In the current economic climate, various methods have been employed, such as reducing the diameter or even modifying the basic construction of the conductors, with the intention of lowering cable costs. All of these methods run counter to the spirit of cabling standards and, in some cases, as we will see later, claim compliance in a potentially fraudulent manner. In this technical report, we discuss these issues before examining the long-term concerns arising from the use of these cables and others with similar specifications.
To understand the situation, we must consider what are known as the conformance requirements of the various cabling standards. The ANSI/TIA-568-C standard, in line with most other TIA standards, states that all statements containing the word "must" constitute mandatory requirements. One such requirement is that channels of a given Category must use cables and patch cords of at least that Category. This statement simplifies everything. If the horizontal and patch cables do not individually meet the requirements stated above, it will not be possible to comply with the ANSI/TIA-568-C standard, regardless of the Category specified for the channel. In contrast, European (EN 50173-x) and international (ISO/IEC 11801) structured cabling standards have a "workaround" clause, known as the "channel conformance approach." This clause allows the use of any cable specification as long as the resulting channel meets the specified performance for the established Class. The intention is laudable and provides freedom to implement new technological developments outside the confines of a specific cable category, but, as in other areas, freedom comes with responsibility. Unfortunately, what we are currently witnessing is the exploitation of this "evasion" clause to the point of exceeding the limits of responsibility. The first steps in this direction were taken with so-called zone cables. Since international cable standards define horizontal and patch cables in separate standards (IEC 61156-5 for horizontal cables and IEC 61156-6 for patch cables), some suppliers decided to independently verify their horizontal cables for conformity to a specific category using IEC patch cable specifications. This results in a cable with less copper and, potentially, a smaller and lighter size.
However, the insertion loss per unit length is 50% higher than that of a horizontal cable of the same Category. As a result, suppliers have had to reduce the maximum length at which these cables should be used, and in doing so, they have invented the concept of a "zone" where such cables can be provided with a channel that meets the standards. The limits of these zones vary between 50 m and 70 m. However, these solutions cannot meet certain requirements: they cannot meet the general requirements of TIA-568-C.2
for links or channels of a given Category because they do not meet the horizontal cable requirements of that standard.
The minimum diameter of 26 AWG conductors is 0.40 mm. Some suppliers are providing cables with a single solid conductor with a diameter smaller than this. Therefore, these cables do not meet the specifications of any horizontal or patch cable in any standard, and, to emphasize the point made in the previous paragraph, they cannot be used to achieve cabling that meets the general requirements for ANSI/TIA-568-C.2 channels of a given Category because the horizontal cables do not meet the requirements of any cable in that standard. However, channels that meet the requirements of a certain Class, according to EN 50173-1 or ISO/IEC 11801, can be achieved by using their "channel conformity approach."
You've probably noticed that we haven't discussed the specifications for permanent links. As mentioned earlier, the ANSI/TIA-568-C standard requires that channels and permanent links of a given Category must use cables and connecting equipment of at least that Category. Unfortunately, if we focus solely on the transmission quality requirements of ANSI/TIA-568-C-2 for permanent links, these are calculated by modeling a 90-meter cable length plus the appropriate connecting equipment. Therefore, even though these zone cables cannot claim to generally or mechanically comply with the TIA-568-C standards, they can specify that their transmission quality meets the stated permanent link quality as long as the links are not too long.
This is what we meant by "contrary to the spirit of cabling standards"—selecting a particular aspect instead of adhering to the actual requirements of a standard.
In contrast, zone cable implementations cannot claim compliance with the permanent links of a specific EN 50173-1 or ISO/IEC 11801 class because the requirements of these standards for permanent links are based on cable length and length modeling, as well as appropriate connecting equipment—and these models are implicitly based on the results of horizontal cables of a given category. Therefore, "patch cable type" insertion-loss cables cannot result in permanent links of any length.
This analysis leads to the complex compliance table above, which reveals the loopholes exploited by suppliers offering zone cables to promote their products.
These suppliers support their products by citing a range of benefits, not only physical or economic, as we saw earlier, but also extending them to areas of social responsibility in terms of reducing material use and waste. Given these justifications, which are clearly reasonable, for introducing zone cables, even if they are based on distorting the standards, we might ask ourselves why these products concern us. One of the main concerns relates to remote power supply in the cables and focuses on the DC loop resistance, a parameter that hasn't been discussed much but which obeys a very simple law of physics: Ohm's Law.
Graphical representation of the difference in heating effect between a compliant and a non-compliant PoE in structured cabling
When balanced cables are used for power supply, two different issues must be considered. First, cables dissipate power as heat, in proportion to their resistance, which, in the case of a solid copper conductor, is inversely proportional to the square of the conductor's diameter. In other words, if the conductor's diameter is halved, the power dissipated per unit length quadruples. Secondly, the temperature reached by the cable depends on its environment (and will be higher if it is in the center of a cable bundle or in isolated routing systems). This temperature increase also has two possible effects: if the cable gets too hot, it will physically disintegrate, but even at lower temperatures, the cable's insertion loss increases, potentially reducing the maximum transmission distance that applications can support. As noted earlier in this technical report, the expected DC resistance of a horizontal cable is no more than 9.5 Ω/100 m. The use of so-called zone cables, which meet the specification of 14.5 Ω/100 m, results in a 53% increase in heat dissipation per meter. Some suppliers are manufacturing cables with conductors smaller than 0.4 mm in diameter, which naturally offer higher resistance figures that will produce more heat. Some of these cables incorrectly claim to comply in some respect with TIA Categories 5e and 6 – against which the increase of its DC resistance is ≥ 60%.
It should be noted that the most reputable zone cable vendors clearly state that they are intended for use in "short" runs within data centers, where remote power is relatively uncommon. However, more recent entrants are specifically suggesting that these cables are capable of delivering remote power in accordance with IEEE PoE and PoE+. While it is true that the power supplied to PoE equipment at the end of these zone cables in short runs will meet the IEEE standard, it is often not made clear that the power loss per unit length along the cable can be significantly higher. Furthermore, one of the compelling selling points for these cables is their smaller cross-sectional area, allowing for more to be installed in the same physical space. This potential combination of higher charge density and higher resistance is clearly something that should be viewed with caution. In this respect, these cables present a similar problem to copper-clad aluminum and copper-clad steel cables, which exhibit a range of DC resistance performance levels that depend on the amount of non-copper material in the conductor. Some copper-clad aluminum or copper-clad steel cables show a DC resistance increase of no more than 40%, while others show values exceeding 200%. Therefore, from this perspective, zone cables fall within the range of these entirely false Category cables.
In this context, it is unfortunate that the test equipment we use to validate our installations is so ineffective at flagging potential problems. It should be acknowledged that the ANSI/TIA-568-C specification for permanent links is length-independent and simply applies a 21 Ω limit for DC loop resistance (the total DC resistance of a looped pair). However, when testing for Category 5e, 6, and 6A limits, the test equipment is not required to flag results that fall outside this limit. In contrast, ISO/IEC and EN standards specify length-dependent requirements. Unfortunately, very few, if any, test equipment vendors specify these limits and simply apply the maximum value of 21 Ω. If they did, no permanent link made with zone cables would meet the requirements of Class D, E, EA, etc.
Finally, experienced data cabling installers are well aware of the connection reliability issues associated with copper-clad aluminum cables and will not install them, even if requested by the customer. However, they tend to overlook the fact that as the conductor diameter decreases, similar problems can arise with all-copper solutions. Connector specifications in connection equipment, according to EN cabling standards, require effective contact for conductors between 0.50 and 0.65 mm². ISO/IEC 11801 expresses its requirements slightly differently, but raises concerns if the conductor diameter falls outside this range. Consequently, using cables with smaller conductors can affect overall compatibility with standards-compliant connectors and, therefore, the reliability of those terminations.
In conclusion, using cables with conductors smaller than 0.5 mm in diameter undoubtedly reduces both cost and cable size. However, some suppliers are exploiting regulatory loopholes to provide these cables, while others go even further, creating cables that disregard standards entirely and falsely claiming compliance with a specific Category through misleading advertising. Although it is acknowledged that these thin-conductor cables have insertion loss results that limit maximum lengths, the most concerning aspect is the associated high DC resistance, which, in remote power supply situations, can lead to excessive temperature increases in cable bundles and unventilated runs. Unless suppliers are fully transparent about these details, supplying these products borders on irresponsibility and is, in some ways, just as concerning as the impact of copper-clad aluminum or copper-clad steel cable solutions. This apparent disregard for DC resistance should concern our industry. While full PoE+ compliance limits power delivery to 25.5–34.2 W per cable, some equipment suppliers are choosing to deliver twice that amount. There also appears to be competition among individual suppliers and industry forums to deliver higher power levels, without any analysis of the impact of their solutions. HDBASE-T offers 100 W of power for televisions, and recently, examples of mid-range insert modules have emerged that deliver even more power to remote devices. CENELEC, the European standards body, has responded to these concerns and has begun developing a technical report that will provide guidance and support for
remote power applications. Figures 1 and 2 above illustrate the difference in heating effect between compliant and non-compliant PoE.
The impact of such non-compliant power solutions, coupled with the use of these thin-conductor cables, is considered a leap of faith. Installers must be extremely careful about the commitments they make in terms of standards compliance (and should thoroughly review the specifications of the cable suppliers). Potential concerns regarding power supply, cable bundle temperature, and possible connector compatibility must be weighed against the commercial advantages offered by cables with "thin" conductors.
This technical report has been prepared by Mike Gilmore, of e-Ready Building Limited, on behalf of Excel.
