Detecting Loose Connections in Grounding Systems
Thermography is widely used to detect defective connections for supply/return conductors within electrical distribution systems. Thermography can also be used to detect loose/deteriorated connections within bonding and grounding systems.
In a perfect world, substation structures and protective fencing surrounding the sub would never become energized. In the REAL world, substation structures and nearby metal components can, and often do, become energized either by leakage current or induction. For safety, all structures near and within the substation are electrically bonded together and wired directly to ground in order to carry this unwanted and potentially lethal power to ground.
Because grounding systems frequently carry current, loose or deteriorated connections will often manifest themselves as hot spots at or near the source of the problem. Because a loose grounding conductor can compromise the integrity of the grounding/bonding system, any inexplicable hot spots should be investigated as soon as possible regardless of temperature rise.
It is recommended that hot spots within a grounding system should be given top priority. Should a grounding connection fail, anyone making contact with the energized portion of the structure could be seriously or fatally injured.
A follow up inspection should be performed once any repairs have been made to ensure that the subject repairs were effective.
Truth, Thermography and the World Wide Web
“Stretchers”, “tall tales” and “selective interpretation of the truth” are politically correct terms that apply to statements that are misleading or false. With no editorial controls, the world wide web is rife with deceptive claims. Because thermography is not immune to inaccurate web postings, thermographers should be cautious in their acceptance of material posted on the web.
Prudent web surfers frequently view material on the internet with a healthy amount of skepticism. All too frequently, the amount of caution is inversely proportional to value of the product being advertised. Further compounding the problem are unscrupulous advertisers who publish misleading information. Some current examples include:
- Brochures for thermal imagers containing images taken with a different model imager
- Publication of specifications that are incomplete or inaccurate
- Literature and trade names suggesting imager models for inappropriate applications
- Obsolete imagers renamed and offered as current models, although manufacturer support is no longer available
For equipment purchases, the above are often exacerbated when the reader is untrained and/or inexperienced with the technology. Before purchasing a thermal imager, be sure to try the subject equipment under the exact conditions you will encounter in the workplace.
When it comes to the internet, the old adage, “You can’t always believe everything you read” is frequently sage advice.
Infrared Imaging and Mold Detection
As concerns regarding indoor air quality increase, there is increasing concern with respect to mold. Used properly, a thermal imager can help identify areas of potential mold growth.
Mold is a ubiquitous single cell organism that tends to favor moist environments. Of the thousand species of mold found worldwide, many are harmless; however, certain species are toxic. Others can cause chronic health problems in humans.
While thermal imagers cannot detect mold directly, they can often detect evidence of the latent moisture often associated with mold presence. When using a thermal imager to detect latent moisture, keep the following in mind:
- Evidence of moisture can only be detected if a temperature differential exists across the surface of the material being inspected.
- Frequently, a delta T can be created by actively heating or cooling a structure or by relying on solar loading of the subject areas.
- Subject building components should be imaged from both indoor and outdoor aspects under the correct weather conditions.
- Suspected moisture presence must be confirmed by independent means.
- A negative finding for latent moisture does not guarantee that mold is not present.
Since moisture presence is not positive proof of mold presence, further laboratory tests will be required to confirm mold within any moist areas detected.
Scheduling IR Equipment for Maintenance
Many thermographers think of the holidays as a time for family, festivities and annual maintenance of their infrared equipment. Planning ahead can help to minimize imager downtime and avoid or minimize program interruption.
Because infrared test equipment plays a key role in an inspection program, minimizing downtime required for service is imperative. Keeping the following in mind can help routine service to proceed more smoothly and ensure a faster turnaround for your imager.
- Schedule routine equipment service and/or calibrations well in advance
- Most service departments require you to obtain a Return Authorization before shipping equipment
- Be sure to include all optics and filters when shipping your system
- Consider scheduling service before or after holidays to avoid service backlogs
- Arrange for replacement equipment if you anticipate a long delivery time for service
When shipping your equipment, enclose a letter stating services required and any problems with the subject equipment. Be sure to affix a Packing List to the exterior of your shipping container noting descriptions and serial numbers of items shipped. Lastly, don’t forget to ascertain Customs requirements if your equipment must be shipped outside of your country for service.
An Emittance Greater Than 1.0 ?
According to the laws of physics, only a perfect blackbody may have Emittance of 1.0. Although the E value of real objects must be less than 1.0, some radiometers allow entry of E values exceeding 1.0. The following describes how these radiometers achieve the impossible.
Emittance is a measure of how well an object radiates energy when compared to a blackbody at the same wavelength and temperature. Emittance for any object is measured on a scale between 0 and 1.0. Since blackbodies (E=1.0) exist only in theory, real world objects will have E values of less than 1.0. The E value of an object can never exceed 1.0.
Assuming that most objects are opaque (T=0), they must be somewhat reflective. When making an infrared temperature measurement, this reflected energy represents an error source. To overcome errors due to reflections, quality radiometers have inputs for reflected temperature. By measuring reflected temperature and entering this value into the radiometer’s computer, this error source is compensated for in the radiometer’s software.
Less sophisticated radiometers often lack inputs for reflected temperature. To compensate for this, these radiometers allow the user to exceed E values of 1.0. Although this overcompensation may allow the user to match a desired reference temperature, it can lead to significant errors. For infrared temperature measurement, the best solution is to use quality radiometric equipment and eliminate or avoid reflections whenever possible.
Tips for Battery Care
Overlooked and underappreciated until they fail, batteries supply the lifeblood of portable test equipment. Proper care of rechargeable batteries can extend service life and maximize run time.
Current choices in rechargeable battery types sound like a recipe for alphabet soup: NiCd, NiMH, and Li-Ion. Advancements in technology have made portable batteries more reliable while reducing required care. Safely obtaining optimum battery performance and longevity is easy if you observe the following:
- Never use batteries for anything other than intended use
- Discharge batteries fully before recharging
- Charge batteries only with the appropriate charger in a well-ventilated area
- Disconnect batteries from charger when charging is complete
- Assign batteries to a specific charger to allow for easier troubleshooting should charger fail
- Inspect charger cables and connections for cleanliness and integrity on a regular basis
- Periodically exercise batteries by discharging and recharging
Lastly, batteries are not immortal. Following the above can help to extend battery life; however, one should plan to replace rechargeable batteries at regular intervals or when run times shorten appreciably. Always dispose of defective batteries properly and recycle whenever possible.
Infrared Roof Inspections From Indoors?
Infrared inspections of flat roofs are a time-tested procedure for detecting evidence of subsurface moisture within a roofing system. Current standards specify infrared inspections be performed from the exterior of the building; however, infrared inspections may be performed from the interior of the building under certain conditions.
Thermography is a dynamic technology. New applications are constantly being developed and existing methodologies are constantly being improved. As an alternative to imaging from the exterior of the building, some have suggested inspecting the underside of the roof deck from the interior of the building
When selecting a vantage point for an infrared roof inspection, the most important consideration is roof construction. Commerical roofs constructed with relatively thin decks and no air spaces between system components may be inspected from either indoors or outdoors.
Prior to tackling an infrared roof inspection from the interior of the building, the following conditions must be met.
- Roof surface should be clean and dry
- Line of sight access to subject roof areas is required
- Space beneath the roof deck should be uniform temperature
- Viewing locations should be selected to eliminate interference from hot or cold objects such as HID lanps and HVAC equipment
Lastly, inspection must be timed to ensure adequate delta T exists between wet and dry insulation. Upon completion of infrared inspection, all data should be veirified by invasive testing.
Remote Monitor for Any Imager
When performing infrared inspections in hazardous or hard-to-reach areas, a remote monitor screen can be a valuable accessory. Combining an after-market LCD monitor or camcorder equipped with a monitor screen can provide a cost effective solution for expanding the functionality of your imager while increasing safety.
Thermal imagers with monocular viewfinders require a thermographer to stand in front of the object being inspected. This requirement can compromise safety by exposing a thermographer to hazardous or high temperature objects.
Several modern thermal imagers offer remote monitor screens as either a standard feature or as an accessory. Traditionally, LCD monitors available from imager manufacturers have been expensive. As a result of technological advancements, a wide array of LCD monitors are now available at affordable prices.
Since many thermal imagers have video output jacks, it is possible to connect an external LCD using a standard video cable. When selecting an external monitor, keep the following in mind.
- Ensure imager video output is compatible with the chosen monitor
- Consult monitor specs to confirm suitability for chosen environment
- Use high quality cables to reduce signal loss
- Beware of tripping hazards that can be caused by onnecting cables
Lastly, choose a monitor with sufficient resolution, brightness and contrast to provide a quality image.
Remote Monitor for Any Imager
Thermography is a proven technology for finding many types of defects within electrical systems. While infrared inspections can assist in PdM efforts, they can also point out a potentially lethal condition that can lead to electrocution and death.
Many AC electrical devices are wired with a grounding conductor. Ungrounded metallic structures and devices can become unintentionally energized if a bare circuit conductor makes contact with the subject structure. In ungrounded structures, improper wiring or defective/deteriorated insulation can allow the structure to become energized up to full circuit voltage. In such cases, anyone touching the energized structure may be electrocuted or fatally injured. One such fatality occurred in May, 2003 when a nine year-old boy made contact with an energized light pole in Columbus, Ohio.
On at least three separate occasions in 2003, thermographers have found evidence of energized structures with a thermal imager. All three findings involved outdoor metal light poles which exhibited inexplicable hotspots where the pole was bolted to the concrete footing. In the Columbus case, a nearby steel fence post also exhibited an inexplicably hot base where bolted to the concrete sidewalk.
For reference we have included thermal images of one of the aforementioned light poles. We urge thermographers to be on the lookout for this potentially lethal thermal anomaly and to immediately notify appropriate personnel should you detect evidence of this condition in the future.
Thermal images show base of metallic light pole operating in excess of 180ºF due to ground fault condition.
Point Radiometers & Spot Measurement Size
With awareness of infrared technology at an all time high, point radiometers have become a common tool in many areas. Frequently, knowledge of proper operation lags behind instrument popularity. Understanding how spot measurement size affects accuracy is imperative to collecting meaningful data.
All radiometers are limited by a characteristic known as spot measurement size or spot size, for short. Spot size is determined by a radiometer’s detector and optics. Typically, spot size increases as distance to the target is increased. For accurate temperature measurement, spot size must always be smaller than the target being measured. When using a point radiometer, be sure to keep the following in mind:
- Point radiometers are usually supplied with a Distance to Spot Ratio value. To determine spot size, divide distance to target by ratio value.
- Point radiometers have minimum focus distances. At lesser distances, spot size will not decrease.
- Single, laser-generated aiming dots do not represent spot size
- Multiple, laser-generated aiming circles/dots often understate spot size
- Beware of stated spot size ratio values. Spot size ratios are frequently quoted at 90% radiance (accuracy) or less
When using a point radiometer, be sure to understand the limits of your instrument and the challenges presented by your target. Always use correct emissivity values and stay within the limits of your instrument.
Temperature Rise as a Severity Indicator
For years, many thermographers have sought to qualify the severity of detected exceptions by measuring temperature rise. Although this technique is widely practiced, failure to understand key issues can lead to misdiagnoses and unplanned downtime.
For over 25 years, thermographers have frequently attempted to qualify the severity of detected exceptions by comparing the temperature of the exception to similar components under similar load or to ambient air temperature. Although qualifying exception severity may be desirable for maintenance planning, it also involves a certain degree of risk management as some exceptions may rapidly deteriorate and lead to an unplanned outage.
To better understand the risks associated with assigning severity to exceptions based upon temperature, it is important to keep the following in mind:
- For highly reflective targets, small emissivity errors can cause significant infrared temperature measurement errors
- Infrared temperatures are subject to errors due to spot measurement size
- The source of an exception may be contained within a device prohibiting direct measurement at the point of origin
- IR temperature measurement is subject to significant errors due to atmospheric conditions such as wind, solar gain and moisture
- The temperature of electrical exceptions can increase dramatically and without warning if arcing should occur
- Qualifying exception severity based upon temperature does not consider the potential impact of an unplanned failure
At present, there is no scientific method for accurately predicting time to failure based upon operating temperatures of electrical or mechanical components. In order to reduce the likelihood of an unplanned failure, every exception detected should be investigated for cause and properly repaired as soon as possible.
Preventing a Transformer Fireworks Display
Infrared inspections of oil filled transformers can help to increase reliability and extend transformer life. Detecting hotspots on the bushings of these transformers may also help to prevent a catastrophic explosion.
Hot spots on transformer bushings are usually due to a loose or deteriorated electrical connection. Frequently, the source of a hot bushing connection is external to the transformer and can be corrected by repairing the defective connection. However, loose connections which originate within the transformer case can represent an extremely dangerous condition.
Loose electrical connections within an oil-filled transformer can lead to a condition known as arcing. When arcing occurs in oil, the molecular structure of the transformer oil breaks down forming several combustible gases. The most significant gases produced are acetylene, hydrogen, methane, ethane, and ethylene.
The amount of gas produced will depend upon the temperature of the arc and length of time; however, even small amounts of gas can lead to a potentially explosive condition. In a sealed, oil-filled transformer these gasses can build to a potentially explosive level within a very short time. In short, combustible gases combined with an arcing condition within a transformer are a recipe for potential disaster.
When inspecting oil filled transformers, any inexplicable temperature rise on bushings should be investigated and corrected immediately. Performing a dissolved gas analysis of the transformer oil is recommended if the cause of the problem is suspected to originate within the transformer.
How Delta T’s Understate Priorities
For years, thermographers have traditionally reported apparent Delta T measurements when documenting their findings. Using a default emittance value between .8 and 1.0, apparent temperature measurements are recorded regardless of actual target emittance. While this methodology is fast and easy, it can lead to significantly understated Delta T repair priorities.
The temperature displayed by a radiometer is largely dependent upon the emittance and reflected temperature values entered into the radiometers computer. Typically, errors in either of these settings will cause temperature measurement errors that are exponential in nature and can cause large errors in reporting Delta T’s.
Example: Using an emittance value of 1.0 a thermographer measures the apparent Delta T between two, uninsulated electrical bus bars to be 44ºC. How much can observed temperature vary due to emittance values?
From the above, the following observations can be made:
- Emittance can have a significant impact on Delta T measurements
- The greater the variation between an object’s true emittance and radiometer settings, the more understated the Delta T
- Repair priorities may be significantly understated if accurate emittance values are not utilized
As there is no way to correct for errors introduced by apparent Delta T measurements, thermographers should utilize correct emittance values whenever possible. As always, all thermal anomalies detected during an infrared inspection should be investigated and proper corrective measures undertaken as soon as possible.
Imager Settings for MCC Inspections
Infrared inspections of electrical distribution systems frequently include motor controllers. Proper imager settings and inspection technique are imperative In order to accurately inspect these critical electrical devices.
Industrial motors of all sizes are frequently controlled by remote devices known as motor controllers. Motor controllers are small to large metal-clad devices containing one or more large solenoids that control starting/stopping, motor speed, and rotation direction.
Motor controllers often contain a number of electrical devices operating at widely differing temperatures. These devices include control circuits, transformers, fuses, circuit breakers, contactors, thermal overloads, and circuit conductors. The temperature of these devices can range over hundreds of degrees.
When performing an infrared inspection, setting a thermal imager’s controls to encompass the whole motor control in a single view is not recommended as significant problems can be overlooked. For best results, we recommend the following:
- Ensure that subject motor controller is under load
- Image from a distance that permits viewing only of the subject controller components.
- Perform inspection in direction of line to load side of motor control circuit
- View subject components individually
- Adjust level/gain settings to optimize image for each component inspected
- Compare features of similar components to each other, noting inexplicable differences
For controllers with multiple contactors, it will be necessary to inspect each contactor individually while under load. Be sure to allow sufficient time for subject contactor to achieve running temperature.
Inductive Heating Hot Spots
Loose connections, overloading and imbalanced loads cause overheating of components within an electrical system. Depending upon construction and operation of the electrical system, a perplexing and possibly serious condition called inductive heating can cause non-current carrying components to overheat.
As current flows through an electrical circuit, a magnetic field forms around the conductor. When current flow is high, a strong magnetic field can develop and extend for several inches around the subject conductor(s). If ferrous materials such as steel are positioned within this magnetic field, they can heat up even though they are not part of the circuit.
Inductive heating can occur on bus supports, cable tray fasteners, bushing skirts and switchgear enclosures. Affected components can become hot enough to cause significant heat damage or even skin burns. The temperature of the affected component will depend upon the strength of the magnetic field, and the composition and location of the affected component.
Because inductive heating can cause components to reach temperatures of over 200ºF, thermographers should pay particular attention whenever combustible materials or dielectric insulation are located near, or in contact with, an inductively heated item.
How FPA Imagers Differ
Most modern thermal imagers utilize a Focal Plane Array (FPA) detector. Although the term FPA is widely used, it is frequently misunderstood. Since detector type can affect imager performance it is imperative to understand the differences among FPA detectors.
The term Focal Plane Array is a non-standard industry term which applies to modern thermal imagers that utilize a detector chip with multiple picture elements configured in a flat, single-plane array. Each pixel of an FPA is an independent sensor capable of detecting infrared energy. When arranged in an integrated array, these pixels form a sensor capable of producing relatively high resolution images compared to older, single or multi-element scanned detectors.
At present, there are two distinct types of FPA detectors:
- Cooled FPA
- Microbolometers (Uncooled FPA)
Cooled FPA imagers are short wave only, contain a Stirling cycle cooler and require approximately 5-7 minutes of cool-down time after initially turning on the unit. Cooled FPAs were initially imtroduced in the mid 1990’s and revolutionized thermography with their small size and high resolution imagery. They have been largely replaced by market demand for uncooled microbolometer imagers.
Uncooled FPA imagers or microbolometers are long wave only, do not contain a cryogenic cooling system and typically require less than one minute to produce an image after initially turning on the unit. Uncooled FPAs were first introduced in the late 1990’s and have seen many improvements over time. Nearly every thermal imager currently being offered for PPM and PdM applications utilizes a microbolometer detector.
Frequency of IR Roof Inspections
The benefits of thermography for condition assessment of insulated roofs are well documented. Performed on a regular basis, infrared thermography can help to extend the overall life of a roofing system when utilized as part of a preventive maintenance program.
As a building component, roofing systems tend to be out-of-sight and out-of-mind. Despite the critical role they play in keeping a facility dry, many roofs garner little attention until they begin to leak. In order to minimize damage, it is imperative that roof leaks be detected and repaired at an early stage.
Many roofs can gain significant quantities of moisture in a very short period of time. In the case of retrofitted roof systems, whole roof sections can become saturated in a matter of weeks while leaking little or no water into the occupied spaces. By the time a roof leak is noticed within the building, replacement may be the only option available.
For best results, insulated roofs should be thermographically inspected at least twice per year (e.g. Spring and Autumn) in accordance with published standards and guidelines. Semi-annual infrared inspections can help to identify new areas of moisture damage and help to ensure that recent repairs are performing in a watertight manner. Infrared findings should be correlated with a thorough visual inspection and other pertinent data to formulate an effective roof maintenance strategy.
For information on infrared training or certification or to obtain a copy of the Guideline for Performing Infrared Inspections of Building Envelopes and Insulated Roofs, contact Infraspection Institute at 609-239-4788.
Infrared Windows for Electrical Switchgear
Traditionally, proper conduct of an infrared inspection of energized electrical switchgear has required that panel covers be opened or removed prior to the infrared inspection. IR transmissive windows and viewports offer an alternative to this practice; however, several important issues must be considered prior to installing windows or viewports.
For many years, safety standards and laws have required that only qualified persons work on or near exposed energized electrical components. As safety standards have evolved, many facilities have sought ways to eliminate exposure of personnel during an IR inspection and the potentially lethal injuries associated with an arc flash.
Currently, a wide variety of commercially available inspection ports and IR transmissive windows are being offered as an alternative to removing panel covers for an infrared inspection. Prior to installing such devices one should bear the following in mind.
- Ascertain spectral response of chosen window to ensure that it is appropriate for use with your imager
- Determine field-of-view for the subject window
- Identify number of windows and positioning to ensure adequate coverage
- Evaluate whether installed viewports will compromise safety by allowing easier access to energized components
- Consult with switchgear manufacturer to ensure that window installation will not void warranty or ratings of switchgear enclosure
Because much of the marketing information for windows is misleading, caution is recommended when considering the installation of windows in switchgear enclosures.
This Tip of the Week was submitted by Vance Cowper, Infraspection Institute Certified Infrared Thermographer #6370. Vance is employed by MCI.
Selecting an IR Training Firm
As thermography has gained in popularity, the demand for training services has also increased. Since operator training can have a profound effect on the success of an infrared program, obtaining quality training is of paramount importance.
At present, there are several firms that offer infrared training and certification. While nearly all infrared training firms refer to their training courses by level (1, 2, or 3), there are no standards which dictate the content of any offered course. As a result, training courses can vary widely between firms.
When choosing an infrared training firm, be certain to:
- Examine course curriculum to ensure that it meets one’s needs
- Ensure that course will be germane to all infrared imagers, regardless of age
- Ascertain if Certification is included with course, its expiration date, and renewal fees
- Determine number of years training firm has been in business – not the
cumulative total of staff years
- Insist that instructors be practicing thermographers with documentable field experience in their area of instruction
Lastly, beware of claims that training is “vendor neutral”. It is impossible for training firms to sell infrared equipment or train for equipment manufacturers without being biased. Firms who train for manufacturers work for manufacturers and cannot provide the unbiased information students deserve. Simply put, no man can serve two masters.
Infraspection Institute has been providing infrared training and certification for infrared thermographers since 1980. Our Level I, II, and III Certified Infrared Thermographer™ training courses meet the training requirements for NDT personnel in accordance with the ASNT document, SNT-TC-1A. All courses are taught by practicing, expert Level III thermographers whose field experience is unsurpassed anywhere in the world. We teach effective, real-world solutions using the latest standards, software and technology. For more information call 609-239-4788 or visit us online at www.infraspection.com.
Ways to Prevent Spam
Spam is that unwanted email that shows up in our email Inboxes on a regular basis. If you are not careful, you may find yourself receiving hundreds of unwanted emails each day. There are a number of actions you can take to limit the amount of unwanted email and preserve valuable time.
Spammers acquire email addresses in various ways. The most insidious is tricking you into confirming your email address. Frequently, the spammer accomplishes this by sending you spam with a message in the text that says something like: “Click here to be removed from our list.”
Of course, the instant you reply, the spammer knows that they have reached a valid email address – yours! You have also just confirmed that you read and respond to email. Ignore the “remove me” choice and just delete the unwanted email
If you use the Out of Office reply feature of your email program, spammers will automatically receive confirmation of your email address when your program responds to their spam by advising them of your absence. If you wish senders to receive a response during your absence, have incoming email routed to a person in your office who can send out a message for you when necessary.
In short, there is no way to prevent spam. However, you can minimize the amount you receive by not confirming your email address to spammers when they send you unwanted solicitations.
This week’s Tip submitted by Accolade Group.
How to Calculate Transmittance
Windows are semi-transparent materials placed between an object and an infrared instrument to separate conditioned from unconditioned spaces. When measuring temperatures through a window, it is imperative to know and enter the Transmittance value of the window into your radiometer’s computer to help ensure temperature measurement accuracy.
Because no object is 100% transmissive, infrared windows will always have Transmittance values of less than 1.0. Following the procedure listed below, it is possible to calculate the T value of any window.
- Calibrated imaging radiometer with a computer that allows user to input Reflected Temperature and Emittance values.
- Blackbody simulator with E > 0.95 heated close to temperature of target to be measured.
- Window that is semitransparent in the waveband of the imaging radiometer.
- Place imaging radiometer at desired distance from blackbody simulator.
- Aim and focus imager on blackbody simulator. Place crosshair on center of blackbody simulator.
- Set imager’s E control to 1.0
- Measure and compensate for Reflected Temperature.
- Measure and note apparent temperature of blackbody simulator.
- Place window directly in front of imaging radiometer’s lens.
- Without moving imager, adjust E control until observed temperature matches value obtained in Step 5 above. The displayed E value is the Transmittance percentage for this window with the subject imaging radiometer. For greater accuracy, repeat above a minimum of three times and average results.
The above procedure is described in detail in the Guideline for Measuring and Compensating for Reflected Temperature, Emittance, & Transmittance available from Infraspection Institute. For more information or to place an order, call 609-239-4788 or visit us online at www.infraspection.com.
NFPA 70E & Energized Electrical Work Permits
On February 11, 2004, the sixth edition of NFPA 70E Standard for Electrical Safety in the Workplace became available superceding all previous editions. In addition to a new look, layout, and title, the latest edition of NFPA 70E contains several important changes including the requirement for an energized electrical work permit.
The 2004 edition of NFPA 70E requires an Energized Electrical Work Permit if live parts are not placed in an electrically safe work condition. NFPA 70E requires that the permit shall include, but not be limited to, the following items:
- Description of the circuit and equipment to be worked on and their location
- Justification for why the work must be performed in an energized condition
- Description of the safe work practices to be employed
- Results of the shock hazard analysis
- Determination of shock protection boundaries
- The Flash Protection Boundary
- Necessary Personal Protective Equipment to safely perform the assigned task
- Means employed to restrict the access of unqualified persons from the work area
- Evidence of completion of a job briefing, including a discussion of any job-specific hazards
- Signature(s) of authorized personnel who are approving energized work
NFPA 70E & Arc-Rated Face Shields
Personal Protective Equipment, including fire resistant clothing, has long been specified by NFPA 70E. The 2004 edition contains several important changes including a new requirement that workers wear an arc-rated face shield.
The 2004 edition of NFPA 70E requires workers to wear an arc-rated face shield if live parts are not placed in an electrically safe work condition and work is to be performed within the Arc Flash Boundary. This new requirement applies to work having a Hazard/Risk Category 2. Face shields must have a minimum arc rating of 8, with wrap –around guarding to protect not only the face, but also the forehead, ears, and neck. A flash suit hood may be used in place of an arc-rated face shield.
For electrical systems that are rated at 600 volts or less, NFPA 70E defines the Arc Flash Boundary as a minimum of 4.0 feet for systems having an available bolted fault current of 50kA. This Arc Flash Boundary distance increases as available fault current and/or clearing times increase and may be calculated using the formulae found in Article 130.3 (A).
Copies of NFPA 70E can be purchased by calling the National Fire Protection Association at 1-800-344-3555 or online at: www.nfpa.org.
The Importance of Follow-up Inspections
Many companies that contract thermographic inspections are usually provided with a technical report clearly identifying areas and conditions that need attention. From the information contained in the report, maintenance personnel investigate suspect areas and make appropriate repairs.
Once corrective actions have been completed, it is extremely important to have the thermographer return to reinspect suspect areas to ensure that the original discrepancies have been properly repaired. One professional infrared testing company reported as many as 80% of exceptions were still present after repairs had reportedly been made. In this case, the follow-up inspection was actually more important than the original inspection.
The follow up inspection is also a good time to have the thermographer inspect equipment that may have been off line or not under load at the time of the initial infrared inspection.
Infrared thermography has the highest return on investment for all of the PPM technologies. It has been calculated at about ten dollars saved for every dollar invested. So, it is important to reinspect after repairs. A follow up infrared inspection can make a fair PPM program into an exceptional PPM program.
Preparing for IR Inspections of Electrical Systems
Perhaps the most common application for infrared thermography is PdM inspections of electrical distribution systems. However, in focusing on the inspection, many overlook the critical step of properly preparing for the inspection.
Proper planning prevents poor performance. For IR inspections of electrical distribution systems, this planning should begin well in advance of the inspection. The following are some of the not-so-obvious considerations that should be part of every inspection.
- Performance standard(s) or Guidelines to be followed
- Safety standards and rules applicable to the work areas
- Thermographer and qualified assistant(s) should be trained as qualified persons as defined by NFPA and OSHA standards
- Necessary Personal Protective Equipment including fire resistant clothing
- Provisions for First Aid and CPR
- Pre-job safety briefing prior to the commencement of the inspection
Lastly, infrared inspections should only be performed by experienced, certified infrared thermographers who thoroughly understand the theory and operation of electrical distribution systems. Properly planning for your next infrared inspection can provide for a safer and more efficient inspection.
For more information on thermographer training and certification, or to order a copy of the Guidelines for Infrared Inspections of Electrical and Mechanical Equipment, call us at 609-239-4788 or visit us online at: www.infraspection.com