What’s the real impact of a broken neutral in a 3-phase 4-wire system?

Question

I’ve read that a broken neutral in a 3-phase 4-wire system can cause serious problems, especially in systems with unbalanced loads, but I’m not entirely clear on what exactly happens when the neutral is lost.

Let’s say the system is supplying a mix of single-phase loads (like in a commercial or residential setup). If the neutral breaks at some point—what are the actual consequences for the connected loads?

Do voltages across phases shift dangerously?
Can it damage appliances or equipment?
How does the system behave differently under balanced vs. unbalanced load conditions?

I’m looking for a practical explanation of what happens electrically and what kind of damage or safety risks it introduces. Real-world examples or typical protection mechanisms would be great too.

Thanks!

LogicLab · Answer

Yeah, losing the neutral in a 3-phase 4-wire system can cause major issues, especially if the loads aren’t balanced (which they usually aren't in real-world setups like homes or small businesses).

What actually happens is this: the neutral point “floats” because there's no solid reference anymore. So instead of each phase staying around 230V, the voltages start to shift depending on the loads on each phase. Light load = lower voltage, heavy load = higher voltage. In the worst cases, one phase might go up to nearly 400V—way more than your appliances are built for. As a result, you'll see major voltage fluctuations in your supply.

There are protection relays and devices that can catch this (like a phase failure relay or neutral monitoring), but not every system has them—especially older setups.

In short: broken neutral = unpredictable and often destructive voltage swings. A real pain to troubleshoot if you don’t catch it quickly.