Student safety 2011 5th edition - Pt 2, Pg 5-12 Flashcards
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How can electricity jump from one conductor to another and what is it called?
Pg 7
Electricity can jump from a conductor, through the air to another conductor–called an arc.
True or false?
Lightening is an extreme example of a natural arc?
Pg 7
true
But Wikipedia claims natural lightning as electric sparks, not an arcs.
What’s electric welding?
Pg 7
A phenomenon when a small electricity arc occurs if a switch is opened/closed, called arcing/switching arc.
Electricity wielding what to join metal pieces together by melting?
Pg 7
Electric welding uses a controlled arc to join pieces of metal together by melting them.
What occurs each time you open/close a switch?
Pg 7
A small arc occurs each time you open or close a switch.
What occurs in equipment feailures and what is it called?
Pg 7
Some types of equipment failures result in a large, uncontrolled arc known as an “arc flash.”
Where can serious arc flash incidents occur and why?
Pg 7
Serious arc flash incidents often occur in buildings/ industries/utilities with high power.
What happens in an arc flash?
Pg 7
an explosion with large amounts of heat can have fatal causes for unprotected ones
But such incidents are rare.
An electric park can make how much temperature?
Pg 7
Temperatures in ranges of 19,000 °C–~4x the Sun’s temperature.
What technology can produce higher temperature than electric arcs?
Pg 7
Only industrial lasers make higher temperatures than elctric sparks.
For an arc flash, what clothing must be worn?
Pg 7
If arc flash is possibile, flame retardant clothing for such use must be worn.
True or false?
An arc makes a flash of light that damage eyes/cause blindness
Pg 7
true
True or false?
Arc flash incidents cannot vaporise parts of an electrical equipment.
Pg 7
false
Arc flash incidents can vaporise parts of an electrical equipment.
If a solid is turned into a gas what may happen?
Pg 7
sublimation-If a solid is turned into gas, it expands enormously, a pressure wave that can reach 300 pounds per sq ft.
E.g. Copper expands by factor of 67,000.
How strong can a sublimation be?
The shock wave can knock you across a room.
A sublimation pressure wave can make sound levels of how much decibels?
Pg 8
Pressure waves make sound levels exceeding 160 dB.
- 100 dB: noise level of a chainsaw/loud rock concert
- 140–180 dB: a jet engine at takeoff, can be harmful to hearing
- 180 dB+: akin to a rocket launch/big explosion sound
Can molten metal fly at high speed like a hand grenade explosion?
Pg 8
Yes, molten metal can fly at high speed like a hand grenade explosion.
What are general characteristics of an arc flash?
Pg 7-8
- extreme heat
- strong flash of light
- powerful pressure waves
- powerful sound waves
- flying parts
- smoke and fumes
When to work on live circuits?
Pg 9
never
This can be as simple as unplugging a lamp before you fix the switch.
Why should you never work on live circuits?
Pg 9
It can involve many people, in different places and very complex procedures in the case of a high voltage transmission line.
Circuits at 50 volts under are often safe to work on live, with what questions to consider?
Pg 9
- Is there an arc flash risk?
- Will I be working in a situation where even 50 volts is a shock hazard?
- Is there damage risk to an equipment?
What’s a meter in electricity?
Pg 10
a device to measure electrical energy usage at home/building/other electrically powered device
What tool to use to check voltage?
Pg 10
a meter or tester
What to check before using a meter to check voltage?
Pg 10
Determine if you need to use voltage rated gloves with the voltmeter.
What if you work on a circuit connected to a source above 50 V/you don’t know what the voltage is?
Pg 10
Use voltage rated gloves with protectors if you test for voltage.
The way to be sure a circuit is dead is T³.
How do you use it?
Pg 10
- Test the meter by measuring the live circuit’s voltage, to confirm that the meter works.
- Test the circuit to work on. 0 volts = circuit is dead
- Test the meter again by measuring a live circuit’s voltage again, to confirm that the meter still works. If the circuit in step 2 was live and blew the fuse in the meter you cannot read a voltage.
What to say when you check between phase conductors and phase, conductors and ground?
Pg 10
do these before saying “it’s off”
Be sure to have a good ________________ when you check to ground. Paint or ____________ can make this difficult.
Pg 10
Be sure you have a good connection when you check to ground. Paint or corrosion can make this difficult.
Power comes in on a what in a 2- pole circuit breaker?
Pg 11
line side connection lugs
The power to the breaker is what volt in a single phase?
Pg 11
North America homes are powered by 120-volt single-phase electricity
When energized, how many volts do connections to a breaker have?
Pg 11
