Shielding Ethernet Data from EMI/RFI
The typical Ethernet cable has four twisted pairs terminated to the eight pins in the clipped "RJ-45" (also, more correctly known as 8p x 8c connector) at either end. The cable used is commonly called "UTP", which stands for unshielded twisted-pair.
If there is an unshielded version, there must also be a shielded version right? That is correct. Today we'll look at STP, or shielded twisted-pair.
The Shielding Disadvantages
Shielding is not an automatic choice for every installation. Why? Because although shielding provides the protection that may be necessary for some environments, it also comes with some serious disadvantages.
The first is weight. A single-shielded Ethernet cable weighs on average about 12% more than an unshielded cable, and a double-shielded Ethernet cable weighs as much as 30% more. That doesn't mean much when you have a single 4oz cable. But what if your building has dozens or maybe hundreds of individual STP cables that run on ladders over a ceiling, under a floor, or behind walls? The combined weight from these cables could be such that they actually damage the rack.
The second disadvantage is flexibility. In permanent installs, this isn't so much of an issue, though you must be careful when pulling the cable through conduit. But in applications where the cable is attached to something moving, like a robotic arm, a swiveling camera, or tools used by manufacturing personnel, the shield can be a problem. A single foil shield can break and the sharp edges of the cut in the shield would grind against the insulation of the individual wires, eventually cutting into it and shorting it out. Your best bet is to get tight-extruded cables rated for continuous flexing to ensure the maximum lifespan over repeated cycling.
Shielding Options
There are several options available if you need a shielded cable for your Ethernet application:
- Single shield cables (sometimes called ScTP) have the lightest available shield.
- Double-shield cables usually have both a foil and braid shield and can provide better protection against EMI/RFI as well as reduce the chance of problems with frequent movement.
- High-flex industrial cables are shielded and built for continuous or high-flex applications, and also have special jacket materials to solve common industrial problems.
- Shielded IP67 rated Ethernet cables use a hood around the male connector that can screw onto the barrel around a female jack to ensure water and dust do not affect the connectors.
- Gigabit-speed and 10-gig speed shielded Ethernet cables provide maximum performance even in high EMI/RFI environments.
- Or if you'd prefer, make your own shielded Ethernet cable with our custom cable configurator!
