| Insulation resistance | IEC 61557-2 | Measures insulation resistance in de-energized circuits to help assess insulation condition. | Check that the tester provides the test-voltage settings and measurement range required for the intended installation and applicable test procedure. | Core function for installation verification and maintenance. |
| Continuity and resistance of protective conductors and bonding connections | IEC 61557-4 | Measures low resistance in earth connections, protective conductors, and equipotential bonding connections. | Look for a dedicated low-resistance continuity function, suitable test leads, and a method for compensating lead resistance where required. | Core function for checking protective-conductor and bonding paths. |
| Loop impedance | IEC 61557-3 | Measures the impedance of fault-current loops, supporting assessment of automatic disconnection by protective devices. | Confirm compatibility with the system and protective devices being tested; an RCD-compatible loop-test method may be useful where applicable. | Core function for many low-voltage installations. |
| Earth electrode resistance | IEC 61557-5 | Measures resistance to earth using methods appropriate to the electrode arrangement and test conditions. | Check which measurement methods the instrument supports and whether the required leads or auxiliary electrodes are available. | Important where the installation relies on an earth electrode. |
| RCD effectiveness testing | IEC 61557-6 | Tests residual current devices used in TT and TN systems as part of assessing protective measures. | Verify support for the RCD types and test procedures relevant to the installation; check that trip-time and, where applicable, trip-current tests are available. | Core function when residual current devices form part of the protection scheme. |
| Phase-sequence indication | IEC 61557-7 | Indicates phase sequence in three-phase systems. | Check that the tester identifies phase rotation clearly and is suitable for the system voltage and measurement conditions. | Useful for three-phase installation checks and equipment connection work. |
| Insulation-monitoring device testing | IEC 61557-8 | Addresses equipment for testing insulation-monitoring devices used in IT systems. | Choose this function when the work specifically involves IT systems and their insulation-monitoring devices. | Specialized; not required for every general installation test kit. |
| Insulation-fault location | IEC 61557-9 | Addresses equipment for locating insulation faults in IT systems. | Check compatibility with the IT system and fault-location method in use; this is usually a specialist requirement. | Specialized maintenance and fault-finding in IT systems. |
| Combined measuring equipment | IEC 61557-10 | Covers combined equipment used to test, measure, or monitor protective measures in low-voltage distribution systems. | For a general-purpose kit, compare the included functions against the tests actually required; a combined instrument does not necessarily include every function in the IEC 61557 series. | Relevant when selecting a multifunction installation tester. |