Overcurrent And Service Equipment Flashcards
Does the electrical code apply to the supply authority?
No.
What is section 6 in the code?
Covers requirements for the installation of consumers services and service equipment.
Applies to all electrical installations operating at 750v or less
What is a combination panel?
The service box and the panel board.
The max height of triplex service drop for landscaped yard
3.5m
The max height of triplex service drop for residential driveway
4m
The max height of triplex service drop for commercial driveway
5m
The max height of triplex service drop for public street, alley, or highway
5.5m
Point of attachment may not exceed _____m above finished grade
9
Max ____V between conductors
300
The distance between the roof and the bottom of the drip loop is ____mm
600
Total length of drip loop allowed
750mm
The TX and primary high voltage conductor are installed by and are the responsibility of
The utility company
Always check with ______ before commencing work
Local utility and inspection authority
Rule 6-300 installation of underground consumer service conductor means:
This rule deal with protection of conductors against damage and sealing of underground conduits where they enter a building
Can you use both PVC FA and TA in a meter base hub?
No. Only FAs can be used. Must use a chase nipple threaded into hub and then FA over the chase nipple.
Which side of the meter base is dedicated?
Line side.
What is the size of a meter base?
450 x 300 x 112.5 mm
What is the purpose of grounding?
Minimize voltage spikes, stabilizes normal voltage to ground. Overcurrent devices can operate faster when responding to ground faults.
Effective grounding occurs when _______
A low impedence ground path is provided
The arching damage to electrical equipment and conductor insulation is closely related to the value of
I^2t
What does the word ‘system’ mean in equipotential grounding system
The service neutral conductor, grounding electrode, cold water pipes, gas pipes, service entrance equipment, jumpers installed around meters. All must be bonded together.
Rule 10-002 sets out objectives of bonding and grounding. What are they?
To protect life from the danger of electric shock, limit voltage upon a circuit, facilitate the operation of electrical apparatus and systems, limit voltage on a circuit when exposed to lightning, limit AC circuit voltages to ground to 150 volts or less on circuits supplying interior wiring systems
When bonding a sun panel, what must be removed?
The bonding jumper, remove and place it on bottom of panel.
What value of current can cause death?
0.01 amp
Cost of electrical energy calculation
Cost = (watts • hours used per day • cost per kWh) / 1000
All protective devices serve the same purpose:
Protect conductors and insulation from excess amounts of heat arising from overload and overcurrent
What is an overload?
Moderate increase in current beyond the normal rates current value
Typical values of overload currents may range as high as _____
6 times the normal current
What is overcurrent?
Extreme increase in current well beyond the normal rates current value
Two types of shorts
Line to ground, and line to line
What is a short circuit?
Larger than normal current which flows outside the normal current path
What is a common cause of arc faults?
Loose connections at terminals
Formula to calculate %Z
%Z = E short circuit / E rated
Formula to calculate fault currents
I short cct = I Full Load / %Z
What is mechanical forces?
High fault currents exerting terrific magnetic stress on bud bars and equipment
How can thermal energy be minimized?
By using a current limiting device that clears a high fault current within the first half cycle
Four important factors in influencing choice of circuit protection.
Voltage rating, current rating, interrupting rating, clearing time
Voltage rating of a fuse must be _______ than the voltage of the circuit
Equal or greater
What are the standard fuse voltage ratings?
125V, 250V, 300V, 600V
What is the interrupting rating?
The maximum short circuit current an over current protective device can safely handle without damaging itself
What interrupting rating do HRc fuses usually have?
200,000A
Time current characteristics compare _______
Fault magnitude and speed of response
Time delay fuses are marked with the letter
D
Non time delay fuses are marked with
P
The higher the current the quicker the fuse opens. This process is
Inverse time current characteristics
What are the two general categories of fuses?
Plug and cartridge
The max voltage allowed for plug fuses is ____
125V between conductors
The two interchangeable plug fuse types
Type C(T), and S
The three types of cartridge fuses
Ferrule contact (flat ends), knife (blades), and bolt on (blades with holes)
What class are standard fuses?
H.
What are standard class H fuses filled with?
Silica sand.
What is the exterior of fuses made of?
Porcelain
What is the purpose of the silica sand in a fuse?
Fire extinguishing powder. Prevents arc from continuing or bursting through the tubing of the fuse.
What type of fuse is a renewable link fuse? Time delay or non time delay?
Non time delay. Link must not be spiked.
Explain how a time delay fuse works.
Consists of two fuse links, joined by thermal cutout unit or overload element, has a copper heat sink, and spring loaded connector. The connector is held in by a soldering pot (low melting point)
Sometimes referred to as dual element
All standard P fuses have an interrupting capacity rating of _______
10000A
What are HRC fuses?
High rupturing capacity. Interrupt large short circuit currents without disintegrating
How does the sand work in an HRC fuse?
Under heavy current and short circuit condition the silica sand turns to a glass like material, blocking formation of an arc.
What are the two types of HRC fuses?
HRCI - protects from overloads and short circuits.
HRCII - protects from only short circuits
Current and voltage rating if Class R fuses.
0-600A, 250v and 600v. 200,000 A interrupting capacity
Amp and voltage ratings of Class J fuses.
0-600A, 600v, 200,000a interrupting capacity. Available in time delay and fast acting
Characteristics of class CA fuses
0-30A
600V
200,000 interrupting capacity
Peak let thru current of 8000A
Non interchanagble
Characteristics of CB fuses
0-60A
600V
200,000A
Peak let through current of 10,000A for 30A or less, 15000A for 31-60A
Non interchangeable
Characteristics of class Cc fuses
0-30A
600V
Interrupting current of 200,000A
Maximum peak let through of 12000A
Non interchangeable
Four types of molded case circuit breakers
Thermal, thermal magnetic, magnetic, solid state
CEC requires all breakers to be ______
Trip free
What does the CEC define a breaker as
Electro mechanical device
What current causes a GFI to trip?
5mA
Ferrule dudes have current ratings from
0-60
Knife blade have current ratings
0-600
What does eutecfic alloy mean?
Low melting point
Max ratings of class H fuses
600v, 600a
What is clearing time
Total time from fault to no current
Max interrupting eating for a class H
10,000A
The only classes that are HRCII
Class C, HRCII Misc
What is the outer shell of a fuse made of?
Class H: porcelain
HRC: fibreglass.
Which type of switch can be used as disconnecting means
Double pole single throw
