Beneficial Cat6 and 6a crosstalk reduction is due to tight twisting and added insulation, with Cat6a reducing crosstalk even more than its predecessor. The Cat6 cable standard resists crosstalk to a higher degree than Category 5e cable. Network Cables Patchcord Cable. Cat5e Interference Specifications In contrast to Cat5, enhanced Category 5 cable features improved crosstalk specifications.
Cat6 and Cat6a Crosstalk Reductions Beneficial Cat6 and 6a crosstalk reduction is due to tight twisting and added insulation, with Cat6a reducing crosstalk even more than its predecessor. Figure 44 — Ground in series resulting in conductive coupling.
The ground connection in series is very common because it is simple and economical. However, this is the ground that provides a dirty ground, due to the common impedance between the circuits.
When several circuits share a ground wire, the currents on a circuit that flow through the finite impedance of the common base line may cause variations in the ground potential of the other circuits. If the currents are big enough, the ground potential variations may cause serious disturbances in the operation of all the circuits connected to the signal common ground. This type of coupled noise exists because the conductor have finite impedance.
The effect can be elliminated or minimized by breaking the ground loops if any and enabling return to the ground. See Figure Figure 46 — Adequate ground and connections avoid conductive coupling.
When the EMI manifests itself in relation to the conduction path, the following technical artifices can be used to:. Some solutions based on galvanic insulation are effective for low and medium frequencies below MHz. Solutions based on high frequency filters are effective in frequencies above MHz.
See figure One of the main goals in projects is to keep all common signal return points at the same potential. With high frequency in the case of inverters up to MHz harmonics are generated by the commuting amplifiers and in these frequencies the ground system looks more like an inductor and capacitor series than a low resistance path.
The use of mesh and twists instead of wires short wires are better for high frequencies for connection at the grounding points are more effective in this case.
Another important goal is to minimize the magnetic coupling between circuits. This is generally obtained by minimum cable separation and cable segregated routing. The radio-frequency coupling is minimized by adequate shielding and grounding techniques. The transients surges are minimized with line filters and power suppressors on the colis and other inductive loads.
A non-technical dictionary defines ground as a point in contact with earth, a common return in an electric circuit and an arbitrary point of zero voltage potential. To ground or connect some part of an electric system or circuit to earth ensures personal safety and, generally improves the circuit work. The grounding systems must execute several simultaneous functions: how to provide personal and equipment safety.
In short, below is a list of basic grounding systems functions:. The neutral conductor is normally insulated and Power supply system used is the TN-S T: point directly grounded, N: masses connected directly to the power supply point grounded, S: distinct conductors for neutral and for protection. The protection conductor basically conducts the mass current to earth. All of housing must be connected to the protection conductor.
The equipotential conductor must work basically as a potential reference for the electronic circuit. Each edification must receive a main equipotentializacion, and the installation located on the same edification must be connected to the main equipotentialization, hence to the same and only ground electrode.
See figures 49 and Functional equipotentialization equalizes grounding and ensures good signal circuits work and electromagnetic compatibility. Figure 50 — Ground and Potential Line in Installations. Figure 51 —Equipotentializing Material. Note figure 52, where there is a generating source of high tension and high frequency noises and a measuring system 25 m far from the control room, and, depending on the signal conditioning, there may be up tot 2.
As long as shield, ground and equalization conditions improve, the ideal situation for measurement is reached.
Figure 52 — Example of how important are grounding and equipotentialization and their influence on signal. In distributed systems, like in industrial process control, whose areas are separated physically and powered by multiple sources, the rule is to have a ground system in each location and the EMI control techniques applied in each signal direction path, as shown on figure Inadequate or even bad grounding may impair more than just equipment safety.
The main effects of inadequate grounding are electrical shocks to users by contact, slow or intermittent response from the protection systems fuses, circuit breakers, etc. The consequence is that the equipment with metallic housings stay exposed to noise on the ground circuits power and lightning. To meet safety requirements, lightning protection and EMI, the ground system should be a zero-impedance plan, whose combination of different current levels would be free from interference.
In other words, this is an ideal condition, which, however, is not confirmed in practice. It is common that AC primary power supply present peaks, surges, spikes that degrade the AC ground. They tipically work as Faraday cage in protection against lighting. However, the circuits are almost always connected to the earth to prevent shock risks.
This system may be seen on figure 53, where the striking feature is a single ground point distributed to the entire installation. Figure 53 — Single-point ground. This configuration is most adequate for low-frequency spectrum and also meets perfectly well the needs of high frequency electronic systems installed in small areas.
Furthermore, this system must be insulated not to work as return path for signal currents, which should circulate through signal conductors with balanced pairs, for example. This parallel grounding eliminates the problem of common impedance, although being detrimental to a big pile of cabling. In addition, the impedance on each wire can be too high and the ground lines can become sources of noise to the system.
This king of situation can be minimized by choosing the right conductor type AWG Cables of larger gauges help reduce the ground resistance, as long as the flexible wire reduces the ground impedance. For high frequencies, the multipoint system is the most adequate, as shown on figure 54, inclusive by simplifying the installation. Multipoint ground systems that use balanced circuits do not show noise problems.
In this case, the noise is filtered and its field is kept between the cable and ground plan. Figure 58 — Degradation on single-point grounding with interconnections and parasitic capacitances. Figure 57 shows an adequate ground whose individual currents are conducted to a single grounding point. Serial connection to ground is very common because it is simple and economical.
However, this grounding provides a dirty ground, due to the common impedance between the circuits. When several circuits share a ground wire, the currents on a circuit flowing through the common finite impedance of the base line can cause variations on the ground potential of the other circuits.
If the currents are large enough, the ground potential variations can cause serious disturbances in the operations of all the circuits connected to the common signal ground. Figure 59 — Inadequate, weather-exposed ground, oxidation and increase of impedance on the ground contact put the system at risk. Modern electronic systems rarely have only one ground. To mitigate the interference, like the common-mode impedance coupling, etc.
Finally, these individual points on each sub-system are connected to the single ground system, where there is the total potential reference of the system. A grounding loop occurs when there is more than one grounding path, generating undesirable currents between these points. These paths form the equivalent to an antenna loop that captures interference currents with high efficacy.
The great majority of field equipment manufacturers, such as pressure, temperature transmitters, positioners, converters, etc, recommends local grounding for their products.
It is common that their housings have one or more ground terminals. When installed, the equipment housing is in contact with the structural part or piping and, consequently, grounded.
If the housing is isolated from any structure point, local grounding is recommended with the shortest possible connection with AWG 12 wire. In this case, be careful in relation to the difference of potential between the grounded point and the panel where the controller PLC is installed. Some makers recommend that the equipment floats, i. For micro-processed, digital communication equipment, some producers incorporate or enable surge or transient protectors.
They provide protection against peak currents and a low impedance path to the grounding point. Always verify the NBR standard for shielding and the connection with the equipotential system of intrinsically safe systems. An intrinsically safe circuit must float or be connected to the equipotential system associated with the classified area only on a single point.
The insulation level required except on one point must be projected to support V on the insulation test in compliance with 6. If this requirement is not met, the circuit should be considered as grounded at that point. More than one ground connection is allowed on the circuit, provided that the circuit is divided in sub-circuits galvanically insulated and each one is grounded at a single point. The shields must be grounded on a single point on the potential equalization conductor.
If necessary, for functional reasons, small ceramic type capacitors below 1 nF and for V are allowed to be installed as other grounding points, as long as the total capacitances do not exceed 10 nF.
Never install a previously installed device without an intrinsically safe system, as the protection zener may be burned and will not work properly on intrinsically safe areas.
Compliant with the IEC spec, to ground means to be permanently connected to earth through a sufficiently low impedance and sufficient conduction capacity to prevent any voltage that might result in equipment or personal damages.
Voltage lines with 0 Volt must be connected to the ground and galavanically insulated from the fieldbus bus. The purpose of grounding the shield is to avoid high frequency noises. Preferably, the shield must be grounded on two points, at the beginning and the end of the bus, as long as there is no potential difference between these two points, allowing the existence of loop current paths. In practice, when this difference exists, it is recommended grounding the shield at a single point, i.
The shield must completely cover the electric circuits through connectors, couplings, splices and distribution and junction boxes. Never use the shield as signal conductor. Always check the shield continuity until the last field equipment segment and analyze the connection and finishing, as the latter must not be grounded on the equipment housing. On classified areas, if it is not feasible the potential equalization between the safe area and the hazardous area, the shield must be connected directly to the ground Equipotential Bonding System only on the dangerous area side.
The IEC standard recommends complete insulation. This method is used mainly in the US and the UK. In this case, the shield is isolated from all grounds, except on the negative souce ground point or the intrinsic safety barrier on the safe side. The shield must be continuous since the beginning of the segment, passing by the junction and distribution boxes and reach the equipment.
This method has the disadvantage that it does not protect totally the high frequency signals and can generate communication intermittence, depending on the cable topology and length. In these cases, the use of metallic channels is recommended. Another complementary way would be to ground the equipment junction boxes and housings on a ground equipotential line on the non-safe side.
These grounds are separated from the safe side ones. Multiple-ground condition is also common, providing more effective protection on conditions of high frequency and electromagnetic noises.
This method is adopted in Germany and some European countries. The shield is grounded on the source negative ground point or on the safe side intrinsic safety barrier and, additionally,on the ground of the junction boxes and the equipment housing.
These are also grounded on the non-safe side. Another complementry condition would be grounding the ground wires in equipotential lines set, bonding the non-safe to the safe side. A simple method of determining the location of electrical interference is by using a portable battery-powered AM radio tuned to a quiet frequency at the lower end of the dial. You should hear static or a buzzing sound as you get close to the source of the interference. The closer you get, the more intense the static will be.
If you cannot locate the interference source in your own house, check with your neighbors to see if they also experience interference. The source may be in their home.
If you cannot determine the source of the electrical interference, contact the customer service department of your local power company. Most power companies will investigate the problem and take steps to correct it.
Transmitter interference Communication systems that transmit signals capable of generating interference include amateur radios, CBs and radio and television stations. Electrical interference and your TV In the presence of electrical interference, you may experience frozen images or intermittent audio while viewing over-the-air television programs.
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