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Dr Zzeus - February 2022


I've been told that all electrical circuitry needs to be checked with an insulation resistance test instrument every five years which would require the removal of every device such as detectors, call points and sounders. Is this correct?

The short answer is that BS5839-1:2017 does not require an insulation test every five years. The British Standards requirements are as follows:

1. Periodic testing

BS 5839-1 does not have any requirement for insulation testing at a five-year period, Additionally, the 18th Edition of BS 7671 makes it clear that the periodicity between inspections of electrical installations is a matter of assessment by the inspector.

Concerns the inspector would consider include:

  • Regulations and legislation, any licencing requirements and insurance obligations, as well as an assessment on the deterioration of the electrical installation.
  • Dismantling of the system is to be avoided during scheduled maintenance and servicing.
  • Fire alarm final extra low voltage (ELV) circuits from the CIE are all wired in fire-resisting cable which is continuously monitored for faults by the CIE. The low voltage (LV) mains cabling is not continuously monitored and must be assessed as part of the general electrical installation.

2. Initial Installation of fire alarm and detection cables

At the initial installation of any fire alarm and detection system cable Clause 38.1 states:

All installed cables with a manufacturer’s voltage rating suitable for mains use should be insulation tested at 500 V d.c. Prior to this test, cables should be disconnected from all equipment that could be damaged by the test.

Insulation resistance, measured at testing, between conductors, between each conductor and earth, and between each conductor and any screen, should be at least 2 MΩ.

Control and Indicating Equipment (CIE) typically have fault sensing for wiring insulation resistance to earth. If this is set at 1 MΩ, the combined effect of all wiring earth insulation resistance ought to be well above this to prevent nuisance fault indications.

For substantial systems, this 2 MΩ minimum needs to be significantly higher than this to attain somewhat in excess of 1 MΩ overall. For a small non-addressable system, 2 MΩ might be acceptable.

Earth continuity and, for mains supply circuits, earth fault loop impedance, should be tested to ensure compliance with BS 7671.

The following tests below should be carried out on completion of the installation work:

  • Where maximum circuit resistance for any circuit is specified by the manufacturer or supplier, measurement of the resistance of every such circuit should be taken.
  • Correct polarity of all circuits is checked where this is required for correct monitoring (Assure operation of any manual call point while all detectors on a circuit are removed).
  • The findings of all tests should be documented and presented to the company or person responsible for commissioning the system.

Any other checks stipulated by the manufacturer of the system must also be carried out at this point. On the model Installation certificate in Annex G of BS 5839-1 it clearly states that the tests in accordance with Clause 38 have been carried out and results provided to the commissioning person.

It often surprises me that many fire alarm and detection companies do not carry out any insulation and continuity tests on cables at installation.

This seems to have stemmed from some of the fire trade associations historically carrying out theory training on fire alarm and detection systems but with no knowledge on the required electrical training and testing.

BS 5839-1 is clear on insulation and continuity testing, and if we do not train technicians how to carry it out, it will not get done.

About the author

Tom Brookes

Tom has a PhD with his dissertation, Creation of pathways for the professional recognition of fire alarm engineers in the UK, gaining maximum credits; he has recently become the first Chartered Engineer in the UK based solely on fire alarm knowledge and skills and is keen to help other fire alarm engineers gain professional recognition.

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