UL 1561 2019-05 PDF

Full title and description

St UL 1561 2019-05 — Standard for Dry‑Type General Purpose and Power Transformers (UL 1561). This entry refers to the UL Standard 1561 with the May 2019 revision/change (often referenced as the 2019-05 change to the existing edition) covering construction, performance and safety requirements for air‑cooled, dry‑type general purpose and power transformers intended for use in accordance with the National Electrical Code (ANSI/NFPA 70).

Abstract

UL 1561 establishes safety, construction and performance requirements and test procedures for dry‑type general purpose and power transformers (air‑cooled, ventilated and non‑ventilated types) and certain exposed‑core and compound‑filled dry‑type transformers above specified ratings. The 2019-05 entry denotes a revision/change issued in May 2019 to the published UL 1561 requirements; it clarifies or amends selected clauses without changing the overall scope for the safe manufacture, testing and marking of covered transformers.

General information

• Status: Active (standard maintained and periodically revised by Underwriters Laboratories).
• Publication date: Change issued May 13, 2019 (the current 4th edition was originally published March 2, 2011; subsequent revision notices include the May 2019 change and later administrative revisions).
• Publisher: Underwriters Laboratories (UL).
• ICS / categories: International Classification for Standards (ICS) — Electrical engineering; Transformers and Reactors (ICS 29.180 / general ICS 29 series).
• Edition / version: 4th Edition (published March 2, 2011) with revision/change issued May 2019 (2019‑05). Later administrative/redline activity occurred in 2023.
• Number of pages: Varies by distributor/format and revision — common published file lengths for the 2011/2019 materials are in the ~50–80 page range depending on packaging and included annexes (typical vendor listings show values such as 54–78 pages).

Scope

Requirements cover general purpose and power dry‑type transformers (air‑cooled, dry, ventilated and non‑ventilated constructions), including step‑up, step‑down, insulating and autotransformer types, and dry‑type reactors where applicable. The standard excludes ballasts for HID/fluorescent lamps, liquid‑filled transformers, many specialty transformers covered by other UL standards, transformers with waveshaping/rectifying circuitry, and transformers with nominal primary or secondary ratings above specified voltages (see clauses for exact exclusions and rating limits).

Key topics and requirements

• Construction and materials: winding and core construction, insulation systems and acceptable materials for dry‑type use.
• Temperature‑rise and thermal classification: defined test procedures and limits for winding and insulation temperature rise and overall temperature class.
• Dielectric and insulation testing: tests for insulation resistance, dielectric withstand (hipot) and related acceptance criteria.
• Short‑circuit and mechanical strength: tests to verify short‑circuit withstand capability and secure mechanical construction.
• Impedance, K‑factor and harmonic considerations: ratings/requirements for transformers intended for nonlinear / harmonic‑producing loads (K‑rated where applicable) and impedance tolerances for listed units.
• Sound, vibration and environmental requirements: acoustic/noise limits and provisions for normal installation environments.
• Marking, documentation and instructions: required nameplate data, ratings, installation instructions and warnings for safe use and listing/labeling.
• Testing and sample selection: acceptance and production test regimes, sample sizes and test methods to demonstrate conformance.

Typical use and users

Manufacturers and designers of dry‑type power and general purpose transformers, electrical equipment test laboratories, product safety and compliance engineers, electrical consulting engineers, specifying engineers, procurement teams and authorities having jurisdiction use UL 1561 to design, test, certify and specify transformers for commercial, industrial and institutional applications where dry‑type transformers are required or preferred. The standard is also referenced by manufacturers seeking UL listing and by buyers requiring UL‑listed transformers.

Related standards

Standards commonly referenced alongside UL 1561 include other UL transformer standards (for example UL 1562 for dry‑type transformers over 600 V, UL 5085 series for low‑voltage transformers, and UL 506 for specialty transformers), relevant IEEE/ANSI/NEMA transformer guidance and the National Electrical Code (ANSI/NFPA 70) for installation. Harmonization efforts with CSA and other regional standards are periodically noted in revision activity.

Keywords

UL 1561, dry‑type transformer, general purpose transformer, power transformer, air‑cooled transformer, ventilation, temperature rise, insulation system, dielectric test, short‑circuit test, K‑rated, UL listing, NEC, ANSI, NEMA.

FAQ

Q: What is this standard?

A: UL 1561 is Underwriters Laboratories’ Standard for Dry‑Type General Purpose and Power Transformers. The entry referenced as "2019‑05" indicates a May 2019 revision/change applied to the existing edition.

Q: What does it cover?

A: It covers safety, construction, performance and required tests for air‑cooled dry‑type general purpose and power transformers (various constructions and ratings within the scope) and specifies exclusions for other transformer types and for units incorporating waveshaping/rectifying circuitry — see the standard’s scope clauses for detailed limits.

Q: Who typically uses it?

A: Transformer manufacturers, test labs, safety/compliance engineers, specifying and consulting electrical engineers, procurement specifiers and authorities having jurisdiction use UL 1561 to design, test, certify and specify UL‑listed dry‑type transformers.

Q: Is it current or superseded?

A: The 4th edition (published March 2, 2011) has subsequent revision changes including the May 13, 2019 change and later administrative/redline updates (e.g., 2023 administrative activity). Users should check the UL catalog or the official UL product/standards store for the most current edition and any redline or amendment documents before relying on a specific clause.

Q: Is it part of a series?

A: Yes — UL 1561 sits within UL’s family of transformer and power equipment standards. Related UL standards (UL 1562, UL 5085 series, UL 506, etc.) cover other transformer types, higher voltage classes or specialty transformer constructions; industry standards and guidance from IEEE, ANSI and NEMA are also frequently referenced.

Q: What are the key keywords?

A: Dry‑type transformer, general purpose transformer, power transformer, air‑cooled, ventilation, insulation system, temperature rise, dielectric test, short‑circuit withstand, UL listing, NEC.