Electrical safety testing

A dielectric voltage withstand test (also known as a hipot test) is done by applying a voltage higher than operating voltage to the device or installation under test. In this test, the electric insulation of a product or installation is put under a voltage stress much higher than its normal operating voltage. If the hipot test is done for type testing purposes, a much larger voltage may be applied.

An insulation resistance test (IR test) measures the electrical resistance of insulation by applying a voltage between two locations, and measuring the resultant current flow. Proper safety precautions must be taken when doing this test, such as exclusion zones, making sure no wires are exposed, and personal protective equipment is worn. To do this test, you need to have an insulation resistance tester, which may be a small hand held battery powered device, up to a larger luggage sized tool able to achieve higher test voltages. Variables to choose before starting an electrical resistance test is the test voltage, test duration, and test points. Acceptable values of insulation resistance vary depending on circuit purpose, industry, and country. Typically, standards will dictate acceptable values. An insulation resistance test can be used for simple go/no-go testing, or for periodic condition assessment, where routine insulation resistance tests are performed, with the results tracked over time. By tracking the insulation resistance of a circuit over time, preventative maintenance may be able to be planned before equipment failure. Insulation resistance is dependent on temperature and humidity variations, therefore the temperature and humidity should be recorded when testing and compensation applied to the measured value given.[1] Many standards and safety agencies have specified the insulation resistance test as a required test for electrical installations and electrical products. This test may be referred to as "meggering', after the company Megger was one of the first companies to commercialize an insulation resistance test meter. These days, many other brands are widely available.

An earth continuity test checks if a metal part is connected to earth. The resistance of the connection to earth can also be measured.

A leakage current test detects current that does not flow back through the circuit. This test may be used as part of testing GFCI or RCD operation.

An Electrical Installation Condition Report (EICR), more commonly referred to as an EICR Inspection, it is designed to provide a thorough assessment of the condition of electrical installations. This report provides invaluable information to ensure that electrical installation is safe and compliant with current regulations. Since it’s so important, one must understand how long such a certificate lasts before needing another round of testing. An EICR, is a comprehensive inspection and testing of the electrical installation in a building, carried out every 5 years or before the expiry of existing EICR report.[3]

The competent person will then issue an Electrical Installation Condition Report (EICR), also known as Periodic Inspection and Testing Report (PIR),[4][5] detailing any observed damage, deterioration, defects, dangerous conditions and any non-compliances with the current safety standard which might give rise to danger.

If anything dangerous or potentially dangerous is found, the overall condition of the electrical installation will be declared to be 'unsatisfactory', meaning that remedial action is required without delay to remove the risks to those in the premises. A typical classification of faults found is:

• C1 – Danger present. Risk of injury. Immediate remedial action required.
• C2 – Potentially dangerous. Urgent remedial action required.
• C3 – Improvement recommended.
• FI – Further investigation required.[6]

A concept introduced in the standard for medical electrical equipment IEC 60601-1.[9][7]

Electrical safety standard set forward by standards organizations across the globe such as the American National Standards Institute (ANSI),[10] Canadian Standards Association,[11] and European Commission in IEC60601-1. MOPP safety standards aim to set basic safety requirements for medical electrical equipment. "With hazardous voltages present in a system a robust and reliable approach to isolation is needed such that multiple and un-related insulation system failures would need to occur before an operator or patient is put at risk. To achieve this, two independent measures of protection are required or a single measure of physical isolation such as creepage/clearance or solid insulation deemed equivalent."[12] In addition to the insulation of the device being powered the additional main points the organizations have set forward with the implementation of the MOPP standards are:[13]

• Leakage current requirements.
  • The maximum allowable patient leakage current is 500µA AC and 50µA DC in normal operation (normal condition, NC) and 1000µA AC or 100µA DC in single failure condition (SFC).[13]
• Requirements for the input stage.
• Temperature measurement and requirements.
• Printed circuit board (PCB) thickness requirements for multilayered boards.
  • The distance for insulation thickness of 0.4 mm or three layers of insulation foil (Prepreg) are acceptable for reinforced insulation.[13]
• Dielectric testing.
• Maximum output energy
• Enclosure and mechanical fire requirements

Example

Example showing the differences between the isolation and creepage requirements for MOOP and MOPP.[14]