follows harmonic severity at the load rather than the kVA. K-20 is not in MGM's catalog; competing lines offer it for the most severe single-phase non-linear environments. Winding material and rise class set thermal margin. Around the K-factor line MGM builds a wider range: vacuum-pressure-impregnated and cast-coil medium-voltage dry-types, and liquid-filled pad-mount and substation units, so a single supplier can cover both sides of an electrical room.
Configurations and options
The catalog offers K-4, K-9 and K-13; K-20 does not appear. Ratings run 15-1,000 kVA with 480 V and 600 V delta primaries into 208Y/120 and 480Y/277 secondaries, at 150 deg C rise on a 220 deg C insulation system, in aluminum or copper windings. Primary taps are six on units of 15-500 kVA and four on 750-1,000 kVA. Every catalogued K-factor model carries the shielded designation in its model number, so an electrostatic shield is part of the K-factor build rather than an extra. Units are DOE 2016 compliant under 10 CFR 431 and UL and CSA listed, designed and tested to NEMA, ANSI and IEEE practice. Enclosure type, impedance and sound level are not stated for the K-factor models in the catalog as of September 2026, so those come off the unit data sheet.
Compatibility and dependencies
The unit sits between a 480 V or 600 V delta switchboard and 208Y/120 or 480Y/277 panels feeding non-linear load, and the specification that has to match is the load's harmonic profile rather than its kVA. A K-13 unit carries nameplate kVA at full non-linear duty where an unrated dry-type would have to be derated for eddy-current heating. The delta primary to wye secondary arrangement makes the secondary a separately derived system with a bonded neutral. The electrostatic shield built into these models is what a specifier calls for where high-frequency transfer to the derived system is a concern. Primary taps, six below 500 kVA and four above, are changed with the unit de-energized, so the tap position has to suit the delivered voltage before energization. Ventilated dry construction needs airflow clearance and a room that can remove the losses.
Pricing and availability
Comparable secondary-market band: 2595–9495 $ per unit. Trend: rising Electrical Trader's price history, published 2026-04-01, puts power transformer prices up 77% between 2019 and 2026 with a 45-95% spread by model, and attributes about half the move to materials: copper up roughly 70% and grain-oriented electrical steel up 80-100% between 2020 and 2025, together 50-55% of production cost. The same series shows the annual rate easing, from 34.58% in 2022 to 8-10% in 2025 with 3-5% forecast for 2026. Terrapin Construction Group put dry-type lead times at 0-2 MVA at 20-32 weeks on 2026-06-10. Lead time, new: Stocked sizes fast-ship; 20-32 weeks class otherwise. Lead time, used or refurbished: 1-4 weeks (dealer stock). Warranty, used: 3-year typical from major US rebuilders.
Lifecycle and maintenance
Cast-resin and VPI dry-type transformers typically serve 25-30+ years with minimal maintenance: periodic cleaning, PD testing on critical units, fan service on AF designs, and torque checks. There is no oil system to sample, so temperature and PD are the condition indicators. Rebuild options are limited compared with liquid units; failed coils are usually replaced rather than repaired, which makes pre-purchase PD and visual inspection decisive for used units.
Thermal and emissions profile
Transformers produce no combustion emissions; the regulatory profile is efficiency and fire class. US low-voltage dry-type units fall under DOE 10 CFR 431 efficiency rules (DOE 2016 levels, amended 2024 with 2029 compliance), and EU-market cast-resin units fall under Ecodesign Regulation 548/2014 Tier 2. Dry-type construction removes oil fire and spill risk entirely, which is why cast-resin units carry IEC 60076-11 fire class F1 and serve indoor and environmentally sensitive sites.
Common failure points
- Partial discharge — PD in resin voids degrading insulation toward failure
- Resin cracking — Cracks from thermal cycling or mechanical shock
- Contamination — Dust and conductive debris enabling surface tracking
- Cooling fans — Failed AF fans derating capacity
- Connections — Loose terminations overheating under load
- Overheating under harmonics — Excess temperature on non-linear loads beyond K-rating
Inspection checklist
Partial discharge: PD test per IEC 60270 practice; readings above 10 pC warrant investigation on cast-resin coils. Resin condition: inspect all coils per IEC 60076-11 practice for cracks and crazing from thermal cycling; any through-crack fails. Insulation resistance: megger HV/LV/ground; polarization index of 2.0 or higher passes. Turns ratio: TTR on all tap positions; deviation beyond 0.5% from nameplate fails. Winding resistance: three-phase balance within 2% between phases. Contamination: inspect for dust and conductive debris between coils; contamination is a leading dry-type failure driver. Cooling fans (AF units): run-test all fans and verify temperature controller setpoints. Temperature sensors: verify RTD or thermocouple channels read within 5 C of a reference at ambient.
Procurement channels
MGM distribution for engineered units and the stocked general-purpose program for fast-ship low-voltage dry types. Used supply is thin: an MGM 75 kVA three-phase dry-type at Genemco carried no published price in August 2026, and the wider low-voltage dry class trades on eBay and Electrical Trader with a site price ceiling of 11,499 USD. New stock comps are the practical benchmark, with Hammond step-up dry-types at 2,595-9,495 USD across 45-225 kVA.
Regional notes
This is a North American product built at Commerce, California, UL and CSA listed with DOE 2016 compliance under 10 CFR 431 and designed and tested to NEMA, ANSI and IEEE practice. The 480 V and 600 V delta primaries are North American and Canadian service voltages, and the K-factor rating scheme itself is the North American convention rather than an IEC one, so an IEC-market unit will not carry a comparable K number. The DOE amended the distribution transformer standards in a final rule published 2024-04-22 with a 2029 compliance date. Dry-type transformers fall inside the Section 232 50% tariff on non-US steel and aluminum content from 2025-08-18.