Nearly 70% of early equipment failures can be traced to design, installation, or startup deficiencies. That’s why it is so important to protect investments in new equipment or systems with acceptance testing. A thorough check of electrical power systems and components before startup can uncover and correct problems that otherwise would lead to larger, costly issues in the future.

Acceptance Testing

Acceptance testing is the physical and electrical inspection and testing of newly installed electrical equipment. This activity involves performing thorough visual and mechanical inspections as well as using calibrated test instruments to ensure electrical components and completed systems operate as designed. It occurs before the electrical system commissioning and startup, and before the new equipment is put into operation.

Taking this initial step verifies the manufactured devices are free from defects, operating as designed and intended, and were not damaged during transport or installation. Acceptance testing also ensures the equipment was properly installed for the application and meets the required specifications.

It is important that acceptance testing be performed by a third-party testing firm that is unbiased and independent in their evaluations. One important role of the testing agency is to enter protective device settings per the system coordination study supplied by an engineer. They will ensure accuracy and verify, using testing, that protection devices trip as intended and operate correctly per the manufacturer. Third-party independent testing also verifies the manufacturer is supplying the specified equipment and that it operates as designed.


Finding system and component anomalies during acceptance testing, while equipment is still under warranty, is important to ensure owners are satisfied. Determining and correcting deficiencies prior to startup can save owners both capital and maintenance dollars by preventing costly outages and equipment repairs.

Ensuring acceptance testing is performed in accordance with the design engineer quality assurance specifications as well as in accordance with standards set by the International Electrical Testing Association (NETA), National Fire Protection Association (NFPA), etc., is very important. These standards set the quality and accuracy expectations for the testing company and specify the equipment to be inspected and tested.

Another critical piece of acceptance testing is the post-energization infrared inspection of the system after it has been put to use. This step can locate hot spots, loose connection overloads, and other issues that are relatively common when a new system is put into operation. Correcting these immediately after the system is online can avoid costly outages, minimize equipment damage while under load conditions, and eliminate arc flash safety concerns.

If issues are not revealed until after a project has been turned over, correcting them requires remobilization involving personnel that may not be familiar with the project, reengaging both the commissioning agent and a testing firm for costly retesting, owner involvement, and more. Correcting defects while under manufacturer warranty is efficient, effective, and avoids unnecessary expenses to all parties.

The Right Partner

Due to the importance of conducting proper acceptance testing, selecting a good acceptance testing firm whose experience and knowledge you can trust is crucial. Consider the following criteria:

  • Independence from the manufacturer to ensure an unbiased, thorough assessment of equipment;
  • The ability to accurately interpret test results to determine the best course of action for each unique customer environment;
  • Previous work experience on similar projects;
  • Technician certification and experience to ensure thorough testing by a trained professional;
  • The firm’s size and its ability to staff with qualified professionals to deliver the project on time and within budget;
  • Awareness of all safety standards to ensure safe work practices;
  • A test equipment calibration program to ensure accurate test results;
  • Affiliations with reputable organizations, such as NETA, NFPA, etc., to confirm a firm’s knowledge and ability to follow proper acceptance testing standards;
  • The ability to perform new and innovative testing services to ensure a complete evaluation and comprehensive recommendations;
  • A nationwide reach with local service abilities to provide the necessary manpower; and
  • A strong financial standing and the ability to be a long-term provider for future testing needs.

Common Issues

Some common issues that are typically found with acceptance testing and can be costly after startup include the following.

Incorrect settings — There is nothing worse than a system put into operation and then suffering an unplanned outage after startup because the protection and controls were not properly set. Devices should be tested and left per the coordination study settings provided. The customer is asked for these settings when the testing company is scheduling the work.

Failure of cabling — Improperly terminated cables can fail months or even years down the road. Inadequately terminated cables will not necessarily fail when energized, but the voltage gradient created by a void or sharp edge on the insulating jacket of an inadequately prepped or terminated cable will degrade the insulation level over time and cannot be detected with a visual inspection. The leakage measurement during testing on the cable will be an indication of the termination quality and ability to handle in-service voltage.

Nuisance tripping of breakers with wrong current transformer (CT) ratios — The pickup of a relay (current level) is based upon the CT ratio. The protection of the system is based upon the identification and proper measurement of the fault current. Improper ratio on the CT may inadvertently trip the protective device on system inrush currents (incorrectly identifying them as fault currents). This can cause an inadvertent, or nuisance, trip of the protective device (e.g., circuit breaker). Operation of the protective device opens the circuit and takes down the power, resulting in an unplanned power outage.

Improper relay logic — Relays are designed to initiate a signal to operate a protective device when the inputs measured reach a level where faults are detected. If the relay inputs initiate a signal on the wrong output, the protective scheme will not operate the protective devices properly, which could result in catastrophic failure of the equipment.

Insulation dielectric compromised and moisture issues — Insulation failure is by far the leading cause of electrical failures. Insulation deteriorates from heat, age, and service contamination. Any particulate, moisture, or device/tool left on the surface decreases the ability of the insulation to prevent the current flow (decreasing its dielectric). At some point, this leakage will create a path to ground, and the current flow will result in a failure. Acceptance testing verifies surface contamination is not an issue during startup.

Improper grounding — Equipment grounds are electrical bonds connecting the electrical equipment enclosures to a ground path. This creates a low-resistance path to ground for fault currents if there is an equipment failure and trips the protective device in the quickest time possible. This action will halt the tens of thousands of amps associated with the fault quickly and prevent the equipment from blowing up or melting. If the equipment is not bonded properly, the fault current will not have an easy path to ground and can build up to explode or, worse yet, travel through a person to ground. Bonding is confirmed during the equipment acceptance testing.

Wrong transformer taps/improper ratios for proper voltage — Transformers do what the name says: transform the voltage level either up or down. The level of the drop or increase is dependent upon the ratio of the primary winding (input voltage) to the secondary winding (output voltage). The transformer uses electromagnetics to transfer the power (there is no conductive path across the windings). If the ratio is incorrect, the expected output voltage will not be proper for the designed usage of the electrical load — device voltage rating. Without proper voltage, the utilization equipment can fail or simply not work correctly. Part of acceptance testing is verification of the transformer turns ration (TTR). This is compared to its design voltages.

In addition to TTR testing, other tests, including winding resistance, insulation resistance, power factor, etc., should be included. The insulation testing is for the insulation capability as described above. The winding resistance ensures the similar resistance measurement is on all three phases so there is not an imbalance or an overheating situation that can occur. A properly designed and built electrical system has similar resistance measurements in all three phases.

Switchgear bus connections not properly assembled — This speaks to bus resistance measurements for proper balance and to avoid overheating. The same current wants to flow through each phase. If there is a connection that is not properly tightened, it can create a high resistance path. When put into operation (under load), the current flow will heat up, going across this higher resistance. This heat can be excessive and cause the insulation to fail over time and then fault. Fault is current flow finding an alternate path to ground. This fault current is really an explosion where the heat is intense enough to melt solid copper bus and equipment and do excessive damage.

Electrical systems are among a company’s most critical assets and can have a big impact on the bottom line. Their production and management costs are high, and failures almost always lead to catastrophic losses. Electrical systems are being operated at higher loads with less time between maintenance intervals and in environments not as designed, which affects both the life and the reliability of the assets. Investing in thorough acceptance testing helps facilities avoid costly downtime, extend equipment life, and improve safety.