Let's break down what you're describing and the likely scenario: "Half normal": This likely means half of the lighting fixtures are wired to a standard lighting circuit, operating on a single phase with a live (L) and neutral (N) conductor. "Half EM/NL": This likely means half of the lighting fixtures are part of an Emergency Lighting circuit. EM/NL stands for Emergency Maintained/Non-Latching. This means the lights are normally on powered by the normal mains, and in a power outage the emergency lights remain on through a battery or other backup power source. The important part here is that they still need a neutral to function normally.

Do they share a neutral? Likely, but it's critical to confirm. The emergency lighting circuit is still normally powered by the normal mains when it's not in emergency mode.

Explanation and Considerations


Normal Operation

When the normal mains power is present, both the "normal" lights and the emergency lights are powered from the same source. They both need a path for the current to return, which is the neutral conductor.2.

Emergency Mode

When the mains power fails, the emergency lights switch to their backup power source. The emergency circuit needs to be designed in a way that it isolates itself from the normal main input.

Important Safety Considerations



Neutral Loading

Sharing a neutral is fine in this configuration, but it's crucial to ensure that the neutral conductor is appropriately sized to handle the combined current of both circuits (normal and emergency). Overloading a neutral can be extremely dangerous and a fire risk.

Circuit Breaker Coordination

Each circuit (normal lighting and emergency lighting) must have its own properly sized circuit breaker.

Qualified Electrician

This type of wiring requires a qualified electrician who understands emergency lighting systems, circuit design, and electrical codes. Incorrect wiring could lead to the emergency lights failing to operate when needed, create a fire hazard, or damage equipment.

In short, it is possible that the circuits share a neutral wire. However, this is a safety critical situation and needs to be verified by a qualified electrician. Flag for review