By Cameron G. Clark: GE Specification Engineer. Contributed by GE Industrial Solutions
Do you know what an arc flash is?
If not, keep reading.
The goal of this article is to give the reader a basic understanding of what occurs during an arc flash incident, and an understanding of some of the terms used in qualifying the danger associated with such events.
What is an Arc?
Most of us are familiar with an arc. The dictionary describes an electric arc flash as “a luminous bridge formed in a gap between two electrodes”.
An Arc Flash occurs during a fault, or short circuit condition, which passes through this arc gap. The Arc Flash can be initiated through accidental contact, equipment which is underrated for the available short circuit current, contamination or tracking over insulated surfaces, deterioration or corrosion of equipment and, or parts, as well as other causes.
An Arc Flash event can expel large amounts of deadly energy.
The arc causes an ionization of the air, and arc flash temperatures can reach as high as 35,000 degrees Fahrenheit. This is hotter than the surface of the sun.
This kind of temperature can set fire to clothing and severely burn human skin in fractions of a second at a significant distance from the event. The heat can also result in ignition of any nearby combustible materials.
Arc Flash temperatures can also liquefy or vaporize metal parts in the vicinity of the event such as copper, aluminum conductors or steel equipment parts. This material rapidly expands in volume as it changes state from a solid to vapor, resulting in explosive pressure and sound waves. The pressure wave can knock workers off balance or off ladders and even throw them across the room against walls or other equipment.
The sound blast can cause eardrums to rupture resulting in temporary or permanent hearing loss. Molten metal can be sprayed by the blast throughout the vicinity. Solid metal debris and other loose objects, such as tools, can be turned into deadly projectiles by the explosion. The bright flash from the event can result in temporary or permanent blindness.
All of these will most likely result in equipment damage as well as personnel injury, and possibly death.
“An Arc Flash event can expel large amounts of deadly energy. The arc causes an ionization of the air, and arc flash temperatures can reach as high as 35,000 degrees Fahrenheit. This is hotter than the surface of the sun”
Code Description
Section 110.16 of the 2008 National Electrical Code requires that electrical equipment be marked to warn qualified personnel of potential arc flash hazards. In order to accurately evaluate the dangers associated with arc flash we must quantify the hazard. The measure, which has been developed to assess arc flash events, is incident energy. This is the energy measured on a surface at a specified working distance from the arc flash location.
For low voltage equipment this is 24 inches, and approximately corresponds to the arm length of a typical worker. The unit used to quantify this energy is cal/cm2. A value of 1.2 cal/cm2 results in 2nd degree burns to bare skin, and 8 cal/cm2 in 3rd degree burns. The incident energy is inversely proportional to the square of the working distance, and directly proportional to the available fault current and duration of an arc flash event.
Some of the other factors which affect incident energy of an arc flash event are the short circuit current available, both from the utility and at specific bus locations in the distribution system, cable size and length, the type of over current protective devices, and the settings of those over current protective devices. The device settings directly influence the duration of thefault for a given value of arc fault current. For this reason there is interest by many, these days, in a temporary second group of setting which reduce the time a breaker takes to clear a fault when a person is working on energized equipment. This can often reduce the hazard significantly. General Electric offers this capability in the Reduced Energy Let Through mode (RELT) of the Entelliguard® TU trip unit.
“Those involved with the design, implantation and evaluation of electrical distribution systems mush have an understanding of arc flash hazards and how to evaluate the hazards as well as minimize or mitigate the hazard to the electrical worker.”
Arc Flash Studies
In order to identify the specific arc flash hazard at a given piece of equipment within a facility, an arc flash study must be performed. There are several software packages available, similarly to short circuit study and coordination study software packages, to facilitate this analysis by a qualified professional electrical engineer. In order to perform the arc flash study a short circuit and coordination study must first be performed or the results of these studies must be available to the engineer performing the arc flash study.
The result of the arc flash study will categorize the hazard at specific equipment based on the incident energy, as well as identify the Arc Flash Protection Boundary (this is the closest approach allowed before PPE must be worn). Inside the Arc Flash Protection Boundary a worker must be wearing the proper clothing, or Personal Protective Equipment (PPE). The main objective of the PPE is to limit the burns to the body resulting from an arc flash event, to a survivable level. (i.e .2nd degree or less).
“Those involved with the design, implantation and evaluation of electrical distribution systems must have an understanding of arc flash hazards and how to evaluate the hazards as well as minimize or mitigate the hazard to the electrical worker.”
Hazard Risk Categories as outlined in NFPA 70E are as follows:
Hazard Risk Category
Clothing
Cal/cm²
0
Non-melting, flammable materials (ie untreated cotton, wool, rayon, or silk, or blends of these materials with a fabric weight of at least 4.5oz/yd²
N/A
1
FR shirt and FR pants of FR coverall
4 Cal
2
Cotton underwear – conventional short sleeve and brief/shorts , plus FR shirt and FR pants
Arc Flash Hazard is a subject that is undergoing increased discussion and scrutiny in today’s safety conscious environment. The intent of the standards in this area is to provide an increased level of safety for the electrical worker.
Those involved in the design, implantation and evaluation of electrical distribution systems must have an understanding of Arc Flash Hazards and how to evaluate the hazards as well as minimize or mitigate the hazard to the electrical worker.
Thorne & Derrick are national distributors of LV, MV & HV Cable Installation, Jointing, Substation & Electrical Equipment – servicing businesses involved in cabling, jointing, substation, earthing, overhead line and electrical construction at LV, 11kV, 33kV, 66kV and EHV. Supplying a complete range of power cable accessories to support the installation and maintenance of low/medium and high voltage power systems:
Thorne and Derrick are proud to be distributors of ProGARM arc flash coveralls and protection.
We can help – should you require arc flash calculators or advice on the type of clothing and protection available please do not hesitate to contact us.
“30,000 Arc Flash Incidents per year” Source: ISHN
Arc Flash Articles
Thorne & Derrick International would like to thank Pat Mynett for allowing us to publish his series of Arc Flash articles – over the course of these articles we have discussed the definitions, dangers, statistics, causes, prevention and protection against arc flash.
Pat is CEO at HV Training and Consulting Pty Ltd and is a High Voltage Specialist.
ProGARM are the leading UK manufacturer of high quality Arc Flash Clothing, Garments & Workwear – Thorne & Derrick work successfully with them Protecting Lives.
Thorne & Derrick are leading Specialist Distributors & Stockists of LV, MV & HV Cable Installation, Jointing, Substation & Electrical Equipment.
Thorne & Derrick International, based in the UK, distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Pulling & Installation Equipment – we service UK and international clients working on underground cables, overhead lines, substations and electrical construction at LV, 11kV, 33kV and EHV transmission and distribution voltages.
T&D, CATU Electrical Safety & Arc Flash Protection Specialists for SAP’s, Linesmen, Jointers & Electrical Engineers – Largest UK Stockist
INVITATION
Thorne & Derrick invite you to join LinkedIn’s largest LV-HV Electrical Discussion Group : Low & High Voltage Power, Cabling, Jointing & Electricals. Discussion subjects include cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV. Network, engage and promote your profile, company or products with over 10,000 influencers.
Arc Flash Inflicts Serious Electrical Burns- HSE Image Of Accident Scene
By Grant Prior for Construction Enquirer
Construction Enquirer is an online only magazine focusing on the latest news stories, contract opportunities and job vacancies – Completely Free.
Arc Flash
Two companies have been fined after a worker received serious electrical burns caused by an arc flash during demolition work.
Chelmsford Magistrates Court heard how on April 12 2017, two demolition workers employed by sub-contractor R B Haigh & Sons were removing electrical distribution equipment from a switchgear room at the former Molecular Products site in Thaxted, Essex.
Alan Banks had been told by the principal contractor that the electrical equipment had been isolated. To reassure his colleague that it was safe he threw a crowbar at the 400V ac equipment.
This came into contact with live exposed wires, causing a flashover and temperatures of several thousand degrees, followed by a subsequent fire.
As a result Banks suffered serious burn injuries and was immediately hospitalised.
An HSE investigation found that the task being undertaken had not been properly planned and suitable control measures were not implemented to ensure the isolation of the electrical power supply.
The principal contractor, A J Wadhams & Co Ltd failed to follow the clear procedures outlined in their risk assessments and method statements, which identified all equipment must be treated as live unless written authorisation proved otherwise.
Russell Haigh and Stuart Haigh (Partners of R B Haighs & Sons) of Thaxted, Essex, pleaded guilty to safety breaches and were fined £80,000 and ordered to pay costs of £3882.65.
AJ Wadhams & Co Limited trading as Wadham Homes of London also pleaded guilty to safety breaches and was fined £80,000 and ordered to pay costs of £3816.60.
After the hearing HSE inspector Adam Hills said “This incident has had a significant impact on Mr Banks life and the injuries could so very easily have been fatal.
“Had the companies followed the control measures outlined in their respective risk assessments, then this incident would not have occurred.
“Never assume that an electrical supply is disconnected. Always check with the Distribution Network Operator or a qualified electrician to obtain written proof of isolation before commencing work.”
ARC FLASH STATISTICS
30,000 Arc flash incidents per year
7,000 Burn injuries per year
2,000 Hospitalisations per year
400 Fatalities per year
“30,000 Arc Flash Incidents per year” Source: ISHN
How To Protect Yourself Against Arc Flash
Arc flash protection is provided by specialist clothing and garments for “head-to-toe” protection – everything from arc flash coveralls to arc flash trousers.
Enhanced and effective arc flash protection is safely achieved by wearing layers of protective clothing and garments manufactured from inherent fibres and which feature specific Arc Flash resilient components. Without the correct high-quality garments, arc protection levels will be compromised.
Guest Post By: Melissa Payne Marketing Executive at IPU Ltd
Industrial Power Units Limited offer arc flash protection systems for switchgear consisting of a protection relay and arc flash detection sensor. It is estimated that there are 8 to 10 arc flash incidents every week in the UK with switchgear often being neglected from protection even though accidents are a common occurrence causing devastating consequences.
Arc Flash Protection System
Arc Flash Protection System Configuration
This short animation shows a basic configuration set-up of an arc protection system. This Arcteq system features AQ110 and 3 AQ101 relays, along with several point sensors. This comprehensive set-up will allow for rapid arc detection (just 2 ms). The quick tripping of the circuit breaker will result in less damage from the arc or arc flash to both electrical equipment and personnel working nearby because it cannot reach full velocity.
Arc Flashes Explained
An arc flash can be produced as the result of a short circuit between different live conductors, a short circuit between a live conductor and an earth under a fault condition, or by separating live conductors during operational conditions.
The result is a powerful explosion of energy. The explosion will vaporise switchgear components as temperatures reach 20,000°C. The direct costs from this are undoubtedly high. The indirect costs from lost production can be even higher.
Arc flash and protection simply cannot be ignored.
Arc Flash Protection
Giving employees arc flash clothing and PPE is the standard response to the threat of arc flashes. Whilst this is an important step to take to protect employees, it won’t protect your equipment. It won’t prevent disruption to your business.
The AQ100 arc flash relay recognises an arc fault through light detection only or a combination of overcurrent and light detection. The relay then sends a trip command to the circuit breaker nearest to the fault. The breaker is opened, the current cut and the arc eliminated.
It takes just 30ms for the arc flash to reach maximum pressure and 100ms for temperatures to reach 20,000°C. The AQ100 arc flash relay will detect the fault in just 2ms and will send the trip command to eliminate the arc in less than 7ms. The ultra-fast speed of the tripping means damage will be limited to just a small section of the LV MV HV switchgear and electrical equipment.
And with selective tripping available, just the circuit breaker of the feeder affected by the fault will trip. The rest of the feeders will stay functional.
The ultra-fast reaction of the AQ100 system will ensure the safety of operating personnel even during an arc flashover.
Don’t underestimate the importance of protecting your equipment as well as your employees.
Life Saving Protection Against Arc Flash – whether working on underground substation cables or overhead transmission lines. Image: Allteck Power Line
Arc Flash 11kV Substation Blast – devastating effects on medium voltage electrical equipment, cables and circuits.
About Industrial Power Units Limited
IPU Group is a privately owned industrial company based in the UK, in West Bromwich, West Midlands – designing, manufacturing and distributing high quality parts and systems for critical diesel and gas engine applications.
IPU supply engineered solutions into other industries where reliability, performance and safety are paramount including: Oil & Gas, Marine, Industrial Engines, Mining & Quarrying and Land Based Industries.
Thorne & Derrick International supply arc flash clothing and protection equipment including coveralls, gloves, helmets, face shields and general head-to-toe PPE is used to protect against flashover – complete range of insulating matting is also available for worker protection when exposed to energised electrical switchgear and transformers.
Typical applications include LV, HV & EHV cable jointing and terminating, fuse pulling, switchgear commissioning, racking circuit breakers, electrical switching and live working on medium and high voltage electricity networks.
T&Dare national distributors LV, MV & HV Cable Installation, Jointing, Substation & Electrical Equipment – we service UK and global businesses involved in cable installations, cable cleating, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.
Since 1985, T&D have established an international reputation based on SERVICE | INTEGRITY | TRUST.
Contact us for 3M Electrical, ABB, Alroc, AN Wallis, CATU Electrical, Cembre, Centriforce, CMP, CSD, Elastimold, Ellis Patents, Emtelle, Euromold, Filoform , Furse, Lucy Electric & Zodion, Nexans, Pfisterer, Polypipe, Prysmian, Roxtec, Sicame, WT Henley.
Invitation
Thorne & Derrick invite you to join LinkedIn’s largest LV-HV Electrical Discussion Group : Low & High Voltage Power, Cabling, Jointing & Electricals. Discussion subjects include cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV. Network, engage and promote your profile, company or products with over 10,000 influencers.
10 Things You Should Know About Electrical Safety & Protection | Image ABB
by Chris Dodds T&D - estimated reading time 5 minutes
T&D Largest UK Stockist – CATU Electrical Safety Equipment For LV HV EHV Electricity Cables, Lines & Substations
The world of electrical safety, insulation and protection is rife with potential hazards and dangers. Electrocution risks prevail throughout low and high voltage power systems – whether by underground cable or via overhead line where the ampere flows danger goes with it.
Electrical Safety Foundation International has confirmed every 30 minutes during the work day, a worker suffers an electrically induced injury that requires time off the job for recovery.
Over the last ten years, more than 46,000 workers have been injured from on-the-job electrical hazards.
Engineers, installers, maintenance and other operatives working on or near HV and LV electrical installations are at risk from the dangers an arc flash, power surge or short circuit can cause.
Arc flash clothing is essential to provide “head-to-toe” worker protection against arc incidents – this includes a complete range of arc flash gloves, arc flash helmets and garments for utility workers carrying out installation and maintenance tasks on LV MV HV underground cables, overhead lines and electrical substation equipment.
Cable jointers working on underground cables, linesmen stringing overhead conductors and SAP’s switching high voltage substations all confront daily dangers of electrocution which can only be moderated by a responsible attitude to electrical safety and risk assessment.
Nothing has changed. Serious injury, high degree burns, electrocution and all to commonly death are the dangers that face these workers daily if the proper electrical safety precautions are not taken.
Here, we take a look at 10 of the most important factors that need to be considered regarding LV-HV Electrical Safety.
The list below is by no means exhaustive, however it does cover 10 of the most pertinent points that must be considered prior to carrying out any electrical installation, maintenance or other work:
Arc Flash – calculation, risk assessment, protection and dangers
Electrical Accidents – causes, courses and cable faults
Electrical Isolation – what is lock-out tag-out?
Electrical Accidents – prevention and risk assessment
Arc Flash Protection – eliminating, reducing and quenching
British Standards – domestic electrical protection and BS7671
Dead or Live – energised or de-energised electrical working
Image: Jim McDonald (Owner/Live Line Training at Powerline Training Consultants)
1. Arc Flash
The most common hazards typically faced when working on LV HV electrical cables, switchgear and substation installations are electrical arcing (often called a ‘flashover’ or ‘arc flash’).
♦ Arc Flash Statistic: According to NFPA and IEEE from 1992 to 2002, over 2,000 workers a year or more than 5 workers a day were victims of an arc flash.
Arc flash can generate intense levels of heat and flames which can cause deep set burns and serious injury. The dangers of arc flash incidents are well documented and calculating the potential level and power of an electrical arc to provide adequate arc flash protective clothing can save lives should an arc flash incident occur.
We recently asked Hugh Hoagland (Partner at ArcWear & e-Hazard.com) and “leading-light” in arc flash protection to recommend the 3 most effective and reliable software packages for Calculating Arc Flash Risk & Hazard in accordance with NFPA 70E and IEEE 1584.
In addition to the intense heat, the levels of ultraviolet radiation from an electrical arc can also cause damage to the eyes. It is often the case that those working with or near electricity do not appreciate the risk of serious injury and consequential damage to equipment that can arise from arcing.
In the case of oil filled switchgear, burning oil and gas can be ejected causing serious injury or death to those nearby and major damage to buildings located in the vicinity of the arc flash blast. Switchgear that may be using SF6 gas as the insulating medium presents other risks that must be controlled and managed as the presence of F-gas is pervasive throughout industries.
These risks are managed effectively through the installation of an SF gas detector. The Crowcon F-Gasis a fixed point gas detector enclosed in an IP54 case and delivers reliable detection of freon gases (F-gases).
The F-Gas monitors levels of a range of refrigerant gases and also sulphur hexafluoride (SF6) and can be connected to any control system that can accept an analogue signal and is ideal for use in substations, switchgear, plant rooms, MV switches, ring main units, contactors and circuit breakers covering the electrical safety and gas detection requirements of the electrical distribution industry.
By providing SF gas detection, electrical safety is improved generally and the potential risks are managed.
Not only is damage to human life a real hazard, electrical fire and the subsequent damage to property and electrical infrastructure can cause considerable financial loss.
GIS Gas Insulated Switchgear 220kV. Image ABB
Adequate training and the lack of it is a continuing theme as a contributory cause of arc flash incidents and accidents….
Occupational Injuries From Electrical Shock and Arc Flash Events – extract from Final Report (2015) by The Fire Protection Research Foundation.
The Full Report is available as Slideshare download :
CATU, a world leader and respected voice in the world of electrical safety recommend the following 5 points to determine the selection of suitable arc flash clothing for protecting against arc flash :
Maximum fault current value
Phase/ground rated voltage at location of risk
Distance between the arc source and the reception source
AC cycle number and the mono or three-phase circuit type
Location of where the arc is produced (confined space)
This information enables an estimate of the arc flash risk level and determines the selection of arc flash clothing and PPE to use : 12 to 100 cal/cm³ or class 1 or 2. Arc flash site surveys and electrical risk assessments can be carried out by specialist service providers. For instance in the UK, ESUK is a specialist company concerned with the safe management of risk associated with LV-HV electrical work activities.
2. Electrical Accidents & Causes
The vast majority of electrical incidents occur because:
People are working on or near equipment that is either thought to be dead but is still live or,
By those working on equipment that is known to be live but they do not have the adequate training or are not using adequate protection equipment.
By not taking the required safety precautions and selecting the correct equipment for protection from the threats mentioned seriously increases the chances of an electrical incident occurring.
Here, we return again to the role of training and professionally educating electrical workers.
Investment both in terms of time and cash is required by responsible contractors to ensure the safety of their greatest asset, their workers.
Train and train some more. Training builds skills and confidence, it reinforces best working practises and should be encouraged throughout the lifetime of the career.
There is no shortage of training resources available, such as the High Voltage Training Courses for HV electrical engineers conducted by EA Technology’s Power Skills Centre.
Whether HV or LV, EA Technology are leading power engineering consultants and their courses and solutions are adopted by utilities across the globe.
Substations Courses
Specialist Courses
Cables Courses
Power Networks Courses
Protection Courses
Tailored Programmes
Pictured: The CableSniffer™ is designed to quickly and accurately detect cable faults. The CableSniffer™ pinpoints low voltage (LV) cable faults by “sniffing” the gases given off by faulting LV cables as the cable insulation burns. Widely used across UK DNO and global power utilities the EA Technology CableSniffer™ significantly reduces the impact of LV cable faults on customer minutes lost and restoration costs.
CableSniffer – Cable Fault Location For Low Voltage Cables
Quite simply, lock-out tag-out (LOTO) is the safety procedure of securely locking machines and equipment with numerous electrical safety padlocks to ensure that it cannot be energised without the necessary workers being present.
LOTO controls the flow of electrical energy and in practice is the isolation of power from the system by physically locking it in safe mode. In most cases, the safety switch has a series of holes through which a number of securing devices are fastened to ensure the switch cannot be turned.
Only the authorised individual is permitted to lock out and is the only one who can unlock the devices. LOTO is vital to to maintain worker safety while these systems are being operated when non-routine activities such as maintenance, repair, or set-up; or the removal of jams, clogs or misaligned feeds are performed.
Send an e-mail to [email protected] to request your FREE copy. Please include within the e-mail your name, ship to address, company and your job title.
4. Electrical Accident Prevention
There are many steps and precautions that should be taken in order to minimise the risk of electrical accidents occurring. Firstly, a risk assessment should always be carried out prior to any work starting and this should focus specifically on the electrical hazards present.
Secondly, the equipment used should be suitable for the application in which it is to be used. It must be properly designed, constructed, installed and maintained so that it does not present a risk of electric shock, burns or explosion.
Certified “explosion-proof” equipment must be used in areas that are classified as hazardous areas where flammable gases and vapours constitute potentially explosive atmospheres. Also where possible live work should be avoided during commissioning and fault finding. There must also always be adequate light, space and access to work safely.
The arc flash point is worth re-iterating and here is why.
According to OSHA, 80% of electrically related accidents and fatalities involving “Qualified Workers” are caused by arc flash / arc blast. Between 2007 and 2011, more than 2,880 fines were assessed for not meeting OSHA regulation 1910.132(d) which averages out to 1.5 fines a day.
As mentioned earlier, the electrical hazard dangers posed by an arc flash or electrical explosion can seriously injure or kill workers and also cause significant financial damage to infrastructure and cause significant downtime. If an electrical arc does occur, it is imperative that workers are already protected by wearing the correct clothing, whether that is insulating gloves, insulating matting, helmets and insulating boots or a full arc flash protection suit.
T&D Largest UK Stockist – CATU Electrical Safety Equipment
Apologies for further product placement, but leading manufacturers have innovated a series of electrical equipment geared towards eliminating, reducing or quenching arc flash.
Here are just 4 of them :
Eaton Arc Flash Reduction Maintenance System
A circuit breaker equipped with an Arc flash Reduction Maintenance System by Eaton can improve safety by providing a simple and reliable method to reduce fault clearing time. Work locations downstream of a circuit breaker with an Arc flash Reduction Maintenance System unit can have a significantly lower incident energy level. Read more.
ABB REA Arc Flash Detection System
Ultra-fast clearing of arc flash faults in medium voltage (MV) switchgear panels is essential in controlling arc flash hazards. Reducing the arcing time through faster detection is the most practical way of reducing incident energy levels and improving workplace safety. ABB’s innovative REA fast arc flash detection system uses fibre-optic sensors to cut the typical relay operating time to less than 2.5 ms – far faster than conventional relay technology. Read more.
Littelfuse Arc Flash Relays
Littelfuse AF0500 and PGR-8800 Arc-Flash Relays help improve safety and reduce equipment downtime in the event of an arc flash. Both relays use reliable light to send a trip signal to the breaker in 1ms to interrupt power before damage occurs. Their simple plug-and-play installation make them the perfect, cost-effective solution to lowering equipment incident energy (HRC). Read more.
Safe-T-Rack Remote Racking Systems
Safe-T-Rack® is an innovative, patented tool for circuit breaker remote racking and control. The product was specifically developed to provide users of low and medium voltage circuit breakers, including GE vertical lift (MagneBlast) designs and a variety of horizontally racked breakers, a comprehensive alternative to arc flash protection garments. Read more.
ABB 15 HK Circuit Breaker Remote Racking System
The video below demonstrates the need for effective arc flash protection as when it does occur, the results can be deadly.
Arc Flash
6. British Standards & BS7671
British Standards
According to UK Wiring Regulations, the main standard governing electrical installations is BS7671‘Requirements For Electrical Installations’.
This BS standard describes how electrical systems and equipment can be designed, conducted and installed in order for them to be used safely – to provide electrical safety in the workplace and in our homes.
Non compliant “BS7671” installations often feature a potentially lethal cocktail of manufacturers devices that may not have been tested as a completed unit – whilst this “pick and mix” attitude might be acceptable practice in Europe, it definitely does not comply with British Standards.
Earlier this year, we joined forces with Michael Halverson, owner of M-Spec Services Electrical Contractors, a respected UK based electrical contractor. We discussed the recent changes to the BS7671 Wiring Regulations and their affect on the selection and installation of Domestic Household Consumer Units.
“Shoddy cowboy builder charged £49,000 to turn our home into a deathtrap. One light switch turning on a bulb elsewhere in the home.” Via Daily Mail.
In addition, further guidance can be taken from three British Standards – BS6423, BS6626 and BS6867.
HSG230 Keeping Electrical Switchgear Safe includes guidance on the selection, use, care and maintenance of high voltage and low voltage switchgear.
When using electrical equipment in explosive atmospheres, certified products must be used and the Dangerous Substances and Explosive Atmospheres Regulations 2002 covers the regulations that should be followed for onshore installations.
For offshore applications, the Offshore Correct Selection & Use Of Equipment Electricity at Work : Safe Working Practices Page 8 of 33 Health & Safety Executive Installations (Prevention of Fire and Explosion, and Emergency Response) Regulations 1995 should be followed.
7. Partial Discharge & High Voltage Cable Breakdown
Partial Discharge Damage To Electrical Cable Insulation. Image HVPD
A Partial Discharge (PD) is an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes.
Partial discharge is an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes.
PD can occur at any point in the insulation system, where the electric field strength exceeds the breakdown strength of that portion of the insulating material.
Electrical failures of three phase HV switchgear are most likely to occur during, or shortly after, switchgear operation. The way switchgear is operated, its condition and the conditions in the electrical system at the time it operates will largely determine whether it will function safely.
The use of handheld partial discharge equipment can be considered for use as an additional safety measure during a routine inspection or when entering a substation. The use of partial discharge detection equipment can reduce the risks to people who perform inspections by providing a warning that something may be wrong.
HV electrical switchgear should not be used where its strength and capability may be exceeded unless there is no potential danger of anybody being exposed to the results. In order to prevent any future danger, switchgear and machines must be adequately maintained and details for guidance on the maintenance of HV electrical switchgear can be found in BS6626.
BS6626 is a British Standard which gives recommendations and guidance for the maintenance of electrical switchgear and controlgear having a rated a.c. or d.c. voltage above 1kV and up to and including 36kV.
Older switchgear may contain parts that were manufactured from asbestos or asbestos-containing materials (ACMs).
Getting it right first time. When electrical installations are commissioned and installed, the correct equipment must be used to not only prevent electrical explosions and arc flash but to also minimise the financial costs associated.
If any old equipment is still in use including old type switchboards and fuse-boards used by electricity distributors, then this is not designed to prevent people touching live conductors and suffering injuries from shock or burns.
Electrical equipment to be used in hazardous areas must be certified for use and have adequate certification.
Consideration must also be given to the environment in which the equipment is being used and whether there is any potential for an explosion or leak to occur.
Potentially explosive atmospheres are regulated under the ATEX Directive in Europe and geo-specific hazardous area classifications cover the rest of the world. Adverse external factors should be considered for the electrical equipment such as excess damp or humidity conditions.
The assessment of the working area must be carried out before work commences – given average travel distance from an oil rig to the nearest hospital (by helicopter) offshore locations consequently have extremely rigorous electrical safety working practises. We covered BP’s recently….
Assessing safe working electrical practices can be divided into four stages :
Deciding whether to work live or dead
Planning and preparations for actions that are common to both dead and live working
Procedures for working dead
Procedures for working live
This basic flow chart for assessing safe working practices helps to assess exactly what should be taken into consideration:
Selection chart for assessing safe working practices
The age of switchgear and other electronic equipment should be taken into account as the risk of catastrophic failure increases with age and a process of assessment should be carried out to decide on the appropriate action for dealing with aged switch-gear.
10. Should You Work Dead Or Live?
Working either live or dead is dependent upon the work being carried out and the equipment being worked upon. Working dead simply means working on or with electrical equipment of which the power source has been switched off. Working live means the opposite – the power is still on and the equipment is live.
Typically, normal policy is to work dead and deciding whether to work dead or live is extremely important. It is normal for utilities to recommend work on or near electrical apparatus to be on de-energised equipment, not live, i.e. isolated.
There are a series of questions and points to consider when deciding between working and working dead live:
Can the normal policy of dead working be carried out?
There are three conditions that must be met for live working to be considered acceptable over dead working. These are: It is unreasonable in all the circumstances for the conductor to be dead? It is reasonable in all the circumstances for the person to be at work on or near that conductor while it is live; and suitable precautions (including, where necessary, the provision of personal protective equipment) have been taken to prevent injury.
Is it unreasonable for the work to be done dead?
There are some circumstances in which it would be unreasonable to make the equipment dead due to the difficulties it would cause. Situations where it may not be technically feasible, a DNO needs to connect a new low-voltage service to an existing main or switching off a system, such as the supply to an electric railway track would cause excessive financial cost.
Identify, assess and evaluate the risks and methods for controlling them
If it has been decided that the work must be carried out live, then a risk assessment is required to evaluate the work on or near the specific equipment and it must be carried out by someone with comprehensive knowledge and experience of the type of work.
Decide whether it is reasonable to work live
The risk assessment should inform managers and supervisors whether it is safe to work live. At this stage the operational and economic factors of the work being live should be taken into consideration and evaluated against the risks of working live.
Decide whether suitable precautions can be taken to prevent injury
Providing the required points have been met, live work can still only be justified if suitable precautions are taken to prevent serious injury arising from the hazards noted in the risk assessment.
Arc Flash – HV Substation Switching
Thorne & Derrick are global distributors for the full range of CATU electrical safety products.
The range that ensures your worker safety and prevents and injury or serious harm occurring.
T&D distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Pulling & Installation Equipment – we service UK and international clients working on underground cables, overhead lines, substations and electrical construction at LV, 11kV, 33kV and EHV transmission and distribution voltages.
Thorne & Derrick invite you to join LinkedIn’s largest LV-HV Electrical Discussion Group : Low & High Voltage Power, Cabling, Jointing & Electricals. Discussion subjects include cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV. Network, engage and promote your profile, company or products with over 10,000 influencers.
With global electricity demand forecast to double by 2050, Thorne & Derrick are strengthening and extending their world-class supply-chain by a Strategic Distribution Agreement (SDA) with a market-leading manufacturer of High Voltage Cable Accessories – our business can now...
The Wind Academy The Wind Academy, the UK leading facility delivering GWO and Technical Trade Training Courses, has marked a major milestone in onshore and offshore wind technician training with the successful delivery of the first-ever GWO High Voltage...
Atmospheres Regulations 2002 covers the regulations that should be followed for onshore installations.
