Electrical measurement instruments are fundamental tools for electrical engineers, enabling accurate assessment of electrical quantities essential for design, troubleshooting, and maintenance in Kenya's power and industrial sectors. Mastery of the basic electrical units and their practical implications ensures precision in diagnostics and effective communication across multidisciplinary teams. This chapter focuses on the core electrical units, providing a detailed understanding crucial for professional practice in electrical engineering.

1.1 Health and safety procedures e.g. PPEs, Hazards, Accidents etc.

Electrical measurement is done on live equipment more often than any other electrical task, so a technician is exposed to danger every time a probe touches a terminal. Health and safety procedures are the fixed habits that stand between a routine reading and an injury: knowing the hazards, wearing the right protective equipment, working in a set order, and acting correctly when something goes wrong. In Kenya, the Occupational Safety and Health Act, 2007 places a duty on the employer to provide a safe workplace and on the worker to follow the safety rules and use the protective equipment provided.

Health and safety procedures before measuring

A safe measurement starts before the instrument is switched on. The following procedure applies whether the job is checking a socket circuit, reading a distribution board or testing a machine terminal box.

1. Plan the job: decide what is to be measured, at which points and with which instrument, and read the circuit diagram where one exists.
2. Assess the risk: note the highest voltage and current that may be present, and whether the circuit can be made dead for the measurement.
3. Isolate where possible: switch off, lock the isolator with a personal padlock and tag it so that nobody switches the supply back on while you work.
4. Choose the instrument: its voltage range and its measurement category must be suitable for the point being measured. Inspect the case, the leads and the probe tips for cracks or exposed metal before use.
5. Prove the instrument: check the meter on a known live source or proving unit, measure the circuit, then check the meter again on the proving source (prove, test, prove) so that a dead reading can be trusted.
6. Take the reading with one hand where the circuit is live, keep the other hand away from metal and earthed objects, and stand on a dry, insulated surface.
7. Remove the leads in the reverse order, switch the instrument off, store it and tidy the work area.

Work on live circuits is allowed only when the measurement cannot be made any other way, and then only by a competent person using insulated tools and the proper protective equipment.

Measurement category and instrument safety

Meters and test leads carry a voltage rating and a measurement category (CAT II, CAT III or CAT IV, defined in the IEC 61010 standard). The category says how much energy the supply behind the measuring point can deliver during a fault, so a higher category gives better protection against a short-circuit arc inside the meter. In outline, CAT II is for equipment plugged into a socket, CAT III is for distribution boards and fixed wiring inside a building, and CAT IV is for the point where the supply enters the installation. An instrument must never be used on a point of higher category than its own marking.

Other safe-instrument practices include:

• Use fused, shrouded leads: leads with finger guards and a meter with a fuse rated for the range protect the user if the wrong range is selected.
• Set the range and function first: many serious meter faults happen when current range is left selected and the probes are put across a supply.
• Never measure resistance on a live circuit: the ohm function applies its own small voltage and can be destroyed.
• Discharge capacitors: capacitors in drives, power-factor correction units and power supplies hold charge after the supply is off and are discharged through a suitable resistor before touching.
• Respect inductive kick: opening a circuit that carries current through a coil can produce a high voltage across the break.

Personal protective equipment (PPE)

PPE is the last line of defence, used together with isolation and safe methods, never instead of them. For electrical measurement the usual items are:

PPE is checked before every use: gloves are inflated and inspected for holes, footwear is dry and undamaged, and anything cracked or out of date is replaced. Jewellery, watches and metal-framed accessories are removed before working near live parts.

Hazards in electrical measurement

A hazard is anything that can cause harm, and risk is the chance that it does. The hazards a technician meets when measuring are:

• Electric shock: current passing through the body can cause burns, muscle contraction, breathing and heart disturbance and death. The danger depends on the current, the path through the body and the time. Residual current devices rated at 30 mA are widely used to give personal protection on socket circuits.
• Arc flash and arc blast: a short circuit through air produces intense heat, light and a pressure wave that can burn the face and hands and throw molten metal.
• Burns: from hot conductors, resistors, transformers and overloaded cables, as well as from arcs.
• Fire: from overheated connections, overloaded wiring and sparks near flammable materials.
• Stored energy: from charged capacitors, batteries and spring-operated switchgear.
• Mechanical hazards: rotating machines, belts and fans near the point of measurement, and falls when working on ladders and poles.
• Wrong use of equipment: wrong range, wrong lead position and damaged leads.

Each hazard is controlled in order of effectiveness: remove it (switch off and isolate), then substitute or guard it, then use safe working methods, and finally use PPE.

Accidents

An accident is an unplanned event that causes injury or damage. Most electrical accidents have a known cause: contact with a live part, a faulty instrument, a skipped isolation step or work by an untrained person.

The response to an electrical accident follows a set order:

1. Make the area safe: switch off the supply or isolate it at the nearest isolator. If that is not possible, separate the casualty from the supply using a dry, non-conducting object such as dry wood or a plastic broom handle. Never touch the casualty first.
2. Call for help: shout for another person, and call emergency services (999 or 112 in Kenya) or the site first-aider.
3. Check the casualty: if they are not breathing, start cardiopulmonary resuscitation (CPR) and continue until help takes over.
4. Treat burns by cooling them with clean running water and cover them with a clean, non-fluffy dressing. A person who has received an electric shock must be examined by a medical worker even if they seem well.
5. Fires on electrical equipment are fought with a carbon dioxide or dry powder extinguisher, never water, and only if it is safe to do so.
6. Report and record: the incident is reported to the supervisor, recorded in the accident register and reported to the Directorate of Occupational Safety and Health Services within the time the Occupational Safety and Health Act, 2007 requires. The cause is investigated so that it does not repeat.

Regular drills, a first-aid kit that is complete and in date, and a posted emergency contact list help every worker to respond quickly.

Chapter Summary

This chapter explored the essential electrical properties of capacitance and inductance, explaining their measurement and significance in electrical circuits. It then detailed fundamental electrical units such as amperes, volts, watts, ohms, farads, and henrys, clarifying their roles in quantifying electrical phenomena. The discussion on measurement standards covered international, primary, secondary, and working standards, emphasizing their importance in ensuring accuracy and consistency. Various electrical measuring instruments including voltmeters, ammeters, ohmmeters, and multimeters were examined with respect to their functions and applications. The chapter also addressed converters, focusing on analogue to digital and digital to analogue conversion processes that facilitate signal interpretation. Measurement presentation mechanisms such as display and recording methods were reviewed to highlight how data is effectively communicated. Finally, the performance characteristics of instruments were analyzed, distinguishing between static factors like precision and repeatability, and dynamic factors such as fidelity and measuring lag, to underscore the reliability of electrical measurements.