Power line CDNs are typically characterized by the Equipment Under Test (EUT) parameters of voltage and current. The power line frequency is fixed so all other parameters are known. Testing on data and signal lines introduces another factor that must be considered, the data transmission type and speed. Basically there are two types of communication, balanced (symmetrical) and unbalanced (asymmetrical) as illustrated below:

Each method has qualities that determine application. For example, symmetrical cables are used typically in high speed communication such as Ethernet. Depending on the application, cables may be either shielded, to reduce external interference or unshielded.

Unsymmetrical communication is typically used for analog or low frequency digital communication. Some examples include RS-232, coaxial and centronics. Coupling requirements are line to line and line to PE.

Symmetrical lines are used for higher speed communication such as Ethernet, CAN bus, RS-422 and RS-485. All lines are surged with reference to PE.

Shielded cables used for unsymmetrical and symmetrical communication provide mechanical protection. Surge energy flows in the shield, not directly in the communication lines. Shielded cables do not require a special CDN, but should be tested using the method shown in IEC 61000-4-5 Figure 12. Both the EUT and Auxiliary Equipment (AE) are isolated from the power supply ground. The surge impulse is then applied directly to the EUT chassis and therefore to the cable shield. Coupling using an 18uF capacitor is recommended and these are built into every EMC Partner surge generator. 

A summary of the connection types and CDNs available from EMC Partner is shown below:

Examples of EMC PARTNER test equipment for the three applications are shown below:

1. Unsymmetrical communication with unshielded lines

These lines are tested according to IEC 61000-4-5 Figure 9. CDN-DATA-4L can be used for both Surge and Ringwave coupling.

2. Symmetrical communication with unshielded lines

These lines are tested according to IEC 61000-4-5 Figure 10 or 11. CDN-UTP8 ED3 can be used for Surge, Ringwave and 10/700us impulse testing on Ethernet lines up to 1000baseT.

3. Shielded Lines

Both unsymmetrical and symmetrical shielded lines are tested according to IEC 61000-4-5 Figure 12. An 18uF coupling capacitor is standard in all EMC PARTNER SURGE impulse generators.