How Were Your Cable Products Tested?

[Ganimedes Reveley]

How Were Your Cable Products Tested?

Cables are everywhere, and they are not cheap. Cables must be tested in advance by manufacturers for safety as well as performance. It is important to know what tests and certifications have been performed on the cable products you expect to install.

Who Approves Installation?
There are authorities outside the enterprise tasked with approving cable installations. These authorities are concerned with safety, but not cable performance. Those concerned with safety are fire marshals, building inspectors, building code enforcers, and the building owner. Part of their responsibility is to ensure that properly tested products are used for the cable installation. There are requirements, such as building codes, that need to be satisfied before the installation can be approved.

Safety Requirements
The safety requirements are focused on the safety of the people who work in the location where the cables will be installed. Underwriters Laboratory (UL) and CSA-International (CSA) are the two primary producers of safety testing standards for the U.S. and Canada.

A primary focus for safety tests is for fire, since slowing fire propagation is such an important part of safety. This test is concerned with how fast the fire spreads; the slower the propagation time, the more time there is to evacuate the building.

The Plenum test (horizontal cable installation) is required for communication cables, optical fiber cables, power limited cables, fire alarm, and community (CATV) antenna-rated cables. The cable tests include how fast the flames spread, and the density of smoke produced by a burning cable. The test lasts 20 minutes.

A separate set of tests is performed for riser cables (vertical cable installation). These tests are required for the same types of cable listed above. The cable tests include how fast the flames spread and the smoke density produced by a burning cable. The difference here is that flames travel vertically in the riser and can produce more rapid combustion. The test lasts for 30 minutes. The standard requires that flame propagation shall not exceed 12 feet during the test. Within the 12 feet of riser, the temperature shall not exceed 850 degrees F.

The cable manufacturer must comply with well controlled manufacturing methods to meet these stringent requirements for the cable jacket (outer covering), and the insulation material inside the cable. Electrical cables must also be tested for:

* Aging of the cable covering and insulation material, which may dry out, crack, and therefore change the fire resistent properties of the cable.
* The maximum voltage the cable can support
* How well the cable works under very cold conditions
* Outdoor rated cables may change their properties as they are exposed to sunlight, which can prematurely age the cable

Optical fiber cables do not have to satisfy all of the tests performed on electrical cables because they carry light, not electricity.

Performance Requirements
Performance testing is done by the manufacturer to provide assurance to the customer that the cables are verified to meet the advertised performance specifications. Performance testing also involves interoperability and network operation.

The performance requirements are contained in a number of standards:

* ANSI/TIA-568-C.2
* ISO/IEC 11801 plus other IEC standards
* EN 50173-1 plus other standards
* IEEE 802.3 standard for Ethernet

Performance testing standards deal with transmission requirements. The primary focus of the performance tests is on useable/operational bandwidth. The bandwidth is measured over a specific frequency range.

It is also defined by the signal-to-noise ratio (SNR). The signal strength relative to the total noise level is very important. As a signal propagates down the cable, the signal strength declines with distance. This is called attenuation. The longer the cable, the greater the noise level generated. Eventually the SNR is so low that the endpoint on the cable cannot read the signal. Therefore there is also a limit to the cable length. For example, a typical Ethernet cable should not exceed 300 meters to satisfy the bandwidth requirement.

There are a few sources of noise. Signals on one pair of wires can pass noise to another pair of wires in the same cable. This is called internal crosstalk. External crosstalk is where the cable picks up noise from sources outside the cable, such as electrical power cables running next to the communications cable. A third noise source is called return loss.

Verifying the Cable
It is worth learning which organizations were used to verify the safety and performance test compliance for your installation. It is best if the testing organization is not related in any way to the manufacturer of the cables.

Look for markers on the cable and/or the cable packaging such as reels, spools, and boxes that specify the standard(s) that have been verified for this product. The marker may look like "ETL Verified" followed by the standard descriptions that apply to this cable. Patch cables need verification for the cable and the connectors attached. The connectors, patch panels, and jacks used with cables can affect the final cable performance. Look for third party verification of the connecting hardware as well.


2013/12/05 10:17:45 Source：nojitter

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