udayraj121's Space http://udayraj121.posterous.com Most recent posts at udayraj121's Space posterous.com Sat, 24 Nov 2012 02:41:00 -0800 PAT Testing in-house: Cost savings http://udayraj121.posterous.com/pat-testing-in-house-cost-savings http://udayraj121.posterous.com/pat-testing-in-house-cost-savings

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If an establishment had 400 electrical items, this would result in an annual cost of about £1000 if this were to be contracted out. However, purchasing a PAT Tester for about £200 and having a firm understanding of the requirements, a comprehensive in-house safety strategy can be put in place. This will result in immediate savings. The option of renting a suitable PAT Tester costing about £75 a month, allows further cost savings.

Usually when one of these shorts occur, it is not immediately a hard short - meaning that initially the contact is intermittent and comes and goes. Every time the short occurs, the compressor torque drops sharply, the compressor may shudder a bit visibly as a result, and this shudder shakes the winding enough to separate the short. While the short is in place, the current through the shorted winding shoots up and a lot of heat is produced. Also, usually the short will blow some sparks - which produces acid inside the air conditioner system by decomposing the freon into a mixture of hydrochloric and hydrofluoric acid.


If it shorts to the housing, it will blow fuses and/or breakers and your ohmmeter will show a very low impedance from one or more windings to ground. If it does not short to the housing, then it will just stop. You still establish the type of failure using an ohmmeter.

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Sat, 24 Nov 2012 02:40:00 -0800 Combined Inspection and PAT Testing http://udayraj121.posterous.com/combined-inspection-and-pat-testing http://udayraj121.posterous.com/combined-inspection-and-pat-testing

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This again is carried out at pre-determined intervals. For the checking of electrical safety, one will require a PAT Tester. There are many PAT Testers available but the ones with pass/fail indications are quite easy to use. All one has to do is plug the appliance into the tester, connect a test lead and press a button. The tester will carry out the required tests and indicate whether the appliance is safe or not.

When a compressor fails short, what happens is that insulation on the wires has worn off or burned off or broken Very Low Frequency AC Hipots. This allows a wire on a motor winding to touch something it should not touch - most commonly itself a turn or two further along on the motor winding. This results in a "shorted winding" which will stop the compressor immediately and cause it to heat up and burn internally.

Bad bearings can cause a failed short. Either the rotor wobbles enough to contact the stator, resulting in insulation damage that shorts the rotor either to ground or to the stator, or end bearing wear can allow the stator to shift down over time until it begins to rub against the stator ends or the housing.

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Sat, 24 Nov 2012 02:39:00 -0800 Formal Visual Inspections http://udayraj121.posterous.com/formal-visual-inspections http://udayraj121.posterous.com/formal-visual-inspections

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This is carried out at pre-determined intervals. It is quite straightforward and consists of visually inspecting the power cable, appliance and plug for any obvious problems and the results recorded. At this stage, it is important to open the plug and check that the wiring is sound. According to the HSE, this stage can result in more than 90% of potential problems being spotted. Some examples of faults that may be observed are shown below.

Users need to be encouraged to look critically for signs of possible hazard every time they use electrical equipment. This can be done easily by making everyone aware of what is considered to be bad practice. Primary Current Injection Test Set is one way of doing this. It is also good practice to introduce this as part of the induction process for new staff or at regular staff meetings.

Testing for a failed open compressor is easy. Pop the electrical cover for the compressor off, and remove the wires and the thermal limiter. Using an ohmmeter, measure the impedance from one terminal to another across all three terminals of the compressor. Also measure the impedance to the case of the compressor for all three terminals.

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Sat, 24 Nov 2012 02:39:00 -0800 Planning your PAT Testing http://udayraj121.posterous.com/planning-your-pat-testing http://udayraj121.posterous.com/planning-your-pat-testing

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The first step is to make an inventory of all the electrical appliances. For every item, one needs to work out the frequency of the maintenance checks, based on the method of protection (i.e. Class I or II), the degree of portability and the environment it is used in.

For example appliances that are handheld whilst in use, such as hair-dryers need to be inspected more frequently than a PC monitor that is moved rarely. An electric fire in a factory needs to be inspected more frequently than one used in an office.

It is essential to prepare a Test Record for each appliance. As the maintenance program is carried out, results and comments can be recorded here. This can be invaluable evidence if there is an incident concerning an appliance and a compensation claim is made.

On completing the maintenance, the appliance has to be labelled. This has to indicate the date that H V Testing Set has taken place and the date after which the appliance should not be used. Equipment that fails should be removed from use and marked appropriately.

Users need to be encouraged to look critically for signs of possible hazard every time they use electrical equipment. This can be done easily by making everyone aware of what is considered to be bad practice. A poster is one way of doing this. It is also good practice to introduce this as part of the induction process for new staff or at regular staff meetings.

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Sat, 24 Nov 2012 02:38:00 -0800 PAT Testing Regulations http://udayraj121.posterous.com/pat-testing-regulations http://udayraj121.posterous.com/pat-testing-regulations

The European High Voltage Testing Set Directive governs the manufacture or importation of electrical appliances. Compliance to this has to be declared and indicated by the display of the CE mark on the product. The responsibility for this lies with the manufacturer or the importer and is policed by the Trading Standards.

However, like cars, it is important to have a maintenance regime for electrical appliances. The Electricity at Work Regulations (1989) requires that electrical appliances be maintained so that they remain safe during use. The implementation of this is up to employers. The HSE or the local authority is responsible for the policing of this.

On completing the maintenance, the appliance has to be labelled. This has to indicate the date that testing has taken place and the date after which the appliance should not be used. Equipment that fails should be removed from use and marked appropriately.

 

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Sat, 24 Nov 2012 02:36:00 -0800 Design of electrical appliances http://udayraj121.posterous.com/design-of-electrical-appliances http://udayraj121.posterous.com/design-of-electrical-appliances

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If appliances that use mains electricity should develop a fault the consequences to the user can be lethal. In the design of electrical appliances steps are taken to prevent this. It is always possible for appliances to become faulty. However, the design precautions taken are such that a single fault will not result in any danger to the user.

On appliances that have large areas of exposed metal, say a PC or an electric fire, this metal is connected to the Earth pin of the mains plug. The idea is that if high voltages should develop within the PC due to a single fault, this cannot reach the user, as the whole unit is enclosed in a "safe" earthed case. This type of protections is known as Class I.

The other way of providing protection is by the use of two separate layers of Insulating Oil Testers. If a single fault resulted in the first layer of insulation being breached, then the second layer of protection is still available. This method is used in handheld appliances such as drills and hair dryers and is generally know as Class II.

Class II appliances are inherently safe and require less frequent testing. They are always indicated by the "double box" symbol.

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