There are 11 entries in the FAQ.
Pages: 1
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| Does the NEC SEFUSE offer any advantage over other pellet types? |
 | Yes, you might compare the following three advantages:
- The Sefuse 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.
- The Sefuse has a 277 V.A.C. rating (for three phase applications).
- The Sefuse is immediately available from Chatham Components' New Jersey inventory.
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| Do you offer a 277 VAC rating (for 3 phase mavens)? |
| Yes, see the SF/E SEFUSE Series chart at the bottom of the data sheet (click here for SF/E Series data sheet). |
| Are there different selection precautions to be taken when using a eutectic vs. a pellet type TCO? |
| 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. |
| Is it best to place a TCO adjacent to a controlling thermostat? |
| Not necessarily since the thermostat might be regulating for
application temperature whereas testing with multiple thermocouples could
determine more appropriate position(s) for TCO placement during fault
conditions. |
| When establishing a second source is it sufficient to just select an alternate TCO with the same opening temperature rating? |
| 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. |
| How quickly does a TCO react? |
| Reaction time depends on ambient operating temperature,
I-squared-R self heating, heat transfer rate through insulation enclosing
the TCO, 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. |
| Does it matter in which direction a TCO is installed? Is there polarity? |
| There is no polarity but mounting direction can be critical in a
pellet type TCO where the outer case is electrically "hot." Thus, if it
attached in the wrong way the TCO's surface could short out and bypass
the circuit from being opened at overheat. |
| Is there ever a time when more than one TCO is used in a design? |
| 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. |
| How close to the opening temperature of the thermal fuse can I run my application? |
| We recommend at least 20°C below the trip point or "fusing off"
point of the thermal fuse. |
| What temperature does the thermal fuse reset itself? |
| Thermal fuses do not reset, 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. |
| Where can I buy a thermal fuse to fix my appliance? |
| Due to product liability we can't supply thermal fuses to
individuals who are doing home repairs. We do often suggest that they may
be able to find a replacement at Radio Shack but
first to take care to examine what made the unit overheat causing the TCO
to do its job and open the circuit; there might be a failed thermostat,
blocked airflow, shorted wires or other condition that needs correcting.
To only replace the TCO could lead to further problems. |
Does the NEC SEFUSE offer any advantage over other pellet types?
