29.1 Commentary

1. Standards Compliance:

● Fire alarm power supplies must conform to BS EN 54-4.

● Extra Low Voltage (ELV) Safety:

● If ELV circuit terminals can be exposed (e.g., when a detector is removed), the power supply must meet the requirements of a Separated Extra Low Voltage (SELV) installation.

● SELV installations must conform to Section 414 of BS 7671:2008+A3.

● Low Voltage (LV) Connections:

● All connections to LV supplies or equipment must use components rated for LV.

● This includes all power supplies and LV interfaces used in the fire alarm system.

● Interfacing with ELV Equipment:

● When interfacing with ELV equipment not intended for removable components (e.g., fire detectors), treat the ELV equipment as if it were LV to maintain electrical safety.

29.2 Recommendations

The following recommendations are applicable.

1. Compliance with Standards:

● System design must meet BS 7671 requirements. CPCs (circuit protective conductors) should be adequately rated.

2. Manufacturer's Instructions:

● Follow the CIE (Control and Indicating Equipment) manufacturer’s instructions for earthing arrangements.

3. Segregation of Circuits:

● LV (Low Voltage) and ELV (Extra Low Voltage) circuits must be segregated as per 26.2n) and Clause 28.

● ELV fire alarm cables sharing containment with other cables must have insulation rated for the highest voltage.

4. ELV Circuits with Removable Components:

● Power supplies must conform to BS EN 54-4.

● In dry conditions, detectors can be freely removed.

● In wet areas (e.g., bathtubs, pools, saunas, agricultural sites), one of the following is required:

a) Circuit voltages ≤15 V d.c. ripple-free or ≤6 V a.c. rms.

b) Use of special tools or techniques for removal.

c) Components must be out of reach of unauthorized personnel.

5. Isolation of Mains Supply:

● Provide local isolation for the mains supply to all system parts.

● Isolation facilities should be near the equipment and lockable to prevent unauthorized use. See Clause 25.

NOTE 2 The contractor responsible for supplying the 230 V mains power supply needs to ensure that the particular device used does actually afford isolation. A number of switching devices do not meet the required isolation performance criteria. BS 7671:2008+A3:2015, Table 53.4, details whether a particular device can be used for the purpose of “isolation”.

29 Electrical earthing