IEC 61558-2-8:2024

Overview

IEC 61558-2-8:2024 is the IEC safety standard for bell and chime transformers and power supply units (including transformers with electronic circuits). This third edition updates the previous 2010 edition, aligning structure and references with IEC 61558-1:2017 and introducing a new symbol for power supply units with a linearly regulated output voltage. It is a group safety publication (IEC Guide 104) and specifies particular requirements and tests to ensure electrical, thermal and mechanical safety for these devices.

Key topics and technical requirements

The standard supplements IEC 61558-1:2017 and covers essential safety and test topics, including:

• Scope & ratings: stationary, single-phase, dry-type, air‑cooled transformers; rated supply voltage ≤ 250 V AC; rated output ≤ 100 VA; no‑load output ≤ 33 V AC or 46 V ripple‑free DC; rated output ≤ 24 V AC or 33 V ripple‑free DC; internal operating frequency ≤ 500 Hz for linear units.
• Classification & marking: mandatory symbols and marking (new symbol for linear regulated outputs), rating plates and user information.
• Protection against electric shock: requirements for SELV/insulation, separation and earthing provisions where applicable.
• Electrical tests: insulation resistance, dielectric strength, leakage current, no‑load and loaded output behavior, short‑circuit voltage tests.
• Thermal & overload: heating tests, short‑circuit and overload protection, and rated load considerations given bell/chime duty cycles (short intermittent loads).
• Mechanical & environmental: mechanical strength, ingress protection, resistance to rusting, component and wiring requirements, creepage/clearance distances.
• Construction & components: rules for encapsulation, internal wiring, terminals, screws, and protective devices.
• Special cases: transformers incorporating electronics and linear vs switch‑mode power supply (SMPS) considerations - SMPS are covered by IEC 61558-2-16 in combination with this part; if conflicts arise, the more stringent requirement applies.

Applications and users

Practical applications include:

• Doorbells, chimes, intercom sound signalling and similar domestic/lighting partial‑load devices.
• Power supplies used where double or reinforced insulation and SELV are required by installation or end‑product standards.

Who uses this standard:

• Transformer and PSU manufacturers, product designers and R&D teams
• Test laboratories and conformity assessment bodies
• Compliance engineers, specifiers and installers in building services and residential equipment
• Certification bodies issuing safety marks

Related standards

• IEC 61558-1:2017 (general requirements)
• IEC 61558-2-16 (switch‑mode power supplies for similar applications)
• IEC 60364‑4‑41, IEC 61140 (electrical installation and protection principles)

Keywords: IEC 61558-2-8:2024, bell transformers, chime transformers, power supply units, safety standard, SELV, transformer testing, linear power supply, IEC 61558.