Over-Current Protection
SIDACtor
Data Book
5 - 12
Teccor Electronics
(972) 580-7777
Weaknesses
Because a fuse will not reset, consideration should be given to their use in applications
where multiple fault occurrences are likely. Examples such as AC strip protectors and
ground fault interrupting circuits (GFIC) are applications where an alternative solution
might be more prudent.
Applications
Telecommunications equipment that is best suited for a fuse is equipment that requires
surface mount technology, accurate longitudinal balance, and regulatory compliance
without the use of additional series line impedance.
Power/Line Feed Resistors
Overview
Typically manufactured with a ceramic case or substrate, power and line feed resistors
have the ability to sink a great deal of energy and are capable of withstanding both
lightning and power cross conditions.
Advantages
Power and line feed resistors are available with very tight resistive tolerances making
them appropriate for applications that require precise longitudinal balance.
Restrictions
Because power and line feed resistors are typically very large and are not available in
a surface mount configuration, these devices are less than desirable from a
manufacturing point of view. Also, because a thermal link is typically not provided,
power and line feed resistors may require either a fuse or a PTC to act as the fusing
element during a power cross condition.
Applications
Power and line feed resistors are typically found on line cards that use over-voltage
protectors that can not withstand the surge currents associated with applicable
regulatory requirements.
Flameproof Resistors
Overview
For cost sensitive designs, small, 1/8W - 1/4W flameproof metal film resistors are often
used in lieu of PTC
’
s, fuses, and power or line feed resistors. During a transient
condition, flameproof resistors open when the resultant energy is great enough to melt
the metal used in the device.
Advantages
Flameproof resistors are cheap and plentiful.
Restrictions
Flameproof resistors are not resistive to transient conditions and are susceptible to
nuisance blows.
Applications
Outside of very inexpensive customer premise equipment, small resistors are rarely
used as a means to protect telecommunications equipment during power fault
conditions.