98
Contacts
Current ratings for multi-contact connectors
Choice of right connector -
contact combination.
The choice of a Trim Trio connector in
combination with a Trim Trio contact is
essential and different for any application
There is considerable misunderstanding in
the field on current carrying capabilities for
the various contacts in the TrimTrio
programme.
The intention of this part is to give guidance
how to interprete the given current ratings in
general and how to calculate them for
particular applications.
The information given is based upon existing
MIL specifications such as:
MIL-C-26482, MIL-C-8384,
MIL-T-7928, MIL-W-5086,
MIL-W-5088, MIL-W-16878, etc. and in
conjunction with long field practice.
Current carrying capabilities
Trim Trio contacts are designed to carry a
specific current, in accordance with the
applicable specification.
This specification will be defined by
following variables:
• Connector size
The more contacts in a connector, the less
current per contact can be loaded.
• Wire size (see table 1)
The cross section will determine the internal
resistance and temperature rise for a given
current.
-Table 1 gives the current ratings for the
various wire sizes commonly used with Trim
Trio contacts.
• Current rating (see table 2)
The current load for a given application will
generate heat.
- Table 2 gives the maximum current
carrying capacity of most of the Trim Trio
contacts, the maximum operating current
and the recommended continuous current.
• Ambient temperature
The combination of the connector size, the
wire size and the current rating will generate
a temperature rise.
This temperature rise + a given ambient
temperature may not exeed the maximum
operating temperature of the connector
material (see performance characteristics for
each connector family).
• Max. current carrying capacity
• Max. operating current
• Recommended continuous current
What do these values mean in practice ?
• Max current carrying capacity
of a contact is defined by the conducting
section of the contact in its smallest area.
The listed values are obtained from several
tests in laboratories under room conditions
(21°C). The contact is considered to be in
free air.
• Max operating current
is the current with which the contacts can
be energized during a longer or shorter
period, without deteriorating and depending
on working conditions.
These are dissipated heat, cooling
provisions, ambient temperature, insulation
material, etc.
• Recommended continuous current
can be applied for all normal cases and
working conditions. The values include a
safety margin. However, there are
restrictions in the application of the given
values. The most important restriction is the
used wire, its sectional area, insulation
temperature range, as well as wires in
bundles.
Military specifications require that for a
cable bundle of 15 conductors or more, the
bundle shall not carry more than 20% of the
total carrying capacity of the bundle.
In smaller bundles, the allowable percentage
of total current may be increased as the
bundle approaches the single wire condition.
This percentage of increase in total current
carrying capacity of the bundle is 6% for
each conductor less than 15 in a bundle.
Table 1 - Current carrying capabilities per wire size
Table 2 - Current carrying capabilities per contact type
AWG wire size wire dia. max.curr. max.oper- recomm.
mm2mm carrying ating curr. cont. curr.
Amp. Amp. Amp.
26 0.13 0.40 3 2 1
24 0.20 0.51 4.5 3 2
22 0.32 0.64 9 5 3
20 0.52 0.81 11 7.5 5
18 0.82 1.02 16 10 7.5
16 1.30 1.29 22 13 10
14 2.10 1.63 32 17 13
size pin dia. type max. curr. max. oper- recomm.
carying ating curr. cont. curr.
Amp. Amp. Amp.
RM / RC 22 13 10
machined
16 .062* SM / SC 22 13 10
1.6 mm 2 piece
stamped
20 .040* SM-W / SC-W 11 7.5 5
1.0 mm 2 piece
stamped