| What is an Arc Flash? | | | | Classification 4 work is to withstand 167.36 J |
| An arc flash is like a bolt of lightening that occurs | | | | cm². As much of the work performed for |
| around energized electrical equipment. It can occur | | | | an IR inspection requires removal of bolted |
| spontaneously and is often triggered simply by | | | | covers, this would be the PPE that is required. |
| the movement of air when an electrical enclosure | | | | Infrared Windows: Eliminate the Controllable Risk |
| is opened. The NFPA has recognized the significant | | | | The first rule in any risk assessment is to |
| hazard of arc flash and is attempting to protect | | | | eliminate the risk if possible. Infrared Windows |
| workers via the latest implementation of NFPA | | | | eliminate many of the risks associated with live |
| 70E-The Standard for Employee Safety in the | | | | inspections since they enable an infrared camera |
| Workplace. | | | | direct view of live electrical components without |
| About 10-15 serious arc flash incidents occur in | | | | the need to open electrical enclosures. They |
| the US each day. Most causes of arc flash are | | | | provide an excellent means of accessing electrical |
| operator induced. | | | | equipment efficiently and safely. In addition, a |
| Most technicians who routinely work around | | | | second qualified technician is not required to open |
| energized electrical equipment are familiar with arc | | | | and unbolt enclosures. An IR viewing window is |
| flash-having seen it first hand. It is thought of like | | | | basically an infrared transparent material with a |
| a major automobile accident: no one really | | | | holder/mounting body. Thermographers may even |
| expects it to happen to them, so people have a | | | | decide to not use a window when inspecting |
| tendency to drive with significantly less caution | | | | energized components at some distance from the |
| than they should. So it is with arc flash, only | | | | cover and use a protective grill in place of a |
| worse. Similar to driving you can make a mistake, | | | | window. The grill must be IP2X certified (the grill |
| or you can be doing everything right when | | | | size must offer protection against foreign objects |
| someone slams into you. | | | | with diameters larger than 12mm). This method |
| Specifically, what is an arc flash? | | | | can significantly reduce the window cost and also |
| An arc flash is electric current flowing through an | | | | has the additional benefit of allowing ultra sound |
| arc outside its normal path where air becomes | | | | inspections of the electrical switchgear. However |
| the conductor of high thermal energy | | | | when using grills, operators will be exposed to live |
| (5000ºC %2B) and generates | | | | electrical components and they must wear the |
| highly-conductive plasma. An arc flash will conduct | | | | appropriate level of PPE identified from the Arc |
| all available energy and generate an explosive | | | | Flash Hazard Analysis of the switchgear. Infrared |
| volumetric increase of gases which blows electrical | | | | Windows eliminate many of the risks associated |
| system doors off and potentially generates | | | | with live infrared inspections since they enable an |
| shrapnel. | | | | infrared camera direct view of live electrical |
| What are the causes of Arc Flash? | | | | components without the need to open electrical |
| An arc flash occurs when the gap between | | | | enclosures. The optics holder design depends upon |
| conductors or conductors and ground is | | | | a number of parameters: the field of view, |
| momentarily bridged. There is always a trigger | | | | equipment lens and window size are all functions |
| event which almost always involves human | | | | of the design and must meet all the parameters |
| intervention. Typical causes and contributing | | | | that the thermographer requires before a holder |
| factors include: | | | | is manufactured. Also, a protective cover should |
| - Accidental contact with energized parts | | | | be included in the design as crystals are very |
| - Inadequate short circuit ratings | | | | expensive and in some cases, extremely fragile. |
| - Tracking across insulation surfaces | | | | Infrared Windows are available in multiple sizes |
| - Tools dropped on energized parts | | | | and can be custom made to retrofit dead fronts |
| - Wiring errors | | | | on distribution and isolator boards. The larger the |
| - Contamination, such as dust on insulating | | | | size of the window, the greater the field of view |
| surfaces | | | | one can see with their IR camera. |
| - Corrosion of equipment parts and contacts | | | | Considerations in Installing Infrared Windows |
| - Improper work procedures | | | | To correctly install infrared windows, the targets |
| An arc flash is electric current flowing in an arc | | | | that require inspection must be identified. Typically, |
| outside its normal path where air becomes the | | | | traditional surveys only look at the bolted |
| conductor. | | | | connections within the switchgear. These are |
| The vast majority of arc flash faults occur when | | | | generally considered to be the "weakest points" |
| the door is open or being opened. The National | | | | or "points most likely to fail." These may include: |
| Fire Protection Agency (NFPA) is the author of | | | | - Cable connections |
| NFPA 70, also known as the National Electric Code | | | | - Bus Bar Connections |
| (NEC). This paper is not intended to provide a | | | | - Isolator or Circuit breaker connections |
| comprehensive review of the information available | | | | The formula for calculating the field visible through |
| in the code, but merely to highlight some of the | | | | an Infrared Window is: FoV = 2 x tan (angle/2) x |
| information that may be related to thermography. | | | | D, where FoV is the width of the object area |
| NFPA 70E is the standard for safe electrical work | | | | that will be viewed, the "angle" is the angular |
| practices. | | | | field-of-view of the camera, and "D" is the |
| The NEC is an electrical design, installation and | | | | distance from the camera (ostensibly the window) |
| inspection standard. It does not specifically | | | | to the objects being viewed. Once a decision has |
| address topics like electrical maintenance and safe | | | | been made about what objects are to be |
| work practices. A national consensus was needed | | | | inspected through the infrared window, the |
| for safety while working around live electrical | | | | number of windows and appropriate size must be |
| equipment. NFPA 70E is the standard for safe | | | | determined as well as where they need to be |
| electrical work practices. NFPA 70E addresses | | | | installed to ensure best coverage (and therefore |
| four specific topics: safety related work practices, | | | | maximum efficiency). The size of the infrared |
| safety related maintenance requirements, safety | | | | window will depend on several factors, including |
| requirements for special equipment and installation | | | | the infrared camera's clear aperture, its ability to |
| safety requirements. NFPA 70 suggests that a | | | | focus on close objects, its ability to be placed as |
| Hazard/Risk analysis must be conducted prior to | | | | close as possible to the window, the camera's |
| working on electrical equipment. The core of the | | | | angular field-of-view and the amount of |
| analysis is based on shock and arc flash | | | | manipulation is possible with the camera when |
| boundaries which must be done by a qualified | | | | viewing through the window. An important |
| electrical engineer. | | | | consideration is how the infrared camera can be |
| Shock Hazards, Flash Hazards and Personal | | | | manipulated when looking through an infrared |
| Protective Equipment (PPE) Selection | | | | window. A high degree of manipulation can have |
| Prior to beginning work around live electrical | | | | the effect of increasing the size of the inspection |
| components, an Energized Electrical Work Permit | | | | area by up to a factor of 3. This means that if |
| must be obtained and should include but not be | | | | the object under observation is 12 inches across, |
| limited to the following: | | | | depending on several factors, it is possible that a |
| - A description of the circuit, the equipment to be | | | | window diameter of 4 inches (for IR window size |
| worked on and the location | | | | calculation purposes) can still be used if the |
| - Justification for why the work must be | | | | operator manipulates the camera from left to |
| performed in an energized condition | | | | right or up and down. |
| - Description of the safe work practices to be | | | | The required size of the window will depend on |
| performed | | | | the following: |
| - Results of the Shock Hazard Analysis | | | | - the size of the objects to be viewed and their |
| - Determination of the Shock Protection | | | | distance from the panel cover; |
| Boundaries | | | | - the infrared camera's angular field-of-view and |
| - Results of the Flash Hazard Analysis | | | | clear aperture; |
| - The Flash Protection Boundary | | | | - the camera's ability to focus on close objects |
| - Identify the necessary Personal Protective | | | | and to be placed close to the window. |
| Equipment (PPE) required to safely perform the | | | | Typically, infrared cameras have a horizontal field |
| assigned task | | | | of view of 25°. Those infrared cameras that |
| - Means employed to restrict unqualified personnel | | | | offer a wide-angle lens option (for example |
| from entering the work area | | | | 50°) permit the user to have a substantially |
| - Evidence of completion of a job briefing | | | | wider field of view, resulting in an increase in |
| - Energized work approval from responsible | | | | viewing area through the same infrared window |
| management, safety officer and owner | | | | size. This can be a great advantage in certain |
| Prior to working with live components, the correct | | | | situations, reducing the size and possibly the |
| Personal Protective Equipment and safe working | | | | number of windows. Other useful infrared camera |
| practice must be determined. | | | | features are close focus capability, small lens |
| NFPA 70E allows for an exemption to the safe | | | | diameter resulting in a small clear aperture, |
| work permit for qualified personnel who are | | | | motorized focus (eliminating the need to get |
| performing tasks such as testing, troubleshooting, | | | | fingers on the lens focus ring and moving the |
| voltage measuring, etc. so long as they utilize safe | | | | camera away from the window) and a chassis |
| work practices and the proper PPE. Prior to | | | | design that facilitates movement at the window |
| working with live components, the correct | | | | such as an articulating camera head that allows |
| personal protective equipment and safe working | | | | the user to look into windows above eye level or |
| practice must be determined by carrying out a | | | | at near floor level. |
| Shock Hazard and a Flash Hazard Analysis. A | | | | The View through an Infrared Window |
| Shock Hazard Analysis will determine the voltage | | | | An infrared window allows a camera operator to |
| to which personnel are exposed, boundary | | | | inspect the inside of an electrical cabinet to check |
| requirements and the proper PPE necessary to | | | | the physical condition of the components that you |
| minimize the possibility of shock to personnel. The | | | | have chosen to inspect. As with traditional |
| shock protection boundaries are identified as | | | | thermographic inspections we can see |
| limited, restricted, and prohibited for the distances | | | | temperature differences very clearly. You need |
| associated with various voltages. | | | | to have the confidence in the infrared windows |
| Unqualified personnel should be notified and | | | | that you are using. They are designed to allow |
| warned of hazards by qualified personnel when | | | | infrared energy to transmit through them at a |
| working at or near the limited approach boundary. | | | | known transmission rate; therefore, if there is |
| When an unqualified person must work inside the | | | | even a slight temperature difference you will be |
| restricted boundary, it is important that they be | | | | able to see that with your IR camera, and be able |
| further notified of the risks and hazards and | | | | to record images for the IR inspection program. |
| continuously escorted by a qualified person. Under | | | | Considerations for Installing Infrared Windows |
| no circumstances should they be allowed inside | | | | Installing an infrared window requires cutting holes |
| the prohibited boundary. It is important that a | | | | into very expensive switchgear. Therefore, it is |
| Flash Hazard Analysis be conducted in order to | | | | very important to be very sure that they are |
| protect personnel from being injured by an arc | | | | installed in the correct location and that the |
| flash. The analysis will determine the Flash | | | | switchgear ratings are not degraded in any way. |
| protection boundary and determine the proper | | | | Before installation, the following factors need to |
| PPE. In so doing, the Flash protection boundary is | | | | be considered: |
| calculated at the distance from energized parts | | | | - NEMA or IP rating of the switchgear and IR |
| where a burn will be "recoverable" (2nd Degree) | | | | windows: Remember to never install an IR |
| and "incurable" (3rd Degree). The guidelines dictate | | | | window of a lower rating than the rating of the |
| that the Flash protection boundary for systems | | | | switchgear. |
| that are 600 volts or less be 4' for clearing times | | | | - Test Certifications: Ensure that the IR windows |
| of 6 cycles (0.1 second) and available bolted fault | | | | have been tested and approved by the |
| current of 50kA or any combination not | | | | certification bodies as the switchgear for which |
| exceeding 300kA cycles. For all other clearing | | | | they are intended (i.e. UL, IEEE. Lloyds). |
| times and bolted fault currents, the flash | | | | - Internal obstacles: Before removing internal |
| protection boundary is normally determined based | | | | Perspex/Plexiglas covers or cables, ensure that |
| on the calculated incident energy of an arc fault | | | | the local safety manager's approval is sought first. |
| taking into account system voltage, available | | | | In some cases you may not be able to totally |
| current, and clearing time (where incident energy | | | | remove the covers and may only be able to |
| is the measure of thermal energy at a specific | | | | modify them by drilling or punching holes to retain |
| distance from the fault). Where it is not possible | | | | the IP2X requirement for some switchgear. |
| to perform these analyses (or they have not | | | | - Explosion Ratings (if applicable): Some panels are |
| been performed), NFPA 70 provides guidelines | | | | positioned in intrinsically safe areas and as such |
| (NFPA 70 Table 130.7-C9a) that can be used to | | | | can never be modified in the field. |
| determine the required PPE based on the task | | | | - Dielectric Clearances: Where IR windows use |
| conducted. In lieu of a Flash Hazard study, | | | | grills or inspection orifices, they must comply with |
| selection of PPE by task is normally allowed. | | | | IP2X (13mm 0.5"), and clients must be made |
| However, for tasks not listed in the table and for | | | | aware of the safe dielectric clearances for the |
| clearing times different then those listed there, a | | | | type of switchgear that they intend to install the |
| complete Flash Hazard Analysis is required. Using | | | | window into. The table shown at the left (from |
| Flash Hazard Analysis or Task Risk Assessment, | | | | IEEE C37.20.2 table A.3) specifies minimum |
| the following table can be used to identify the | | | | distances from live components, and it is |
| correct PPE: | | | | recommended that these be considered as a |
| Thermography Inspection Practices Infrared | | | | standard for grills/inspection orifices. |
| cameras have been used to identify problems in | | | | When using Infrared Windows, it is important to |
| electrical systems for many years. Problems in | | | | correct for the transmission specification of the |
| electrical systems manifest themselves by | | | | window and the emissivity of the component that |
| connections and conductors becoming overheated | | | | is to be inspected through the IR window. One |
| as the result of increased resistance, the result of | | | | way of correcting for the effects of the window |
| loose or corroded connections, or load imbalances. | | | | is by adjusting the camera's emissivity value for |
| An infrared camera can readily identify these | | | | an object of known temperature until the |
| problems in a thermal image and is an excellent | | | | camera's reading is correct. For objects at the |
| method for identifying failing or problem | | | | same ambient temperature and emissivity, the |
| components prior to a failure. A failure can disable | | | | new emissivity value can be used. |
| an electrical system and cause significant lost | | | | When using Infrared Windows, it is important to |
| production, equipment damage and bodily injury. | | | | correct for the transmission loss of the window |
| Insurance companies use infrared electrical | | | | and the emissivity of the component that is to be |
| inspection to help determine risk profiles and rates | | | | inspected through the IR window. |
| for industrial customers. More recently, | | | | Another way of using IR windows is to prepare all |
| thermographers have found that they can use IR | | | | components that are to be inspected so that |
| to prevent and predict failures to help further | | | | they have the same emissivity (for example, with |
| reduce down time equipment failure and increase | | | | electrical tape, emissivity paint, IR-ID Labels). In |
| overall safety. | | | | this case, all components being inspected will have |
| Often, during thermography inspections, panel | | | | the same transmission rate and emissivity |
| covers are removed and subsequently replaced, a | | | | readings; consequently, the results gathered will be |
| method that conflicts with the requirements of | | | | far easier to compare. |
| NFPA70E. | | | | Can IR Windows Carry a Generic Arc Rating? |
| Like visible cameras, infrared cameras require a | | | | Electrical switchgear takes on many different |
| direct-line-of-site view of an object. In most cases | | | | shapes and sizes. The surface areas and |
| surveys are hampered by cabinet designs that | | | | volumetric elements of the cabinets are different |
| obscure the target components being inspected | | | | with each model, type and rating. Each cabinet is |
| and thermographers are put at risk by having to | | | | subjected to the testing that is laid down by the |
| open cabinets or doors in an attempt to gain | | | | certification bodies such as UL, IEEE, etc. This test |
| access to the internal components. IR surveys of | | | | is completed on the cabinet assemblies and not |
| electrical systems are best conducted when the | | | | the components that make up the assembly. |
| system is under heavy if not peak electrical load, | | | | Electrical cabinet designs and dimensions are |
| which requires the thermographer to perform the | | | | infinite, and we therefore CANNOT or MUST NOT |
| inspection in and around live electrical components. | | | | use the data from one cabinet design for another |
| Typically, electrical system covers are removed | | | | design unless they are identical in every way. This |
| during thermography inspections and subsequently | | | | is why components never carry a generic arc |
| replaced. This working method conflicts with the | | | | rating and must be subjected to industry standard |
| requirements of NFPA 70E. | | | | tests to confirm that they conform to the |
| Recommendations of NFPA70E as they relate to | | | | minimum required level of mechanical strength and |
| Thermography Inspection | | | | environmental properties for the electrical cabinets |
| NFPA 70E recommends that only "qualified" | | | | and assemblies which they are going to be fitted |
| personnel be allowed to perform work inside the | | | | into. |
| flash protection boundary. Thermographers must | | | | Conclusion |
| be accompanied by "qualified" individuals if they | | | | Because of the frequent occurrence of arc flash |
| intend to have panel covers removed. Both the | | | | in industry, it is extremely important to be aware |
| thermographer and the additional person should be | | | | of the risks associated with inspection of high |
| in full PPE. One way NFPA 70E determines Hazard | | | | voltage switchgear and related items. Concerns |
| and Risk and the required PPE is based on the | | | | about operator safety due to an arc-flash event |
| activity that you are conducting around the | | | | are causing inspectors to adopt new practices in |
| equipment. Risk potentials are determined on a | | | | accordance with NFPA 70E, the standard for safe |
| scale from 0-4, where 4 indicates the highest risk | | | | electrical work practices. Shock and Flash Hazard |
| potential. For example, removal of a bolted cover | | | | analyses are required in many situations. Personal |
| on 600V equipment carries a hazard/risk | | | | Protective Equipment recommendations are also |
| classification of 3 and that goes up to a rating of | | | | available. One new common safety practice |
| 4 on voltages greater than 600V. As this work | | | | involves the use of infrared transparent windows |
| occurs within the Flash Protection boundary, the | | | | which eliminate many of the risks associated with |
| appropriate PPE must be worn. The required | | | | live infrared inspections since they enable an |
| minimum PPE for Hazard/Risk Classification 3 | | | | infrared camera to have a direct view of live |
| work is to withstand 104.6 J/cm², and the | | | | electrical components without the need to open |
| required minimum PPE for Hazard/Risk | | | | electrical enclosures. |