P-NET shield connection
Cable shield is connected to ground in both ends of each cable.
The shield must be connected to ground (chassis) as close to the cabinet entrance point as possible. The shield is connected using a clamp or an EMC-safe cable gland (PG-gland) or other method that can ensure an efficient high frequency connection. The shield connection should cover as wide an area and have as low a resistance as possible. Never connect the shield to ground by a “pigtail” !
The ground connection is made be removing a short section of the outer jacket to reveal the shield for the connection. The end of the cable is routed to the terminals with it’s shield and jacked intact.
Connection of the cable shield in both ends of all cables may contradict the traditional method of bus cable grounding, which prescribed the cable shield to be connected to ground in one place only.
Based on extensive tests as well as practical experiences the method of grounding all cable ends has proved to increase the systems EMC properties and is recommended as the installation method.
When grounding both ends of the communication cables it must be ensured that each cabinet is efficiently grounded to avoid the communication cable shield to serve as potential equalization.
If a device is not connected to ground, a good connection must be ensured between the shield of the in-going cable and the shield of the out-going cable.
When bus cables with 2 x twisted pairs are used, the pair interconnecting ‘S’ terminals must be connected to ground in one point only. This avoids the ‘S’ reference potential to be free floating.
Exception to the rule:
If 4-WIRE P-NET devices or sections of 4-WIRE P-NET are connected to the same physically network, the ‘S’ terminal must NOT be connected to ground.