Principles of application of shielded cables

• The shielding of the external and internal cables of the control panel should always be connected to the main protective earth (with grounded frame of the control panel) only on one side of the cable.

• In metal control panels, the shielding of the external cables should best be connected on the input of the control panel with its grounded casing.

• In plastic control panels, the shielding of the external cables should be connected as close as possible to the control panel input with the grounded mounting plate.

• The shielding should be connected with its largest cross-section directly to the grounded surfaces of the control panel (or the mounting plate, etc.); if terminals are used, the shielding must first be unbraided, twisted and then directly connected to the terminals, with no other wires used.

• The shielding should never be connected using other wires.

Fig. 1. An example of connecting cable shielding in the control panel

Options:

1. The shielding of the external cable is connected to the ground via a metal grommet designed for the connection of the shielded cables, the outer shell of the cabinet and the protective terminal. This method is the most efficient, because it reduces to the minimum the interference radiated into the cabinet. Suitable bushings are supplied e.g. by the IES company (and cable glands by Progress MS EMV). The shielding of the internal cable is connected to the ground via metal clamps, mounting plates and protective terminals.

1. The shielding of the external cables is connected to the ground via a metal clamp, a mounting plate and a protective terminal. The shielding of the internal cable is connected to the ground via metal clamps, mounting plates and protective terminals. This method, or any other similar one, is suitable mainly for plastic control panels with a metal mounting plate.

2. Here is illustrated an inappropriate connection. Although the cable shielding is connected to the protective terminal, the wire connection degrades the shielding effectiveness and the long loop causes an introduction and radiation of electromagnetic interference into the control panel.