Resistance and continuity
Continuity testing confirms that each conductor of a cable is unbroken from end to end and correctly identified, while shield continuity testing confirms that the metallic shield of a shielded cable is intact and connected. A low-resistance reading means a good path, and an open or high reading points to a break, a poor termination or a damaged shield.
Continuity testing on power cable answers two simple questions: does each conductor carry current from one end of the run to the other, and is the metallic shield of a shielded cable intact along its length and connected at its terminations. Conductor continuity is checked on low-voltage cable and on medium- and high-voltage cable by connecting a low-resistance ohmmeter or continuity tester between the two ends of each conductor, with the far end looped or the two ends accessed together. Shield continuity is checked on shielded medium- and high-voltage cable, where the shield is a layer of copper tape, wires or a corrugated metallic sheath that surrounds the insulation to confine the electric field, drain charging current and carry fault current. A reading is taken between the two shield terminations, or between the shield at one end and the ground connection. The test also verifies phasing and identification, because a conductor that reads continuous to the wrong terminal exposes a wiring error before the cable is energized. It is one of the simplest tests in the program and one of the most informative per minute spent.
A cable that looks perfect can still be open, damaged during pulling, or wrongly terminated. Conductor breaks, strands cut by a lug that was crimped incorrectly, and connections that were never made are among the commonest installation errors, and they are found easily and cheaply before energizing. The shield matters as much on shielded cable. If the shield is open, damaged or not grounded, the electric field is no longer confined, the insulation stress becomes uneven, and partial discharge or tracking can begin at the point of discontinuity. A shield that cannot carry fault current may overheat or be destroyed during a ground fault. Because the effects of a faulty shield develop over months or years, the problem may not show in other tests. Continuity checks are therefore done at acceptance to prove the installation, after repairs or splicing, and during maintenance where damage from excavation, rodents, corrosion or heat is suspected. They also confirm identification of conductors before they are connected, protecting both equipment and people.
Continuity is a measurement of resistance at a very small value. A low-resistance ohmmeter passes a small direct current through the conductor or the shield and reads the voltage drop, from which it reports the resistance of the path. A sound conductor shows a very low resistance that depends on its size, material and length, and a break shows an open circuit or a value far above expectation. A partial break, such as a few strands cut at a terminal, shows as a higher reading and not as an open. Shield resistance is typically larger than that of a conductor of the same length, because shield wires or tape are thin, and its value depends on the construction, so the reading is compared with expected values for that type and length. Connections at each end contribute their own resistance, which is why clean, tight terminations matter. Because the current used is small, the test does not stress the insulation. Temperature changes the resistance of copper and aluminum, and a long run in a cold or hot environment can read differently from one on the bench, so conditions are noted.
The cable is de-energized, isolated from every source and load, proven dead and grounded under the owner's procedures, with surge arresters, electronic equipment and anything else that could be affected disconnected. Both ends are accessed and clearly identified. For conductor continuity, a low-resistance ohmmeter or a continuity tester is connected between the ends of each conductor in turn, using a temporary jumper at the far end or a second operator and a communication link, and each reading is recorded against the conductor identity. Where the instrument allows, the far end of each conductor is also checked against the others to confirm that there are no unintended connections and that phasing and identification are correct. For shield continuity, the shield termination or ground connection at each end is accessed, and the instrument is connected between them or between the shield and the ground bar, taking care that the shield is not bonded elsewhere in a way that would create a parallel path. The measurement is repeated for each cable in a multi-cable run. Connections under the clamps are cleaned for a good contact. Results are read with the length and size of the cable in mind, and any abnormal reading is confirmed by a second measurement before the cable is judged.
The record identifies each cable, conductor or phase, and shield tested, with the reading for each, the instrument and its calibration status, the length and construction of the run as far as known, the ambient temperature and the date. It notes the identification of the conductors at both ends, any phasing or labeling corrections made, and the condition of the terminations when seen. Where a reading was abnormal, the retest and any corrective action are recorded with the values before and after. This information gives later tests a baseline and lets a technician judge whether a change in a reading comes from the cable or from the connection.
This page states no limit. Conductor continuity is judged simply: a sound conductor reads as a low-resistance path consistent with its size and length, and an open or abnormally high reading marks a break or a poor connection that must be found and corrected before the cable is energized. Shield continuity is judged by comparison with the expected value for the shield construction and length, with the manufacturer's data and with the readings of the other cables of the same type in the same run, and a shield that reads open or far above its peers is treated as defective. Trending against earlier results can reveal slow deterioration, for example from corrosion. The tests are called for in the sections on low-voltage and on medium- and high-voltage cable in ANSI/NETA ATS-2025 for acceptance and ANSI/NETA MTS-2023 for maintenance. For the values and the way each treats the result, consult your own licensed copies of the standards and the cable manufacturer's data.
At acceptance, continuity proves that every conductor and shield is intact after pulling, terminating and splicing, and it confirms identification. In maintenance it is used when damage is suspected, after repairs, or as part of a larger cable program that also includes insulation resistance, jacket integrity and other diagnostic tests. Low-voltage cable calls for conductor continuity and identification, and it is often done together with insulation resistance. Shielded medium- and high-voltage cable adds shield continuity, and the construction of the shield, whether copper tape, concentric neutral wires or a metallic sheath, determines how the reading looks and where it should be measured. Cables with concentric neutrals may have a measurable resistance along the neutral wires that is compared with the expected value for the size and length. Where shields are grounded at both ends or at a single point, the grounding arrangement matters for the test setup. Continuity says nothing about the condition of the insulation, so it complements, and does not replace, the insulation and diagnostic tests.
The equipment classes and standard sections that call for this test, and the UltraDb forms that carry it.
It means there is no complete path from one end to the other, so the conductor is broken or disconnected somewhere, or the far end was not looped. The next steps are to confirm the setup, check the terminations and identify the break before the cable is energized.
The shield has a different job and a different construction. It confines the electric field, carries charging and fault current and must be intact and grounded. A shield fault does not show in conductor continuity, so it is checked on its own with the readings compared against the expected value for the shield type.
No. Continuity only shows that the metallic path is complete. Insulation condition is checked with insulation resistance and other diagnostic tests, so continuity is normally one part of a set of cable tests and does not replace the others.
A partial break, such as strands cut under a lug, still conducts but with a higher resistance, so it appears as a reading above what the size and length predict or above its sister conductors. A low-resistance ohmmeter reveals it, while a simple buzzer-type tester may not.
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