ELECTRICAL SYSTEMS Flashcards
0
Q
Energy is what? What is a synonym?
A
The product of power and time, also called work.
1
Q
What is an ampere?
A
The unit if flow of electrons in a conductor equal to 6.251 x 10 to the 18th electrons passing a given section in one second
2
Q
What is impedance? What do you measure it in?
A
Resistance in an alternating current (AC) circuit, measured in ohms.
3
Q
What does a power factor mean?
A
The phase difference between voltage and current in an alternating current circuit
4
Q
What is reactance?
A
Part of the resistance in an alternating current system, caused by inductance and capacitance.
5
Q
What is an ohm?
A
The unit of resistance in an electrical circuit
6
Q
What is a volt?
A
The unit of electromotive force that will cause a current of 1 A to flow they a conductor whose resistance is 1 (upside down horse shoe)
7
Q
What is a watt?
A
The unit of electrical power
8
Q
What is the basic definition of electricity?
A
Energy created by the flow of electrons
9
Q
Name the 4 components of a basic electric circuit.
A
- A conductor
- The actual flow of electrons (current), (I)
- The electric potential causing electrons to move (voltage), (V)
- Some type of resistance to the flow (R)
10
Q
What is Ohm’s law (formula)?
A
I = V/R
The current in a circuit is directly proportional to the voltage and inversely proportional to the resistance.
11
Q
How is power expressed in physics? What formula describes Watts interns of voltage and current? What’s a cute way to remember this?
A
Power is the rate at which work is done.
W = V * I Watts = voltage x current
Cute as PIE…. P = IE
Power (watts) = current x electromotive force (voltage)
12
Q
What is the principle of electromagnetic induction?
A
When a conductor is moved in a magnetic field, a voltage is induced…. The direction of movement determines the polarity of the voltage (positive or negative). When a coil of conductor is rotated within a magnetic field, a voltage of alternating polarity is produced.
13
Q
Amplitude of the sine curve means how much ______ there is. The distance between peaks is a cycle which in the US is ______ or _____ __.
A
Voltage… 60 cycles per second (60 hertz)
14
Q
When do you call it impedance instead of resistance? And therefor Ohm’s law is like so…
A
In an AC current
I = V / Z
15
Q
What is the formula for wattage (power) in an AC current?
A
W = V * I * pf
… You have to add the power factor
16
Q
In an AC current impedance comprises ____ and _____…. The added different bt an AC and a regular circuit is therefore:
A
Resistance and reactance, causing a phase change between voltage and current, the difference is represented by the power factor.
17
Q
What is the formula for measuring how much energy there is in a circuit?
A
E = W * t Energy = Work x time
18
Q
What are the two basic types of circuits? Describe their basic difference.
A
Series and parallel. In a series the current remains the same through consecutive runs between loads placed one after the other and the voltage changes (drops) from one to the next while the current stays the same throughout. In a parallel circuits three loads are placed next to each other with the same voltage. Each has a different current but in the end they all add up.
19
Q
Conductor gauge sizes range from what to what?
A
American wire gauge AWG 16 (smallest at 0.058 in dia.) to 0000 (largest at 0.460 in dia.)
20
Q
What size or smaller designates a wire?
A
8 AWG or smaller.
21
Q
What does ampacity mean?
A
This is the current-carrying capacity
22
Q
What are the two basic types of conductors? Describe basic differences in size and cost.
A
Copper and aluminum. Aluminum needs to be larger in diameter diameter to carry the same amperage, but it is lighter and generally cheaper in large sizes. Copper is more cost-effective and small and medium – sized wire and cable. Aluminum has problems with oxidation causing resistance and overheating.
23
Q
What is the tradename for nonmetallic sheathed cable? And what kind of building is it suited to?
A
Romex. Used in wood – frame residential buildings three stories or less, inexpensive to install because it doesn’t require conduit.
24
What is the tradename for flexible metal – clad cable? Why is it useful for remodeling work?
B capital X cable., Plastic – insulated conductors in a continuous spiral wound a strip of steel tape. It is useful for remodeling because it can be pulled through existing spaces within a building.
25
What are busbars and when are they used? What is a group of them called?
Push bars are rectangular ball bars of copper for very high currents, when large cables become expensive and awkward to tap into. When several busbars are assembled in a special metal housing it is called a bus duct or busway.
26
Name three types of rigid steel conduit, and describe their basic advantage of.
Rigid steel conduit. It's the heaviest and connected to junction boxes and devices with threaded fittings. Intermediate metal conduit. Has the inner walls. Electric metal tubing. It's the lightest of the three, installed with special pressure fittings as it is too thin to thread. It is easier and faster to install, but cannot be used in hazardous areas.
27
What is commonly referred to as flex?
Flexible metal conduit.
28
The national electrical code places limits on the number of Ben's in conduit between pull boxes. How many 90° bends do they allow between pull boxes? What else do they limit?
Four. They also limit the number of wires or cables that can be threaded through a certain size of conduit. This limits heat buildup inside the conduit.
29
Describe an underfloor duct.
Steel raceway cast into a concrete floor add regular spacing. It carries power and signal wiring from the main electrical closet to each distribution duct, tapped at close intervals.
30
Describe a cellular metal floor.
This raceway is part of the structural floor. It is basically metal decking used as cable raceway.
31
What is under-carpet wiring?
This is pretty obvious, huh? It's been, flat wire lay down under carpets. It must be used with carpet tiles so that it is readily accessible.
32
When do you use AC current and when do you use DC?
The common is AC. DC is used in some elevator motors and for low voltage applications like sign systems, controls, etc.
33
What is the most common voltage supplied to residences and very small buildings in the US?
120/240 V, single – phase, three – wire system
34
What is the voltage system often use for larger buildings?
The 120/208 V, three-phase four-wire system. It allows for a variety of electrical loads.
35
Also for larger buildings, the same as the 120/208 V system, except for higher voltages, is?
The 277/480 V, three-phase, four-wire system. These buildings have predominately 277 V fluorescent lighting, which requires smaller wiring. Small, step down transformers are used were 120 V service is needed for receptacles and other equipment.
36
The largest electrical service to large commercial buildings in factories is…
2400/4160 V, three-phase four-wire system
37
What did Transformers do?
Change alternating current voltages, either up or down
38
Why do transformers need to be located at an exterior wall and vented to the outside?
They generate a lot of heat
39
With regards to energy companies what is a load factor?
The ratio of the average power used to the maximum power demand. A low load factor implies an inefficient use of energy and a high demand charge to the customer.
40
Name a bunch of terms that all describe the same thing: the avoidance of peak electricity use. How is it accomplished?
Load control, load shedding, peak demand control, and peak load regulation. Nonessential electrical loads are shut off once a certain electrical usage is reached.
41
What is the switchgear?
This is the central electrical distribution Center, composed of switches, circuit breakers, and cables or busducts that distribute power to other parts of the building.
42
What is a ground fault interrupt her? What purpose does it serve?
Ground faults can be dangerous because the current required to trip the circuit breaker is high and small currently can continue unnoticed until someone receives a dangerous shock or fire develops. The GFI is a device that detects these leaks, disconnecting the hot wire to the circuit or appliance.
43
Where are the three places GFIs are required?
Kitchens, bathrooms, and out of doors
44
What is the purpose of a split wired receptacle?
This means that one outlet is always energized but the other is controlled from a wall switch. This allows floor lamps and other devices that normally plug in to be controlled with the switch.
45
What is the minimum height off the floor for mounting outlets for forward reach accessability for wheelchairs?
15 inches
46
What is the difference between a two way switch, a three way switch, and a four way switch?
A two way switch controls one electrical device. A three way switch is win one electrical device is controlled by two switches. A four way switch is win three switches control the same electrical device.
47
What is the difference between emergency power and standby power?
Emergency power is required for the safety of occupants, supplied by generators are batteries. Standby power is to provide continuity in case there is an interruption in electrical service.
48
What is the common word for visually evaluated radiant energy? (It is a form of electromagnetic radiation. With wavelengths that range from 400 nm for Violet to 700 nm for red.)
Light
49
Transmittance or coefficient of transmission is the ratio between what and what?
The ratio of total transmitted light to total incident light… Basically this means the light that goes through the window to the light that gets reflected off the window
50
What is the transmittance of clear glass? What is the transmittance of frosted glass (a range)?
Clear glass has a transmittance of about 85%. Frosted glass is between 70 and 85%
51
What kind of surface causes specular reflection?
Smooth, polished services, such as a mirror or chrome
52
What is the opposite of transmittance?
Reflectance
53
What kind of surface causes diffuse reflection?
Are uniformly rough surface, like matte wall
54
What is candlepower?
The unit of luminous intensity approximately equal to the horizontal light output from an ordinary wax candle. In the S I system this unit is the candela
55
What is illuminance?
The density of luminous flux incident on a surface in lumens per unit area. 1 lumen uniformly incident on one square foot of area produces an illuminance of 1 foot candle.
56
What is a lumen?
A unit of luminous flux equal to the flux in a unit solid angle of one stir radian from a uniform point source of one candle power. On a unit sphere of 1 foot radius an area of one square foot will subtend an angle of one steradian. Because the area of a units fear is 4pi a source of one candlepower produces 12.57 lm
57
Because the area of the units fear is 4pi, a source of one candlepower produces how many lumens?
12.57 lm
58
What is luminance?
The luminous flux per-unit of a projected or apparent area and unit solid angle leaving a surface, either reflected or transmitted.
59
The equation for luminance is... , also called what?
Candelas per square meters. Also called the nit.
60
Do you and exercise calculating footlamberts and nits... And lux
for more information this is on page 93 of the ballast Guide
61
What is luminous intensity?
The solid angular flux density in a given direction measured in candlepower or candelas
62
Common term often used to describe what luminance is… But it is somewhat misleading since this term includes the physiological sensation of the adaptation of the eye whereas this as luminance is the measurable state of object luminosity
Brightness
63
What is the critical zone for direct glare?
The area above a 45° angle from the light source. Draw a simple diagram.
64
What does the visual comfort probability (VCP) factor evaluate?
Direct glare... This factor is the percentage of normal observers who may be expected to experience visual comfort in a particular environment with a particular lighting situation.
65
What is reflected glare? And what is its zone? If it interferes with the viewing task it is also called what?
When a light source is reflected from a viewed surface into the eye. It is located below the 45° angle from the light source usually. If it interferes it is called a veiling reflection.
66
What is contrast with regards to illumination?
This is the difference in illumination level between one point and nearby points
67
Name some decent limits on brightness ratios in different settings
1:1/3 between the task and adjacent surroundings. 1:1/5 between the task and more remote starter surfaces. 1 to 10 between the task and more remote later services.
68
What are the three types of man-made light sources?
Incandescent, fluorescent, and high intensity discharge
69
Why is the tungsten halogen lamp smaller than a standard incandescent and made of Quartz?
Because the filament burns under higher pressure and temperature.
70
How does the tungsten halogen achieve a longer life?
Part of the tungsten filament is burned off but mixes with the halogen to be redeposited on the filament instead of on the wall of the bulb, resulting in a longer life of the filament.
71
Reflector (R) and parabolic aluminized reflector (PAR) lamps have increased efficiency. Why?
A reflective coating built into the lamp allows more precise be in control. They are both available in flood (wide) and narrow (spot) beam dispersal patterns.
72
What are elliptical reflector (ER) lamps?
They have an even more efficient beam of light. They are use for downlights with deep baffles are small openings.
73
How large is an MR 16 and why?
MR stands for miniature reflector. 16 designates the diameter of the reflector an eighth of an inch
74
What are the two sizes of low-voltage miniature reflector lights?
MR-11 and MR-16
75
What is the basic make up of an incandescent lamp?
This is a tungsten filament placed inside a sealed bulb containing an inner gas.
76
What is the basic make up of a fluorescent lamp?
A mixture of inner gas and the low-pressure mercury vapor. When the lamp is energized and mercury arc is formed that creates ultraviolet light. This invisible light strikes a phosphor coated bulb, causing the bulb to fluoresce and produce visible light.
77
What is the difference between preheat, rapid started, and instant start fluorescent lamps?
Pre-heat lamps are really used anymore. Rapid start lamps have a constant low current in the cathode allowing them to start with in about two seconds. Instant start lamps have a high enough voltage to start the ark in the tube immediately without preheating.
78
What is a ballast?
A device in every fluorescent lamp which supplies appropriate starting and operating voltages and limits the current. Ballasts produce noise and heat.
79
Ballasts I rated by letter. What is the difference between class A and class F?
Class A is rated for the lowest ambient noise spaces where is class F is suitable only for noisy environments.
80
What does F40T12WW/RS describe?
A fluorescent lamp, 40 W, tubular, 12/8 inches in diameter (or 1 1/2 in), warm white color, with a rapid start circuit.
81
What is the efficiency of a standard incandescent lamp? What is the efficiency of a cool white fluorescent lamp?
Less than 20 lm per watt versus 80 lim per watt
82
What are the general elements of high-intensity discharge (HID) lamps?
There is mercury vapor, metal halide, and high and low pressure sodium.
83
What is the range and efficiency of mercury HID lamps?
30 lm per watt to 50 lm per watt
84
What is the efficiency of metal halide lamps, which are similar to mercury lamps except with added halides of metals added to the arc tube.
Between 50 lm per watt and 100 lm per watt
85
What is the efficiency of high-pressure sodium HID lamps? What makes them more efficient?
Between 80 lm per watt to 140 lm per watt. And electric arc passes through hot sodium vapor. The ark tube must be made of a special ceramic material to resist attack by the hot sodium.
86
What is the efficiency of low-pressure sodium HID lamps? What trait do they exchange for their increased efficiency?
They produce about 150 lm per watt, but they also produce monochromatic light in a deep yellow color
87
What is the difference between direct lighting, semi direct lighting, and indirect lighting systems?
These describes luminaires. Direct lighting provides all light output on the task. Semi direct lighting but the majority of light down with a small protect percentage towards the ceiling. Indirect lighting throws all the way towards a reflective ceiling where it illuminates the room by reflection.
88
What is a torchére?
A freestanding light fixture that throws it's light towards the ceiling
89
Describe how the color rendering index (CRI) works.
It measures how closely the perceived colors of an object illuminated with a test source versus with the daylight of the same color temperature turned out the maximum rating of 100 at a rating of 85 or more is very good.
90
How do you measure how much illumination appears on the surface with regards to the point source? What is the formula for calculating this illumination from the source perpendicular to the surface?
The illumination on the surface varies directly with the luminous intensity of the source and inversely with the square of the distance between the source and the point. The formula is:
E = 1 / d squared
(See page 100)
91
What is the formula to calculate the illumination on a surface whose source is not perpendicular to it?
E = 1 * cos of the angle / d squared
| see page 100
92
What does the zonal cavity method calculate? What are the four factors uses? What is the formula?
The # of luminaries require to light a space. You need to know lumen output of lamps, number of lamps and each luminaire, The coefficient of utilization, and the light loss factor
The number of luminaries =
(Footcandles)(area of room)
/
(number of lamps)(lumens per lamp)(CU)(LLF)
93
What is the coefficient of utilization mean with regards to luminaries?
It represents the fact that not all of the lumens produced by the lambs reach the work surface. The CU ranges from 0.01 to 1.00 depending on the design of the light fixture and the characteristics of the room
94
What is the light loss factor?
This is a fraction representing the amount of light that will be lost due to lumen depreciation (light loss with age) luminaire dirt depreciation (light loss due to accumulated dirt on lamps)
95
What is an alternative to the zonal cavity method?
An isolux chart or an isofootcandle chart, a diagram that shows the lines of illumination produced by specific luminaire by a particular manufacturer....
Better yet use a computer
96
What is the minimum lighting level for emergency lighting?
One footcandle
97
How do perimeter protection security systems work? Name a few varieties.
They secure the entry points to a space or building...
Magnetic contacts used on doors and windows to sound an alarm when contact is broken
Glass break detectors sense when a window has been broken with the metallic foil or small vibration detector mounted on the glass
Window screens which set off an alarm when their cut or broken
Photoelectric cells to detect with the beam has been broken by a door opening or someone passing through
98
Name some types of area or room protection
Federal electric beams, infrared detectors, audio detectors, pressure sensors (which detect weight on the floor,) ultrasonic detectors, microwave detectors
99
What are the four basic types of fire detection devices? Describe each one briefly.
Ionization detector. Responds to products of combustion ionized particles rather than to smoke.
Photoelectric detector. Response to smoke which obscures a lightbeam in the device.
Rise-of-temperature detectors. Disadvantage is that flames must be present before alarm temperature reached.
Infrared detectors and ultraviolet radiation detectors, which also do not give early warning
100
What is current and what is it's basic formula?
Flow of electrons/charge over time
I = delta-Charge / delta-Time
101
In terms of desire what is voltage?
How badly the electrons want to get to the other side... The potential difference between positive and negative
102
What is Ohms law in words and formula?
The voltage is proportional to the current through a circuit and vise versa
```
V = I*R
V/R = I
```
103
What do you measure current in? What do you measure resistance in?
Amperes… Ohms…
