Loop (impedance) testing assures that fuses and circuit breakers installed in an electrical system will still operate if a fault occurs. When a fault occurs, a circuit can be disconnected fast enough to prevent it overheating and potentially causing a fire, injury, or electric shock. Loop checking is important for businesses for safety reasons because it protects workers, buildings, assets, public liability, business continuity, and insurance. IEC 62382 Ed. 2.0 b:2012— Control Systems In The Process Industry – Electrical And Instrumentation Loop Check provides a methodology for executing a loop check.
What Are the Characteristics of an Effective Loop Check?
Loop testing verifies that sufficient current will flow to operate a fuse or circuit breaker, protecting a faulty circuit within a predetermined time. As the last systematic check before mechanical completion, IEC 62382:2012 specifies that a loop check must ensure that:
- All E&I documents (loop sheets, etc.) are available and correspond to their latest revision
- All instrumentation and equipment is delivered according to the design specifications if not already verified during FAT or quality check during equipment receiving
- Installation has occurred in accordance to engineering documents, applicable codes and local regulations
- Loop functionality is correct
What Is IEC 62382?
IEC 62382:2012 describes the steps recommended to complete a loop check. A loop check comprises the activities between the completion of the loop construction (including installation and point-to-point checks) and the start-up of cold commissioning. IEC 62382:2012 is applicable for the construction of new plants and for expansion/retrofits (i.e., revamping) of E&I installations in existing plants (including PLC, BAS, DCS, panel-mounted and field instrumentation).
This standard does not include a detailed checkout of power distribution systems, except when they relate to the loops being checked (i.e., a motor starter or a power supply to a four-wire transmitter).
For application in the pharmaceutical or other highly specialized industries, additional guidelines (for example, Good Automated Manufacturing Practice (GAMP)), definitions, and stipulations should apply in accordance with existing standards, for example, for GMP Compliance 21 CFR (FDA) and the Standard Operating Procedure of the European Medicines Agency (SOP/INSP/2003).
What Are the Phases of a Loop Check?
A loop test means that every circuit is tested to assure that the actual loop impedance does not exceed that specified for the protective device installed in that particular circuit. A loop check follows the electrical and instrumentation and control system (E&I) construction phase and factory acceptance testing (FAT) of the distributed control system (DCS) in a project. The actual loop check in IEC 62382:2012 involves three phases:
- Documentation checkout: check for the completeness and consistency of loop documents, including any documents from the installation or FAT.
- Visual inspection of loop devices for correct installation and tagging
- Function check: a testing device is used to exercise all the components of the loop (including hardware, wiring and software). It checks that all the components function correctly and that the DCS or panel readouts are accurate.
IEC 62382 Ed. 2.0 b:2012— Control Systems In The Process Industry – Electrical And Instrumentation Loop Check is available on the ANSI Webstore.