when only a few wires are terminated and when the ability to  disconnect the wires is desired. The in-line terminal junction  is environment resistant. The terminal junction splice is  small and may be tied to the surface of a wire bundle when  approved by the OEM. Selected connectors must be rated for continuous operation  under the maximum combination of ambient temperature  and circuit current load. Hermetic connectors and connectors  used in circuit applications involving high-inrush currents  should be derated. It is good engineering practice to conduct  preliminary testing in any situation where the connector  is to operate with most or all of its contacts at maximum  rated current load. When wiring is operating with a high  conductor temperature near its rated temperature, connector  contact sizes should be suitably rated for the circuit load.  This may require an increase in wire size. Voltage derating  is required when connectors are used at high altitude in  nonpressurized areas.  To accommodate future wiring additions, spare contacts are  normally provided. Locating the unwired contacts along  the outer part of the connector facilitates future access. A  good practice is to provide two spares on connectors with  25 or fewer contacts; 4 spares on connectors with 26 to  100 contacts; and 6 spares on connectors with more than  100 contacts. Spare contacts are not normally provided on  receptacles of components that are unlikely to have added  wiring. Connectors must have all available contact cavities  filled with wired or unwired contacts. Unwired contacts  should be provided with a plastic grommet sealing plug. Connectors must be of a type that excludes moisture entry  through the use of peripheral and interfacial seal that are  compressed when the connector is mated. Moisture entry  through the rear of the connector must be avoided by  correctly matching the wire’s outside diameter with the  connector’s rear grommet sealing range. It is recommended  that no more than one wire be terminated in any crimp style  contact. The use of heat-shrinkable tubing to build up the  wire diameter, or the application of potting to the wire entry  area as additional means of providing a rear compatibility  Mating of adjacent connectors should not be possible. In order  to ensure this, adjacent connector pairs must be different in  shell size, coupling means, insert arrangement, or keying  arrangement. When such means are impractical, wires should  be routed and clamped so that incorrectly mated pairs cannot  reach each other. Reliance on markings or color stripes  is not recommended as they are likely to deteriorate with age.  [Figure 9-161] Wires that perform the same function in redundant systems  must be routed through separate connectors. On systems  critical to flight safety, system operation wiring should be  routed through separate connectors from the wiring used  for system failure warning. It is also good practice to route  a system’s indication wiring in separate connectors from its  failure warning circuits to the extent practicable. These steps  can reduce an aircraft’s susceptibility to incidents that might  result from connector failures. Wire Installation into the Connector Adjacent Locations Voltage and Current Rating Sealing Spare Contacts for Future Wiring Figure 9-161.  Connector arrangement to avoid wrong connection. Figure 9-160.  Rectangular connectors.  9-95