ALLPCB
Overview
In power systems, a live neutral at the distribution room is a common but problematic issue. If a voltage tester indicates about 70 V to earth, this usually points to leakage or poor grounding in the system. Rapidly locating and resolving such faults is essential. This article summarizes responses from several contributors and discusses possible causes and solutions.
Possible causes
First, understand why the distribution-room neutral becomes live. This is often caused by phase conductors leaking current, causing current to return to the supply via abnormal paths and thus energize the neutral. Poor grounding or excessively high earth resistance can also be a cause.
Troubleshooting methods
Contributor A recommended a sequential disconnection and measurement method. By disconnecting circuits one by one and measuring, the fault range can be progressively narrowed until the leakage point is found. This method is time-consuming but practical, especially in complex environments such as factories.
Contributor B suggested checking the conductor joints between the transformer neutral point conductor and the distribution-room neutral. If conditions allow, measure the neutral current at the transformer neutral point to determine whether there is an abnormal current. Also consider whether the neutral conductor cross-section is sufficient to avoid overheating or conductor failure due to undersized wiring.
Grounding and PEN conductor checks
Contributor C pointed out that the main PEN terminal strip earth resistance may be too high. Check whether any buried PEN conductors are broken. A practical resolution cited was installing a larger buried cable to reduce earth resistance.
Contributor D emphasized the importance of the earthing mesh. The earthing network near the transformer may have excessive earth resistance or insufficient earth electrodes. One recommendation was to use two galvanized flat straps, 40 x 4 mm, buried to a depth less than 0.7 m and welded to the functional neutral. Another case involved driving two 60 x 6 mm galvanized angle irons near the low-voltage cabinet as earth electrodes, which resolved a similar issue.
Summary and safety
Solutions for a live neutral in the distribution room cover multiple areas. In addition to sequential disconnection and checking conductor joints, attention must be paid to earth resistance and the condition of the earthing network. Select the appropriate measures based on the specific situation. When performing these operations, always follow safety procedures and applicable regulations to prevent accidents.
