Delta VFD-ED Series, User Manual

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Appendix A. EMC Standard Installation Guide | VFD-ED
A-8
Lo
ng
P
E
Painted
sheet metal
HF
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
Equipment
Cable
Equipment
A B
Earth plane
Equipment
Cable
Equipment
A B
Earth plane
Cable
Very good
Good
Accompanying cable
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 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