Conductor resistance (DCR) in PoE applications results in heat generation in the cable. Typically, Cat6 and Cat7 have larger conductor sizes than Cat5e patch cables. Cables with a larger conductor size can reduce more conductor resistances. Generally speaking, the heat generated in the cable will be reduced with the same ratio of the conductor resistance reduction. Cat6 cables tend to have about 80% of the DCR of Cat5e, thus only about 80% of the heat generation. The larger the conductor size of the cable, the better.
Cable construction is also a factor causing the temperature rise of a cable. Copper cable can be divided into UTP (unshielded twisted pair cable) and STP (shielded twisted pair cable) two types based on cable structure. Usually, cables with metallic or foil shields are proven to dissipate more heat than UTP cables. Higher heat dissipation leads to cooler cable. When using Cat6 F/UTP cable, more than 40% heat can be dissipated compared to Cat6 UTP. If allowed, picking Cat7 S/FTP cable with a foil shield around each pair can dissipate more heat than Cat6 and Cat6 F/UTP.
The previous two factors will affect the cable temperature to some degree. Cables with high-temperature ratings allow for a higher amount of power to be dissipated. Typical temperature ratings for cables are 60°C, 75°C and 90°C. If the temperature of a cable rises, the electrical performance will be degraded. And it’s not good for the cable’s physical performance and longevity. Normally Speaking, shielded cables are less likely to be affected by temperature than UTP cables.
When selecting PoE network cables, make sure that you are comparing apples to apples. Copper clad aluminum vs. pure copper cables, the former use aluminum instead of copper wire. Some people may choose the copper clad aluminum cable (CCA cable) on account of the tight budget, which may lead to network issues from using inferior materials to transmit the signal. The CCA cables have much higher DC resistance than copper cables. If the resistance is not compensated, the voltage drop will be greater for any channel length. Longer lengths will exceed TIA’s channel DCR requirements, limiting the voltage available to the device. Higher resistance causes radiant heat to build up faster, and this may cause damage to the device. 100% copper network cabling is a safer and reliable choice for PoE applications.
The amount of power that the PoE device requires for operation can’t be ignored when selecting PoE cables. The power requirement will dictate which IEEE standard to follow and what the minimum category cabling to be used. Although each standard regulates a minimum category of cabling, other factors are important to be considered including voltage drop and heat dissipation. Voltage drop determines how much of the supplied power reaches the receiving device. The energy that is lost over the length of the cable transforms to heat and is referred to as heat dissipation. Excessive heat build-up can cause an increase in attenuation as well as premature aging of the cabling jacket.
Data Transmission Requirements
Another factor to consider is the data transmission requirement (e.g., 1000BASE-T, 10GBASE-T) of the device(s) being utilized. Devices such as megapixel IP cameras may require higher grade PoE cables in order to deliver the video signal as well as the required power.
The last factor is the cable installation configuration which has a large effect on the heat dissipation ability. Heat will be kept within the cable as high thermal resistance and high conductor temperature occur with large cable bundles or other installation factors. The larger the cable bundle size, the higher the temperature, no matter what cable category and construction structure.
Here provides several specific installing tips for PoE cabling:
- Get well-prepared before deploying, and never just wing it.
- Check your network devices to verify that they are PoE compliant.
- Make use of different media in the whole cabling design.
- Do not run cable near devices that generate electrostatics.
- The PoE cable installation is not a one-and-done, please prepare for the future upgrades.
- Think about your budget for the whole cabling installation, and find a cost-effective solution from a reliable supplier.