Specifications

15
Schneider Electric
Review
(continued)
Protection against penetration
Common mode currents coming from the outside must be evacuated by the earthing
network at the entrance to the site to limit potential differences between items of
equipment.
All conducting conduits (cables, conducting pipes, insulated pipes carrying
conducting fluids, etc.) entering a building must be earthed at the entry point by a
connection that is as short as possible.
Install lightning arresters at building entry points for:
b Power cables.
b Telecommunications cables.
b Signal cables (data, alarms, access control, video surveillance, etc.).
The effectiveness of such devices depends on how they are installed. Lightning
arresters (varistors, spark gaps, etc.) are connected directly to the electrical
switchboard ground or to the protected equipment. Connecting a lightning arrester
simply to earth, instead of ground, is ineffective.
If possible, install switchboards housing power, telecommunications and signal
circuit protection devices near the earth connection bar.
For data links between buildings, fibre optic
media are strongly recommended to totally
eliminate ground loop problems between
buildings.
E52279
01
N
02
03
Network
01
02
03
Shielding
isolating
transformer
Mains
cable
Upstream LV
lightning arresters
Switchboard ground
Transformer
ground
PE
Earth
Cabling Guidelines