Warning – Never Use Internal Data Cable Externally

by | Mar 26, 2016 | Article

Internal grade copper cabling is not designed to withstand the elements.

External grade data cables designed for outdoor use have a special jacket to withstand the elements. If a cable designed only for internal use is installed externally, sunlight and ice will break down the jacket over time and will let water in. Even before the water causes a short circuit, the characteristics of the cable will change. Transmission errors will occur which may not be immediately obvious. It’s likely that corrupted packets will be retransmitted until they get through but this will lead to a slowing of the network before the eventual catastrophic failure of the link.

Some cables are designed and constructed to only be used outdoors. The jacket protects the cable but gives off toxic fumes in the event of a fire. Therefore the British Standards state that these cables must not be routed more than 2 metres inside buildings. They have to be terminated or joined to internal cables within 2 metres.

A number of cables, particularly fibre optic cables, are designed for both internal and external use.

The photo shows some cables we found on the roof of a Milton Keynes school. These have (or had!) LSZH (Low Smoke Zero Halogen) jackets and should only be used internally. As you can see, the jacket had deteriorated in the sunlight, cracked and fallen off, exposing the twisted pairs inside the cable. This has created several potential points of failure in the IT network.

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