LP Cable: When It’s Necessary (and When It’s Not)

As IP-enabled devices are designed to draw more power to provide end-users with enhanced features, they will require more power. As more power is required, the amount of current running through the cable rises - and the amount of heat generated within the network cable increases. Bundled cables are especially vulnerable to higher temperatures; the heat generated by the current passing through the inner cables can't escape, contributing to higher overall temperatures. This could ultimately push cables beyond their rated temperatures, reducing performance and reliability.

Because of this phenomenon, Underwriters Laboratories (UL) developed the Limited Power (LP) certification for cable. The LP listing certification verifies that a cable has been evaluated to carry the marked current “under reasonable worst-case installation scenarios without exceeding the temperature rating of the cable.” As this new certification rolls out, we’re receiving lots of questions – and noticing some uncertainty – about what it means. So here’s what you need to know about LP cable.

What is LP Cable?

Simply put, an LP cable has been certified by UL as one that doesn’t exceed its temperature rating under certain conditions (after correcting for an ambient temperature of 30 degrees C). This is achieved by manufacturing the cable with insulating and jacketing material that can handle higher temperatures.

How are LP Cables tested?

UL bundles 192 cables together in an enclosed, 6-foot-long, non-metallic conduit filled with insulation at both ends. The cables are subjected to different currents, and UL keeps track of the temperature rise inside the cables. The amperage is increased from 0.5A to as high as 1.0A, or until the temperature inside the cable bundle reaches the rated temperature. The amperage is then recorded, and this value becomes the LP rated amperage. An LP rating is always coupled with a specific current, which is the current that the cable can handle on each conductor without exceeding temperature ratings.

When do you need LP Cable?

Most applications don't require the use of LP cable. There are two situations where LP cable may be called for:

1. Power-supplying equipment is capable of power over 60W
2. Power-supplying equipment higher than PoE Type 3 is being used

The vast majority of today's PoE applications deal with power delivery below 60W, and PoE Type 3 or lower. In these situations, LP cable isn't necessary.

How does temperature rise impact LP Cable?

Although LP cable is certified by UL as one that doesn't exceed its temperature rating under certain conditions, it's important to note: Regardless of the cabling - LP certified or not - if higher temperatures are introduced into the cable, the cable's reach is negatively impacted due to higher insertion loss at elevated temperatures. Even if it is LP certified, an LP cable may not reach its full 100m distance. The LP certification does not change this fact. To achieve the full 100m channel under maximum PoE conditions, cabling that has sufficient insertion-loss margin beyond the standard when measured at 20 degrees C - in order to still meet insertion loss requirements at the highest rated temperatures - must be used.

To learn more about the effects of temperature rise on cable – including LP cable – stay tuned for next week’s blog, where we’ll discuss the topic in more detail. Meanwhile, Belden is happy to answer any questions you have about LP cable. We can help you determine whether it is necessary for your application, and tell you more about Belden’s 10GXS LP cable solution. You can also learn more about our futureproof data center solutions here.