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CROSS Safety Report

Poor electrical safety standards in fire alarm installation

Report ID: 1158 Published: 21 May 2024 Region: CROSS-UK


Overview

A reporter raises concerns regarding electrical safety practices associated with a fire alarm system installation.

Key Learning Outcomes

For building owners, developers, and facilities managers:

  • Ensure that fire detection and alarm engineers you engage can demonstrate their competence in electrical safety, as well as fire alarm system design and installation

For designers, engineers, and contractors:

Full Report

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A concern was received regarding electrical safety practices. Specifically, the reporter is concerned about:

  • the protection against electrical overcurrent
  • the fire alarm system's integrity once it is exposed to high temperatures, and
  • the electrical safety of earthing

In their opinion, the origin of the problem is "the deliberate misinterpretation of the word ‘radial’ within BS7671 & BS5839-1". Their view is that both standards encourage the use of the cheapest wiring methods with the cheapest component parts. The reporter asserts that the cheapest options of both solutions are incompatible with each other which raises safety concerns.

They continue to describe some of their concerns in more detail, specifically:

  1. The use of a fusing factor of 1.45 in the calculation of the nominal value of circuit breakers to be used, most frighteningly about circuits currently referred to as radials, resulting in no overcurrent protection against a 'wrapped' fuse occurrence.
  2. That radial fire alarm system component parts are used in the installation of two zone and loop wired fire alarm systems, which has already caused the failure of a loop fire alarm system in a fire event, and the system was cut in half horizontally.
  3. The slow and deliberate removal of electrical safety earthing one part at a time, culminating in the removal of the main supplementary bonding conductor from incoming gas mains. This leaves the gas pipework exposed to a fault of negligible impedance when an electrician cures nuisance tripping of a residual current device (RCD) by using aerosol antiperspirant, rather than insulation resistance testing and faulty cable replacement.

Finally, the reporter says that they consider it crucial that TT electrical systems (which are the simplest form of earthing electrical systems, aiming to protect persons) incorporate an RCD main switch.

Expert Panel Comments

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The Expert Panel notes significant examples of poor practice, rather than problems with the standards being deficient. 

Essentially, the reporter highlights the need for competent persons to be working on electrical installations such as fire alarm systems. This report also highlights the need for effective regular inspection and testing, as well as enforcement.

...significant examples of poor practice, rather than the standards being deficient

It is noteworthy that both BS 7671 and B5 5839-1 are safety standards, and whilst they provide minimum requirements and recommendations neither standard proactively promotes the cheapest method, as suggested by the reporter.

Regarding item 1 of the reporter's list, the Expert Panel suggests that the current (I2) causing effective operation of the protective device should not exceed 1.45 times the lowest current carrying capacity (Iz) of any of the conductors of the circuit. I2 is found in the product standard or from the device manufacturer. It is worth noting that the wrapped fuse occurrence cited is not relevant in terms of design but is a misuse case.

The requirements for fault protection and additional protection by an RCD are clearly set out in BS 7671. A TT earthing system is common in domestic premises, and whilst less common in blocks of flats is still a recognised means of effective earthing.

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