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Smaller But Fully Functional Backshell for Cable Connector

Features include reduced size, shield termination, strain relief, and protection against EMI.

An improved design for the backshell of a connector for a shielded, multiple-wire cable reduces the size of the backshell, relative to traditional designs of backshells of otherwise identical cable connectors. Notwithstanding the reduction in size, the design provides all the functionality typically demanded of such a backshell, including (1) termination of the cable shield (that is, grounding of the shield to the backshell), (2) strain relief for the cable, and (3) protection against electromagnetic interference (EMI). A traditional backshell design provides for termination of the cable shield inside the backshell. To accommodate the shield, the interior of the backshell must contain wasted volume and, consequently, must be larger than would otherwise be necessary. The present improved design provides for termination of the cable shield on the outside of the backshell, thereby eliminating the need for wasted interior volume and enabling a reduction in size. In particular, the backshell is now only about one-third as large as a corresponding traditional backshell.

As shown in the figure, the improved backshell includes a backshell body, a cover, and a band clamp. There is a hole in the backshell near its left (as shown in the figure) end to allow the cable shield to pass through to the outside of the backshell. The backshell body is fitted with a threaded coupling nut for securing this connector to a mating connector.

When the cover and the backshell are put together, lips in the form of mating corrugations along the edges of the cover and backshell help to prevent EMI by eliminating any straight path along which electromagnetic waves could penetrate to the cable wires. A male tab on the upper right corner of the backshell body mates with a female tab on the right end of the cover for latching the cover in place when the band clamp is tightened.

The procedure for assembling the cable, the backshell, and the rest of the connector is the following: The cable is placed through the coupling nut on the backshell body, the insulation on the cable wires is stripped back, and each wire is crimped to a connector pin. The pins are inserted in the connector. The coupling nut is threaded onto the connector. The shield (assumed to made of braided wire) pulled through the hole on the cover. Tape is wound around the cable near the left end of the backshell to provide strain relief. The cover is latched in place on the backshell body. The band clamp is tightened around the cover/backshell-body assembly with the shield squeezed between the cover and the band clamp. Once electrical continuity between the shield and the backshell has been verified, the shield is trimmed and the cable is examined for proper strain relief.

If the cable is unshielded or if termination of the shield is not needed, then except for omission of the steps involving the cable shield, the assembly procedure remains as described above. The design of the backshell for such a case can also remain the same, except that optionally, the hole near the left end of the cover can be eliminated because it is not needed.

This work was done by Chuong H. Diep of Hamilton Sundstrand Space Systems International, Inc. for Johnson Space Center.

Title to this invention, covered by U.S. Patent No. 7,044,795, has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457 (f)}. Inquiries concerning licenses for its commercial development should be addressed to:

Gregory Stephenson,
Assistant Intellectual Property Counsel
Hamilton Sundstrand
One Hamilton Road
Windsor Locks, CT 06096-1010

Refer to MSC-23670-1, volume and number of this NASA Tech Briefs issue, and the page number.