Electrical Safety

Question 1

Normal household current

Answer 1

1 circuit = 1500 Watts/15 Amps
5 milliamps will trip a ground fault circuit interrupter

Question 2

Electric current in milliamps

Answer 2

1-5 can feel it
5-10 can’t let go
10-50 increasing pain, SOB
50-100 probably fatal

Question 3

Distribution lines

Answer 3

2400-40000 volts
Transformers reduce volts to 347/600 for industrial and 120/240 for residential. 1 to 3 transformers. Look for presence of pole # (yellow ID tag).

Question 4

Transmission lines

Answer 4

Wood 69000-115000
Steel 115000-500000

Question 5

“Dump the feeder”

Answer 5

Enmax can dump the feeder to an area within seconds of being notified. Power can still be introduced by privately owned generators or solar panels, wind turbines. Lines are not dead until grounded.

Question 6

City of Calgary

Answer 6

34 high voltage substations
6 lower voltage substations
Sulphur Hexafluoride (SF6) inorganic, colourless, odourless, and non-flammable greenhouse gas. Full PPE.

Question 7

Pole fires

Answer 7

Do not use water, wait for enmax who will use dry chemical extinguishment

Question 8

Step potential

Answer 8

Risk of electrocution based on the possible voltage running through the ground. If power line falls and touches ground, it can create a pool of electricity up to 15 m away. SHUFFLE, never walk (heel does not pass your toe).

Question 9

Radio-frequency (RF) radiation

Answer 9

Two areas of the body, the eyes and the testes, are particularly vulnerable to RF heating because of the relative lack of available blood flow to dissipate the excessive heat load.

Question 10

Properties of electricity

Answer 10

Potential difference (voltage), current flow, and resistance.

Question 11

Voltage

Answer 11

Difference in electrical potential between 2 points in a circuit (like water pressure). Measured in volts.

Question 12

Current

Answer 12

Flow of electrical charge (like rate of flow of water in a pipe). Measured in Amps.

Question 13

Resistance

Answer 13

Different materials have different resistance to the flow of electricity (like the effect of friction on the flow of water in a pipe). High resistance materials are called insulators. Low resistance is Conductors. Measured in Ohms.

Question 14

Grounding

Answer 14

Mechanically connecting the isolated wires and equipment to the earth, with sufficient capacity to carry any fault current and to ensure the wires and equipment remain at the same potential (same volts) as the earth (ground).

Question 15

What causes the majority of electrical fires

Answer 15

Arcing - sudden flash of electricity between 2 points of contact. Extremely hot (20 000C). Usually associated with a short circuit or a current interruption at a switch point or loose terminal. Arcing can ignite combustible material or gases within the area.
Overheating - Overloading conductors and motors. Danger when amount of electrical current exceeds the capacity conductors and the equipment designed to carry.

Question 16

Insulators

Answer 16

Porcelain, glass, and plastic

Question 17

Conductors

Answer 17

All metals (iron, copper, lead, aluminum, silver, and gold), humans (largely water and dissolved minerals)
Semi-conductors - Wood, earth, and rubber tires. Depends on moisture content and contaminants.

Question 18

Low or secondary voltage

Answer 18

Less than 750 volts. Home heating systems, appliances, outlets and lights usually operate at 120/240 volts or less. Commercial and industrial settings range from 120-750 volts, when interrupted can produce explosive electrical flashes as a result of a higher levels of current, known as fault current, which can exceed 8000 volts.

Question 19

Safe limits of approach clearance of power line contact and live wire

Answer 19

7m or 23 ft power line
10m or 33 ft live wire

Question 20

Aerial device

Answer 20

Competent worker designated as a signaller to observe proximity to power line. Operator must be on the aerial device or a ground gradient mat.

Question 21

Key fact

Answer 21

Electricity seeks all paths to the ground. More current will flow through the path of least resistance.

Question 22

Potential gradient (or voltage difference)

Answer 22

Step potential - The further apart x and y are, the greater the electrical contact hazard.
Touch potential - Electricity would flow through your body if you were to place your hand on an energized source while your feet were at some distance from the source.

Question 23

Effects of electricity on the body

Answer 23

Dependent on the amount of current and the length of time the body is exposed to it. Approx 1 amp to light a 120 watt bulb. It is the AMP that kills or injures. Less than 1 amp can kill.

Question 24

Dazzle

Answer 24

Temporary blindness from sheer brillance of the flash

Question 25

Treatment

Answer 25

Before any treatment can be given, the electrical hazard must be eliminated. Effects can be delayed up to 24 hours.

Question 26

Portable generators

Answer 26

Should be bonded neutral type (bonded to frame neutral). Neutral wire is bonded to generator frame. Position in dry area.

Question 27

Capacitor

Answer 27

Store energy and can produce lethal amounts of current even when power is off.

Question 28

Fuse cutout

Answer 28

Acts like a circuit breaker in a house. If power surge occurs, the fuse cutout will blow open preventing damage to the transformer and customers equipment.

Question 29

Recloser

Answer 29

Both transmission and distribution power lines protected by automatic circuit breakers and by reclosers. If power line is open, recloser will after a short period of time attempt to close and re energize the power line. Most located in substations in AB.

Question 30

Vehicle tire pyrolysis

Answer 30

Electricity flowing through the tire causes a chemical decomposition and sets the stage for pyrolysis. Can result in sudden explosive failure up to 24 hours after contact. Same goes for deflated tires.

Question 31

EV and hybrid vehicles

Answer 31

High voltage energy within batteries and wiring can carry as much as 650 volts DC. High voltage line usually orange and runs along underside of chassis. Use ABC fire extinguisher as first.

Question 32

Water on electrical fires

Answer 32

Avoid directing hose streams directly onto energized electrical equipment and use dry chemical ext when possible. If water used, minimum of 100 psi at nozzle, fog spray set to 30 degree pattern, at least 10m (33ft) away, solid bore, straight streams and foam should be avoided as they are excellent conductors, watch for water run off.

Question 33

Arc over hazard

Answer 33

High voltage power lines are insulated by air space. An intense fire of a transmission power line may degrade the insulating quality of air to the point of enabling electricity to jump to the ground surface, if flames reach within 2m (7ft) of the live conductors. Dense smoke can also create this problem. This creates a potential gradient and a step potential hazard. Voltage unknown, fire engulfing structure, arc over hazard, stay back at least 32m (100ft).

Question 34

Objects contacting or in close proximity to power lines

Answer 34

Potential for severe shock. Electricity can jump or arc across to nearby conductive objects.

Question 35

Underground power equipment

Answer 35

Underground power lines can supply primary (8000 to 25000 volts) and secondary (120/240 and 347/600 volt) electrical power. Underground cables normally buried at least 1m (3ft) below the ground level.

Question 36

Vehicle crashes

Answer 36

Have operator stay inside vehicle if safe to do so until power shut off

Question 37

Transformer

Answer 37

Device used to step up or down voltages. Contain large amounts of cooling insulating oil that is combustible and has a flash point of 145C.

Question 38

Conservator

Answer 38

Large tanks at the top of transformers allow for expansion and contraction of the cooling oil when the transformer is carrying load.

Question 39

Bus bars

Answer 39

Metal conduits or pipes that are used within substations to carry the electricity from transformers to other devices.

Question 40

Fires in substations

Answer 40

Usually involve combustible insulating oil in transformers, circuit breakers, and capacitors. Keep on-lookers back at least 100m (330ft) due to risk of explosion.

Question 41

Polychlorinated biphenyls (PCBs)

Answer 41

Were used as cooling and insulating oil in transformers as they don't support combustion. Mostly been replaced by mineral oils because PCBs are an environmental contaminant.

Question 42

Turning off main power switches

Answer 42

Use left hand and turn away when shutting off power. Fault currents may have energized the grounded electrical box.