Frequently Asked Questions

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The Restriction of Hazardous Substances directive. RoHS is European Union Directive 2002/95/EC on the Restriction of Certain Hazardous Substances in Electrical and Electronic Equipment. It was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state. This directive restricts (with exceptions) the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment.

RoHS restricts the use of the following six substances:

  • Lead (Pb)
  • Mercury (Hg)
  • Cadmium (Cd)
  • Hexavalent chromium (Cr6+)
  • Polybrominated biphenyls (PBB)
  • Polybrominated diphenyl ether (PBDE)

The maximum permitted concentrations in non-exempt products are 0.1% or 1000 ppm (except for cadmium, which is limited to 0.01% or 100 ppm) by weight. The restrictions are on each homogeneous material in the product, which means that the limits do not apply to the weight of the finished product, or even to a component, but to any single substance that could (theoretically) be separated mechanically—for example, the sheath on a cable or the tinning on a component lead.

The RoHS 2 directive (2011/65/EU) is an evolution of the original directive and became law on 21 July 2011 and took effect 2 January 2013. It addresses the same substances as the original directive while improving regulatory conditions and legal clarity.


Due to product liability we can’t supply thermal fuses to individuals who are doing home repairs.


Thermal fuses do not reset. They are considered “one-shot” thermal fuse or cutoffs, or TCO’s. They are used as a safety back up to protect an appliance or product from overheating and catching on fire. It is often used in conjunction with a thermostat, to protect the appliance should the thermostat fail.


The manufacturers installation instructions must be followed. In general, we recommend at least 20°C below the trip point or “fusing off” point of the thermal fuse.


Absolutely. Many products have more than one “hot spot.” Examples are transformers, battery packs, coffee-makers, pop-corn poppers, all of which can have different overheated locations due to the nature of the particular failure mode.


There is no polarity but mounting direction can be critical in a pellet type TCO where the outer case is electrically conductive. Thus, if it attached in the wrong way the TCO’s surface could short out and bypass the circuit from being opened at overheat. The manufacturers installation instructions must be followed.


Reaction time depends on ambient operating temperature, resistive self heating, heat transfer rates, and heat dissipation due to air flow past the TCO and through the mounting location. Therefore, comprehensive testing must be performed to assure the TCO opens before a fault condition can develop into a catastrophic failure.


We strongly recommend performance testing to insure any differences between the two TCO sources do not exceed safe limits. This should apply, as well, to products from the same supplier who has undergone a part number alteration or made a manufacturing location move. Satisfactory continued listing of the TCO by the various agencies does not necessarily assure identical performance in an application.


Yes. Pellet types are subject to shortened life expectancy resulting in nuisance opening when normal operation is too close to the rated opening temperature of the TCO.

This end-of-life experience is also shortened by temporary heat overshoots that contribute to pellet shrinkage. We encourage at least a 20 degree C. buffer between normal ambient temperature and the rated opening temperature of the TCO. Similarly, thermal gradients across the TCO’s housing or due to leads being at different temperatures can contribute to sublimation reducing pellet size. For further depth on this factor of pellet aging we recommend reviewing U.L. Standard 1020. Eutectic thermal fuses have the advantage of simplicity of operation. There are no moving parts, springs or contacts. They use a two phase eutectic element that simply melts when it reaches the formulated temperature. Surface tension then separates the eutectic metal, opening the circuit. Eutectics come in a greater variety of sizes, axial and radial designs and generally are better for low current applications where small physical size is important.


Design testing must performed to determine the proper location.


Yes. The SEFUSE brand has a ceramic pipe introduced at the epoxy-sealed end to support the lead and guards against rupture of the epoxy that in other manufacturers’ designs produces loss of the critical seal; this is shown in the NEC Schott TCO Epoxy Supported Tube Diagram.


Yes. Pellet types are subject to shortened life expectancy resulting in nuisance opening when normal operation is too close to the rated opening temperature of the TCO. This end-of-life experience is also shortened by temporary heat overshoots that contribute to pellet shrinkage. We encourage at least a 20 degree C. buffer between normal ambient temperature and the rated opening temperature of the TCO. For further information on this topic we recommend reviewing the technical specifications from the manufacturer

Eutectic thermal fuses have the advantage of simplicity of operation. There are no moving parts, springs or contacts. They use a two phase eutectic element that simply melts when it reaches the formulated temperature. Surface tension then separates the eutectic metal, opening the circuit. Eutectics come in a greater variety of sizes, axial and radial designs and generally are better for low current applications where small physical size is important.