Technical Bulletin: Topic: Insulation resistance testing for fire, water, lightning and smoke damaged wiring and electrical distribution systems (Megohmmeter Testing)

Today Mr. Brian Blanchette of IDEAL Industries, Inc.’s Test & Measurement Division held the first in a series of training classes focused on insulation resistance testing. Sponsored by ER Inc. (Electro-Mechanical Recertifiers, Inc.²) of Ocean City, MD. in a joint session including AMP Electrical Contracting, Inc.³, also of Ocean City, MD. This training class was devised to ensure that the project managers, electricians and consultants are properly performing electrical inspections and correctly using insulation resistance testing equipment as well as how to properly interpret the test data. The importance of proper insulation resistance testing and techniques are applicable after flooding, fire or lighting damage events which impact the wiring system of a building.  Electro-Mechanical Recertifiers, Inc. provides technical and engineering power related reports to insurance carriers and risk managers who have experienced an event affecting buildings wiring system, power distribution gear or electronics and equipment from computers and IT components to compressors and all types of machinery.

Insulation resistance testing is commonly referred to as “megging” insulation, but that is a confusion of a particular brand name and the actual function. Insulation testing is in reality the use of a specialized tester that generates a current at selectable voltages that confirms the quality of electrical insulation, a dielectric material. 

Insulation testing is mandated throughout most of the world both as proof testing before new installations are energized, and also as a critical part of continual maintenance of all electrical gear.  

The Insulation Tester, also known as a Megohmmeter, tests the quality and  condition of the insulation or outer jacket covering wires in a wiring system.  The insulation of individual conductors is performed before commissioning a facility as well as periodically after installation to ensure the insulation properties have not degraded over time.  Testing at normal operating voltage can determine if the wiring jacket has been compromised or damaged in a way that will cause excessive current leakage leading to a short circuit.   Regular insulation testing prevents catastrophic failure of electrical equipment, and prevents unplanned downtime. 

A portable handheld battery operated insulation tester uses DC current and is considered to be a non-destructive test.  By pressurizing the insulation to nameplate voltage and higher voltages, any current leaking through the insulation is measured and displayed as a resistance in millions of ohms, (megohms).  Even brand new insulation allows a tiny amount of current to pass through, so when current is applied to a system, wiring circuit or a motor winding, you can measure and record the effect of time, moisture, heat, and cold on the insulation.  Applying the proper voltage for the proper amount of time is essential to a successful test as too high a test voltage can damage sensitive equipment, and tests run for too short a time period do not indicate the proper leakage current.  Insulation testing must never be done on live circuits and should only performed by trained electricians or equipment technicians.

According to Mr. Blanchette the importance of insulation resistance testing should not be minimized.  This testing method allows for engineers, testing agencies, electricians, equipment technicians and consultants to take a “look” at the condition of the insulation on wires buried deep within the ground, hidden inside structures walls or pulled through building pipe conduit.  An insulation test is a “snap shot in time” that accurately determines the condition of the insulation at that time, temperature and moisture level.  Multiple tests can be performed that further define the quality of the insulation, and the possible contamination or moisture content.

Unless rated for use underwater, wire that has been submerged and completely soaked wire will not pass minimal insulation requirements.  Water under pressure almost always permeates common dielectric materials like vinyl, plastic and rubber.  Insulating materials can sometimes be dried out and after proper testing can be salvaged and brought back to original quality.  When the wiring is clean, dry, and tested to confirm that any current leakage meets the requirement, then the wire may be put back into service. Experts are aware of electrical devices and conductors that can be cleaned and tested, and those that need to be replaced.  Smoke or heat damaged wire may have other problems. Smoke contains soot that is corrosive and can break down the polymers and compounds in PVC, rubber and other materials used in insulating jackets.  This soot can be highly corrosive and needs cleaned and tested or may be at risk of critical failure in the future. Improper cleaning and painting of outer jackets may harm the outer insulating cover and result in premature failure. Excessive heat can cause thermal damage meaning the thermal set temperatures of the jackets substrate during manufacture may have been physically or chemically altered and at certain levels the conductor may also be affected by the heat damage. Physical inspection and electrical testing are important to ensure that the thermal damage has not melted and carbonized the insulation surrounding the conductors that will eventually result in a dead short.

The insulation testing techniques, properly performed and documented, confirm the condition of the dielectric material of each conductor and circuit in the wiring system at a specific point in time.  Eliminating catastrophic failure of building wiring systems by means of a proper insulation testing program provides clients a scientific method to ensure them that their electrical distribution system is intact at a specific point in time- this is peace of mind. 

Periodic, regularly scheduled insulation testing is often performed by electricians or testing personnel in factories as part of the preventive maintenance of the switchgear and motors.  Over time electrical systems degrade due to sunlight, vibration, moisture, chemical or extreme temperatures.  Regular Preventive Maintenance is the best tool to prevent downtime and failure.  

In summary, insulation testing after a disaster event occurs, or as part of a regular maintenance schedule ensures that electrical systems are safe to be energized. The value of the Insulation Resistance Test is to locate failed insulation before a failure, but also to monitor the slow degradation of insulation in critical systems.  Insulation testing with a safe battery operated tester will help find and help identify issues for repair or replacement when insulation past its useful age, unseen damage from vibration, poor installation methods and potential failures from imposed contaminates and other external sources of physical damage affecting the condition of the wiring.  Insulation testers can also used to confirm that power distribution equipment and wiring may be reenergized after being wet. The NFPA70⁵ recognizes this level of testing and recommends it under different conditions as an approved testing methodology.

Also auditing the class and involved in writing and reviewing our consulting reports at ER Inc. and helping us to refine and  constantly upgrading our safety programs, work methodology, technical processes, chemistries and how contaminates affect the various substrates as well as oversight of our third party testing protocols was Mr. Rick Renshaw of Renshaw Engineering of Salisbury, MD. Rick is holds a P.E. designation in many states and operates as the independent consulting electrical engineer under agreement with Electro-Mechanical Recertifiers, Inc. as our staff consulting engine

Insulation resistance testing should be used as an evaluation tool to determine the condition of installed wiring affected by vibration, shock damage, expansion & contraction, time, as well as other outside factors being introduced to the wiring system including but not limited to sources such as clean water damage, storm (salt water) surge, heat, oil, grease, chemical occurrences, and fire or outside flooding.

For all your electronics restoration and equipment needs call ER Inc. when you experience a disaster event.  Additionally when you need consulting assistance or reports after a power outage, lighting event, flood or fire that might have compromised your clients or your electrical system call us. For an expedited on-site analysis and subsequent report. ER Inc. is sensitive to time issues of insured’s and client being out of business and down.  Getting businesses back in business is our business. Call ER Inc. at 877-378-4183 for all your consulting needs.

¹ ©2011 IDEAL INDUSTRIES, INC. All rights reserved

² ®ER Inc. and Electro-Mechanical Recertifiers, Inc. is a registered corporation in Ocean City, MD, USA

³ ®AMP Electrical Contracting, Inc. is a registered corporation in Ocean City, MD, USA

⁴ AVO, MEGGER, POWERDB, PROGRAMMA and STATES are registered trademarks of Megger Group Limited or its subsidiaries. Copyright © Megger Limited 2011

⁵ NFPA70 is part of the National Fire Protection Act and governs the NEC or National Electrical Code

This press release is provided courtesy of Electro-Mechanical Recertifiers, Inc. © 2011 for the general education of our clients and for their exclusive use while recovering from a disaster event or occurrence.

For release March 26, 2011