{"id":"transformer-pad-mounted","version":"0.3.0","classification":{"uniformat":"D5010"},"names":["Transformer, pad-mounted liquid-filled"],"aliases":["pad mount transformer"],"service_life":{"median_years":33.5,"range_years":[25,45],"range_basis":"source_spread"},"pm_tasks":[{"task":"Inspect solid insulation for discoloration","frequency":"P1Y","reference":"TM 5-692-1 Maintenance of Mechanical and Electrical Equipment at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities: Recommended Maintenance Practices","url":"https://www.wbdg.org/FFC/ARMYCOE/COETM/tm_5_692_1.pdf","page":165,"checklist":"Table 20-5 Transformers (primary distribution)"},{"task":"Oil dielectric strength test","frequency":"P1Y","reference":"TM 5-692-1 Maintenance of Mechanical and Electrical Equipment at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities: Recommended Maintenance Practices","url":"https://www.wbdg.org/FFC/ARMYCOE/COETM/tm_5_692_1.pdf","page":165,"checklist":"Table 20-5 Transformers (primary distribution)"},{"task":"Oil acidity test","frequency":"P1Y","reference":"TM 5-692-1 Maintenance of Mechanical and Electrical Equipment at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities: Recommended Maintenance Practices","url":"https://www.wbdg.org/FFC/ARMYCOE/COETM/tm_5_692_1.pdf","page":165,"checklist":"Table 20-5 Transformers (primary distribution)"},{"task":"Oil color test","frequency":"P1Y","reference":"TM 5-692-1 Maintenance of Mechanical and Electrical Equipment at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities: Recommended Maintenance Practices","url":"https://www.wbdg.org/FFC/ARMYCOE/COETM/tm_5_692_1.pdf","page":165,"checklist":"Table 20-5 Transformers (primary distribution)"},{"task":"Verify transformer alarms","frequency":"P1Y","reference":"TM 5-692-1 Maintenance of Mechanical and Electrical Equipment at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities: Recommended Maintenance Practices","url":"https://www.wbdg.org/FFC/ARMYCOE/COETM/tm_5_692_1.pdf","page":165,"checklist":"Table 20-5 Transformers (primary distribution)"},{"task":"Inspect transformer enclosure for rust and oil leaks","frequency":"P2Y","reference":"UFM 3-550-07 Operation and Maintenance (O&M): Exterior Power Distribution Systems","url":"https://www.wbdg.org/FFC/DOD/UFC/ufm_3_550_07_2026.pdf","page":89,"checklist":"5-2.2.4.1 Time-Base Preventative Maintenance (transformers)"},{"task":"Check and record transformer gauges","frequency":"P2Y","reference":"UFM 3-550-07 Operation and Maintenance (O&M): Exterior Power Distribution Systems","url":"https://www.wbdg.org/FFC/DOD/UFC/ufm_3_550_07_2026.pdf","page":89,"checklist":"5-2.2.4.1 Time-Base Preventative Maintenance (transformers)"},{"task":"Take oil sample for dissolved gas analysis (DGA)","frequency":"P2Y","reference":"UFM 3-550-07 Operation and Maintenance (O&M): Exterior Power Distribution Systems","url":"https://www.wbdg.org/FFC/DOD/UFC/ufm_3_550_07_2026.pdf","page":90,"checklist":"5-2.2.4.2 Time-Based Predictive Maintenance (transformers)"},{"task":"Infrared scan for hot spots under load","frequency":"P2Y","reference":"UFM 3-550-07 Operation and Maintenance (O&M): Exterior Power Distribution Systems","url":"https://www.wbdg.org/FFC/DOD/UFC/ufm_3_550_07_2026.pdf","page":90,"checklist":"5-2.2.4.2 Time-Based Predictive Maintenance (transformers)"}],"basis":[{"type":"public_document","life_type":"planning","title":"CNA e-Tool Estimated Useful Life Table","by":"U.S. Department of Housing and Urban Development","url":"https://www.hud.gov/sites/documents/eul_for_cna_e_tool.pdf","page":3,"code":"HUD CNA 3.2.8.2.3","label":"Transformer","years":30,"note":"Same life for family and elderly properties. US multifamily housing. HUD's row is a site electric utility transformer."},{"type":"public_document","life_type":"accounting","title":"Handbook for Optimised Deprival Valuation of System Fixed Assets of Electricity Lines Businesses, 30 August 2004","by":"Commerce Commission (New Zealand)","url":"https://comcom.govt.nz/assets/pdf_file/0023/61484/comcom-elbodvhandbookforsystemfixedassets-aug2004-2.pdf","page":37,"code":"Table A.1","label":"DISTRIBUTION TRANSFORMERS – Ground Mounted, Single/Two Phase, 22/0.4 and 11/0.4 kV, Cable Entry – 22/0.4 kV, 100 kVA to 1,500 kVA","years":45,"note":"Printed page 35. Ground-mounted (pad-type) distribution transformers of an electricity network, oil-filled in NZ practice; all eight sizes 100-1,500 kVA have Standard Life 45 years. Heading printed as 'Single/Two Phase'. Utility network assets (2004). Regulatory valuation for electricity lines businesses, superseded as a valuation method by the Commerce Commission's Input Methodologies (from 2010). Only the ground-mounted distribution transformer rows map to a library component."},{"type":"public_document","life_type":"accounting","title":"Handbook for Optimised Deprival Valuation of System Fixed Assets of Electricity Lines Businesses, 30 August 2004","by":"Commerce Commission (New Zealand)","url":"https://comcom.govt.nz/assets/pdf_file/0023/61484/comcom-elbodvhandbookforsystemfixedassets-aug2004-2.pdf","page":37,"code":"Table A.1","label":"DISTRIBUTION TRANSFORMERS – Ground Mounted, Single/Two Phase, 22/0.4 and 11/0.4 kV, Cable Entry – 11/0.4 kV, 100 kVA to 1,500 kVA","years":45,"note":"Printed page 35. As the 22/0.4 kV row; all eight sizes 100-1,500 kVA have Standard Life 45 years. Utility network assets (2004). Regulatory valuation for electricity lines businesses, superseded as a valuation method by the Commerce Commission's Input Methodologies (from 2010). Only the ground-mounted distribution transformer rows map to a library component."},{"type":"public_document","life_type":"design","title":"Design standards: employer's requirements – Technical Manual (ER-DFE-XX-XX-T-X-0201, revision A-C01)","by":"Department for Education (England)","url":"https://assets.publishing.service.gov.uk/media/6971f649d8adeaf266040501/ER-DFE-XX-XX-T-X-0201-Technical_Manual-A-C01.pdf","page":275,"code":"5.7.4","label":"High voltage (HV) switchgear, transformers and packaged substations: 35 years","years":35,"note":"Printed page 275. HV transformers on a school site (packaged substations); type not stated. Minimum life expectancy (design requirement) for DfE-funded school buildings. Minimum design requirements placed on contractors for school buildings, not observed replacement ages. Section 5.1.4 (sanitaryware) refers to CIBSE Guide M Appendix 12.A1 'in general'."},{"type":"public_document","life_type":"planning","title":"Energy Conservation Program: Energy Conservation Standards for Distribution Transformers (final rule), 89 FR 29834, April 22, 2024","by":"U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy","url":"https://www.govinfo.gov/content/pkg/FR-2024-04-22/pdf/2024-07480.pdf","page":113,"code":"IV.F.8","label":"Transformer Service Lifetime: \"a distribution of lifetimes, with an estimated average of 32 years and a maximum of 60 years\"","years":32,"note":"Printed page 29946. Covers all distribution transformers, including low-voltage dry-type (building dry-type) and medium-voltage liquid-immersed (pad-mounted). Mean of a distribution; the maximum is 60 years. Same value also stated on p.5 (printed 29838) and in Table IV summary on p.101 (printed 29934)."},{"type":"public_document","life_type":"accounting","title":"General depreciation rates (IR265), July 2021","by":"Inland Revenue (Te Tari Taake), New Zealand","url":"https://www.ird.govt.nz/-/media/project/ir/home/documents/forms-and-guides/ir200---ir299/ir265/ir265-2021.pdf","page":34,"code":"POWR","label":"Transformers","years":25,"note":"Printed page 34. Power generation and electrical reticulation category; type not stated. Also 'Transformers 25' under ELEC p.15. Printed DV 8%, SL 6%. Tax depreciation lives set by the Commissioner of Inland Revenue for New Zealand income tax, not engineering or asset-management lives; they are banded and often short (e.g. reticulation piping 25 years). The July 2021 edition was the newest PDF reachable; the online Depreciation Rate Finder may hold later determinations."}],"confidence":{"grade":"C","sample_size":null},"open_questions":["Every source here is a published planning, design or accounting life. None is observed replacement data.","Some maintenance intervals come from TM 5-692-1, an Army manual for mission-critical (C4ISR) facilities; they may be tighter than typical commercial practice."],"contributors":["unfinished.one editors"],"last_reviewed":"2026-10-22","canonical_url":"https://unfinished.one/c/transformer-pad-mounted","versioned_url":"https://unfinished.one/c/transformer-pad-mounted/v/0.3.0","licence":"CC-BY-4.0","citation":"unfinished.one (2026). Transformer, pad-mounted liquid-filled, v0.3.0. https://unfinished.one/c/transformer-pad-mounted/v/0.3.0"}