Protection against lost neutral connection
Since most events require large amounts of electrical energy, we tend to use 3-phase electricity. This means a connection with five separate lines: protective earth (also known as ground), neutral, and three phase lines (L1, L2, L3). Between the shared neutral line and each phase line, you typically have 230V. The neutral line acts as a reference and anchor point for the entire system.
The myth of zero neutral current
There is a common, but incorrect, belief that no current flows through the neutral line when a 3-phase supply powers a multichannel power distributor with multiple single-phase outlets. In reality, zero neutral current only occurs if all three phases draw exactly the same amount (and type) of current. This can be true when powering 3-phase motors, but for modern AV equipment, this is almost never the case.
A real-world example
Let’s say you are powering an LED display consisting of 120 panels, split into three groups of 40 panels, each supplied from a different phase. Balanced? As far as distributing the load across the three phases, yes. But will this result in zero neutral current? Absolutely not, unless each panel draws exactly the same current which practically never happens. The current drawn by each LED panel is almost directly proportional to its brightness and the image being displayed. The neutral current is the imbalance of all three phase currents. With an LED display showing constantly changing images, the neutral current will shift right along with it.
Stable neutral connection – voltages balanced across all phases
How neutral current imbalance develops
Look at this image: it shows the three phase lines (L1 to L3) and their common reference point – the neutral connection. The length of each arrow represents voltage.
Now imagine that each arrowhead is a pulling force, proportional to the current drawn by that phase. If all three arrowheads pull equally, then removing the neutral reference point will have no effect – the system will stay balanced, with all neutral-to-phase voltages remaining at 230V.
However, if, for example, L1’s arrowhead pulls much more than L2 and L3, the common reference point will shift. L1’s arrow will become shorter (lower voltage), while L2 and L3’s arrows will become longer, meaning the voltage on those phases will rise dangerously.
Lost neutral – dangerous voltage imbalance and phase shift
What happens when devices begin to fail?
As devices powered by L2 and L3 begin to fail under overvoltage and lose connection, their current draw (“pull”) will reduce. This will cause the reference point to shift even further, creating even greater voltage swings across the phases. All of this happens in fractions of a second. No fuses, circuit breakers, or residual current devices (RCDs) will stop this from happening – because these devices only monitor current, not voltage.
Why neutral connections fail
Why would a neutral connection be lost? It happens more often than you might think, and for many reasons.
For example:
A rented cable where a previous user disconnected the neutral
A poor or loose connection
A cable damaged during setup or run over by a forklift
These are real-world examples we’ve seen time and time again.
How StageSmarts protects against neutral loss
Clearly, this needs to be protected against and with a system from StageSmarts you get this as part of the package.
We recognised the impact of this problem and we developed our own loss-of-neutral sensor system that rapidly disconnects the system from the main supply. This happens in a fraction of a second, fast enough to prevent serious and costly damage to your equipment and reputation.
