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What do you need to know to make sure a piece of electrical equipment is safe? There is a right and wrong way to test appliances. You can find information in the Standard AS/NZS3760:2010 which covers not only how to test but also the environment for frequency of inspection and testing which is now based around usage. Testing can be quick and easy if you have good equipment and the right training. What tests need to be done? The correct tests required to be carried out on your Class I or Class II appliance in the following order: Visual Inspection Earth Continuity Test Insulation Resistance Test Leakage Test Further tests have to be performed on leads, RCDs etc Before any testing can be carried out, we need to determin what type of equipment it is eg CLASS I (earthed) or CLASS II (double insulated). What does this mean : Class 1 Equipment Class 1 electrical equipment is equipment that relies on the Protective Earth and basic or single insulation for its safety - such items usually have quite a lot of exposed metal and are often quite heavy. Some examples of Class I equipment could be dishwashers/washing machines/irons/fridges/ electrical machinery/drill presses/saw benches/bench grinder etc, But some small appliances like hand drills, saws, plainer can also be Class 1. Modern hand held tools today are usually Class 2 This type of appliance is often referred to as an 'earthed' appliance Class II Equipment Class II electrical equipment relies on two effective layers of insulation. This type of appliance is often referred to as a 'double insulated appliance It will normally be marked with the doublebox symbol Note: Most modern electrical hand held equipment is Double Insulated but we must confirm this as part of our testing process. RCD (Residual Current Device) - an RCD is used for increasing electrical safety and is designed so that it will disconnect the power when the residual current (That’s current that could flow through the body) reaches or nears a preset value. For RCDs designed to protect people this figure must be less than 30 milliamps. Isolation Transformer - this is used for increasing electrical safety and is designed so that the two sets of windings (Coils) (the primary and secondary) are separated from each other by at least the equivalent of that required to achieve double insulation, thereby ensuring that the electricity from the secondary (output) side is isolated from earth. EPOD (Electrical Portable Outlet Device) - this is a multiple outlet device and will commonly be called a multibox in New Zealand or a power board in Australia. How to carry out the testing: The Visual Inspection (this test is carried out on all types of equipment) This is very important as approximately 90% of faults can be found by this inspection. The Visual Inspection is not just an check for broken parts; it basically everything about the appliance. The basic requirement is that it should be as it came from the manufacture when it was new. This part of the testing process may involve: Smelling Pulling on leads Tapping the appliance Check for cracks or holes, no missing screws or other components Shaking nothing is loose or broken Turning some part/s, any locks or retaining screws Checking by trying to see that retractable guards actually retract... and all manner of other things may be done to ensure that it is safe to operate. Then depending on whether the equipment is Class I or Class II the following tests are done: For Class 1 (earthed) equipment Earth Continuity Test - this may be done with an Ohm Meter or a Portable Appliance Tester (PAT). The Standard AS/NZS3760: 2010 requires that the resistance is less than 1 Ohm or alternately an electrical test current for PATs of 100mA to 25 Amps. Insulation Test/Leakage Test - a leakage test shall be done on appliances that have internal switching that is only activated when the equipment under test is powered at operating voltage. For equipment that does not have internal switching as above then a 500 Volt insulation test is an acceptable alternative. For Class II (double insulated) equipment Insulation Test or Leakage Test - a leakage test shall be done on appliances that have internal switching that is only activated when the equipment under test is powered at operating voltage. For equipment that does not have internal switching as above then a 500 Volt insulation test is an acceptable alternative. For Cord Extension Sets Earth Continuity Test Insulation Test or Leakage Test Cord extension sets with re-wireable plugs fitted need to also have, in addition to the above tests, a Polarity Check The Fittings (Plug & Socket) also must meet specific safety requirements For RCDs Earth Continuity Test Insulation Test or Leakage Test Trip Time Test - in addition to the above tests RCDs shall have a trip time test performed on them at the time period specified in Table 4 AS/NZS3760: 2010 Tests required in more detail: EARTH TESTING The difference between using a Multimeter and a PAT Tester with a high current earth bond capability is that a Multimeter does a Continuity Test where as a PAT Tester does an Earth Bond or Earth Integrity Test. The PAT test is far superior and will show up more faults. There is a VERY BIG DIFFERENCE between the two tests. Legally it is a requirement - but is it really necessary? Potentially the most dangerous appliances are Class I appliances (earthed appliances) eg microwave ovens/bench grinders and the like, but also in this category are extension leads. Class I appliances are designed to have an earth - this means that in the example of a hand held drill the metal body of the drill is connected to earth - literally to the ground via an earth conductor which goes right back to the building switchboard and then into the ground the building is sitting on. If this conductor is damaged anywhere then the consequences can be fatal. It is obvious therefore that this conductor needs to be tested. How can this be done properly? Unfortunately, most people believe they are carrying out the testing properly if they are using a Multimeter, but this types of instrument will not usually pick up an earth fault unless there is a complete break in the conductor. There is another type of tester available on the market that people, including many electricians, may not be aware of - it is called a Portable Appliance Tester or 'PAT' for short. The PAT is specifically designed to test electrical safety and does all the different tests necessary to ensure the electrical safety of the appliance and makes testing easy. IMPORTANT NOTE: Its very important to first ensure that the Earth is satisfactory before undertaking the Insulation Resistance Test Doing safety testing with just a Multimeter or similar type of instrument is NOT SAFE. An earth conductor substantially damaged or not there means that in a situation where a fault occurs the operator becomes the earth ie the operator becomes the means by which the active 230 Volts supply returns to earth - likely killing the person in the process!! It is essential that when an earth conductor is needed that it is able to pass the earth current required otherwise you or someone else will become the earth. You should by now be able to see the difference between an Earth Bond and Earth Continuity Test ie an earth bond test shows whether the earth conductor is in a satisfactory condition; whereas an Earth Continuity Test (100 milliamps or less) using Multimeters and the like will possibly only show the earth is connected, not its' condition. INSULATION RESISTANCE TESTING Insulation Resistance Tests must not be carried out using Ohmmeters or Multimeters because these meters only produce a small battery voltage in the region of 1.5 to 9 volts. This small voltage is insufficient to pressure test the insulation to expose any weakness in it and therefore is totally inappropriate for Insulation Resistance Tests. Insulation Resistance Testers and PAT Testers on the other hand are specifically designed to produce 500 Volts (or even greater voltage values for some applications) which places the insulation under stress. This test will indicate any weakness that may break down under normal use on the 230 Volt supply. Itis a requirement that the resistance measured by the Insulation Tester in this way should be not less than 1 Megohm (1,000,000 ohms) for an electrical appliance to pass this test. A practical example showing how a Multimeter or Ohmmeter is inappropriate to test the insulation resistance of an electrical appliance is detailed by the following example: A 230 Volt floor polisher has a partial insulation breakdown between the motor windings and the earthed metal case. The polisher when in use and at its normal operating temperature, causes the sub-circuit protective fuse to blow as a result of the insulation breaking down to the earthed metal frame. The polisher, when tested with an Ohmmeter or Multimeter, does not indicate the presence of a fault, as the meter voltages are so low that they do not stress the insulation and therefore do not reproduce the breakdown that occurs when the appliance is in use. However, testing the same polisher with an Insulation Resistance Tester producing an output of 500 Volts causes the insulation to break down under test, thereby indicating a low insulation resistance value and the presence of a fault path. NOTE: The importance of a sound low resistance earth continuity conductor is paramount to the safety of any electrical appliance that requires an earth. A test as described above would not achieve anything if the integrity of the earth were not first proven to be in good condition. Should the appliance have an open circuit earth continuity conductor, it would produce a high resistance test result, but in fact when the appliance was plugged in it would enliven the case and expose a potential shock hazard. Alternative Leakage Test as required AS/NZS3760:2010 LEAKAGE TESTING This test was first introduced in the 2003 version of the Standard and it can be used to replace the 500 Volt Insulation Test. The advantage a Leakage Test has over and above the 500 Volt Insulation Test is that the Leakage Test when carried out on an appliance at operating voltage ensures the whole of the appliances' circuitry is fully tested. The old 500 Volt Insulation Test would not fully test many appliances ie those with internal switching that required operating voltage to activate switches. Hence an appliance may test safe and not be, when tested with a 500 Volt Insulation Test. Some fatalities could have been prevented if a Leakage Test had been done instead of the 500 Volt Insulation Test. NOTE: A 500 Volt insulation test is an adequate test providing all of the appliances' circuitry can be tested using this method. RCD USE & TESTING Unfortunately we can all be careless around electricity -RCDs can give limited protection against a fatal shock An RCD is specifically designed to minimise the risk of a fatal electric shock when working with electricity. It is an electronicsensing device which constantly monitors the balance of the current flow in the live and neutral conductors to ensure that should even a minor leakage occur the RCD will switch off the power within 300 milliseconds (for personal protection RCDs) ie in less than the time of a single heartbeat -which could mean the difference between life and death. You need to remember the following: 1. When properly connected an electric current flows through the live wire on its way to the appliance and returns to the supply circuit via a neutral wire 2. If for some reason the current 'leaks' (through dampness, frayed wiring, faulty connections etc) the current will take the most direct path to earth - often through a persons' body. In this situation if the power is not disconnected instantly then there is a strong possibility that the person will die. 3. The path taken by the current also contributes to the severity of the electric shock. An electric shock that flows from the hand through the arms and to the chest will affect the breathing and heartbeat. 4. The greatest contributing factor to the severity of an electric shock is the exposure time to the current. An RCD cuts off the power in less than the time of a single heartbeat Testing an RCD can be done in 2 ways: 1. A push button test on the RCD, requires no test instrument but it is NOT A SAFETY TEST . 2. By the use of an RCD Tester, an RCD Tester is designed to check the trip current and trip time. Most RCD Testers can measure the trip time from 1 millisecond to 2000 milliseconds and the trip current which must not exceed 30mA or 10 mA for RCD that protects children, sick people or the elderly. Safer Site Appliance testing courses cover all of this information in detail and comprehensive handouts are provided along with practical hands on testing experience on real appliances. . These courses can certify you as a competent person to legally test appliances. Contact: Kerry Harris. 021 722493, Email : [email protected] Web www.safersite.co.nz