Ground wires

Calculation of long-term interference voltages is involved with a multiconductor problem which, in contrast to the short-term interference that derives from a one-pole grounding short circuit, in this case is related to the superposition of alternating magnetic fields of all the conductors of one or several three-phase systems as well as the ground wire. 

It is hypothesized that one of two scenarios could have created the ignition. Possibly, the grounding rod was placed closer to the filter than previously, giving the conditions for a brush discharge between the filter and the grounding rod. It is also possible that the grounding rod wire was closer to the isolated drum than previously in this case a spark could have jumped between the drum and the grounding wire. 

In AC you have Power wire (Black), Grounding wire (White), Grounded wire (Green)... 

Approved lightning protection systems are the integrally mounted system, the separately mounted shielding system (mast type), and the separately mounted shielding system (overhead ground wire). Details of all of these systems are described in the Ref... 

If a noise current of 100 mA at 1 MHz is to find its way into the ground wire between the two devices, the noise voltage must be 2 V, which is enough to cause the devices to lose communication and perhaps even sustain damage, depending on the device sensitivity. This example is a simple situation consisting of only two devices however, hundreds and perhaps thousands of such devices or circuits might be present in an actual computer or communication data center. All these devices require a common reference from which to operate. This is accomplished by the use of the SRG. 

Wiring problems were found in the electrical panel supplying the computers, such as with the neutral wires in the ground terminal and ground wires in the neutral terminal. This configuration caused a portion of the neutral return current of the load... 

Conducted emission is a measure of the level of EMI propagated via a conducting medium such as power, signal, or ground wires. Conducted emission is expressed in millivolts (mV) or microvolts (pV). 

Common impedance noise. Common impedance noise is developed if there is an impedance in common to several devices. Consider the following example Fig. 8.3) The power supplies of two devices are connected as indicated in Figure 8.3a. They have part of the ground wire in common, which means that the potential of the ground terminal of each device is influenced by the current drawn by the other device. The voltage drop across the ground wire is due to its finite resistance. Figure 8.3b shows how to connect two instruments correctly. 

Naturally 220 V represents a greater hazard than 110 V. It should be kept in mind that the laboratory is often served with 220 V in a three-wire system, with 110 V each side of ground. If 110-V outlets are supplied with a ground wire and one side of the 220-V line, as much as a 220-V difference can be obtained in accidental contact between circuits plugged into outlets serviced by opposite sides of the 220-V line. 

The grounding wires should radiate away from the structure, be strip conductors and should not be bonded to the structure. The overhead wires should be far enough from the structure to eliminate side-flashing which was described earlier and the protective angles from the wires must cover the building structure. 

Figure 10. Electric field lines in the vicinity of an elevated grounded wire...

Ground wire from connector to rack-panel ground post... 

The grounding scheme was modified (Fig. 2) to alleviate the problems. Separate ground wires were run directly to each individual connector and then attached to the system ground bus by means of a heavy ground strap. Ground potentials were reduced to only a few millivolts and erratic operation w as eliminated altogether. 

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