§715 — Extra-low-voltage lighting installations

The 714 outdoor lighting guide covers the general requirements for outdoor lighting at mains voltage. This article covers a separate chapter, §715, which applies specifically to lighting supplied at extra-low voltage: a maximum of 50 V AC or 120 V DC, such as LED strips, some halogen spotlights, and decorative shop-window lighting powered via a transformer or supply at low voltage.

Scope

§715 (IEC 60364-7-715) applies to fixed lighting installations supplied from a source with a rated voltage of at most 50 V AC or 120 V DC — so not battery-powered torches, but fixed installations such as LED strip systems in shops, halogen extra-low-voltage lighting in ceilings, and comparable applications where a transformer or switching power supply steps the voltage down from mains level.

Why low voltage does not automatically mean "safe enough"

A common misconception is that a lower voltage by definition means lower risk, and that the usual overcurrent and short-circuit protection requirements would therefore be less strict. §715 in fact highlights a different risk that becomes prominent with extra-low-voltage lighting: because the power stays the same while the voltage is low, the currents in the extra-low-voltage wiring and connectors rise proportionally higher. That raises the risk of overheating of cabling and connectors and of fire risk at the supply transformer itself, particularly with cheap or incorrectly sized transformers.

Overcurrent protection on the primary side

When selecting protection on the primary (mains-voltage) side of the supply transformer, the transformer's own inrush (magnetising) current must be taken into account: a transformer draws a significantly higher current than its rated current for a brief period at switch-on, which can cause an overly sensitive protective device to trip unnecessarily. For small transformers (up to 50 VA), a self-resetting overcurrent protective device (such as a PTC element) is permitted as an alternative to a conventional fuse or circuit breaker.

Suitable transformer types

As a source for an extra-low-voltage lighting installation, a safety isolating transformer to IEC 61558-2-6 is required — this transformer type provides the galvanic isolation and constructional safeguards needed for the secondary side to actually be regarded as extra-low voltage, unlike an ordinary, non-certified step-down transformer.

Practical relevance

When designing or assessing an LED-strip installation, halogen extra-low-voltage lighting, or comparable extra-low-voltage lighting, it is important to check that the source is a suitable safety isolating transformer (IEC 61558-2-6), that the primary protection accounts for that transformer's inrush current, and that the extra-low-voltage wiring itself has sufficient cross-section for the (relatively high) current at the power level involved — not only for the low voltage.

Common mistakes

Equating low voltage with "no fire risk" — the fire risk of the supply transformer itself and of undersized extra-low-voltage wiring remains an explicit concern under §715.
Using an ordinary, non-certified transformer instead of a safety isolating transformer to IEC 61558-2-6.
Not accounting for the transformer's inrush current when sizing the primary protection, resulting in unnecessary tripping.
Sizing the extra-low-voltage wiring based on the voltage rather than on the actual (higher) current that belongs to a given power at extra-low-voltage level.