8.1.2 Tools for the Job
It is a good idea to get organised for the survey and the following is a non-exhaustive list of tools for the job.
- Accurate callipers for measuring the outside diameter of cables.
- Cable sizing tables.
- High resolution camera.
- Non conducting tape measure and/or laser measure.
- Measuring wheel.
- Non-metallic torch.
- PPE – see separate section on planning for safety.
- Quick calculators to determine “what ifs” for such as electrode configurations and dynamic safety risk assessments. (Provided with this guide)
- Calculators for sense checking relay settings as you go along. (Provided with this guide)
- Hazard report forms – to report serious hazards that are spotted to the duty holder.
Anything that is taken onto site must be declared to the duty holder along with test certificates for all equipment including tools and access equipment. Any electrical equipment should be tested and calibrated where necessary. Permission may be required for cameras as some sites are commercially or security sensitive.
8.1.3 Planning for Safety
The risk assessment and method statement should have been completed and agreed and most importantly followed by all stakeholders. I have resisted the urge to provide a sample document here because of the plethora of different environments that may be encountered. The following considerations are, however, the salient points that need to be addressed.
Risk of inadvertent switchgear tripping. What is the consequence of inadvertent switchgear trips? Consider who may be harmed and how, maybe the inspection work is in a hospital setting or supplies are to emergency services or for environmental protection purposes.
Authorisation levels. Make sure that you are competent for the tasks which also means that you can recognise at all times the limits to your own competence. This is a discovery mission, and it may be unfamiliar equipment or circumstances arise in which case it is time to stop. This is particularly the case with high voltage switchgear and the HV authorised person for the site must be in attendance when entering and inspecting HV substations and enclosures.
Accompaniment. Avoid lone working when carrying out inspections and entering switch rooms and substations. Anyone giving accompaniment should know what to do in an emergency so it will usually be necessary to be accompanied by someone who is competent to make the system safe and avoid injury.
Opening of equipment cubicles and doors to facilitate inspections. This should always be with client approval and adherence to electrical rules and procedures.
Interaction with switchgear should be avoided. The operation of switchgear by an external service provider should not be permitted. Any electrical measurements that may be necessary should be subject to a separate risk assessment and in collaboration with the duty holder.
Personal Protective Equipment – The provision of PPE is essential for any inspection where there is a risk of injury from all hazards including the arc flash hazard. The requirements for the selection and use of arc rated PPE have been comprehensively covered earlier in this guide, not forgetting other hazards including electric shock. So, what level of arc rated PPE should you wear?
From a practical point of view, a strategy of wearing a single layer of comfortable garments, complemented with appropriate head, face and hand protectors will probably work for the majority of low voltage inspections up to 400 volts alternating current. The next question is, which inspections are in the majority and which ones could be in the minority where this strategy will not work?
This is where the calculation tools that are available with this guide at ea-guide.com will be of assistance. Armed with the tools, technical experience and site knowledge, it is now possible to approach the viability of the single layer solution by exception.
Upstream Protective Device Less Than 100 amperes.
For equipment, which is supplied by circuit breakers and fuses below 100 amperes, the vast majority of incident levels will be below 1.2 cal/cm2 at a working distance of 600mm regardless of the prospective short circuit current. This approach will work where the upstream device is a current limiting fuse such as NH DIN or BS88 fuses or for miniature circuit breakers up to IEC 60898-1 types B&C or moulded case circuit breakers where the instantaneous setting is no greater than 10 times the nominal current rating. This is assuming that the protective device is capable of withstanding and breaking the prospective short circuit current.
At very low prospective short circuit current levels, the time to disconnect may increase and as a result, so will the incident energy level. There is a calculator which accompanies this guide that lists LV Fuses and MCBs up to 125A calculator against which the actual incident can be checked against. It is recommended that this is used as it includes all five IEEE 1584 Electrode configurations.
Upstream Protective Device More Than 100 amperes.
Use of the generic circuit breaker calculator, available within the store, will allow you to build up a list of exceptions where the incident energy levels are below the arc rating of the PPE for the protective devices greater than 100 amperes.