For all protective conductors, including main and supplementary bonding conductors, electricians must perform continuity test using a lowreading ohmmeter. Earthing facts and terms you should always remember eep. If you need protective bonding, well bond the water and gas pipes to the main earth terminal in your home. In electric power distribution systems, a protective earth pe conductor is an essential part of the safety provided by the earthing system. Principles and testing methods of earth ground resistance. Protection against damage to property by fire and heat arising. The conductor that connects to the star point in a threephase system, or that carries the return current in a singlephase system, is called neutral n. This is a discussion of the basic principles behind grounding systems and how grounding is related to safety and the effective operation of circuit protection devices such as fuses and circuit breakers. Home electrical wiring includes 110 volt outlets and 220. Since the concern is low frequencies, it is resistance rather than inductance which determines the conductor impedance. Earth conductors are also referred to as earth or earth lines and are designated by the letters pe, which stand for protective earth.
Many pat testers nowadays do not have the ability to test an earth by applying 10 amps or 25 amps through the protective earth conductor it is our belief that. Main earthing conductors are to be minimum 120 mm2 or as otherwise required by. Electrical question about the pe or protective earth. Pme protective multiple earth pnb protective neutral bonding 0. Components of electrical earthing system earth continuity conductor or earth wire. Remember that this includes the main protective conductor and the earthing conductor. How electricians test continuity of protective conductors. The size of earth continuity conductor from 15hp to connecting point d is 12swg while for 2hp each motor, the conductor size would be 14swg. Description of earthing, and a look at some of the regulations applicable to it. When a fault occurs, current flows from the power system to earth. Voltimum the principles protective multiple earthing.
So, although the ground system had low earth ground resistance values when initially installed. Engineering data for copper and aluminum conductor electrical cables 102 hilltop road, ramsey, nj 07446 201. Johnston neca executive director, standards and safety 1 welcome to a neca webinar based on the national electrical code. Historically, some have traditionally favoured a higher test current of 25a or 10a originating from the iec 606011 requirements on the premise that it will best. Sep 03, 2019 the objective of the test is to measure the currents flowing through the protective conductor or the metallic parts of the earth. Exposed metal parts on class i equipment are connected to this earth wire. When appliances have high protective conductor currents, substantial electric shocks can be received from exposedconductiveparts andor the earth terminal if the appliance is not earthed. Both earth and main protective bonding conductors are 6mm, which i understand was typical back then. Earthing conductors which are defined in bs 7671 as a protective conductor connecting the main earthing terminal of an installation to an earth electrode or other means of earthing must be adequately sized particularly where buried partly in the ground, and be of suitable material and adequately protected against corrosion and mechanical damage. However, if the incoming supplies are at 11kv and the transformers are in the ownership of the user, the lv supplies may. Generally the protective earth system is also used as a functional earth, though this requires care. Where earthfault loop impedance measurement of the installation is carried out, this will remove the.
Protective conductor current pcc operating mode enables you to measure the current. The protective conductor touch current test is an alternative or complementary test to the insulation tests of section 15. Meaning that the neutral and protective earth is combined. It is measured between any accessible earthed parts and the earth pin of the plug.
The first step to verifying conductor shortcircuit protection is to calculate the shortcircuit current fault levels throughout the electrical system. Supports touch current and protective conductor current. Electrical installations level 3 pearson schools and fe colleges. Poor grounding contributes to downtime but a lack of good grounding is also dangerous and increases the risk of equipment failure. However the touch voltage will be limited by the connection to earth of the bonds and their resistance. Upgrading earth and bonding is gonna be tough as run up cavity and round the corner, i aint never gonna pull a new cable through without some demolition.
Again, an earthfault loop impedance test cannot be conducted before an installation. Its ability to conduct makes it possible to use it as a measurement reference. As commissioning involves the initial energising of an. Pat calculator earth continuity limit plugtest ltd. To measure the insulation resistance between live conductors and earth, the com. Connection to ground also limits the buildup of static electricity when handling flammable products or electrostaticsensitive devices. That part of the earthing system which interconnects the overall metallic parts of electrical installation e. But, if the area of a path for current is large enough, resistance can be quite low and the earth can be a good conductor. Measuring range including preset null values 2 resolution 10m. Distribution power systems may be solidly grounded, with one circuit conductor directly connected to an earth grounding electrode system.
Class i equipment is fitted with a three core mains cable containing a protective earth wire. Appliances with different work settings, such as a hair dryer, are often set to their highest setting during the test. The test is referred to as a low current, off power frequency injection test. It is most important that appliances with such high protective conductor currents are properly connected with earth before any supply is connected.
What is the difference between protective earth and a. They also have the greenandyellow colour combination, whereby both colours are reserved for this conductor type, and offer protective earthing for people and animals as well as electrical installations earth conductors in electrical installations are fitted. Principles of electrical grounding john pfeiffer, p. Abb protection books siemens ee basics schneider electric cts. The conductor wire, which is connected among different electrical devices and appliances like, distribution board, different plugs and appliances etc. The test current, commonly between 2 and 20 amps, causes an earth potential rise epr at the earth grid under test, where the voltage of the soil at the earth grid rises with respect to the surrounding area. Hi all, having a debate about the following regulation at work and wanted to know peoples thoughts. For all protective conductors, including main and supplementary bonding conductors, electricians must perform continuity test using a. Testing final circuits for zs could cause a current to flow in the parallel paths of metalic service pipes. The pe designates the termination for the protective earth or in our usa terminology the ground. A fault current ac voltage drop of less than 2 volts.
Only use the greenyellow dual colour if the conductor also performs the protective function the terms noiseless earth or clean earth must not be used 17. The protective conductortouch current test is an alternative or complementary test to the insulation tests of section 15. Effectively has no inductance or capacitance for fault currents. A practical guide to earth resistance testing weschler instruments. Even so, application of the formula will in many instances result in a protective conductor having a smaller csa than that of the live conductors of the associated circuit. Frameearth protection singlebusbar this protection scheme is basically an earth fault system which simply measures the fault current flowing from the switchgear frame to earth.
Basic electrical installation testing it is therefore important to have. The only tests that are required by the iet code of. For main equipotential bonding, there is no single fixed value of resistance above which the conductor would be deemed unsuitable. The next step is to check the shortcircuit current rating of wire and cable, based upon the calculated shortcircuit fault current available and the overcurrent protective device selected. Inspection of earthing arrangements and protective conductors. The sizing and hence resistance of the earth protective conductor will therefore be determined largely by the prospective fault current available from the rest of the system. What is the difference between protective earth and a ground. In practice when pat testing, measuring the actual resistance of the earth wire within the cable is impractical, therefore the r value is. The objective of the test is to measure the currents flowing through the protective conductor or the metallic parts of the earth. Debate in the medical industry on the most appropriate test current for checking the integrity of the protective earthing conductor of medical devices has been around for many years. In the first years of telegraphy, the earth was used as the conductor that completed the energizing circuit. Using a long test lead, test between the earth bar in the consumer unit and the cpc at each accessory point. They define this type of electrical system as a combined or c.
Opencircuit voltage 5v dc measuring current 200ma dc nominal accuracy. Personal protective grounding for electric power facilities. Reference earth neutral earth is that part of the earth, particularly the surface outside the area of influence of an earth electrode or an earthing system, in which there are no detectable voltages resulting from the earthing current between any two random points. Due to the high starpoint impedance, singlepole conductor to earth faults do not lead to an effectively flowing short circuit, but to an earth fault. Frame earth protection singlebusbar this protection scheme is basically an earth fault system which simply measures the fault current flowing from the switchgear frame to earth.
As the earth wire is known as the circuit protective conductor, this test is now referred to as the protective conductor current test. The earth is basically a huge chunk of iron coated with some melted metals and on top of that, saltwater and land again rich in minerals. Now i have looked at gn3 and also bs7671 page 158 notes under table 61. A 230v circuit containing a surge protection device is to be tested for insulation resistance and the device cannot be removed. Many pat testers nowadays do not have the ability to test an earth by applying 10 amps or 25 amps through the protective earth conductor it is our belief that this is a step backwards as far at pat testers, and safety, are concerned. Okonite 1 printed on post consumer paper 12017 okonite cables. Earth faults occur in isolated or compensated networks. Which earth continuity test is the right one to perform. Main earthing conductors are to be minimum 120 mm2 or as otherwise required by the particular section of the specification.
Over time, corrosive soils with high moisture and salt content and high temperatures can degrade ground rods and their connections. The test is usually performed when the equipment under test is running in its normal operating mode. A work area that is made an equipotential safe working zone by the application of personal protective grounds. Types of tests electrical equipment testing metrotest.
The basic understanding of an earthing protection system. For all protective conductors, including main and supplementary bonding conductors, electricians must perform a continuity test using a lowreading ohmmeter. Protective earthing conductor sizing calculation is based on a selected standard such as nfpa 70 nec section 250. What is the name of the protective conductor that connects the main earthing terminal of an installation to an earth electrode or other means of earthing provided by the distribution network operator. The supply neutral conductor, often referred to as a pen combined protective and neutral or cne combined neutral and earth conductor, is terminated at the distributors switchgear cutout where connection of the earthing conductor to the supply neutral is achieved by means of an internal link provided by the distributor. However, the fault current flowing in this way is, as a rule, much lower than that of a short circuit. The next step is to check the shortcircuit current rating of wire and cable, based upon the calculated shortcircuit fault. Actually, the earth is a relatively poor conductor of electricity compared to normal conductors like copper wire. A ct is mounted on the earthing conductor and is used to energize a simple instantaneous relay as shown in figure 41. Objectives of electrical earthing protective earthing.
The conductor that connects the exposed metallic parts of the consumers electrical installation is called protective earth pe. The earthing of low voltage networks in the uk is largely determined by the low voltage supplies. Select the circuit to be tested in the distribution board and remove the line conductor from the mcb. This seminar is the first in a short series of electrical grounding and bonding webinars presented by neca. On single phase supply systems, insulation testing is normally undertaken using a test voltage of 500 v. An earth ground connection of the exposed conductive parts of electrical equipment helps protect from electric shock by keeping the exposed conductive surface of connected devices close to earth potential, when a failure of electrical insulation occurs. Electrical question about the pe or protective earth connection. Your assessment of the earths potential being zero is a measure of conductivity.
As the earth wire is known as the circuit protective conductor, this test is. Continuity of protective conductors this test is to ensure that. How electricians test continuity of protective conductors eep. Size and price versus functionality is what the compromise has become. The earth does have many free ions possibly you meant to say electrons. Erection of earthing arrangements tnc, tns, tncs, tt.
General requirements for electrical earthing or grounding. The earth continuity test is a designed to test the resistance of the protective earth of an appliance andor the supply lead. Protective earthing pe conductor sizing software cable. This provides the earth connection, for functional reasons or due to the level of disturbance. Fusing occurs due to the heating effect of the test current the current flows, generating heat and the wire melts apart resulting in an open circuit. Earth is the term for the earth as a location and for the earth as material, e. The appliance is plugged into the tester and while 230v mains is being applied, the tester measures the current flowing through the earth wire. Erection of earthing arrangements tnc, tns, tncs, tt eep. If you already have protective bonding, our engineers check and certify that its up to scratch sometimes it can look like youre protected when youre not.
Before everything, a safe isolation procedure must be carried out. Where the r value is the resistance of the protective conductor earth wire within the supply cable. Should a fault develop inside the equipment and the exposed metal comes into contact with the mains, the earthing conductor will conduct the fault current to ground. What is the difference between neutral and ground wires. Engineering data for copper and aluminum conductor electrical. The only tests that are required by the iet code of practice are. In practice when pat testing, measuring the actual resistance. Connect the line conductor to the earth conductor for simplicity, connect it to one of the spare terminals on the earth bar.
Just been to a 1981 tncs installation to fit new cu. In the event of a damaged protective earthing conductor, where most strands are broken, a high current test may also detect the damage by fusing the cable. Protective multiple earth pme separate neutral earth. Also contains an example of calculating the minimum size of protective conductor. When the power company only brings over normally current carrying wires phase and neutral only, they call the neutral wire a pen conductor, because it is both a protective earth pe and a neutral n.
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