Precision Pin and Socket Contacts Catalog 65910
Revised 1-03
3
Dimensions are in inches and Dimensions are shown for Technical Support
millimeters unless otherwise reference purposes only. USA: 1-800-522-6752 Central America: 52-55-5-729-0425
specified. Values in brackets Specifications subject to change. Canada: 1-905-475-6222 South America: 55-11-3611-1514
are metric equivalents. Mexico: 01-800-733-8926 www.tycoelectronics.com
Current Carrying Capabilities
The total current capacity of
each contact in a given connec-
tor is dependent upon the heat
rise resulting from the combina-
tion of electrical loads of the
contacts in the connector
arrangement and the maximum
ambient temperature in which
the connector will be operating.
Caution must be taken to ensure
that this combination of condi-
tions does not cause the internal
temperature of the connector to
exceed the maximum operating
temperature of the housing
material. Several variables which
must be considered when deter-
mining this maximum current
capability for your application
a r e :
■Wire Size —Larger wire will
carry more current since
it has less internal resistance
to current flow and generates
less heat. The wire also con-
ducts heat away from the con-
n e c t o r .
■Connector Size —In general,
with more circuits in a connec-
tor, less current per contact
can be carried.
■Current Load Distribution —
Spreading those lines with
greater current loads through-
out the connector, particularly
around the outer perimeter,
will enhance heat dissipation.
■Ambient Temperature — W i t h
higher ambient temperatures,
less current can be carried.
Current Rating Verification
Can a contact rated at 10
amperes carry 10 amperes?
Maybe yes, but probably not.
The reason lies in the test condi-
tions used to rate the contact. If
these conditions do not ade-
quately reflect the application
conditions, the actual allowable
current levels may be lower than
specified levels. For example,
many manufacturers, including
Tyco, test a single contact in air.
This gives an accurate measure
of the basic current-carrying
capacity of the contact. Use the
contact alone in air and it can
certainly carry 10 amperes. Use
it in a multi-position connector
surrounded by other current-
carrying contacts or in high
ambient temperatures, and
the contact should carry less
c u r r e n t .
Similarly, as the contact ages
and stress relaxation, environ-
mental cycling, and other degra-
dation factors take their toll, the
contact’s current-carrying
capacity decreases. A prudent
design must set current levels
for such end-of-design-life
(EODL) conditions.
as well by convection, the maxi-
mum T-rise will be realized at a
lower current level. Conse-
quently, the allowable current
level must be lower to maintain
an acceptable T-rise.
For a given connector, the cur-
rent level will be set by the load-
ing density. A connector
containing 50% current-carrying
contacts will permit higher cur-
rents (per contact) than a con-
nector will at 75% loading. The
loading percentage assumes an
even distribution of contacts
within the housing. If all 10 con-
tacts are grouped together in
one section of a 20-position con-
nector, the loading density may
approach 100%.
The Importance of EODL
As stated, T-rise in a contact
depends on both resistance and
current. As it ages, a contact’s
resistance will increase. The
contact designer will specify a
maximum resistance for the con-
tact, this level is the end-of-
design-life resistance. Before the
contact is tested for current,
Tyco subjects it to a sequence
of tests that exercises the major
failure mechanisms and thereby
simulates EODL conditions.
Conditioning includes mating
cycling, industrial mixed-flowing
gases, humidity and tempera-
ture cycling, and vibration to
sequentially introduce wear, cor-
rosion, stress relaxation, and
mechanical disturbance.
P r e s e n t a t i o n
The presentation of current-
carrying capacity in AMP
product specifications includes
two parts:
■First, a base curve showing
current levels versus T-rise for
a single circuit and the largest
wire size. This represents the
maximum current capacity of
the contact. The curve is usu-
ally flat up to 75°C ambient
and then drops off. Up to
75°C, the 30°C T-rise limits the
amount of current, and above
75°C the current must be
reduced to keep the combina-
tion of ambient temperature
and T-rise from exceeding the
maximum operating tempera-
ture of 105°C.
Practical current-carrying capac-
i t y is not an absolute, but an
application-dependent condition.
New Method Simplifies Ratings
To help the designer set the
appropriate current level, Tyco
Electronics has developed a
method of specifying current-
carrying capacity. This method
takes into account the various
application factors that influence
current rating.
The method can be summarized
as follows:
■The contact is aged to EODL
conditions by durability
cycling, thermal cycling, and
environmental exposure.
■The contact’s resistance sta-
bility is verified.
■The current necessary to pro-
duce the specified tempera-
ture rise is measured. This
T-rise is usually 30°C.
■A rating factor is determined
to allow derating of multiple
contacts in the same housing
and for different conductor
s i z e s .
T e m p e r a t u r e
One other factor influencing cur-
rent levels is the maximum oper-
ating temperature, for example,
105°C. If the application has a
high ambient temperature (over
75°C) the contact’s T-rise is
limited by the maximum operat-
ing temperature. For example,
an application temperature of
90°C limits the contact T-rise to
15°C. Since current produces
heat (the I2R law), the current
must be lowered to limit the
T - r i s e .
A contact’s T-rise depends not
only on its I2R Joule heating, but
also on its ability to dissipate the
heat. Consider a contact in a
multi-contact housing. Joule
heating in multiple contacts will
raise the local ambient tempera-
ture. Since the contact will not
be able to dissipate its own heat Graph shows the relationship between base current, ambient tempera-
ture, and contact T-rise.
Current Carrying Capabilities
75
60 56 50
45
35
23
7.5
60
45
30
15
0
Type XII Upgrade
Size 8 Upgrade
.125 POWERBAND
Size 8
Type XII
Type I, Type II/III+
Upgrade
Type III+, Type II,
Type III+Posted
Size 20 Upgrade
20 DF
CONTACT CURRENT GUIDE Maximum Current (Amperes) for Largest Wire Size
Figure 1
13 11.85