Hi Bob:
Yes, detachable cordsets can and do tend to heat at the equipment
end.
Consider the construction:
a) At the equipment end of the cord, the wires are connected to
the IEC 320 appliance coupler terminals. This connection
introduces contact resistance.
b) At the interface between the appliance connector (cord end)
and the appliance inlet (equipment side), the appliance
coupler involves friction-fit connections. These connections
introduce contact resistance. This contact resistance is
subject to wear of the surface, and reduction of the contact
force as a function of the number of insertions and with-
drawals.
c) Within the equipment, the appliance inlet has connections to
the internal equipment wiring. If the construction is some-
thing other than a printed-wiring board soldered connection,
the connections introduce contact resistance.
Power is dissipated in the form of heat in the three contact
resistances according to:
P = I x I x R
Consider also that copper is a good thermal conductor. So, the
three contact resistances, in relatively close proximity, contribute
to a noticable heated system (assuming a current approaching rated
current of the appliance coupler).
The most significant contributor to heating is (b). This contact
resistance increases with insertions and withdrawals.
All of the contact resistances can increase with on-off cycling,
which results in temperature cycling. Temperature cycling, with
its attendant expansion and contraction, will cause the mechanical
connections to loosen, thus increasing the contact resistance.
Finally, long-term temperatures can increase the affects of copper
oxidation, which can increase the contact resistance. (Ideally,
the macroscopic connections SHOULD be gas-free to prevent
oxidation.)
Worst-case, if the copper temperature gets high enough, the system
can go into thermal runaway, where the R continues to increase,
dissipating more and more power. Often, the end-result is a fire.
An appliance coupler meeting IEC 320 specs will carry full load
indefinitely without overheating. This assumes that the
construction includes large-area, gas-tight connections at each
terminal.
But, high insertion/withdrawal cycles will degrade (b), and you
can expect the assembly to become warm to touch. If this occurs,
you should replace the cord.
Best regards from San Diego,
Rich
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Richard Nute Quality Department
Hewlett-Packard Company Product Regulations Group
San Diego Division (SDD) Tel : 619 655 3329
16399 West Bernardo Drive FAX : 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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