Voltage alarms: phase-to-neutral or phase-to-phase, and what limits?

[ShiftAnalyst]

Our analyzers provide both phase-to-neutral voltages (L1N, L2N, L3N) and phase-to-phase voltages (L12, L23, L31). We want to set voltage alarms because some of our machines reset during voltage dips, and we'd like to correlate those resets with the supply.
I'm not sure which voltages to use for the alarms, and what limits are reasonable. If I set them too tight, operators will get dozens of alarms per day; too loose and we miss the events. How do others approach this?

[Technical Support]

Good question. Here is a practical approach.
Which voltage to monitor
- Phase-to-neutral (L1N, L2N, L3N): best for single-phase loads, control circuits and most electronics. Many machine controls are fed phase-to-neutral, so dips that reset controllers usually show up here first.
- Phase-to-phase (L12, L23, L31): relevant for three-phase motors and drives.
In a low-voltage network both are useful; for your reset problem, start with phase-to-neutral.
How to set the limits
1. Find the nominal voltage of your network and the tolerance band your utility or national regulation guarantees, and the voltage range in your machines' specifications.
2. Set two levels:
- Warning: a moderate deviation from nominal, logged but with low priority.
- Critical: a larger deviation, close to the level where machines are known to reset.
3. Watch the values for one or two weeks before fixing the limits, so they match your real network.
Avoiding alarm floods
- Use a short delay or a small hysteresis if your system supports it, so a value oscillating around the limit doesn't create dozens of alarms.
- Monitor all three phases, but group the alarms per panel to keep the list readable.
Important limitation
Very short dips (a few cycles) can be faster than a normal polling interval. If you want to capture them reliably, check whether your analyzers have their own event or min/max recording, and read those values instead of relying only on periodic samples.
Correlating with resets: record the reset times from the machines and compare them with the voltage history of the same panel.