Emergency light circuit sensing

Part E4 of the National Construction Code (NCC) sets out the objectives for visibility in an emergency, covering emergency lighting, exit signs (visibility & identification) and warning systems (awareness) in buildings;

In this article, we cover the need for circuit sensing, especially when artificial lights and emergency lights are on separate subcircuits.

When emergency and artificial lighting are on separate final subcircuits in the same area, it’s possible that a failure in the artificial lighting circuit may not trigger the automatic and instantaneous activation of the emergency lights, which may affect the safety of occupants in an emergency.

When the emergency and artificial lights are on separate final subcircuits, the emergency lighting system may not detect the loss of power in the artificial lighting circuit, as there is no direct connection or signal to trigger their activation.

To address this, Australian Standard AS/NZS 2293.1:2018 sets out the requirement for the sensing of the electrical supply of normal lighting circuits as follows;

AS/NZS 2293.1:2018
Clause 1.5.32 Monitored supply
The electrical supply to normal lighting luminaires, failure of which is sensed by the emergency lighting system.

and;

AS/NZS 2293.1:2018
Clause 2.3.3 Sensing of supply failure
Within a designated area the failure of the normal supply to final subcircuits supplying lighting to that area shall cause each emergency luminaire and exit sign in the area served by the subcircuit to be automatically connected to its emergency power source.

NOTE: This requirement does not preclude other emergency luminaires and exit signs, connected to subcircuits that might not have lost supply, from also being automatically connected to their emergency power sources in response.

Where any part of a designated area is served by more than one normal lighting subcircuit, the arrangement and connection of the emergency luminaires and exit signs shall be such that the illuminance provided by the normal lighting luminaires on the circuits that are sensed for loss of supply is not inferior to that provided by the required emergency lighting.

In New Zealand, where non-maintained exit signage is used, it shall be configured to be energized in the event of activation of the fire alarm system.

NOTES:

1. See Figures C1, C2 and C3 of Appendix C for example circuit arrangements.
2. See Clause 3.3 for additional requirements which may impact upon the connection of emergency luminaires and exit signs for testing purposes.
3. In New Zealand, where generators are permitted to provide emergency lighting power supplies, refer to Clause F6 of the New Zealand Building code.

Where an emergency light or lights are on a different final subcircuit from the normal (artificial) lighting in the same area, a "sub-circuit sensing device" or "power sensing device" is required to be installed (typically at or within the electrical switchboard) where the electrical circuits commence.

There are a range of these "sub-circuit sensing device" available from different manufacturers that support the monitoring of one or more separate normal lighting final subcircuits.

These devices solve the problem by sensing the power from one or more normal lighting final sub-circuits and then activating a contactor to enable the operation of the emergency lighting circuit in the same area.

These devices may also include integrated the the required emergency light and exit sign test facilities described in Section 3 of AS/NZS 2293.1:2018.

Where the automatic and instantaneous operation of emergency lights in a building does not occur when the artificial lighting in that area has failed, then this poses a risk to health, safety and amenity of the building.

Workers conducting tests of emergency lights and exit signs in buildings should verify that the failure of artificial lighting final subcircuits in a given area, operate the emergency lights in that same area.

NOTE: Testing this functionality may pose a problem and risk to the existing occupants of a building for the duration of the test.

To verify the operation of the emergency lights in the same area of the artificial lighting, where the power supply for each is on its own final sub-circuit, the following general procedure may be employed;

1. Conduct relevant precautions & check with the building owner, building owners agent or occupant of the building prior to conducting the test;
2. Ensure that the failure of the circuits will not adversely affect the occupants of the building or other powered devices for the duration of the test;
3. Verify the emergency lights and artificial (normal) lighting circuits are on their own discrete separate final sub-circuits.  This will typically require the skills, knowledge and experience of a competent and licensed electrician.
4. Confirm the area of each artificial (normal) lighting sub-circuit and the corresponding emergency light circuit in that area. Note that one emergency lighting circuit may be operated by the failure of one or more artificial (normal) lighting sub-circuits.
5. Where safe to do so, conduct a test of each artificial (normal) lighting sub-circuit by isolating the power to that circuit (typically operating a circuit breaker) and verify the automatic and instantaneous operation of emergency lights in that area.
6. Record the results of each test, documenting the area tested and each circuit or circuit breaker affected.
7. Reinstated the circuit to its normal operation condition.

Where a failure of the automatic and instantaneous operation of emergency lights in an area is identified, it may be considered a defect for the purposes of satisfying the requirements of the NCC and AS/NZS2293.1

Where the emergency lights fail to operate automatically and instantaneously where power is lost to the artificial (normal) lighting in the same area it may be considered a defect.

This depends somewhat on the date of construction of the building or the date of installation of the emergency lights.

Notwithstanding, people entering a building have a reasonable expectation that the building will be safe to occupy and exit in the event of an emergency.  Building owners, agents of owners and occupiers have a responsibility and duty to ensure the safety of the occupants of the building consistent with the Objectives set out in the National Construction Code.

Always the question arises that if the Objective of the NCC and a requirement of the Standard does not exist, is it a defect?

The answer to this question may depend on the  date in which the building was constructed and approved or a seperate matter of workplace health and safety.

For most buildings constructed or substantially altered after 2005 will require the facility to monitor the power supply of seperate final sub-circuits in the same area, meaning that an argument can be made that it was a requirement of the the Australian Standard at that time.

From a workplace health and safety standpoint, its reasonable to assume that an occupant of a building should reasonably expect the safe egress from the building in the event of a fire or other emergency where the artificial lighting has failed.

Where a defect of this nature exists, that is the emergency lights do not operate automatically and instantaneously in the event of a power failure of the normal lighting in the same area.

The solution is to scope and install an appropriate power sensing device that operates the emergency lights in the same area.

This will require the supply and installation by an appropriately licensed and experienced electrician of the following;

1. Identification and quantity of each affected artificial (normal) final sub-circuit at each electrical switchboard; and
2. The installation of one or more power sensing devices for each affected area (based on the aforementioned quantities. Note that the number of final sub-circuits that can be sensed by the power sensing device depend on the make, model and manufacturer of the power sensing device; and
3. The installation (if required) of a contactor to activate the emergency lighting final sub-circuit, triggered by the operation of the power sensing device.
4. A functional test to verify the operation of the new arrangement;
5. Updates to labelling, drawings or other baseline data required by the Standards.
6. A certificate of electrical safety or equivalent in your jurisdiction.

In this article, we’ve covered the importance of circuit sensing for emergency lighting systems, particularly when normal and emergency lights are on separate final subcircuits.

Without proper circuit sensing, emergency lights may not activate when artificial lighting fails, posing a risk to building occupants. Compliance with the NCC and AS/NZS 2293.1 ensures that emergency lighting activates automatically and instantaneously, providing safety during emergencies.

Maintenance providers, building owners, agents of owners and occupants should ensure that power sensing devices are installed where needed and regularly tested, ensuring the safety of occupants.