The Understanding of Ground (Electricity)

From Wikipedia, the free encyclopedia

In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.

Electrical circuits may be connected to ground (earth) for several reasons. Exposed metal parts of electrical equipment are connected to ground, so that failures of internal insulation will trigger protective mechanisms such as fuses or circuit breakers in the circuit to remove power from the device. This ensures that exposed parts can never have a dangerous voltage with respect to ground, which could cause an electric shock if a grounded person touched them. In electric power distribution systems, a protective earth (PE) conductor is an essential part of the safety provided by the earthing system.

Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor (see single-wire earth return).

For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a “ground” is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard.

The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles may be spoken of as having a “ground” connection without any actual connection to the Earth, despite “common” being a more appropriate term for such a connection. This is usually a large conductor attached to one side of the power supply (such as the “ground plane” on a printed circuit board) which serves as the common return path for current from many different components in the circuit.

A typical earthing electrode (left of gray pipe), consisting of a conductive rod driven into the ground, at a home in Australia. Most electrical codes specify that the insulation on protective earthing conductors must be a distinctive color (or color combination) not used for any other purpose.

The Significance of Grounding

Today people are beginning to understand the importance of a continuous grounding system. One of the most beneficial reasons is that it helps protect your home, electrical devices, and your family from electrical surges. With your system being grounded all of the excess electricity in the system goes to the earth ground, instead of into devices connected to your electrical system, such as a tv, computer, etc…

Your home may already face issues due to improperly trained electricians not connecting the ground wires on light switches, fixtures, and other devices. Your home may have been built and wired prior to a grounding system being required in your jurisdiction.

One of the biggest hazards is when a person has a home with a 3 prong dryer plug and they have a 4 wire dryer. They convert the dryer cord to a 3 prong and try to make that work, but they are only getting 220 volts when the dryer also needs a 120-volt leg to operate the control panel. If you use the designated ground wire for the Neutral you run a risk of fire and electrical shock. The Neutral is an insulated conductor while a ground wire is often just a bare copper wire. The Neutral carries any unbalanced load in the system which happens regularly. So as this unbalanced load energizes the bare ground wire, which has been bonded to the dryer. Now any and all of the unbalanced electrical energy will energize the dryer causing it to shock you. If your hands are wet, it can be very dangerous for you, if you have one hand on your washer, you have now completed a circuit which could really do a great deal of harm to you, your children, anyone using your dryer. Further, a lightning strike or a surge in your electrical system will fry your dryer.

The electrical system is a loop, power comes in on the Hot Leg (Ungrounded Conductor) and returns to the utility company on the Neutral Leg (Grounded Conductor), your electrical bill is the amount of electricity that does not return to the utility company. So if you have your unbalanced load going to the ground rather than returning to the utility company you have a higher electrical bill plus there is something called Ground to Earth Voltage. This is when voltage is sent to the ground (your yard) and energizes the yard, which can be deadly during a storm.

To protect your home and system add a grounding system to your home. On Receptacles in the house with just a 2 wire system, place a GFCI Receptacle at the front of the circuit and provide personal protection to all receptacles down line of the GFCI. Install a Surge protector at your panel for a whole house protection. Use point of use surge protection devices for electronic equipment, such as surge power strips for computer usage and a surge protection receptacle for devices such as a flat screen tv.

So while people are beginning to understand the importance of a continuous grounding system, electrical engineers and manufacturers have developed a means to protect you, your family, your electronic, and your home. You should have a qualified electrical contractor ensure that you have a properly grounded system.

Source: terrellelectric

Isolated Ground

From Wikipedia, the free encyclopedia

An isolated ground (IG) is a local ground connection used with a supply, one of the common earthing arrangements used with domestic mains supplies.

Isolated Ground Devices

Description

The primary reason for the use of isolated grounds (IG) is to provide a noise-free ground return, separate from the equipment grounding (EG) return. The EG circuit includes all of the metal conduit, outlet boxes, and metal enclosures that contain the wiring and must be grounded to provide a safe return path in case of fault currents. The IG provides an insulated, separate ground path for the ground reference in electronic equipment, such as computers, hospital equipment, and audio equipment. IG does not break ground loops, which can damage equipment like computers, printers, etc.. Interconnected computer equipment often benefits from single-point grounding.

Isolated grounding system for branch circuits

IG is only used with special equipment that require it. The IG is typically insulated and separate all the way back to the point of earth grounding rod outside of the building. The IG is NOT connected neutral or any other. Due to the installation of a separate, insulated conductor and the associated special outlets required, IG circuits are more expensive to install than standard power circuits.

Its main downside is that an insulated grounding connection has higher impedance than a non-isolated grounding connection, and no redundancy, so safety is reduced. Isolated ground receptacles are allowed in patient care areas, but only when installed outside the immediate patient care vicinity.

Domestic Supplies

Until the 1950s, isolated ground domestic mains supplies tended to have no Residual-Current Device (RCD) or Earth Leakage Circuit Breaker (ELCB), and too high a ground impedance to blow a fuse if a live-to-earth fault occurred. This could leave metalwork in the house live. The use of Residual Current Devices (RCDs) or formerly ELCBs with such installs solved this problem. Such installs are called EEBAD (Earthed Equipotential Bonding and Automatic Disconnection).

The British term for isolated ground is “IT”, from the French terre isolée.

Noise

An isolated ground, if installed correctly, can reduce some electrical noise. However, complete power conditioning and protection usually requires additional devices such as a surge protector or an uninterruptible power supply. If the receptacle is not installed correctly, it can create a dangerous installation.

Floating Ground

From Wikipedia, the free encyclopedia

Most electrical circuits have a ground which is electrically connected to the Earth, hence the name “ground”. The ground is said to be floating when this connection does not exist.

An example showing mains-powered electronic instruments with a floating ground.

Conductors are also described as having a floating voltage if they are not connected electrically to another non-floating conductor. Without such a connection, voltages and current flows are induced by electromagnetic fields or charge accumulation within the conductor rather than being due to the usual external potential difference of a power source.

Applications

Electrical equipment may be designed with a floating ground for one of several reasons. One is safety. For example, a low voltage DC power supply, such as a mobile phone charger is connected to the mains through a transformer of one type or another, and there is no direct electrical connection between the current return path on the low-voltage side and physical ground (earth). Ensuring that there is no electrical connection between mains voltage and the low-voltage plug makes it much easier to guarantee safety of the supply. It also allows the charger to safely only connect to live and neutral, which allows a two-prong plug in countries where this is relevant. Indeed, any home appliance with a two-prong plug must have a floating ground.

Another application is in electronic test equipment. Suppose you wish to measure a 0.5V potential difference between two wires that are both approximately 100V above Earth ground. If your measuring device has to connect to Earth, some of its electronic components will have to deal with a 100V potential difference across their terminals. If the whole device floats, then its electronics will only see the 0.5V difference, allowing more delicate components to be used which can make more precise measurements. Such devices are often battery powered.

An example showing mains-powered electronic instruments with a floating ground.
Thirdly, a floating ground can help eliminate ground loops, which reduces the noise coupled to the system. An example of such a configuration is shown in the image on the right. Systems isolated in this manner can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous. This is particularly likely if the floated system is near high voltage power lines. To reduce the danger of electric shocks, the chassis of the instruments are usually connected separately to Earth ground.

Safety

Floating grounds can be dangerous if they are caused by failure to properly ground equipment that was designed to require grounding, because the chassis can be at a very different potential from that of any nearby organisms, who then get an electric shock upon touching it. Live chassis TVs, where the set’s ground is derived by rectifying live mains, were common until the 1990s.

Exposed live grounds are dangerous. They are live, and can electrocute end users if touched. Headphone sockets fitted by end users to live chassis TVs are especially dangerous, as not only are they often live, but any electrical shock will pass through the user’s head. Sets that have both a headphone socket and a live chassis use an audio isolation transformer to make the arrangement safe.

Floating grounds can cause problems with audio equipment using RCA connectors (also called phono connectors). With these common connectors, the signal pin connects before the ground, and 2 pieces of equipment can have a greater difference between their grounds than it takes to saturate the audio input. As a result, plugging or unplugging while powered up can result in very loud noises in speakers. If the ground voltage difference is small, it tends to only cause hum and clicks.

A residual current device can be incorporated into a system to reduce but not eliminate the risks caused by a floating ground.

Ground Loop (Electricity)

From Wikipedia, the free encyclopedia

In an electrical system, a ground loop or earth loop occurs when two points of a circuit both intended to be at ground reference potential have a potential between them. This can be caused, for example, in a signal circuit referenced to ground, if enough current is flowing in the ground to cause two points to be at different potentials.

Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. The use of differential connections can provide rejections of ground-induced interference. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide.

Simplified circuit illustrating a ground loop.

Grounding System Tester

Megger Digital Ground Tester Overview

  • 2, 3 and 4 point testing
  • Stakeless or clamp-on testing option
  • ART (Attached Rod Technique) capability
  • Multiple, user selectable test frequencies
  • Resistance measurement range to 200 kΩ
  • IP54 rated
  • Warning indicators prevent test failure
  • Simple one button operation
  • Included leads, stakes, calibration certificate and rugged carry case
  • Optional earth testing kit (ETK) available

The DET4 contractor series includes

  • DET4TD2: Dry-cell battery powered basic 4-terminal tester
  • DET4TR2: Rechargeable battery powered basic 4-terminal tester
  • DET4TC2: Dry-cell battery powered 4-terminal tester with selectable test frequencies, greater measurement sensitivity and attached rod technique and stakeless measurement capability
  • DET4TCR2: Rechargeable battery powered 4-terminal tester with selectable test frequencies, greater measurement sensitivity and attached rod technique and stakeless measurement capability
  • Megger DET4TC2 and DET4TCR2 Digital Ground Testers

DET4TC2_DET4TCR2_Digital Ground Terster

  • Megger DET4TD2 and DET4TR2 Digital Ground Testers

DET4TD2_DET4TR2 Digital Ground Terster