Solution To Emc: Grounding - Delta EB3000 Series User Manual

A-3 Solution to EMC: Grounding
The leakage current of an electronic equipment is conducted to ground via the grounding wire and the
ground electrode. According to Ohm's law, potential differences may arise when the electrode's
ground and the ground's ground resistance are different.
According to Ohm's law, the earth resistance for electrode and the ground are different; in this case,
potential differences may arise.
A-3-1 Protective Grounding & Functional Grounding
Please carefully read the following instructions if two types of grounding are applied at the same time.
Protective grounding is applied outside buildings and must have low resistance. On the other hand,
functional grounding can be applied inside buildings and must have low impedance.
The goal of EMC is to avoid any interference effects. Grounding for EMC can be distinguished by
frequency. For frequencies lower than 10 kHz, a single point ground system should be used and for
frequencies higher than 10 kHz, a multiple point ground system should be used.
Single Point Grounding: all signal grounds of all IT equipment are connected in series to form a
•
single reference point. This point can be grounded directly to earth; to the designated grounding
point or to the safety point that is already grounded.
Multiple Point Grounding: all signals of all IT equipment are grounded independently.
•
Hybrid Grounding: this type of grounding behaves differently for low and high frequencies. When
•
two pieces of IT equipment (A and B) are connected via a shielded cable, one end is connected
directly to ground while the other end is connected to ground via a capacitor. This type of
grounding system fulfils the criteria for high and low frequency grounding.
Floating grounding: the signals of all IT equipment are isolated from each other and are not
•
grounded.
DC current flows evenly throughout the conductor section. But AC current flows towards the
conductor's surface as frequency increases; this is called the "skin effect". It causes the effective
cross-section area to be reduced with increasing frequency. Therefore, it is suggested to increase the
effective ground cross-section area for high frequencies by replacing pigtail grounding by braided
conductors or strip conductors. Refer to the Figure A-5 below.
Appendix A. EMC Standard Installation GuideEB3000
A-7