Due to a catastrophic failure of an HV circuit breaker which lead to an explosion/fire, and which was lucky not to result in any fatalities, HSE have issued a safety alert aimed at:
- All duty-holders with responsibilities for the safe operation and maintenance of High Voltage (HV) and Low Voltage (LV) circuit breakers, and
- Any specialist electrical maintenance contractors who provide services that include the maintenance of HV and LV circuit breakers.
Mechanisms are designed to disconnect a circuit at high speed and with a high degree of reliability, from the associated electrical system when an electrical fault is detected. However, MCCB’S (Moulded Case Circuit Breakers) and MCB’s (Miniature Circuit) are, due to their design, excluded from the HSE’s alert requirements.
It is vital for safety that HV and LV circuit breakers are checked for functionality and maintained periodically as prescribed by the original manufacturer’s instructions and as per the requirements defined in HSG230 (Keeping Electrical Switchgear Safe), and also in-keeping with the codes of practice provided in the British Standards (6423, 6626 and, 6867) which denote the standards to apply when conducting maintenance of low or higher voltage switchgears and controlgears.
If during a functional test or during periodic planned preventative maintenance, and especially if the “timing test” of the circuit breaker has demonstrated that the mechanism is slow to operate, or in extreme cases sticking, (possibly due to old lubrication becoming congealed), it would be best practice to relubricate the mechanism. The planning for this activity should involve the identification of the correct lubricant to be applied and how it should be applied (using the manufacturer’s instructions and recommended lubricants). The instructions should also explain that prior to re-lubrication, the mechanism should be cleaned with a suitable (compatible) cleaning product.
Observations made by Inspectors during separate routine inspections, which occurred whilst routine maintenance of circuit breakers were occurring, have been added to evidence gathered during another recent HSE investigation into an incident where an employee marginally escaped serious injury due to the catastrophic failure of a HV circuit. The combination of said observations and said evidence highlighted that what was understood to be common knowledge in the switchgear industry, i.e. “that the incorrect use and application of lubrication had been a major cause of maloperation in switchgear which had very serious consequences”, was no longer recognised as such. In addition, some HV and LV specialist electrical maintenance contractors and end users commonly use aerosol based multi-purpose lubricants for BOTH cleaning and relubrication tasks”.
This investigation’s findings
HSE determined that the same physical product was used for both of the maintenance activities, despite the product only being suitable for the cleaning of the mechanism and NOT for lubrication.
The investigation concluded that “stiction” – the friction which tends to prevent stationary surfaces from being set in motion – of the failed circuit breaker was due to an incorrect aerosol based multipurpose lubricant being applied to the circuit breaker mechanism when it was maintained and reported as operating satisfactorily (less than three months prior to the incident).
This conclusion was based on the independent forensic analysis work conducted during the investigation, which identified that the multipurpose lubricant used during the maintenance of the failed circuit breaker prior to the incident evaporated by 75% of its original weight within 2 weeks of application. The analysis concluded that for this reason, multipurpose lubricants containing solvents (e.g. white spirit) are unsuitable for use as a lubricant of this type of HV and LV switchgear.
In addition, historical research by other organisations recommended that hydrocarbon sprays or solvents should NOT be used on circuit breaker mechanisms.
What to do now
Duty-holders and Specialist Electrical Contractors who have responsibility for the safe operation and the maintenance of either HV and LV circuit breakers should: review their current maintenance procedures regarding these devices, ensure they are following the manufacturer’s instructions, and ensure they are aware of and are following the requirements of the aforementioned health and safety guidance and the relevant British Standards.
Specifically, it should be assured that the maintenance procedure stipulates that the manufacturer instructions regarding the cleaning and lubrication of the circuit breaker mechanism are to be followed, and that the maintenance is conducted at the appropriate intervals and by selecting and applying the correctly specified lubricants.
It should be noted that if a manufacturer’s approved procedure is followed for this activity, it will be unlikely that an aerosol based multipurpose lubricant will be used other than for cleaning, and that it is typical that instructions regarding this activity advocate the use of two separate types of products.
The following provide the duties that are required to be managed in this regard:
- Section 2(1) of the Health and Safety at Work etc. Act 1974 states that it shall be the duty of every employer to ensure, so far as is reasonably practicable, the health, safety and welfare at work of all his employees.
- 3(1) of the Health and Safety at Work etc. Act 1974 states that it shall be the duty of every employer to conduct his undertaking in such a way as to ensure, so far as is reasonably practicable, that persons not in his employment who may be affected thereby are not thereby exposed to risks to their health or safety.
- 4(2) of The Electricity at Work Regulation 1989 requires as may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger.
- 5(1) of The Provision and Use of Work Equipment Regulations 1998 requires that every employer shall ensure that work equipment is maintained in an efficient state, in efficient working order and in good repair.
If this alert has raised questions or you need to discuss any other health & safety related issue, please do not hesitate to contact your health & safety consultant or the main office for advice/assistance.