PAT testing or portable appliance testing is an important part of any Health & Safety policy. This document is intended as a guide to both the legal implications and to the technical requirements.
The Health & Safety Executive states that 25% of all reportable electrical accidents involve portable appliances. The Electricity at Work Regulations place a legal responsibility on employers, employees and self-employed persons to comply with the provisions of the regulations and take reasonably practicable steps to ensure that no danger results from the use of such equipment. This in effect requires our implementation of a systematic and regular program of maintenance, inspection and testing.
The Health & Safety at Work Act (1974) places such an obligation in the following circumstances:
• 1. Where appliances are used by employees.
• 2. Where the public may use appliances in establishments such as hospitals, schools, hotels, shops etc.
• 3. Where appliances are supplied or hired.
• 4. Where appliances are repaired or serviced.
The level of inspection and testing required is dependant upon the risk of the appliance becoming faulty, which is in turn dependant upon the type of appliance, the nature of its use and the environment in which it is used.
The Institution of Electrical Engineers publishes the “Code of Practice for In-service Inspection and Testing of Electrical Equipment” (ISBN: 978-0-86341-833-4) . This guide forms the basis for portable appliance testing in the U.K.
The legislation of specific relevance to electrical maintenance is the Health & Safety at Work Act 1974, the Management of Health & Safety at Work Regulations 1999, the Electricity at Work Regulations 1989, the Workplace (Health, Safety and Welfare) Regulations 1992 and the Provision and Use of Work Equipment Regulations 1998.
The Health & Safety at Work Act 1974 puts the duty of care upon both the employer and the employee to ensure the safety of all persons using the work premises. This includes the self employed.
The Management of Health & Safety at Work Regulations 1999 states:
“Every employer shall make suitable and sufficient assessment of:
• (a) the risks to the health and safety of his employees to which they are exposed whilst at work, and
• (b) the risks to ensure the health and safety of persons not in his employment arising out of or in connection with the conduct by him or his undertaking.”
The Provision and Use of Work Equipment Regulations 1998 states:
“Every employer shall ensure that work equipment is maintained in an efficient state, in efficient working order and in good repair.”
The PUWER 1998 covers most risks that can result from using work equipment. With respect to risks from electricity, compliance with the Electricity at Work Regulations 1989 is likely to achieve compliance with the PUWER 1998.
PUWER 1998 only applies to work equipment used by workers at work. This includes all work equipment (fixed, transportable or portable) connected to a source of electrical energy. PUWER does not apply to fixed installations in a building. The electrical safety of these installations is dealt with only by the Electricity at Work Regulations.
The Electricity at Work Regulations 1989 states:
“All systems shall at all times be of such construction as to prevent, so far as reasonably practicable, such danger.”
“As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as reasonably practicable, such danger.”
“‘System’ means an electrical system in which all the electrical equipment is, or may be, electrically connected to a common source of electrical energy and includes such source and such equipment”
“‘Electrical Equipment’ includes anything used, intended to be used or installed for use, to generate, provide, transmit, transform, rectify, convert, conduct, distribute, control, store, measure or use electrical energy.”
Scope of the legislation (ref EJM)
It is clear that the combination of the HSW Act 1974, the PUWER 1998 and the EAW Regulations 1989 apply to all electrical equipment used in, or associated with, places of work. The scope extends from distribution systems down to the smallest piece of electrical equipment.
It is clear that there is a requirement to inspect and test all types of electrical equipment in all work situations.
- The Health & Safety at Work Act 1974
- The Management of Health & Safety at Work Regulations 1999
- The Electricity at Work Regulations 1989
- The Provision and Use of Work Equipment Regulations 1998
Who is Responsible
The Provision and Use of Work Equipment Regulations 1998 (PUWER) requires, every employer to ensure that work equipment is suitable for the purpose for which it is provided, only used in the place and under the provisions for which it is provided. It also requires every employer to ensure work equipment be efficiently maintained and kept fit and suitable for its intended purpose. It must not be allowed to deteriorate in function or performance to such a level that it puts people at risk. This means that regular, routine and planned maintenance regimes must be considered if hazardous problems can arise.
Regulation 3 of the Electricity at Work Regulations 1989 recognises a responsibility that employers and many employees have for electrical systems.
“It shall be the duty of every employer and self employed person to comply with the provisions of the Regulations in so far as they relate to matters which are within his control”.
This requires training to be implemented at UKV and maintained at appropriate and regular intervals. We already have a PowerPoint presentation which is shown at 6 monthly intervals and at induction. We will extend the scope of the training in line with electrical hazards indentified in the workplace.
Portable Appliance Equipment
There are many European standards and guidance notes regarding portable appliances and equipment, though they do not establish a common and specific definition of such equipment. Even so, there does seem to be a consensus of opinion that such equipment is either hand held whilst being connected to the supply, or is intended to be moved whilst connected to the supply, or is capable of being moved without undue difficulty whilst connected to the supply.
It is usual for this equipment to be connected to the supply via a plug and socket; however, this is not a requirement for electrical equipment to be deemed portable or transportable. It is common to define a portable appliance by saying that it is ‘anything with a plug top on the end of it’. This is a mistake as it may mean that there are some appliances in the system that are never tested.
The National Association of Professional Inspectors and Testers (NAPIT) define a portable appliance as ‘any electrical item which can or is intended, to be moved whilst connected to an electrical supply.’
The IEE Code of Practice gives guidance on the various equipment types:
An appliance of less than 18kg in mass that is intended to be moved whilst in operation or an appliance which can easily be moved from one place to another, e.g. vacuum cleaner, toaster, food mixer, etc.
Movable equipment (transportable)
This equipment is either:
18 kg or less in mass and not fixed, e.g. electric fire.
Equipment with wheels, castors or other means to facilitate movement by the operator as required to perform its intended use, e.g. air conditioning unit
Hand Held equipment or appliances
This is portable equipment intended to be held in the hand during normal use, e.g. hair dryer
Stationary equipment or appliances
This equipment has a mass exceeding 18kg and is not provided with a carrying handle, e.g. refrigerator
This equipment or an appliance which is fastened to a support or otherwise secured in a specific location, e.g. bathroom heater
Appliances/equipment for building in
This equipment id intended to be installed in a prepared recess such as a cupboard or similar. In general, equipment for building in does not have exposure on all sides because one or more of the sides, additional protection against electrical shock is provided by the surroundings, e.g. built in electric cooker
Information technology equipment
Information technology equipment includes electrical business equipment such as computers and mains powered telecommunications equipment, and other equipment for general business use, such as mail processing machines, VDU’s photo-copiers
Assessing the frequency of testing
The Health & Safety Executive offers no absolute rules on the frequency of the testing and inspection of portable appliances. The Memorandum of Guidance on the Electricity at Work Regulations suggests that ‘regular inspection of equipment is an essential part of any preventative maintenance programme’, but no attempt is made to specify the intervals of time implied by the word ‘regular’. The reason for this omission is obvious; different situations require different measures in order to meet the requirement that the danger is prevented. The factors which affect the frequency of testing must be assessed by the duty holder who thereby makes the judgement.
In arriving at a judgement as to the frequency of testing, a duty holder is likely to assess the following factors:-
• 1. The environment – equipment installed in a benign environment will suffer less damage than equipment in an arduous environment
• 2. Users – if the users report damage as and when it becomes evident, hazards will be avoided. Conversely, if equipment is likely to receive unreported abuse, more frequent inspection and testing is required
• 3. The equipment construction – the safety of a Class 1 appliance is dependant upon a connection with earth of the electrical installation. If the flexible cable is damaged the connection with earth can be lost. Safety of Class 2 equipment is not dependent upon the fixed electrical installation
• 4. The equipment type – appliances which are hand held are more likely to be damaged than fixed appliances. If they are Class 1 the risk of danger is increased, as the safety is dependant upon the continuity of the protective conductor from the plug to the appliance.
Estimate of Risk Level
This is a simple calculation to give an estimate of the level of risk of items of electrical equipment.
Start with a BASE RISK of 0 POINTS then add:
• •2 points if the item is used in a wet or corrosive environment OR uses water or a corrosive substance in its operation. (e.g. Kettle)
• •2 points if it has a flexible supply cord that is subject to flexing OR that is subject to harsh treatment.
• •1 point if it has a heating element OR 240V electric motor.
If the sum is 2 points or more it is GROUP A, High Risk
If the sum is 1 point it is GROUP B, Medium Risk
If the sum is 0 points it is GROUP C, Low Risk
The IEE Code of Practice recognises four test situations.
• 1. Type Testing to an appropriate standard
• 2. Production testing
• 3. In-Service testing
• 4. Testing after repair
This document is limited in covering topics concerned with In Service Testing only.
This is the testing carried out as a routine to determine whether the equipment is in a satisfactory condition.
In-Service testing will involve the following:
• (a) Preliminary inspection
• (b) Earth continuity tests (for Class 1 equipment)
• (c) Insulation testing (Which may sometimes be substituted by earth leakage measurement)
• (d) Functional checks.
Electrical testing should be performed by a person who is competent in the safe use of the test equipment and who knows how to interpret the test results obtained. This person must be capable of inspecting the equipment and, where necessary, dismantling it to check the cable connections.
If equipment is permanently connected to the fixed installation, e.g. by a flex outlet or other accessory, the accessory will need to be detached from its box or enclosure so that the connections can be inspected. Such work should only be carried out by a competent person.
Who should carry out the Inspection and Testing?
The Electricity at Work regulations states that:
“No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger, or where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work”
The IEE Code of Practice states, those carrying out the inspection and testing must be competent to undertake the inspection and, where appropriate, testing of electrical equipment and appliances having due regard of their own safety and that of others. What should be considered is that the ‘danger’ to be prevented, includes not just the dangers which may arise during the testing procedure to the tester and others, but also the dangers which may arise at a later date as a result of using equipment which has not been effectively tested.
The tester must have an understanding of the modes of electrical, mechanical or thermal damage to electrical equipment and appliances and their flexes which may be encountered in any environment.
Training must include the identification of equipment and appliance types to determine the test procedures and frequency of inspection and testing. Persons testing must be familiar with the test instruments used and in particular their limitations and restrictions so as to achieve repeatable results without damaging the equipment or the appliance.
PAT Testing Training
All people involved in the PAT testing process need to be trained and competent to do so.
The Test Operative
The person undertaking the testing must be competent to inspect & test an electrical appliance in order to determine if it is safe to use based on the inspection and test results. Training will be required and must cover the following areas:
• Identification of equipment types
• Appropriate test procedures
• Frequency of inspection & testing
• Visual inspection
• Correct use of test instruments
• Record keeping
In most cases this will be the person doing the testing. This is the person responsible for formal visual inspections of the equipment. Training will be required in order to correctly visually inspect the equipment including checking the cable and the plug, including the internal wiring.
The Administrator / Duty Holder
Administrators have a legal responsibility to ensure that all electrical equipment in their charge is safe. Training may be required in order to understand their responsibilities. Training should include:
• Understanding of the IEE Code of Practice.
• Record keeping of the inspection and testing and repairs.
• Appropriate intervals for re-inspecting and re-testing.
• Interpret recorded test results and take appropriate action.
The person repairing Faulty Equipment.
The person responsible for repairing any faulty equipment must be trained and competent to do so. Equipment must be re-tested following the repair and record kept of the repair.
Users of the equipment should be able to check for obvious faults before switching on and using it. They must also know what to do if they find a fault. Training may be required.
Training and Qualifications
No specific qualifications are required to under take the PAT testing, rather that they must be competent to do so. However a City & Guilds 2377 – Inspection and Testing of Electrical Equipment, qualification is available. The City & Guilds 2377 course has been designed jointly by the IEE and City & Guilds.
A competent person is defined as – ‘A person possessing sufficient technical knowledge or experience to be capable of ensuring that injury is prevented.’
Formal visual inspections should only be carried out by persons competent to do so. The results of the inspection must be documented.
The following must be considered when carrying out the inspection
Suitability of the equipment/environment
The equipment should be assessed for its suitability for the environment or the nature of the work being undertaken. When the work environment is harsh or hazardous particular care needs to be taken when selecting the equipment and assessing the frequency of inspection and testing.
A check should be made to ensure the equipment is installed and is being operated in accordance with the manufacturers instructions. Notwithstanding the manufacturers’ instructions, the following are examples of items which should be checked:
• (a) Cables located so as to avoid damage
• (b) Means of disconnection/isolation readily accessible
• (c) Adequate equipment ventilation
• (d) Cups, plants and work material correctly placed to avoid spillage
• (e) Equipment positioned to avoid strain on cord
• (f) Equipment is being operated with the covers in place and any doors are closed
• (g) Indiscriminate use of multi-way adaptors and trailing sockets is avoided
• (h) No unprotected cables run under carpets
Disconnection of equipment
The means of isolation from the electricity supply must be readily accessible to the user, i.e. in normal circumstances it must be possible to reach the plug and socket without to much difficulty.
The condition of the equipment
Prior to the commencement of the users should be asked if they are aware of any faults and if the equipment works correctly. The following items need to be inspected:
• (a) The flexible cable
• (b) The socket outlet, if known
• (c) The appliance
• (d) The plug head
Some of the following checks may not be possible for equipment fitted with a non-rewirable plug
• (i) Check detachable power cords to Class 1 equipment incorporates a CPC
• (ii) Identify signs of overheating
• (iii) Internal inspection; cord security, polarity, connections
• (iv) If non-rewirable plug; cord security, burning odours
• (v) Correct size fuse fitted, BS marked, ASTA marked
• (vi) Security of plug cover
• (vii) Check the flexible cable connections and anchorage at the equipment, if practical
Electrical testing of portable equipment will involve the following:
• (i) Earth bond continuity tests
• (ii) Insulation resistance testing
• (iii) Functional checks
(a) Earth Bond Test (Class 1 equipment only):
Readings should show less than 0.1+R Ohms (where R is the resistance of the lead)
Tested at a current of 1.5 times the rating of the fuse and no greater than 25A for a period of between 5 and 20 seconds or with a short-circuit test current within the range 20mA to 200mA.
(b) Insulation Resistance Test:
The applied test voltage should be approximately 500 Vdc
• Class 1 heating equipment < 3kW 0.3M Ohms
• Class 1 All other equipment 1M Ohms
• Class 2 Equipment 2M Ohms
• Class 3 Equipment 250k Ohms
(c) Optional Tests:
Flash Test: No flashover or breakdown shall occur
Operation/Load test: Compare reading with stated details on nameplate
Earth leakage test:
• Class 1 Handheld Appliances 0.75mA
• Other Class 1 Appliances 3.5mA
• Class 2 Appliances 0.25mA
It shall be the duty of every employee while at work:
(a) to co-operate with his employer so far as is necessary to enable and duty placed on that employer by the provision of the Regulations to be complied with: and
(b) to comply with the provision of these regulations in so far as they relate to matters which are within his control.”
It has been seen that it is a defence under Regulation 29 of the Electricity at Work Regulations for a duty holder to ‘prove that he took all reasonable steps and exercised all due diligence to avoid the commission of that offence’. It seems clear that the most effective method by which a duty holder can prove this in court would be by producing records to convince the court that the defendant had acted within either the letter or the spirit of the law. Records are essential if a proper and organised system of testing is to be established.
The keeping of suitable records then is essential. They provide evidence for the defence in the event of a prosecution; more practically, such records enable the close monitoring of the equipment highlighting potential faults or adverse trends. They are also essential in forming an accurate assessment of the necessary frequency of testing. For example, if over a number of consecutive test cycles few or no failures were recorded then he duty holder may consider reducing the frequency of tests, obviously the converse may also apply.
Replacement of appliance flexes
For flexes to be protected by the fuse in a BS1363 plug there is no limit to their length, providing their cross-sectional areas are below:
Other considerations such as voltage drop may limit flex lengths. Smaller csa’s than those given are acceptable if flex lengths are restricted. However, for replacement purposes the above simplified guidance is appropriate.
The maximum lengths recommended for extension leads are not applicable to appliance flexes or cord sets.
For the convenience of users, appliance manufacturers have standardised on two plug fuse ratings- 3A & 13A and adopted appropriate flex sizes. For appliances up to 700W a 3A fuse is used, for those over 700W a 13A fuse is used.
A variety of fuse ratings (1A, 2A, 3A, 5A, 7A, 10A 13A common ratings in bold) are available.
The fuse in the plug is not fitted to protect the appliance, although in practice it often does this. Appliances are generally designed to European standards for use throughout Europe. In most countries the plug is unfused. If an appliance needs a fuse to comply with the standard it must be fitted within the appliance. The fuse in the plug protects against faults in the flex and can allow the use of a reduced csa flexible cable. This is advantageous for such appliances as electric blankets, soldering irons and Christmas tree lights, where the flexibility of a small flexible cable is desirable.
With some loads it is normal to use a slightly higher rated fuse than the normal operating current. For example on 500 W halogen floodlights it is normal to use a 5 A fuse even though a 3 A would carry the normal operating current. This is because halogen lights draw a significant surge of current at switch on as their cold resistance is far lower than their resistance at operating temperature.
Choosing Portable Appliance Testing Equipment
When you start looking for a portable appliance tester, the first thing you will notice is the large range you have to choose from. For simplicity we can place the PAT testing equipment in one of three distinct categories. The following is a guide to the different types, and highlights features to look for.
Simple PASS/FAIL types
PASS/FAIL or GO/NO GO, type testers give a simple pass or fail test result allowing no interpretation of the test data. These testers generally only carry out insulation and earth continuity tests. Most PASS/FAIL PAT testers do not have a selectable Earth Continuity test current.
The IEE Code of Practice states that the earth continuity of the appliance can be tested either:
A – With a current between 20-200mA while flexing the lead of the appliance or,
B – A current not less than 1.5 times the rating current of the appliance, and no greater than 25 amps.
If the earth circuit on an appliance is susceptible to corrosion such as those found in a fridge, washing machine, kettle or dryer then you should test these appliances with the higher earth current to ensure any potential corroded earth wires are suitably stressed. To test IT equipment the tester must be able to perform an earth bond test at the lower current of between 20 – 200mA
The disadvantage of this type of tester is that the high current types (usually 25A) are unsuitable for testing IT equipment and the low current types (usually 100mA) are unsuitable for testing general electrical appliances. A further disadvantage with all the PASS/FAIL type of testers is the earth bond pass limit is set, allowing no interpretation of the test result. The IEE Code of Practice requires the earth bond resistance to be no greater than 0.1 Ohms + the resistance of the cable. A tester with a set Earth Continuity limit of 0.1 Ohms will wrongly fail equipment with long leads or low csa that may have a higher resistance. Some testers avoid this by setting the limit higher, usually 0.3 Ohms, but these do not comply with the IEE Code of Practice and may still wrongly fail equipment.
PASS/FAIL testers have the advantage of being easy to use but have a limited practical use.
Manual PAT Testers
Manual PAT testers give much more functionality than the simple PASS/FAIL testers but do require a level of understanding to correctly interpret the test data. As well as the standard Insulation and Earth Continuity tests, many also carry out Earth Leakage and Load tests. Look for testers with selectable Earth continuity test currents enabling the testing of IT equipment.
Downloadable PAT Testers
For testing large amounts of equipment a testers that automates the process and has recording capabilities is more suitable. These testers are able to initiate a pre-programmed test sequence via a shortcut menu. Test data, including the overall PASS or FAIL result, is stored for downloading or printing out. These testers often have a bewildering amount of features, some of the important ones to look for are:
Multiple Earth Paths ability: It is important to choose a PAT tester with the ability to make accurate earth bond measurements, even when multiple earth paths exist. Most PAT testers can measure earth leakage over multiple earth paths, but this is not the same as checking the integrity of an appliance’s main earth. For example, consider the common office computer, which often has several other devices attached to it via a screened data cable – for example a printer, monitor or scanner.
An earth return path can still exist even if the earth bond wire in the cord of a computer is faulty.
If you buy a PAT tester that does not automatically cater for earth bond measurement under Multiple Earth Path conditions, the only way to ensure you are actually testing the earth bond of the computer is to disconnect it from all other ancillary equipment. The end result is an increase in test time, and a significant reduction in the number of tests you can do in a day.
On-board help: PAT testers can be complicated instruments and there is nothing worse than having to hunt for that ever-elusive manual. A PAT tester with on-board help that walks you through the tests and displays on-screen connection diagrams when you need them is a definite advantage.
Multiple Voltage Insulation Testing: With the advent of the EMC regulations in Europe, an increasing number of appliances have used filters to manage conducted emission problems. These surge filters can cause inconsistent test results with PAT testers that use a 500V insulation test. Buy a PAT tester with the option of a 240/250V insulation test.
110V Testing: If you intend on testing large amounts of 110V equipment look for a tester that is able to carry out a full Leakage and Load test at 110V. Most testers stating 110V testing are only able to perform sub-leakage tests on 110V equipment.
PAT Testing Labels
All equipment that has been tested and inspected must be clearly identifiable. This usually achieved by labelling the equipment with a PAT Testing label.
The label/sticker must contain the following
• Unique identification code to enable equipment to be indefinable
• The status of the equipment following the testing ie. PASS or FAIL
• The date the equipment was tested together with the re-test period or the re-test dat
The above information on the label is designed to enable the equipment to be easily identifiable even if several similar items exist within the same premises and also indicate to a non-technical user if the equipment is due for re-testing or should not be used.
Additional information contained on the label may include fuse rating, engineers initials, company name or logo.
Many modern PAT testers are able to read bar-coded labels and this is particularly suitable for the identification code. Barcodes should ideally contain both the barcode and the numerical number underneath.
Labels or stickers can vary in design but should be of suitable quality that they can readily stick to a variety of surfaces. They should also be durable and hard wearing to such an extent that they are capable of withstanding the period between testing without deterioration. The label should be positioned in a prominent position where it can be clearly seen.
Equipment failing the inspection and testing must be put beyond use and clearly labeled with a sticker indicating that it has failed.
RCDs are often known by other names, eg., earth leakage circuit breakers (ELCB) or safety switches.
An RCD is an electrical safety device specially designed to immediately switch the electricity off when electricity “leaking” to earth is detected at a level harmful to a person using electrical equipment. An RCD offers a high level of personal protection from electric shock. Fuses or overcurrent circuit breakers do not offer the same level of personal protection against faults involving current flow to earth. Circuit breakers and fuses provide equipment and installation protection and operate only in response to an electrical overload or short circuit. Short circuit current flow to earth via an installation’s earthing system causes the circuit breaker to trip, or fuse to blow, disconnecting the electricity from the faulty circuit. However, if the electrical resistance in the earth fault current path is too high to allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow to earth for an extended time. RCDs (with or without an overcurrent device) detect a very much lower level of electricity flowing to earth and immediately switch the electricity off.
RCDs have another important advantage – they reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. This is particularly significant in older installations.
How They Work
RCDs work on the principle “What goes in must come out”. They operate by continuously comparing the current flow in both the Active (supply) and Neutral (return) conductors of an electrical circuit.
If the current flow becomes sufficiently unbalanced, some of the current in the Active conductor is not returning through the Neutral conductor and is leaking to earth.
RCDs are designed to operate within 10 to 50 milliseconds and to disconnect the electricity supply when they sense harmful leakage, typically 30 milliamps.
The sensitivity and speed of disconnection are such that any earth leakage will be detected and automatically switched off before it can cause injury or damage. Analyses of electrical accidents show the greatest risk of electric shock results from contact between live parts and earth.
Contact with earth occurs through normal body contact with the ground or earthed metal parts. An RCD will significantly reduce the risk of electric shock, however, an RCD will not protect against all instances of electric shock. If a person comes into contact with both the Active and Neutral conductors while handling faulty plugs or appliances causing electric current to flow through the person’s body, this contact will not be detected by the RCD unless there is also a current flow to earth.
On a circuit protected by an RCD, if a fault causes electricity to flow from the Active conductor to earth through a person’s body, the RCD will automatically disconnect the electricity supply, avoiding the risk of a potentially fatal shock.
Examples of equipment recommended to be protected by a RCD
• • Hand held electric power tools, such as drills, saws and similar equipment.
• • Tools such as jack-hammers, electric lawn mowers.
• • Equipment on construction sites.
• • Equipment such as appliances which move while in operation, such as vacuum cleaners and floor polishers.
• • Appliances in wet areas such as kitchens, including kettles, jugs, frying pans, portable urns, food mixers/blenders.
• • Hand held appliances such as hair dryers, curling wands, electric knives etc.
• • Cord extension leads.
• Suggested testing intervals for portable RCD’s
- Type of environment in which equipment is used Push-button test(by user) Test for operation By an Electrician
- Factories, workshops and places of work of manufacturing, repair, assembly, maintenance or fabrication Daily, or before every use, whichever is the longer 12 months
- Other commercial environments with no special protection, e.g., laboratories, tea rooms, office kitchens, and health care establishments 3 months, or before every use, whichever is the longer 2 years
- Office environment where equipment is not subject to constant flexing of the supply cord 3 months 2 years
- Hire equipment Before each hire Before each hire
• Testing of non-portable RCDs on switchboards or inbuilt into socket outlets must be carried out on a regular basis. This includes both push button testing by the user and inspection testing for operation by an electrician. Unless operated from time to time, an RCD may “mechanically freeze” and not trip when required.
Push-button testing by the user only confirms satisfactory mechanical performance of the tripping mechanism of the RCD. It does not replace inspection testing for operation by a licensed electrical worker.
As non-portable RCDs are far less susceptible to damage than portable RCDs, they are not subjected to the same testing and inspection procedures. In the case of non-portable RCDs, push button testing is recommended at three monthly intervals.
• After tripping out, an RCD must be re-activated
Safe work practices – Managing electrical safety in the workplace
Employers must carry out a risk assessment to identify potential workplace electrical hazards and to access the likelihood of injuries from the exposure to these hazards. This will enable appropriate control measures to be implemented.
General precautions – Always ensure that:
• An accessible and clearly identified switch near each fixed machine to cut off power in emergency is provided.
• For portable equipment, socket-outlets are close by so that equipment can be easily disconnected in an emergency.
• Electrical equipment used in flammable/explosive atmospheres should be designed to stop it from causing ignition.
• Double adaptors and ‘piggy back plugs’ are not used.
• The wattage of all bulbs in light fixtures and lamps are checked to make sure they are the correct wattage. Replace bulbs that have a higher wattage than recommended to prevent overheating that could lead to a fire.
• Light bulbs and other equipment which could easily be damaged in use are protected. There is a risk of electric shock if they are broken.
• Suspect or faulty equipment is taken out of use, labelled ‘DO NOT USE’ and kept secure until examined by a competent person.
• Where possible, tools and power socket-outlets should be switched off before plugging in or unplugging.
• Equipment is switched off and/or unplugged before cleaning or making adjustments.
• There is provision for all equipment to be stored carefully, securely and safely.
• Workers using electrical equipment are trained and supervised.
• Electrical installations are safe e.g., by providing enough power outlets.
• Worn or frayed cords are replaced.
• Leads, wiring and cables are in good condition and in the correct position.
• PVC insulation tape should not be used to repair damaged cords. Have the cords replaced.
• Machinery is unplugged before cleaning.
• Enough socket outlets are providing – overloading socket outlets by using adaptors can cause fires.
• All connections to power points are made using the correct plugs.
• Isolating transformers and residual current devices (RCD) are used.
• The electricity supply is isolated from earth and has a voltage between conductors not exceeding 230 volts.
• No part of a crane, digger, excavator, drill rig or other mechanical plant, structure or scaffold is brought closer than 4 metres to an overhead line without the written consent of the powerline owner.
• Equipment suitable for the working environment is used, eg, cordless tools for wet and damp conditions.
• Electric risks can sometimes be eliminated by using air, hydraulic or hand-powered tools.
• The main board is locked and the switches are safe and identified.
An electric shock can occur upon contact of a human or animal body with any source of voltage high enough to cause sufficient current flow through the muscles or nerves. The minimum detectable current in humans is thought to be about 1 mA. The current may cause tissue damage or heart fibrillation if it is sufficiently high.
An electric shock is usually painful and can be lethal. The level of voltage is not a direct guide to the level of injury or danger of death, despite the common misconception that it is. A small shock from static electricity may contain thousands of volts but has very little current behind it due to high internal resistance. Physiological effects and damage are generally determined by current and duration. Even a low voltage causing a current of extended duration can be fatal. It should be noted, however, that Ohm’s Law directly correlates voltage and current for a given resistance; thus, for a particular path through the body under a particular set of conditions, a higher voltage will produce a higher current flow.
‘Let go’ current
With sufficiently high current there can be a muscular spasm which causes the affected person to grip and be unable to release from the current source. The maximum current that can cause the flexors of the arm to contract but that allows a person to release his hand from the current’s source is termed the let-go current. For DC, the let-go current is about 75 mA for a 70-kg man. For alternating current, the let go current is about 15 mA, dependent on muscle mass.
The perception of electric shock can be different depending on the voltage, duration, current, path taken, etc. Current entering the hand has a threshold of perception of about 5 to 10 milliamperes (mA) for DC and about 1 to 10 mA for AC at 60 Hz.
Tissue heating due to resistance can cause extensive and deep burns. High-voltage (> 500 to 1000 V) shocks tend to cause internal burns due to the large energy (which is proportional to the square of the voltage) available from the source. Damage due to current is through tissue heating.
A low-voltage (110 to 220 V), 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA. With DC, 300 to 500 mA is required. If the current has a direct pathway to the heart (e..g, via a cardiac catheter or other electrodes), a much lower current of less than 1 mA, (AC or DC) can cause fibrillation. Fibrillations are usually lethal because all the heart muscle cells move independently. Above 200mA, muscle contractions are so strong that the heart muscles cannot move at all.
Current can cause interference with nervous control, especially over the heart and lungs.
Issues affecting lethality
Other issues affecting lethality are frequency, which is an issue in causing cardiac arrest or muscular spasms, and pathway – if the current passes through the chest or head there is an increased chance of death. From a mains circuit the damage is more likely to be internal, leading to cardiac arrest.
The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-frequency AC tends to interfere more with the heart’s electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain. Generally, higher frequency AC current tends to run along the skin rather than penetrating and touching vital organs such as the heart. While there will be severe burn damage at higher voltages, it is normally not fatal.
It is believed that human lethality is most common with AC current at 100-250 volts, as lower voltages can fail to overcome body resistance while with higher voltages the victim’s muscular contractions are often severe enough to cause them to recoil (although there will be considerable burn damage). However, death has occurred from supplies as low as 32 volts.
Electrical discharge from lightning tends to travel over the surface of the body causing burns and may cause respiratory arrest.
Point of Entry
- Macroshock Current flowing across intact skin and through the body. Current travelling from arm to arm or between an arm and a foot is likely to traverse the heart and so is much more dangerous than current travelling between a leg and the ground.
- Microshock Direct current path to the heart tissue
Avoiding danger of shock
Current electrical codes in many parts of the world call for installing a residual-current device (RCD or GFCI, ground fault circuit interrupter) on electrical circuits thought to pose a particular hazard to reduce the risk of electrocution.
It is strongly recommended that people should not work on exposed live conductors if at all possible. If this is not possible then insulated gloves and tools should be used. Also, remember there can be a voltage potential between “neutral” wires and ground. The neutral wire from a high-wattage appliance will have nearly as much voltage potential to ground as its hot wire. However, even a low-wattage appliance isn’t safe against electrocution from its neutral wire.
If both hands make contact with surfaces or objects at different voltages, current can flow through the body from one hand to the other. This can lead the current to pass through the heart. Similarly, if the current passes from one hand (especially the left hand) to the feet, significant current will probably pass through the heart.
The recommended first aid for someone who had received a severe electrical shock has three major components
• Call for help
• Make sure the victim is no longer in contact with the electrical current source. Turn off all power if this can be done quickly.
• Check for breathing and heart beat and apply cardiopulmonary resuscitation, if necessary
PAT TESTING & PAT TESTING INFORMATION – UKV HEALTH & SAFETY
Martin Button – Managing Director