Ground Loops; Earthing Systems - Delta C2000 Series User Manual

If the grounding wire is too long, its inductance may interfere structure of the building or the control
cabinet and form mutual inductance and stray capacitance. As shown in the following figure, a long
grounding wire could become a vertical antenna and turn into a source of noise.

3.2 Ground Loops

A ground loop occurs when the pieces of equipment are connected to more than one grounding path.
In this case, the ground current may return to the grounding electrode via more than one path. There are
three methods to prevent ground loops
1. Use a common power circuit
2. Single point grounding
3. Isolate signals, e.g. by photocouplers
Cable
Equipment
A
Earth plane
In order to avoid "Common Mode Noise", please use parallel wires or twisted pair wiring. Follow
this rule and also avoid long wires, it is suggested to place the two wires as close to each other as
possible.

3.3 Earthing Systems

The international standard IEC60364 distinguishes three different earthing system categories, using the
two-letter codes TN, TT, IT.
The first letter indicates the type of earthing for the power supply equipment (generator or
transformer).
T: One or more points of the power supply equipment are connected directly to the same earthing
point.
I: Either no point is connected to earth (isolated) or it is connected to earth via a high impedance.
The second letter indicates the connection between earth and the power supply equipment.
T: Connected directly to earth (This earthing point is separate from other earthing points in the power
supply system.)
N: Connected to earth via the conductor that is provided by the power supply system
The third and forth letter indicate the location of the earth conductor.
S: Neutral and earth conductors are separate
C: Neutral and earth are combined into a single conductor
Equipment
Equipment
B
5
Good
Cable
Accompanying cable
A
Very good
Cable
Earth plane
Equipment
B