Underwriters Laboratories standard UL 1449 has become the primary safety standard for surge protective devices (SPDs). It describes the materials and installation requirements for SPDs used for the protection of AC electrical circuits. The standard has been revised twice in the past few years. A major safety testing initiative (UL 1449 2nd edition) became effective February 2007, and additional administrative and methodology changes (UL 1449 3rd edition) became effective in September 2009. The 3rd edition also includes new independent performance testing requirements.
UL 1449 3rd edition completely supersedes preceding editions. From September 2009 on, all equipment brought onto the market must satisfy these new requirements in order to qualify for the UL label. Practically all North American surge standards now revolve around 3rd edition, and are now purposely aligned with other standards, including UL 1283, 2008 National Electrical Code™ Article 285, NEMA LS-1, ANSI/IEEE C62 documents and others.
The Littelfuse Industrial High Energy Thermally Protected Varistors
Series TMOV34S represent a new development in circuit protection. It
consists of a 33mm square MOV which offers high surge capability (40kA)
together with an integrated thermally activated element designed to open
in the event of overheating. The Varistor has a third indicator lead
which may be used to indicate that the MOV has been disconnected from
the circuit. This third lead facilitates connection to monitoring
circuitry. The Littelfuse Thermally Protected Varistors Series TMOV34S
provide quick thermal response due to the proximity of the thermal
element to the MOV body. The integrated configuration also offers lower
inductance for improved clamping performance to fast over voltage
Littelfuse UL1449 3rd Edition Overview
EPCOS SIOV Metal Oxide Varistors feature a wide operating voltage range of 11 to 1100 VRMS, high surge current ratings up to 8 kA, and no derating up to 85 °C ambient temperature. These SIOV leaded varistors meet UL 1449 3rd Edition requirements. Applications include lighting, radio and TV equipment, and household appliances.