Swapping Phase and Neutral

Will an electronic energy meter measure accurate when I invert phase and neutral during installation? This question came up recently.

Single Phase Meter

If phase and neutral is swapped, the single phase meter still records the energy accurate. It does also not matter whether you invert on the mains-side or on the load side.
This is part of the fraud-prevention measures in CLOU energy meters. If you have a meter from another manufacturer, you need to ask.
If the meter has logging capabilities, you will see this as event in the tamper logbook.

Three-phase four wire meter

Let’s make a theoretical approach first. From the meter side you will have extremely unbalanced voltage conditions because now a phase is building the star connection.

Practically the same thing happens in the grid.
We pull at the meter a phase-potential on neutral. This is a classical shortcut. Either a protection relay or a breaker will trip. Typically, the meter with the phase-neutral inversion is installed together with several other meters behind a distribution transformer. Latest this transformer has a protection.

phase-neutral-displacement
phase-neutral-displacement

In the unlikely event that your meter is the only one behind the distribution transformer and the neutral line is not grounded you can expect something like shown in the graphic. The voltage angles and magnitudes are additionally depending on the unbalance of the load.
Home appliances might be damaged and the meter accuracy is unpredictable.
A tamper will be logged.

This article is simplified to give you a brief idea. For three-phase four wire systems always make sure that you connect the neutral at the designated terminals and with the right cross-section. The N-current can reach factor 1.5 of the phase current depending on the phase loads and harmonics.

Thank you for reading.

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