Eaton DS-3 / DT-3 ventilated dry-type
Eaton DS-3 and DT-3 ventilated dry-type transformers, the 600 V class workhorses of low-voltage distribution.
Eaton DS-3 / DT-3 ventilated dry-type is one of 32 data center transformers tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.
Eaton DS-3/DT-3 dry-type dossier: 7.5-1,500 kVA at 600 V class, DOE 2016 efficiency, used units from 1,500 USD, inspection checklist, failure points.
Why it matters
Every data hall runs on this class: the last transformation before the panelboard. DOE 2016 efficiency rules, amended in 2024 with 2029 compliance, split the fleet into compliant and legacy stock, and Section 232 tariffs of 50% on imported dry-type content from 2025-08-18 push buyers toward domestic and used supply. Correcting the Power Xpert mislabel keeps SecondWatt's catalog credible with electrical engineers.
Who buys it
Electrical contractors, plant engineers, and data center fit-out teams buy DT-3 class units for 480-to-208Y/120 step-down in electrical rooms, alongside commercial building retrofits. Buyers pick used units for same-day availability at a fraction of distributor price, accepting shorter warranties; the class is a commodity where testing costs can exceed the hardware discount.
Role in the data center
480 V to 208Y/120 step-down for mechanical loads, offices, and low-density IT space; the commodity transformer of every electrical room build-out.
Key specifications
| Single-phase range | 7.5-333 kVA |
|---|---|
| Three-phase range | 7.5-1500 kVA |
| Voltage class | 600 V |
| Temperature rise | 150 std; 115 / 80 optional C |
| Enclosure | NEMA 2; 3R with weathershields |
| Efficiency standard | DOE 2016 (10 CFR 431) |
| Sound option | 3-5 dB below NEMA ST-20 |
| Example distributor SKU | V48M28B7516CU (75 kVA, 480D-208Y/120) |
| Observed refurb price | 1,500 (75 kVA, 1-yr warranty) USD |
Technical summary
Single-phase (DS-3): 7.5-333 kVA Three-phase (DT-3): 7.5-1,500 kVA Voltage class: 600 V Temperature rise: 150 C standard; 115 C / 80 C options Enclosures: NEMA 2 (3R with weathershields) Windings: aluminum or copper Efficiency: DOE 2016 per 10 CFR 431 Sound: low-sound options 3-5 dB below NEMA ST-20 Grounding: NEC 450.10(A) ground bar Legacy catalog lineage: Cutler-Hammer V-prefix numbers MV extension: ventilated MV dry-type line above 600 V
Pricing and availability
Comparable secondary-market band: 2295–24995 $ per unit. Trend: up Lead time, new: Distributor stock to 20-32 weeks by size. Lead time, used or refurbished: 1-2 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.
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 Connections — torque-check HV and LV terminations; thermal-scan at first energization and re-check within 12 months Clearances — verify electrical clearances and enclosure IP rating match the installation environment Class verification — confirm fire/environmental/climatic classes (F1, E2/E3, C2/C3) against nameplate Harmonic suitability — verify K-factor rating (K-4/K-13) against the intended non-linear load profile Core and frame — inspect for shipping damage and loose core bolts; verify single core ground Energization test — verify secondary voltage within 5% on all phases and no abnormal sound level Records — factory test certificate, PD test data, and service history; missing PD data reprices the unit
Procurement channels
Distributor stock (State Electric and peers) for new; EMSCO, Electrical Trader, Maddox webstore, and eBay for used and refurbished. The class trades openly with published prices, unusual in the transformer market.