ELECTRICAL 2

Question 0

What is the formula for power in watts in terms of voltage and current? … Don’t forget to modify it for an AC current! … Can you modify it for a three-phase motor too?

Answer 0

P = V * I

P = V * I * pf

P = V * I * pf * the square root of 3

Question 1

Direct current systems are more often used for what kind of application?

Answer 1

Low-voltage

Question 2

What is a solenoid?

Answer 2

A wire wound spirally around an iron core to produce a magnetic field and that is used as an electromagnetic switch

Question 3

What is the most basic form of power generation?

Answer 3

A single – phase alternator

Question 4

What do transformers do?

Answer 4

They change the voltage of an AC circuit to a higher or lower value

Question 5

A coil or winding with more turns will have a higher what?

Answer 5

Voltage

Question 6

What are transformers called when they increase the voltage? And when they decrease it?

Answer 6

Step up and step down transformers

Question 7

Transformers don’t waste a lot of energy but what they do waste turns into…?

Answer 7

Heat

Question 8

Ventilate a transformer. Because if a large one overheats it could…

Answer 8

Explode

Question 9

The primary winding on a transformer is used for _____ and the secondary winding is used for _____.

Answer 9

Input… Output

Question 10

How do electric heaters work?

Answer 10

They are the same as heating coils and furnaces and hairdryers.

A length of stainless steel wire forms a coil. This wire is simply a resistance to the current, which generates heat.

Question 11

Are electric heaters efficient?

Answer 11

They are super efficient, but unfortunately electric power plants are only about 30% efficient… So in a broad sense, no.

Question 12

Three – way switches can be controlled from how many points?

Answer 12

Two

Question 13

What are DC motors used for?

Answer 13

Small-scale applications and for elevators which need continuous and smooth acceleration

Question 14

Larger motors are usually what kind of motor?

Answer 14

Three – phase induction motors

Question 15

All motor should be protected against ____ _____, which shut off the power when any part of the motor or housing gets too hot?

Answer 15

Thermal relays

Question 16

What does a capacitor do?

Answer 16

Improves the power factor in a circuit

Question 17

In residential construction outlets should be no farther than __ feet apart.

Answer 17

12

Question 18

What is a panelboard?

Answer 18

A set of fuses or circuit breakers that control the circuit loading in a building. A central distribution point for branch circuits for a building, floor, or part of the floor.

Question 19

Many circuit that carries a motor should have the rated load multiplied by___ in order to determine the wire size.

Answer 19

And .25. Motors should run on no greater than 80% of the capacity of the circuit.

Question 20

Which is the safest type of conduit and what is it made out of? … What is a cheaper alternative?

Answer 20

Conduit, made out of schedule 40 plumbing pipe

Cheaper alternative with thinner walls is intermediate metallic conduit

Question 21

What is the thinnest of conduits?

Answer 21

Electrical metal tubing EMT

“This conduit is so thin we need an EMT!!”

Question 22

Can you use “flex”? … Also called Greenfield. … Okay what is it actually called? And where can’t you install it?

Answer 22

Flexible metal conduit… Can’t be installed underground

Question 23

What is the long name for BX cable?

Answer 23

Similar to “flex”, it is called interlocked armored cable. It is a prewrapped set of wires in an interlocking metal spiral armor.

Question 24

In small residential construction or where you don’t need to use conduit, what can you get away with using?

Answer 24

Romex!!! Plastic-sheathed wire.

Don’t embed it in concrete obviously!!! And don’t use it in commercial garages.

Question 25

How much of a percentage of voltage drop is allowed in lighting circuits? Answer good supporting motors?

Answer 25

You’re only allowed to drop 3% in a voltage in a lighting circuit.

5% for a motor circuit

Question 26

What is a short circuit?

Answer 26

When 2 conductors that are next to each other lose so much insulation that a current flows directly between them. With little resistance a very high current may result, causing the wires to get very hot.

… Or any situation where the current is flowing where it shouldn’t.

Question 27

What are fuses?

Answer 27

Shutoff (safety) devices. Little cartridges that get hot enough to melt (and shut off the circuit ) when the current flow is too high.

Question 28

What are circuit breakers?

Answer 28

Devices that automatically disconnect a circuit when the current is excessive. Unlike a fuse they can be reset.

Question 29

What is a typical item to ground wires to?

Answer 29

Steel cold water pipe in the plumbing system, which should provide a direct path into an under the ground

Question 30

What is the service drop?

Answer 30

This is all of the electrical services arriving onto the site… Wires for the mainline, transformer, a meter and a disconnect search

Question 31

Enlarge your buildings meters measure not only consumption but also ____ ______.

Answer 31

Peak demand … Because dramatic peaks require the utility company to build more power generating capacity to meet that peak, which then sits idle. This is an efficient and expensive.

Question 32

What do you get from the utility company if you have a dramatically higher peak demand?

Answer 32

Demand surcharge

Question 33

Minimum distance from transformer to meter

Answer 33

150 feet