Network technologies

Preventing failure of network connectors for mobile medical equipment

Connections to Ethernet network infrastructure may be compromised by failure of the ubiquitous RJ45 UTP modular jack connector.

The 'Registered Jack' connector system was introduced in the 1970s by AT&T (Bell Telephones) in the US to replace bulky telephone jacks. The RJ connector system is now used worldwide for data and voice communication systems.

Their use in data communications has almost always presumed that the connectors are only subject to infrequent connect/disconnect cycles. A PC or telephone might only be relocated a couple of times a year. In data communications switching equipment, a jack might only be moved once or twice during the entire lifetime of the equipment. The TIA/EIA1-568-B standard stipulates a minimum of 750 mating cycles before failure.

However, a quick survey of modular jacks for data outlets shows that this figure is typically 1000-2000 cycles but may be as low as 200 cycles. While this is adequate in many situations, it is far from adequate in a clinical environment, where mobile equipment is used.

For instance a mobile digital imaging system in a surgery unit might reasonably be connected and disconnected to an RJ45 jack several times in a 24-hour period. This could potentially lead to the failure of a low-cost socket within in a few months of installation. Similar failures may also be encountered on medical devices and mobile computing equipment such as laptop PCs.

In our experience, the quality of the connection jack is something that is not specified in contracts with datacoms installers. Apparently, little or no distinction is currently made between datacoms installations for clinical and administrative environments.

The wiring systems used in clinical areas may or may not be of a higher quality, but the quality of the modular jacks installed in them will not necessarily be any better than anywhere else. In addition to the uncertain reliability of this connector system in clinical environments, there is also the ease with which they are damaged by the use of excess force and misalignment of the connector parts.

Possible solutions

We investigated the possibility of using a more reliable ruggedised connector system. There are a number of connector systems for industrial Ethernet, but these are by and large incompatible with existing RJ45 installations.

Two RJ45 compatible systems are currently available: water resistant booted connectors offered by Tyco2, Bulgin3 and others and the metal overshell style such as the Amphenol4 RJField or Neutrik5 EtherCon.

The polymer booted devices are intended for outdoor, marine and industrial applications and may have limited applications inside medical devices. They also require the purchase or construction of special cable assembles which limits their compatibility with existing equipment. The Amphenol system is very rugged but has a 33mm unit width, much larger than the standard 25mm jack module.

The Neutrik EtherCon connector system uses a metal shell to protect the RJ45 cable plug and assures correct alignment with the socket. The protective shell is designed to be retrofitted to existing RJ45 cables.

The socket accepts either standard RJ45 connectors or connectors fitted with the shell. The reliability is quoted as being greater than 1000 cycles. The EtherCon shells can be made non-latching if required. This is advantageous in mobile applications where it guards against wall jacks being ripped out. The non-latched shell will provide more than enough friction lock to hold the connector into its socket.

The downside of this solution is the cost; a typical EtherCon socket is about twice the price of a modular jack. The cable shell also adds to the cost, the total being about £7.50 per plug and socket combination. There may also be difficulty in fitting these bulkier sockets into multiple (2,4 and 6 way) wall plates.

It is also worth considering using short male-female extension leads to protect data outlets and medical equipment from connector failure. Making the extension socket non-latching also protects against rip-out damage. In addition, various ready-made cable economisers or short patch-cord and RJ45 coupler combinations from Videk6, Belkin7, Prosignal8 etc, could be used to achieve the same protection. Replacement of the extension leads is far less costly and less problematic as having a wall socket fail in a critical care unit.

Alex Birkett, Department of Medical Physics, University College London Hospitals NHS Trust.