Thermal Cutoffs (TCO)
Safety Precautions (Handling Precautions)
The following are precautions for individual products. Please also refer to the precautions common to EMI Filters,
ESD Suppressors, Fuses, and MR Sensors shown on page EL113 of this catalog.
Design Applications
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1. Use the TCO within their specified temperature and electrical ratings.
1) Use the TCO under the maximum operating temperature specified in the individual specification.
Using the TCO under a higher temperature than the maximum operating temperature may cause premature
opening or opening delay.
• When the TCO is continuously used at the temperature close to the functioning temperature, the TCO may
operate while being used.
• When the TCO is continuously used at the temperature higher than the maximum operation temperature, the
TCO may be degraded and may not operate normally at the specified temperature.
2) The holding temperature is defined as the highest temperature at which the TCO is activated continuously at
the rated current for 168 hours. The TCO can not be used over 168 hours exceeding the holding temperature.
3) Equipment should be designed so that its over shoot does not exceed the maximum temperature limit after
the TCO operates.
4) If the TCO is activated by voltage higher than the rated voltage or current higher than the rated current, the
TCO produces excessive heat, resulting in premature opening. The arc generated at this condition of operation
will result in an abnormality of appearance (crack on body) and insufficient insulation.
• When TCO is operated in an abnormal mode while the rated voltage and/or the rated current being
exceeded, it may not cut off the circuit .
5) Thermal element may be transformed and TCO may open when it is used in the environment from which an
excessive temperature change (such as outdoor) is repeated. Investigate the environment where TCO is used.
6) Where transient overload is expected to be applied, repeat the tests under the worst conditions.
7) The TCO cannot be used as a current sensitive fuse.
2. To fully use the function of the TCO, a suitable TCO for each equipment application must be selected.
1) Tests should be repeated for the finished equipment to confirm that the TCO does operate as expected.
2) To improve thermal response of the TCO, put the main body of the TCO and the lead wires(terminals) as
close to the heat source as possible and the place where the TCO is evenly heated.
If the temperatures transferred to the main body and to the lead wires(terminals) are largely different from
each other, improper operation can be expected, causing arcing and deterioration of insulation.
3. Avoid application of excessive vibration and mechanical stress to the TCO. Otherwise, failure of the fusible
alloy or lead wires, or damage to the main body may result.
4. The following 1) and 2) are precautions for thin type TCO (MP, ML and MU series)
1) TCO body and terminals must be properly fixed when the TCO is mounted in the equipment. It may cause
breaking of thermal element and/or terminals, or damages of the TCO body, or other failure when the body or
terminals is not properly connected. Avoid a transport under the condition with a connection only a single side
of terminal and the equipment as it might cause breaking of thermal element and/or terminals, or damages of
the TCO body, or other failure due to the vibration or mechanical stress on the transportation.
2) When TCO is mounted in the equipment, terminals must be aligned with the body. If TCO body and terminals
are mutually mounted askew, it might cause breaking of thermal element and/or terminals. Also after assembling
TCO in the equipment, avoid pulling, bending, pushing stress and twisting stress in the TCO body and terminals
in order not to cause breaking of thermal element and/or terminals, or damages of the TCO body.
5. When sealing the TCO with resin, select a resin that does not corrode the seals or the lead wires(terminals).
When sealing the overall TCO with resin, determine the fixing conditions by repeating the test using your final
product to check whether or not the resin properties (e.g. expansion, contraction, and curing temperature)
affect the TCO and whether or not the TCO can operate normally.
6. When immersing equipment with a TCO in varnish or solvent and then drying it, repeat the test to check whether
or not the varnish or solvent used dissolved the coating of the TCO or caused damage, such as cracks, before
performing the treatment again.
7. Do not use under the following environments.
1) In liquids such as water, oil, chemical and organic solvents
2) In direct sunlight, outdoors or in dusty atmospheres
3) In places where water condensation occurs
Use in the following environments may affect the performance of the TCO; Verify performance and reliability
before production use.
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(1) In places full of corrosive gases such as sea breeze, Cl2, H2S, NH3, SO2 and NO2
(2) In environments with high static electricity and/or strong electromagnetic waves.
8. Do not use the TCO in aerospace equipment, atomic energy equipment, military weapons, life saving
equipment, etc.
Instruction
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1. Forming and Cutting
1) Lead wires(terminals) are to be bent or cut at least 3 mm away from the TCO seals to avoid damaging the
TCO . (axial / radial type) or body (thin type). The TCO seals (axial / radial type) shall not be grasped with
any tools or holders. Terminals of thin type TCO are to be grasped before they are bent . (See Fig.1)
2) The lead wires and terminals shall not be nicked, fractured or burned.
The body and/or seals must not be damaged, burned or overheated.
3) It is recommended that experimental assembly trials, should be done so that it can be verified that manufacturing
procedures will not exceed the maximum tested "pull" and "push" forces of 20 N (MP and ML series:5 N,
MU series:10 N) and 5 N respectively on the lead wires (terminals), or induce excessive twisting or the like.
4) Do not repeat bending terminals of thin type TCO.
Design and specifications are each subject to change without notice. Ask factory for the current technical specifications before purchase and/or use.
Should a safety concern arise regarding this product, please be sure to contact us immediately.
Jul. 2008
