为什么在布线工程的初期阶段就要开始进行测试？
很多合约商觉得做越少的测试越好。这就是为什么他们希望在项目初期阶段和完成阶段进行测试。福禄克网络公司的 Bob Jensen 解释了为什么要花时间来对您的安装进行测试，甚至在工作的初期阶段就应该做测试，才可节省宝贵的时间、金钱并避免出现故障。
请看来自于Electrical Contractor Products 在线杂志的文章。 ecpzone.com：“在将网络施工隐藏在石膏和水泥板之前的初期阶段就进行测试可以有更多的机会来修复故障。如果在初期阶段后再来修复故障电缆和有问题的链路将会花费大量时间和金钱。在初期阶段进行测试可以帮助合约商避免在建筑工程后期引起的问题，避免不同的合约商之间相互指责，还可满足业界标准。”
Rough-In Testing Doesn't Have to be a 'Tragedy'
By Bob Jensen, Fluke Networks
Follow standards to make it fast, easy and profitable.
"To test, or not to test: that is the question. Whether 'tis nobler in the mind to test at rough-in and rest assured on a job done right the first time, or to gamble one's work in order to save a little time and money – only to risk even bigger overruns in both areas."
—Faux Shakespeare
Shakespeare parody aside, electrical contractors face a dilemma worthy of the legendary playwright's tragic tales.
From the outset of any cable installation, a contractor faces a testing dilemma that can effectively make-or-break a project and ultimately their own bottom-line. In order to make the installation profitable, the job needs to be done quickly, correctly and with as little rework as possible. The dilemma comes from deciding when to test and how thorough the testing should be.
Testing at rough-in offers the chance to fix problems before the installation is hidden behind sheetrock and plaster. It is prohibitively expensive and time deficient to repair faulty cable and broken links after the rough-in stage. Testing at rough-in helps a contractor avoid problems caused by later stages of construction, avoid finger pointing between different contractors and meet industry standards.
It's the last goal—meeting industry standards—that will ultimately allow the contractor to save time and money. Adhering to a set of pre-defined, expert-proven standards makes rough-in testing fast, easy and profitable. By working to standards, a contractor can formally gauge work quality from the early stages of construction and can communicate the results back to the customer. Translation: standards allow for discovery of little problems before they turn in to bigger, budget-blowing, time-wasting, lawsuit-generating, full-blown issues.
However, testing to prevent a worst-case scenario is not exactly a top priority for most contractors. In fact, it's usually just the opposite. Testing takes time and costs money. And from the outset, it's every contractor's primary goal to save as much time and money as possible. So a contractor has two choices: invest mildly in testing equipment and the time it takes to adhere to industry standards for preventative maintenance, ensuring a profitable install; or eliminate the small investment and save the money, banking on every job to be mistake-free.
If only Shakespeare were alive today. The "save the money" approach is a tragedy in the making.
Standard of Standards
Residential cabling standards have evolved since first introduced in the 1990s. The initial standard was only concerned with telephony and data networking within a home and concentrated on ISDN. Since, networks have progressed significantly with the proliferation of cable modems and xDSL. So did the requirements for testing those networks. In 2004, the ANSI/TIA 570-B standard debuted. The new standard is fully-integrated to include all residential systems like the previously ignored areas of whole-home audio, control systems and security systems. The 570-B standard serves as the ultimate reference for residential cabling and networks that in which everyone in the custom install business can feel confident, including designers, integrators, installers, builders and consumers.
The 570-B standard serves especially well as a guide for installers. It provides a simple, three-step test: 1) visual inspection at rough-in; 2) verification at rough-in; 3) either qualification or certification after finishing.
The visual inspection detects obvious problems such as checking for kinks and knots, and making sure the correct separations are kept from electrical wiring and other communications cabling as interference is unfavorable with electronic systems.
Either during or after visual inspection, the installer should use a verification test tool to ensure the cables are connected correctly. Using a verification tool is perhaps the most crucial element of the 570-B standard because this is the last chance to fix a problem before it gets expensive. This is the make-or-break stage for the contractor's profitability. It is also the point in the process where the cabling contractor needs to start protecting his work. Verifying the installation, and documenting the results, is invaluable if a sheet rock screw pierces a cable. Documenting the condition of the installation at the time the next contractor goes to work can save a lot shouting later on. After finishing, it's time to document the actual performance of the installation. This is the purpose of qualification and certification and the tools used to run the tests.
Qualification is a test of the cable to make sure it can handle the type of network traffic that's expected of it. Standard 570-B says: "Cable qualification tests the cabling to determine that certain network technologies (e.g., 100BASE-TX, Firewire) will perform on the cabling system". Qualification tools occupy a middle ground. They are much more powerful than verification tools, and are designed to allow minimally trained operators to determine if existing cabling 'works', and if not, why not. However they in no way compete with or replace cable certification tools, which perform a powerful and unique function.
Certification is the most rigorous of all cabling confidence tests. A certification test tool makes many types of measurements across predefined frequency ranges and compares the detailed results to the 570-B standard. The results from these measurements determine if a link is compliant with a category or Class of cable (e.g., category 5e, category 6, Class D). Furthermore, certification test tools commonly provide advanced graphical diagnostics and offer feature rich reporting capabilities. An important difference with certification tools is that they alone are capable of providing a certain "Pass" or "Fail" on the cabling.
Of course, being able to provide the type of documented results that qualification and, more thoroughly, certification tools offer enables the contractor to prove a job well done to the customer. This also negates the chance for finger-pointing and accusations between the customer and among several possible contractors.
Right Tool for the Job
There are a specific test tools available that meet contractor demands at rough-in and verification phases of testing under the 570-B standard.
When shopping for the right verification tool, remember that there are two basic categories. Toners and probes are used to identify cables and check basic wire connectivity (some digital toners can make difficult cable identification easier, too).Verification tools perform wiremap tests, serve as a cable/room locator and identifier, work as tone generators, and measure length via TDR (length to cable and length to opens or shorts).
Don't Be the Contractors' 'Hamlet'
The time-crunched and cost-conscience contractor shouldn't view testing to standards as an unnecessary 'hoop' to jump through. By simply choosing the right tools and adhering to the simple 570-B standard, testing at rough-in is a net-savings rather than an expense.
The new 570-B standard defines rough-in testing as the first two steps—visual check and verification—of its easy, three-step process. Those two first steps are so easy, in fact, they can often be performed concurrently.
So, remember that the next time you have to rip-down the sheetrock, it would have been faster, simpler and cheaper to catch the problem at rough-in. In short, don't let rough-in testing be your personal Shakespearean tragedy. We all remember how Hamlet ended. The prince died when he acted on impulse instead of a planning ahead. Your business doesn't have to suffer the same fate. Thinking ahead and following the 570-B standards will make rough-in testing fast, easy and profitable.
Bob Jensen, RCDD is the Standards and Technology Development Manager for Fluke Networks, Everett WA. He chairs the TR-42 Engineering Committee as well as the TR-42.2 Subcommittee for Residential Infrastructure (TIA/EIA-570-B). In addition, he is a principle member to NFPA Panel 16 (National Electrical Code).