Electricity – Friend Or Foe

According to a survey, nearly 1200 people die in the country like United States each year from electric shocks on 120V or 277V circuits. Death occurs when voltage pushes electrons through the human body, particularly the heart... - Aqeel Ahmad

September 5, 2015

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It was 22.07 hrs, a hot and humid night of July 1988 in my Submerged Arc Furnace control room wall clock, telephone rang. There was a desperate call from our 230kV receiving station yard about an oil leakage in one of our Minimum Oil Circuit Breaker (MOCB).The shift was about to end in next 45 minutes at 23.00 hrs.

I joined Steel Authority of India (SAIL)’s Ferro Alloy Plant just 15 days ago as a Graduate Engineer Trainee (my first job). Only after 10 days of formal training, I was made shift in-charge, sole electrical engineer in the plant to decide during the shift operation, due to staff shortage. I contacted transport department for the vehicle to rush to yard but my request was humbly dumped to dust bin as all vehicles were busy due to end of the shift duties. I, therefore, decided to move ‘on foot’ to yard, which was almost 800 meters away from control room. Yard was in the outer periphery of the plant at the edge of Tadoba Animal Sanctuary. On our yard’s water reservoir, a family of leopard was spotted recently.

Breathing heavily, my heart was thumping violently between my ribs, I was pretty nervous and cursing myself under the breath. In my five years engineering college life; I had not worked on any minimum oil circuit breaker before. Actually, what is taught in our class room and what we face on shop floor are poles apart. I was about to step in yard’s panel room at 22.48 hrs., I heard a big bang, earth was shaking under my feet. What happened next is a history and need not mention here. God once again spared us with a severe warning only. During departmental enquiry, it was found serious electrical safety breach. Operator was in a hurry to go home, due to end of the shift, did something unimaginable in normal course, bypassing electrical safety. At that moment, I had decided to learn thoroughly the first chapter of electrical engineering i.e. electrical safety.

“Everything in the universe is made up of atoms, and atoms are made of electricity. Electricity is all throughout space, because of the loose electrons in space. There are electrons inside stars, and on all planets. Lightning is just one form of natural electricity. When life started in the beginning on our planet, electricity probably had something to do with it. And inside your body, your thoughts are really little spurts of electricity that travel along your nerves and between cells in your brain. When a person has a seizure, that is when too much natural electricity gets loose in their brain and probably when we die, it is because of any vital electric circuit failure in our body!”

Electricity is a form of energy that is inside us as well all around us from micro-volts to mega-volts. It is our best friend as long as we treat it properly but might be much more lethal than king cobra and may result into death with slight mishandling….so no excuse, no second chance!

According to a survey nearly 1200 people die in the country like United States each year from electric shocks on 120V or 277V circuits. Death occurs when voltage pushes electrons through the human body, particularly the heart. An electric shock from as little as 50VAC for as little as 1 sec can disrupt the heart’s rhythm, causing death in a matter of minutes.

The severity of electric shock depends on the current flowing through the body, which is a function of the electromotive force (E) in volts, and the contact resistance (R) in ohms. Put these values into the formula I=E/R to find out how much current will flow through the body. Electric shock can come in several forms like

Electric sensation

Tingle sensation occurs at about 0.25 to 0.5 mA for an adult female and between 0.5 to 1 mA for an adult male (It varies according to internal resistance of our body).

Uncomfortable feelings

Current greater than 1 to 2 mA is very uncomfortable.

Maximum permissible limit

The maximum let-go threshold level for a female is about 9 mA and about 15 mA for a male.

Fibrillation level

This is a function of current over time. For example, you will get fibrillation with 500mA over 0.2 sec or 75 mA over 0.5 sec. But what is fibrillation? It is muscular twitching involving individual muscle fibers acting without coordination.

Dangerous limit

This is the current level at which humans lose muscle control; the electricity causes muscles to contract until current is removed.

According to IEEE Std. 80, you can determine the maximum safe shock duration by the formula,

T=0.116÷(E÷R),

where T is duration in seconds, E is the electromotive force in volts, and R is resistance of the person, which is assumed 1,000 ohms in the following example but varies upon skin conditions like (1) wet (2) moist (3) dry (Figure below).

Electrical injuries overview

Electrical injury occurs when an electric current runs through a portion of the body, usually from either a man-made source or lightning. The outside of the person’s body may appear to have only minor injuries, but internal injuries may still be significant.

As current enters the body (source), it causes surface to deep burns, damages muscles and organs as it passes through the body, and eventually exits at another distant point (ground), which causes a second burn or wound. The electrical current may trigger irregular heartbeat or stop the heart entirely. Among man-made sources, direct current (DC) tends to throw people from the source after one shock. Alternating Current (AC) is more dangerous. AC causes muscle spasms that often prolong contact with the power source, which increases the extent of the injury.

What happens during electric shock?

Makes you fall down
Muscle contraction
Seizures
Dehydration
Burns
Fractures
Clotting of blood
Tissue death (narcosis)
Respiratory/heart/kidney failure

Steps to follow

Do not attempt to move the victim from current source
First step is to switch off the current source
Otherwise, move the source using a wooden stick
Attend to the victim
Check for breathing
No breathing, do cardio pulmonary resuscitation (CPR)
Call emergency medical aid
If breathing, do a physical examination
Treat for minor burns
Re-establish vital functions
Excessive burns may require hospitalisation/ surgery
Supportive care must be provided

Prevention

Steps to prevent electrical injury depend on the following aspects:

Proper design, installation, maintenance of electric devices
Educating the public regarding electrical devices
Keep electrical gadgets out of children’s reach
Learn to respect electricity and electrical devices
Never compromise on electrical safety
Install proper earthing/grounding

Grounding / earthing

There are a number of good reasons to ground but primary among them is to ensure personnel safety. Good grounding is not only for the safety of personnel but to provide for the protection of plants and equipment. A good ground system will improve the reliability of equipment and reduce the likelihood of damage as a result of lightning or fault currents. In the US, it is called grounding while in Europe/India ‘Earthing.’

How does the earthing work?

The basic idea of an electrical safety earth (or ground) is the same everywhere. The chassis of the equipment is connected to an earth pin on the mains outlet. This is then connected through the house wiring and switchboard to an electrically solid earth point, which is commonly a (copper) water pipe buried deep into the ground.

Should a fault develop within the equipment that causes the live conductor to come into contact with the chassis, the fault current will flow to earth, and the equipment or main switchboard fuse or circuit breaker will blow. This protects the user from electric shock, bypassing the dangerous current directly to earth, rather than through the body of the person who just touched it.

Domestic protection measure:

Earth leakage circuit breakers (RCD – Residual Current Detectors) measure the current in the active and neutral conductors. If these differ by more than a few milliamps, the circuit is disconnected. The principle is simple – if the current in the two wires differs, some of it must be going somewhere that is undesirable, so the supply is interrupted immediately. These safety circuit breakers are very fast acting, and have saved many lives since their introduction. The 50mA that will kill you is detected by the breaker, and the power is disconnected – fast! Most of these type of breakers will operate on as little as 20 mA, so you are not only protected against major faults, but also against excessive AC leakage caused by faulty insulation or moisture.

Main earth connection

‘How should I connect the mains safety earth to the chassis?’ The regulations change from one country to the next, but the principles are the same. The figure below shows a view of the basic connection, which is very safe. The lug used must be an approved earth lug.

I learnt many useful tips in my career abroad, which we usually ignore in our day to day life in India and compromise with electrical safety aspects. Electrical tools and their proper use and selection are very important for any engineer or technician.

List of essential tools

You are already familiar with some of these tools; others are limited to the electrical trade. These tools will cut, strip, and twist wires and will secure electrical boxes, light fixtures, switches, and receptacles. Good cutting and stripping tools prevent wires and insulation from getting nicked and enable you to work with wire in tight areas such as small boxes. The following tables list the basic hand tools for electrical work and some more specialised tools.

Claw hammer for securing boxes to studs and joist
Long-nose pliers for bending wires
Lineman’s pliers for Pulling wires & cutting
Diagonal pliers for Cutting in tight spaces
Slotted screwdriver for securing switches and receptacles
Phillips screwdriver for securing switches and receptacles
25-inch measuring tape for setting box heights and so on
Keyhole saw for cutting through walls and ceilings
Hacksaw for cutting flexible, armoured cable
Wire stripper for stripping wire insulation
Cable stripper for stripping cable insulation
Flashlight for working in dark spaces
Voltage tester for testing for current
Receptacle analyser for testing for electrical faults
Continuity tester for testing for interruptions in the path of current
Adjustable wrench for tightening rigid conduit connectors.

Description of some important tools:

Claw Hammer: A 16 oz with a steel or fiberglass handle and non-slip grip is the best. Look for build in shock absorption, heat treated metal, smooth face head and rubber grip.
Locking Pliers: Known by the name Vice Grip Pliers, adjustable tightening aperture allows these wrenches to lock on to nuts, bolts, pipes and all kinds of things.

Screwdriver Set: Possibly the most important in your list of hand tools. A half dozen or so slot (flat tip) and Philips (star point) is essential. And, using the right screwdriver for the job is important as well. Look for: heat-treated, corrosive resistant, rubber handle, comfort grip, nickel-chrome plated.
Utility Knife: hold and handle to see how they feel in your hand. You’ll be cutting things with a razor blade, so it’s wise to get one you can hold securely.
Tape Measure: You need a good one. Look for stud markings (16″, 19.2″, 32″) in red for easy locating, positive blade lock, heat treated spring and at least a 25 feet range.
Hand Saw: These are designed for use on wood and can become damaged if cutting other materials. Get at least a 15″ blade, wooden or fiber/rubber hand & heavy duty.
Hacksaw: This is the tool for cutting everything but wood. A ‘fixed frame hacksaw’ has a metal frame which holds a removable blade (get a 10″ saw). Look for easy blade changing, sturdy, 24 tooth blade.
14″ Pipe Wrench: Combined with your locking pliers, this tool is what you’ll need for most plumbing jobs – PVC or metal. Look for high strength steel, jaw opening up to 2″.
7″ Needle Nose Pliers: For more delicate work, mostly in regard to electrical work, these are among the most abused of all tools in the entire list of hand tools. These are for holding small wires and things to solder, twisting SMALL metal wire and jobs like that. Look for drop-forged, heat hardened, corrosion resistant.
8″ Wire Cutter/Stripper: For electrical work, this is really the tool you need if you reconfigure your entertainment system, work on electric yard tools or any job requiring the stripping of speaker wires, F connectors, ring type terminals or electrical wiring. Look for comfort grip handles, durable blades and different sized crimping nests.
Electrical Tester: This little tool is the one you need to make sure the device is turned off and to see if an outlet, switch or appliance is live. Important info if you’re planning to stick your hand in and touch electric wires. Look for one that lights up on voltages between 80 and 500 volts.
Power Drill: Okay, not on your list of hand tools, but corded or battery powered, one cannot survive the tests of modern life without a drill. A 3/8″ drill with motor (corded) or 18VDC (cordless) with screw-driving bit storage, keyless chuck, variable speeds & reversible.

Multimeter

A multimeter capable of reading up to 600 AC volts is necessary. It should also be able to detect continuity. A clamp on style of multimeter with amperage capability is preferable.

Tick tester (non contact voltage detector)

Every electrician should be equipped with a non contact tick tester and many have a spare tester in the truck as well as one in their pocket. Testers that use ordinary AAA batteries are preferable.

What are the best tools?

The best tool is one that:

Fits the job you are doing
Fits the work space available
Reduces the force you need to apply

How do you know if you have a problem with tool?

You may have a problem if you have any of these symptoms:

Tingling
Swelling in the joints
Decreased ability to move
Decreased grip strength
Pain from movement, pressure, or exposure to cold or vibration

Tips for selecting hand tools

Select the tool

Tool with sleeve: For single-handle tools used for precision tasks: Select a tool with a handle diameter of 1/4 th inch to 1/2 inch.
Closed grip span – open grip span: For single-handle tools used for power tasks: Select a tool that feels comfortable with a handle diameter in the range of 1 1/4 inches to 2 inches. You can increase the diameter by adding a sleeve to the handle.
Tool Handle: Select a tool that is coated with soft material. Adding a sleeve to the tool handle pads the surface but also increases the diameter or the grip span of the handle.
Tool Grip: Select a tool that has a non-slip surface for a better grip. Adding a sleeve to the tool improves the surface texture of the handle. To prevent tool slippage within the sleeve, make sure that the sleeve fits snugly during use.

Routine maintenance of tools: Cleaning, lubricating, tightening, simple tool repairs, hand sharpening and adjustments using engineering principles.

Important tips to avoid electrical accident