EMC Grounding Schemes

EMC Grounding Schemes

EMC Grounding Schemes is three type ;-

(a) Single Point Ground Scheme
(b) Multi Point Ground Scheme
(c) Hybrid Grounding Scheme 

(a) Single Point Ground Scheme 

• In case of single point ground all subsystem grounds are ties to single ground. This single ground point is tied to structural ground, signal ground, shield ground, AC primary and secondary power grounds. These individual ground planes from each subsystem are finally connected by the shortest path to the system ground point of reference potential.

Fie. 1. Single Point Ground Configuration 

• This is shown in Fie. 1. The intent in using a single-point ground system is to prevent currents of two different subsystems from sharing the same return path and producing common impedance coupling.
• This type of grounding scheme is suitable for low frequencies where physical length of the interconnections is less than operating wavelength. Major issue with these connections are faced in following situations:

1. Interconnecting cables are used, especially ones having cable shield with sources and receptors operating over a length more than /20.
2. Parasitic capacitance exists between subsystems, or equipments housing or between subsystems and the grounds of other subsystems.

Problems faced by Single Point Ground Scheme 

Fie. 2  Unintentional coupling between ground wires in a single point ground system 

• Three subsystems shown in Fie. 2 have the same source and is referred as the"daisy chain" or series connection method. This technique has the obvious problem permitting common impedance coupling between the grounds of the two subsystems.
•  This  underscores the need to be cognizant of the return paths for the currents where they are possible to determine. the parallel connection shown in Fig.2 is the ideal single point ground connection however dependent on the length of these connections.
• However, it, too, suffers from the disadvantage that the individual ground conductors will have certain impedance on the length of these connection.
• In a distributed system these connection wires may need to be lang if we strictly adhere to the single point ground system.
• Ground  wire having high impedance may negate their positive effect. Also the return current flowing through these wires may radiate efficiently other ground wires and produce coupling between the subsystems like cross talk.
• Hence creating radiated emission problem. The degree to which this occurs depends on spectral contents of the return signal. Higher the frequency of return signal, it radiate more which will result in high coupling that is more EMI Thus Single Point Grounding is rarely used in EMC grounding.

(b) Multi Point Ground Scheme

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