| PVC, LSZH, and Polyurethane: Know your cable jacket choices |
When you need to buy bulk cable or cable assemblies, you're probably concerned about things like conductor AWG size, shielding for EMI/RFI, connector molding construction, gold plating on the connectors and, ultimately, will the signal get from point A to point B quickly and with minimum loss or distortion. That's a lot of factors to think about! So why would you spare a thought to the jacket that just goes around the conductors?
It turns out that the cable jacket can be much more important than you may think. Choosing the wrong cable jacket type can have implications in a range of things, from extending the life of your cable, to using the cable in the field, to basic health and safety. Fire Codes
Click here to see L-com's video on jacket flammability codes.
Click here for a .pdf tip explaining some of the different cable jacket types.
The most important aspect of any building or vehicle installation is how it impacts the safety of those working in and around it. In particular, you should consider how the cable will respond in the event of a fire. In most cases, a PVC jacket will be fine to use as a patch cord or for single in-wall runs. But when you have many cables running in a confined space, like a Plenum area of an office building, there are a couple of dangers with using PVC jackets.
The first danger is "leaping". In a typical building, one of the first defenses against a catastrophe when a fire breaks out is to control the fire and stop it from quickly spreading. However, PVC cable jackets burn very easily and fire can actually "leap" from room to room or from floor to floor simply by burning along the cables in the Plenum. For that reason, local and national building codes often require a Plenum rated jacket (sometimes called CMP, UL-910, or OFNP rated) which is self-extinguishing and will not allow the fire to burn along it.
The other danger is that PVC releases hazardous gasses when it burns. In a typical building with good fire exits, you can get out into the fresh air. But for confined aerospace, marine, and military applications, getting outside isn't always an option. In those cases, and in cases of rooms where it is not easy to get out quickly, you should always use a "low smoke zero halogen" cable (LSZH). Cable Corrosion
Another problem with PVC is that it can corrode over time in certain conditions. One is oil. PVC is a petroleum-based substance that will begin dissolving if coated with oil. As oil and grease is common in busy factories and industrial settings, the life of a cable used there can be drastically improved by specifically getting an oil-resistant jacketed cable, such as Polyurethane.
Another condition that may reduce the life of a cable is UV exposure. Cables that are installed where they may be in direct sunlight for extended periods of time will need to be replaced more often unless you pick a UV-resistant jacket. Again, Polyurethane is a good choice, or any of several similar compounds (like Polyethylene, etc). Cable Colors
The color of a cable jacket is not merely an aesthetic choice. One of the advantages of cables and patch cords is that they can be unplugged or re-plugged to suit future needs. However, that only works if you plug the right cable into the right jack, and when you consider that future needs might not occur until months or years after an installation, you can understand the headaches that will occur at drop points and in cluttered wiring closets if the layout isn't clear. The easiest way to prevent these headaches is to set up a color-coded system from the start. If you designated that blue cables always access the Ethernet, red cables for VoIP or phones, green cables for video security surveillance, etc., you will have a much easier time down the road. Introducing new black-jacketed PVC premium double-shielded