LTRN
0458 553 200
tag@ltrn.com.au
Different Equipment requires different tests. The types of equipment are listed below, followed by more detailed descriptions of the actual tests performed.
A class I appliance has a outer casing which is at least partly made of metal which is grounded. Examples include fridges, toasters, computers, some drills. Most things with metal casing.
For this equipment, the Earthing Continuity, Insulation and Leakage Current tests will be performed.
Class II appliances are double insulated and thus do not require a grounding wire to be connected. They may still have a grounding wire in the plug and even the cord, but it is not actually connected to the casing of the equipment. The casing of most Class II appliances is non conductive (plastic, wood etc).
All Class II appliances must either say "Double Insulated" or have the Double Insulated symbol (a Box within a Box) on the label. For some older equipment, these two were never present, but they are deemed class II by construction. We assess this exception on the basis of the age of the equipment and the cord which it uses to plug into the wall, if there is no grounding in the cord and it seems that it is the original cord, then the equipment was never intended to be grounded and thus must be double insulated
For Class II equipment, the Earthing Continuity Test need not be performed, since there is no Earthing to be tested. The Insulation and Leakage Current tests are performed.
All power leads and power boards (EPOD's - Electrical Portable Outlet Device) count as Class I equipment, since they are required to provide grounding to the devices which plug in to them. Although it is not required by AS/NZS3760:2003, the polarity of the cords is also tested (that is, the Active connects only to Active, Neutral to Neutral and Grounding to Grounding.) For power boards, each outlet is tested separately.
Some power boards (EPOD's) have surge protectors in them (MOV's) which turn off the equipment when voltage exceeding 'normal' voltage is applied. This protects expensive equipment from power surges through the mains due to lightning etc. Most of these surge protectors turn off the equipment when the voltage reaches around 260v, which can give false readings on some test and tagging equipment which test at 500v. At LTRN, we test most equipment at 500v as is the standard in AS/NZS3760:2003 (this is a substantially different type of power to a power surge, it will not damage your equipment), but also have the ability to test such Surge Protected Equipment at 240v, which is normal operating voltage for Australian outlets to ensure that we do not unnecessarily fail safe equipment.
Safety Switches, or RCD's (residual current devices), require higher testing than other equipment. Some Test and Tag companies are unable to test such equipment due to the expensive equipment and difficulty in testing. At LTRN we do test such equipment, but at a slightly higher cost than other equipment. These are tested with the RCD test as below
The design of Class I appliances is such that any electrical faults will be contained within the case. Since this case is made of Metal, the faults may connect live power to the case which, without grounding, will electrocute anyone who touches it. In order to prevent this, the casing is grounded, which means that all of the metal in the case is connected via a wire to the earth. This connection provides an easy path for the electricity to take. Since electricity always takes the path of least resistance, it is essential that this path contains less resistance than anyone who could possibly touch the equipment. It is also essential that this path contains so little resistance that if the equipment shorts out to the earth, it will blow a fuse due to the fast flow of electricity through the fuse.
A human being has variable resistance, but it will always be in excess of 1 million ohms. The resistance allowable between the earthing of Class I equipment and the Ground as around 3 Ohms, and the proportion of that allowed from the metal case to the plug on the cord is 1 ohm. This test ensures that the resistance is less than 1 Ohm.
The Insulation test ensures that there is very little connection between the Active / Neutral circuitry of an appliance and its casing. If there were this connection, it would cause the casing to become live, creating a very dangerous situation. The test ensures that the resistance is no less than 1 million Ohms, meaning that very little current passes between the Active / Neutral connection and the Casing.
In Class I equipment, this is easy to do, since the casing is also grounded (as per the first test) making the test a simple measurement from Active and Neutral to the Ground.
In Class II equipment, there is no grounding, so the connection must be tested between any exposed metal on the casing and any accessible conductive material (metal) on the casing of the appliance. This includes screws, bolts, some switches etc. At LTRN, we understand that sometimes plastic can become conductive, especially due to age around switches etc, and so we also test to ensure that there is high insulation provided by the plastic around danger areas.
Many Test and Taggers will only check this using a PAT (Portable Appliance Tester) which will test only one, single point on the equipment. Whilst LTRN does use a PAT, it also uses manual methods which can quickly test every bolt, screw, nut or exposed metal on the class II appliance. Just because one screw is safe does not mean that another hasn't pierced the live wire and become extremely dangerous.
Some equipment will not be able to be tested unless it is switched on and running. This third test actually runs the equipment and ensures that there actually is no current passing through the grounding wire or exposed metal (depending on the Class of the appliance)
The RCD test ensures that Safety Switches are working correctly within set limits. There are two tests which LTRN perform. The first creates a small short circuit which will not be noticed my most RCDs, then slowly increases the short circuit until the safety switch blows. This measures the current at which the switch blows. The second creates a large short circuit and measures the time taken for the switch to blow. The allowable values are determined by the type of RCD being tested. The other tests for class I equipment are also performed on RCD's