Lubrication of circuit breakers

Health and Safety Executive - Safety notice

Introduction

Investigation into an explosion of a HV circuit breaker indicated that recently carried out maintenance may have been a causal factor. The incident resulted in catastrophic failure of the HV circuit breaker leading to fire / explosion and could have resulted in fatal injuries. Maintenance of HV and LV circuit breakers typically involves both the cleaning and lubricating of the operating mechanism. The HSE investigation found that the same physical product was used for both maintenance activities, but evidence shows the product was in fact only suitable for cleaning and NOT lubrication. This situation may have arisen because of the availability of different products, (for different purposes), within the same product range, or changes to the products composition over time whilst retaining the original name. It is essential that the correct product is used for each task.

Background

HV and LV circuit breaker mechanisms are required to operate at high speed to disconnect electrical faults with a high degree of reliability from the associated electrical system. To ensure the required performance is retained it is vital that the circuit breaker operating mechanisms are functionally checked and maintained periodically as per the requirements defined in relevant good practice HSG230^[3], BS 6423^[4], BS 6626^[5] and, BS 6867^[6] and as prescribed in the original manufacturer's instructions.

If during functional testing (including circuit breaker timing tests) or during periodic planned preventative maintenance it is observed that the mechanism is slow to operate, it is good practice to relubricate the mechanism, adhering to the recommendations given in the manufacturer's instructions. During the planning stage, this will involve identifying the correct type of lubrication to be applied to different parts of the mechanism and how it should be applied. In extreme cases, where the circuit breaker mechanisms are observed to be sticking due to old, congealed lubricant, it is common practice to apply a cleaning product to remove this prior to re-lubrication. Care should be taken to ensure that the cleaning products are compatible with the circuit breaker following the recommended procedure given in the manufacturer's instructions before reapplying the manufacturer recommended lubricants.

It should be common knowledge in the switchgear industry that the incorrect use and application of lubrication has been a major cause of maloperation in switchgear and can lead to very serious consequences. However, observations made during several recent routine planned inspections relating to the maintenance of circuit breakers together with the findings from a recent HSE investigation - where an employee marginally escaped serious personal injury when an HV circuit catastrophically failed - has highlighted that this information may no longer be common knowledge. HSE routine inspections and investigation found evidence that some HV and LV specialist electrical maintenance contractors and end users commonly use aerosol based multi-purpose lubricants for BOTH cleaning and re-lubrication tasks.

The recent HSE investigation into the failed HV circuit breaker concluded that 'stiction' in the failed circuit breaker may have been a result of an incorrect aerosol based multipurpose lubricant being applied to the circuit breaker mechanism. This happened even though the circuit breaker had been maintained less than three months prior to the incident and was reported to be operating satisfactorily. Independent forensic analysis work conducted during the investigation showed 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^[7,8].

Action required

Duty-holders and Specialist Electrical Contractors with responsibilities for operation and maintenance of HV and LV circuit breakers (excluding MCCB's and MCB's) should review their current maintenance procedures associated with cleaning and lubrication of HV and LV circuit breakers and ensure they meet with the requirements defined in HSG 230^[3], BS 6423^[4], BS 6626^[5], BS 6867^[6] and as prescribed in the manufacturer's instructions. In particularly, the maintenance procedure should ensure that the manufacturer instructions on cleaning and lubrication of the circuit breaker mechanism are followed at appropriate intervals, including the selection and application of the correctly specified lubricants (typically this will be two separate types of product).

Note: This activity is unlikely to involve the use of aerosol based multipurpose lubricants other than for cleaning, following an approved procedure as prescribed by the manufacturer.

Regulation 4(2) of The Electricity at Works Regulation 1989^[1] 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.

Regulation 5(1) of The Provision and Use of Work Equipment Regulations 1998^[2] requires that every employer shall ensure that work equipment is maintained in an efficient state, in efficient working order and in good repair.

Regulation 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.

Regulation 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.

Relevant legal documents

• The Electricity at Work Regulations 1989, Regulation 4(2)
• The Provision and Use of Work Equipment Regulations 1998, Regulation 5(1)
• The Health and Safety at Work etc. Act 1974, Regulations 2(1) and 3(1)

References

1. HSE HSR 25 The Electricity at Work Regulations 1989. Guidance on the regulations. Back to reference of footnote 1
2. HSE L22 Safe use of work equipment. Provision and use of work equipment. Approved code of practice and guidance. Back to reference of footnote 2
3. HSE HSG 230 Keeping electrical switchgear safe. Back to reference of footnote 3
4. BS6423:2014 Code of practice for maintenance of low-voltage switchgear and controlgear. Back to reference of footnote 4
5. BS6626:2010 Maintenance of electrical switchgear and controlgear for voltages above 1 kV and up to and including 36 kV. Back to reference of footnote 5
6. BS6867:2013 Maintenance of electrical switchgear and controlgear for voltages above 36 kV. Code of practice . Back to reference of footnote 6
7. Doble Circuit Breaker Mechanism Lubricant Performance Assessment: Investigation and Field Experience Dated 2015. Back to reference of footnote 7
8. EPRI Electric Power Research Institute, Circuit Breaker Lubrication, Compatibility and Selection, Laboratory Assessment 3002000776, Technical Update December 2013. Back to reference of footnote 8

Further information

Contact the original circuit breaker manufacturer for more information on this subject.

Alternatively contact the HSE and speak with one of the Specialist Electrical Inspectors for further information on this subject by contacting your local HSE Office.

General note

Please pass this information to a colleague who may have this product/equipment or operate this type of system/process.