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Polarisation index

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Polarisation Index.

The insulation resistance and polarization index tests of an electric motor or generator has been regarded as a useful tool in evaluating its windings for build up of dirt or moisture, deterioration of the insulation, fitness for high potential tests and suitability for further operation. IEEE Standard No. 43- 2000 covers how the producer should test, determining Insulation Resistance and Polarization Index in detail.

Polarisation Index,the better way to IR test. Insulation of the system prevents winding faults. The stator winding is generally designed to achieve asatisfactory service life of typically 20+ years. But it all depends on the enviroment of operation.Generally insulation is in the form of organic compounds that contains water as a part of chemicalmake-up. Excessive temperature rise dehydrates and oxidizes and makes the insulation brittle.Subsequently it disintegrates under vibration and shock.As the life of a generator or motor mainly depends on the insulation, the condition of the insulationshould be ascertained at a regular interval. Insulation Resistance (IR) and Polarization Index (PI) aretwo universally accepted diagnostic tests for insulation tests. These have been in use for more than 75 years.The IR test measures the resistance of the electrical insulation between the copper conductors andthe core of the stator or rotor. Ideally the value of this resistance is infinite since the purpose of theinsulation is to block current flow between the copper and the core. But in practice, it is not possible.However, the resistance should have a high value to avoid any appreciable leakage current. Lowervalue of IR indicates that the insulation has deteriorated.PI is a variation of the IR test. It is the ratio of IR measured after voltage has been applied for 10minutes (R10) to the IR measured after one minute (R1), i.e. PI = R10 / R1 A low value of PI indicates that the windings may have been contaminated with oil, dirt etc or absorbedmoistures. In the test, a relatively high DC voltage is applied between the copper conductor and thestator or rotor core usually between the winding and ground as the machine core & body aregrounded). By applying Ohm's law, IR (Rt) at time t is then, R1 = V / It V is the DC Voltage applied and It is the current flowing in the circuit. The characteristics of the insulation are such that the current. It is not constant and it varies with time.The purpose of measuring PI can be understood by knowing the flow of the different currents in the insulator. There are four currents in the insulator. There are fourcurrents that may flow when a DC voltage is applied to the winding. These four are: Capacitive Current (la) Conduction Current (IR) Surface leakage current (IL) Polarization current (Ip) Capacitive Current: Insulator behaves as a capacitor when a DC voltage is applied to a capacitor, a high charging current first flows and then it decays exponentially. The size of the capacitor and the internal resistance of the voltage supply, typically a few hundred kilo ohms, set the currents decay. In case of generator or motor windings, the current effectively decays to zero in less than 10 seconds. Since the capacitive current contains little diagnostic information, the initial IR is measured once the capacitive current has decayed. Hence the first IR measurement has been set as one minute to ensure that this current does not distort the IR calculation. Conduction Current: This current is due to the flow of electrons between the copper and the core. This is galvanic current through ground wall. Such a current can flow if the ground wall has absorbed moisture, which can happen on the older thermoplastic insulation systems. The current may also flow if there are cracks, cuts or pinholes in the ground insulation and some contamination is present to allow current to flow.This current is constant with time. With modern insulation this current usually is zero (as long as there no damage to the insulation). Surface leakage Current: This is constant DC current that flows over the surface of the insulation. It is caused by conductive contamination (oil or moisture mixed with dust, dirt, insects, chemicals etc) on the surface of the windings. This current is also constant with time. Polarization Current: Electrical insulation is hygroscopic in nature and presence of moisture will be there either in low quantity or in excess. Water molecules are very polar. When an electric field is applied across the insulation start absorbing electrons from the hydrogen molecules causing ionization of hydrogen. In other words, the molecules constituting water align in the electric field, just as magnetic field. The energy required to align the molecules comes from the current in the DC test voltage supply. This current is called polarization current. The water becomes completely polarized when the absorption of electron from hydrogen merging with oxygen is completed. Once the molecules are all aligned, the current stops. The approximate time for complete polarization is 10 minutes. That is why the IR is measured after 10 minutes of applying voltage. Now, the total current is the sum of all above currents, i.e.It = Ic + IR + IL+ 1pAs we have analysed, after one minute, lc is zero.So It (1 minute) = IR + IL + IpAs we have seen that, after 10 minutes, Ip is zero,So It (10 minute) = IR + IL PI= Ir + Il + Ip / Ir + Il = R10 / R1 Effect of Temperature on IR One may argue that by measuring argue that by measuring IR after one minute, one can diagnose the condition of the insulator. If it is less, the insulation will be considered to have been deteriorated.Unfortunately, just measuring IR has proved to be unreliable, since it is not tenable over time. The reason is that IR is strongly dependent on temperature. A 10°C increase in temperature can reduce IR by 5 to 10 times. When readings of temperature and insulation resistance are plotted on ordinary equally divided co-ordination, a curved characteristics is obtained. On the other hand if graph paper is used on which the insulation scale is laid out in logarithmic division, the graph becomes a straight line. Further, the effect of temperature is different for each insulation material and type of contamination. Although some temperature correction graphs and formulae are given in the IEEE-43 and some other books, they are acknowledged as being unreliable for extrapolation by more than 10°C. The result is that every time IR is measured at different temperatures, one gets a completely different IR. This makes it impossible to define a scientifically acceptable IR value over a wide range of temperatures. Importance of PI PI was developed to make interpretation of results less sensitive to temperature. PI is the ratio of two IR at two different times. Temperature of the winding does not rise during the test period of 10 minutes. So it is fairly assumed that both R10 and R1 are measured at same winding temperature. Then the temperature correction factor will be same for both cases and will be cancelled during the calculation of Pl. Thus PI is relatively insensitive to temperature. Further in the formula of PI, the polarization current is used as a 'yard stick' to see if the leakage and conduction currents are excessive. If these later currents are much larger than the polarization current, the ratio will be about one. It is known from the experience that, if PI is about one, leakage and conduction currents are large enough that electrical tracking will occur. Conversely, if the leakage and conduction current are low compared to polarization currents, PI will be greater than 2, and experience shows that electrical tracking problems are unlikely. Thus during test, if we see the decay in the total current or rise in the IR in the interval between 1 minute and 10 minutes, then this must be due to polarization current ( since the leakage and conduction currents are constant with time) which implies that the leakage and conduction currents are low.   Interpretation of Polarisation Index results PI Condition of item under test <1.0 Hazardous 1 - 1.5 Bad 1.5 - 2.0 Doubtful 2.0 - 3.0 Adequate 3.0- 4.0 Good > 4.0 Excellent   If a very high initial IR reading >5GΩ is found then further PI tests are not needed.  

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Frequently Asked Questions

Please see the Electrical Testing menu above for a complete description of Electrical Testing & safety in the place of work and in your home .In particular how and why we test the way we do. We are situated on the Kent, Sussex and Surrey borders.This electrical testing site has been designed and built by GadSolutions and is hosted on one of their servers.

You should be aware that to do the electrical testing the entire installation needs to be de-energised for 5 minutes (do you have a server?). Each circuit while it is being tested needs to be de-energised while the test takes place. Except for production lines normal businesses can carry on with minimal disruption

We can usually offer a very quick service if it is required with night time working if day time access is limited due to business requirements. We work weekends if it is required, and can liaise with production staff if a maintenance shut down is planned.

Read more: Polarisation index

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The electricity at work Regulations

Complete electrical testing services.

The electrical safety testing Company

Electricity at work Regulations.

Electricity at work regulations,statutory requirements. Electricity at Work Regulations 1989 (EAWR) places a legal responsibility on employers and employees, as duty holders, to ensure that electrical systems used at work under their control are safe. Legal Requirements

To achieve compliance with the legal requirements of the Electricity at Work Regulations 1989 requires proof that an electrical system is safe, which involves amongst other things, proper inspection and testing of a system by competent people and the creation and maintenance of records. Electricity at Work Regulations 1989 is law in the United Kingdom. Electricity At Work Regulations 1989 (EAWR) The regulations as stated below are an overview of the UK regulations. For a comprehensive guide please refer to the latest version of the HSE document "Memorandum of Guidance on the Electricity At Work Regulations" - available from HMSO or technical bookshops. PART I INTRODUCTION Citation and commencement 1. These Regulations may be cited as the Electricity at Work Regulations 1989 and shall come into force on 1st April 1990. "approved" means approved in writing for the time being by the Health and Safety Executive for the purposes of these Regulations or conforming with a specification approved in writing by the Health and Safety Executive for the purposes of these Regulations; "circuit conductor" means any conductor in a system which is intended to carry electric current in normal conditions, or to be energized in normal conditions, and includes a combined neutral and earth conductor, but does not include a conductor provided solely to perform a protective function by connection to earth or other reference point; "conductor" means a conductor of electrical energy; "danger" means risk of injury; "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; "firedamp" means any flammable gas or any flammable mixture of gases occurring naturally in a mine; "injury" means death or personal injury from electric shock, electric burn, electrical explosion or arcing, or from fire or explosion initiated by electrical energy, where any such death or injury is associated with the generation, provision, transmission, transformation, rectification, conversion, conduction, distribution, control, storage, measurement or use of electrical energy; (a) any coal mine; or (i) there has occurred below ground an ignition of firedamp; or "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. (ii) more than 0.25% by volume of firedamp is found on any occasion at any place below ground in the mine; (b) any other mine in which- "safety-lamp mine" means- (a) a numbered regulation or Schedule is a reference to the regulation or Schedule in these Regulations so numbered; (b) a numbered paragraph is a reference to the paragraph so numbered in the regulation or Schedule in which the reference appears. Interpretation 2.—(1) In these Regulations, unless the context otherwise requires- (2) Unless the context otherwise requires, any reference in these Regulations to- (a) employer and self-employed person to comply with the provisions of these Regulations in so far as they relate to matters which are within his control; and (b) manager of a mine or quarry (within in either case the meaning of section 180 of the Mines and Quarries Act 1954 to ensure that all requirements or prohibitions imposed by or under these Regulations are complied with in so far as they relate to the mine or quarry or part of a quarry of which he is the manager and to matters which are within his control. (a) to co-operate with his employer so far as is necessary to enable any duty placed on that employer by the provisions of these Regulations to be complied with; and (b) to comply with the provisions of these Regulations in so far as they relate to matters which are within his control. Persons on whom duties are imposed by these Regulations 3.—(1) Except where otherwise expressly provided in these Regulations, it shall be the duty of every-(a) employer and self-employed person to comply with the provisions of these Regulations in so far as they relate to matters which are within his control; and (b) manager of a mine or quarry (within in either case the meaning of section 180 of the Mines and Quarries Act 1954 to ensure that all requirements or prohibitions imposed by or under these Regulations are complied with in so far as they relate to the mine or quarry or part of a quarry of which he is the manager and to matters which are within his control. (2) 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 any duty placed on that employer by the provisions of these Regulations to be complied with; and (b) to comply with the provisions of these Regulations in so far as they relate to matters which are within his control. PART II GENERAL Systems, work activities and protective equipment4.—(1) All systems shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger. (2) As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger. (3) Every work activity, including operation, use and maintenance of a system and work near a system, shall be carried out in such a manner as not to give rise, so far as is reasonably practicable, to danger. (4) Any equipment provided under these Regulations for the purpose of protecting persons at work on or near electrical equipment shall be suitable for the use for which it is provided, be maintained in a condition suitable for that use, and be properly used. Strength and capability of electrical equipment 5. No electrical equipment shall be put into use where its strength and capability may be exceeded in such a way as may give rise to danger. (a) mechanical damage; (b) the effects of the weather, natural hazards, temperature or pressure; (c) the effects of wet, dirty, dusty or corrosive conditions; or (d) any flammable or explosive substance, including dusts, vapours or gases, Adverse or hazardous environments 6. Electrical equipment which may reasonably foreseeably be exposed to-shall be of such construction or as necessary protected as to prevent, so far as is reasonably practicable, danger arising from such exposure. (a) be suitably covered with insulating material and as necessary protected so as to prevent, so far as is reasonably practicable, danger; or (b) have such precautions taken in respect of them (including, where appropriate, their being suitably placed) as will prevent, so far as is reasonably practicable, danger. Insulation, protection and placing of conductors 7. All conductors in a system which may give rise to danger shall either- Earthing or other suitable precautions 8. Precautions shall be taken, either by earthing or by other suitable means, to prevent danger arising when any conductor (other than a circuit conductor) which may reasonably foreseeably become charged as a result of either the use of a system, or a fault in a system, becomes so charged; and, for the purposes of ensuring compliance with this regulation, a conductor shall be regarded as earthed when it is connected to the general mass of earth by conductors of sufficient strength and current-carrying capability to discharge electrical energy to earth. Integrity of referenced conductors 9. If a circuit conductor is connected to earth or to any other reference point, nothing which might reasonably be expected to give rise to danger by breaking the electrical continuity or introducing high impedance shall be placed in that conductor unless suitable precautions are taken to prevent that danger. Connections 10. Where necessary to prevent danger, every joint and connection in a system shall be mechanically and electrically suitable for use. Means for protecting from excess of current 11. Efficient means, suitably located, shall be provided for protecting from excess of current every part of a system as may be necessary to prevent danger. (a) cutting off the supply of electrical energy to any electrical equipment; and (b) the isolation of any electrical equipment. Means for cutting off the supply and for isolation 12.—(1) Subject to paragraph (3), where necessary to prevent danger, suitable means (including, where appropriate, methods of identifying circuits) shall be available for- (2) In paragraph (1), "isolation" means the disconnection and separation of the electrical equipment from every source of electrical energy in such a way that this disconnection and separation is secure. (3) Paragraph (1) shall not apply to electrical equipment which is itself a source of electrical energy but, in such a case as is necessary, precautions shall be taken to prevent, so far as is reasonably practicable, danger. Precautions for work on equipment made dead 13. Adequate precautions shall be taken to prevent electrical equipment, which has been made dead in order to prevent danger while work is carried out on or near that equipment, from becoming electrically charged during that work if danger may thereby arise. (a) it is unreasonable in all the circumstances for it to be dead; and (b) it is reasonable in all the circumstances for him to be at work on or near it while it is live; and (c) suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury. Work on or near live conductors 14. No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless- Working space, access and lighting 15. For the purposes of enabling injury to be prevented, adequate working space, adequate means of access, and adequate lighting shall be provided at all electrical equipment on which or near which work is being done in circumstances which may give rise to danger. Persons to be competent to prevent danger and injury 16. 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. PART III REGULATIONS APPLYING TO MINES ONLY Provisions applying to mines only 17.—(1) The provisions of regulations 18 to 28 and Schedule 1 shall apply to mines only; and the provisions of that Schedule shall have effect in particular in relation to the use below ground in a coal mine of any film lighting circuit (as defined by paragraph 1 of that Schedule) at or in close proximity to a coal face. (2) Expressions to which meanings are assigned by the Mines and Quarries Act 1954 shall, unless the contrary intention appears, have the same meanings in regulations 18 to 27 and Schedule 1. Introduction of electrical equipment 18. Before electrical equipment (other than equipment approved for the purposes of regulation 20(1)) is first introduced into any underground part of a safety-lamp mine to which the Coal and Other Mines (Surveyors and Plans) Regulations 1956 apply, the manager shall submit to an inspector a copy of the ventilation plan required to be kept for that part by regulation 9 of those Regulations, on which the intended locations of that equipment shall be shown, together with a copy of any schematic diagram relating to that part prepared for the purposes of regulation 24(1). (a) equipment of a kind approved for that purpose; (b) equipment approved pursuant to regulation 20(1); (c) equipment the use of which was lawful in such zones immediately before the coming into force of these Regulations; (d) equipment which has received a certificate of conformity or a certificate of inspection in accordance with Council Directive 82/130/EEC on the approximation of the laws of the Member States concerning electrical equipment for use in potentially explosive atmospheres in mines susceptible to firedamp, as adapted to technical progress by Commission Directive 88/35/EEC: (e) equipment such as is specified in regulation 21(2); (f) equipment which is not capable of producing incendive electrical sparks in normal use; or (g) electrically-powered equipment not permanently installed in the mine but required occasionally for monitoring, testing, recording and measurement, and used where the concentration of firedamp is 0.8% by volume or less in accordance with suitable rules drawn up by the manager to ensure that danger will not thereby arise, which rules shall in particular include provision for personal supervision of that equipment by a competent person and testing for firedamp when it is in use; Restriction of equipment in certain zones below ground 19.—(1) At every safety-lamp mine containing any zones below ground in which firedamp whether or not normally present is likely to occur in a quantity sufficient to indicate danger, there shall be prepared a suitable plan identifying such zones. (2) Electrical equipment shall not be energised in such zones unless it is-and any lights which conform with this paragraph shall be permitted lights in any mine such as is specified in paragraph (1). (a) cut off the supply of electricity to any electrical equipment situated at the place where the said concentration was detected; or (b) (where this is not possible) take all reasonably practicable steps to make such equipment safe; or (c) (if the taking of the measures specified in sub-paragraphs (a) and (b) above does not fall within the scope of his normal duties) report the matter to an official of the mine who shall ensure that those measures are taken; Cutting off electricity or making safe where firedamp is found either below ground or at the surface 20.—(1) Where any person at a mine detects firedamp in a concentration exceeding 1.25% by volume in the general body of the air either below ground at that mine or at any place on the surface thereat where any exhauster in a firedamp drainage system is installed, firedamp is monitored or its heat content measured, he shall forthwith-except that the provisions of sub-paragraphs (a) to (c) above shall not apply if the electrical equipment is approved for the purpose of remaining energised in such circumstances or (in the case of a safety-lamp mine) is electrical equipment such as is specified in regulation 21(2). (2) If the supply of electricity to electrical equipment is cut off or the equipment made safe in accordance with paragraph (1), it shall remain in that condition until the senior official on duty at the mine having determined that it is safe to do so, directs that such precautions are no longer necessary. (3) If the supply of electricity to electrical equipment is cut off or the equipment made safe in accordance with paragraph (1), details of the time, duration and location shall be recorded. Approval of certain equipment for use in safety-lamp mines 21.—(1) Subject to paragraph (2), no electric safety-lamp, gas detector, telephone or signalling equipment or other equipment associated therewith or required for the safety of persons shall be taken or used below ground at any safety-lamp mine unless it is equipment which has been approved pursuant to regulation 20(1) or (in the case of electric safety-lamps) is of a type for the time being approved pursuant to section 64(2) of the Mines and Quarries Act 1954. (2) Nothing in paragraph (1) shall prevent the taking or use below ground at any safety-lamp mine of any electrical equipment which was, before the coming into force of these Regulations, approved pursuant to regulations 20 and 21A of the Coal and Other Mines (Electricity) Regulations 1956. Means of cutting off electricity to circuits below ground 22. At every mine at which electrical equipment which may give rise to danger is installed below ground and is supplied from a power source at the surface of the mine, switchgear shall be provided at the surface for cutting off the supply of current to that equipment, and adequate provision shall be made for the operation of that switchgear, including such means of communication as will, so far as is reasonably practicable, enable the switchgear to be operated in case of danger. Oil-filled equipment 23. Electrical equipment using oil as a means of cooling, insulation or arc suppression shall not be introduced below ground at a mine. (a) be prepared and kept in the office at the mine; and (b) show the planned settings of any circuit electrical protective devices. Records and information 24.—(1) Suitable schematic diagrams of all electrical distribution systems intended to be operated at the mine (other than those operating at a voltage not exceeding 250 volts) shall, so far as is reasonably practicable- (2) Copies of such portions of the schematic diagrams prepared pursuant to paragraph (1) as are necessary to prevent danger and which show at least those parts of the electrical system which are served by switchgear operating at a voltage in excess of 250 volts shall be displayed at each place where such switchgear is installed. (3) Plans on a suitable scale shall be kept in the office at the mine showing, so far as is reasonably practicable, the position of all permanently installed electrical equipment at the mine supplied at a voltage in excess of 250 volts. Electric shock notices 25. Where, at any place at a mine, electric arc welding is taking place or electrical energy is being generated, transformed or used at a nominal voltage in excess of 125 volts a.c. or 250 volts d.c., a notice shall be displayed in a form which can be easily read and understood and containing information on the appropriate first-aid treatment for electric shock and details of the emergency action to be taken in the event of electric shock. Introduction of battery-powered locomotives and vehicles into safety-lamp mines 26. No locomotive or vehicle which uses an electrical storage battery, either partly or wholly, as a power source for traction purposes shall be introduced below ground at a safety-lamp mine unless it is an approved locomotive or vehicle. Storage, charging and transfer of electrical storage batteries 27. At any mine in which electrical storage batteries are used below ground, those batteries shall, so far as is reasonably practicable, be used, stored, charged and transferred in a safe manner. Disapplication of section 157 of the Mines and Quarries Act 1954 28. Section 157 of the Mines and Quarries Act 1954 (which provides a defence in legal proceedings and prosecutions in certain circumstances) shall not apply in relation to any legal proceedings or prosecutions based on an allegation of a contravention of a requirement or prohibition imposed by regulations 18 to 27 or by or under Schedule 1. PART IV MISCELLANEOUS AND GENERAL Defence 29. In any proceedings for an offence consisting of a contravention of regulations 4(4), 5, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 25, it shall be a defence for any person to prove that he took all reasonable steps and exercised all due diligence to avoid the commission of that offence. (a) any person; (b) any premises; (c) any electrical equipment; (d) any electrical system; (e) any electrical process; (f) any activity, (a) the conditions, if any, which it proposes to attach to the exemption; and (b) any other requirements imposed by or under any enactment which apply to the case, Exemption certificates 30.—(1) Subject to paragraph (2), the Health and Safety Executive may, by a certificate in writing, exempt-or any class of the above, from any requirement or prohibition imposed by these Regulations and any such exemption may be granted subject to conditions and to a limit of time and may be revoked by a certificate in writing at any time. (2) The Executive shall not grant any such exemption unless, having regard to the circumstances of the case, and in particular to-it is satisfied that the health and safety of persons who are likely to be affected by the exemption will not be prejudiced in consequence of it. Extension outside Great Britain 31. These Regulations shall apply to and in relation to premises and activities outside Great Britain to which sections 1 to 59 and 80 to 82 of the Health and Safety at Work etc. Act 1974 apply by virtue of Articles 6 and 7 of the Health and Safety at Work etc. Act 1974 (Application outside Great Britain) Order as they apply within Great Britain. (a) the master or crew of a sea-going ship or to the employer of such persons, in relation to the normal ship-board activities of a ship's crew under the direction of the master; or (b) any person, in relation to any aircraft or hovercraft which is moving under its own power. Disapplication of duties 32. The duties imposed by these Regulations shall not extend to- Revocations and modifications 33.—(1) The instruments specified in column 1 of Part I of Schedule 2 are revoked to the extent specified in the corresponding entry in column 3 of that Part. (2) The enactments and instruments specified in Part II of Schedule 2 shall be modified to the extent specified in that Part. (3) In the Mines and Quarries Act 1954, the Mines and Quarries (Tips) Act 1969 and the Mines Management Act 1971, and in regulations made under any of those Acts, or in health and safety regulations, any reference to any of those Acts shall be treated as including a reference to these Regulations. Signed by order of the Secretary of State. Patrick Nicholls

In case you miss any information or just want to give us feedback, please feel free to contact us.

Frequently Asked Questions

Please see the Electrical Testing menu above for a complete description of Electrical Testing & safety in the place of work and in your home .In particular how and why we test the way we do. We are situated on the Kent, Sussex and Surrey borders.This electrical testing site has been designed and built by GadSolutions and is hosted on one of their servers.

You should be aware that to do the electrical testing the entire installation needs to be de-energised for 5 minutes (do you have a server?). Each circuit while it is being tested needs to be de-energised while the test takes place. Except for production lines normal businesses can carry on with minimal disruption

We can usually offer a very quick service if it is required with night time working if day time access is limited due to business requirements. We work weekends if it is required, and can liaise with production staff if a maintenance shut down is planned.

Read more: The electricity at work Regulations

  • Hits: 4050