Powerpoint - Circuit Protection Flashcards
A _____ is designed to be the weakest link in an electrical circuit
fuse
Fuses contain a metal strip of alloy that melts before the ________ do
conductors
Dual element fuses (time delay) operates with a built in time delay to allow for ________ overloads such as motor starting
temperature
Dual element fuses have _____ fuse elements, one for overloads and one for short circuits
two
Overcurrent protection:
- a current that exceeds some predetermined value that includes short circuits and ________
overloads
A _____ circuit is a current larger than normal which flows outside its normal path
short
An _______ is a current larger than normal but still flows within its normal path, normal range, within 3-6 times the FLA
overload
Overload protection devices must respond rather ______
slow
Overcurrent and overload devices must be wired in ______ with the cat being protected
series
Name two forms of overcurrent protection
fuses, circuit breakers
higher voltage means a _______ fuse
longer
__________ current rating is the maximum amount of current the fuse is designed to carry for long periods of time
continuous
Interrupting capacity is the max ______ circuit current an overcurrent device can safely interrupt
short
Plug fuse colour coding
Blue __A
Pink __A
Red__A
Green __A
Blue - 15A
Pink - 20A
Red - 25A
Green - 30A
Ferrule type cartridge fuses are used up to ___AMps
60 amps
Knife type fuses are used from 60A- ____A
60-600
Standard code fuses have an interrupting capacity of _______amps
10,000amps
High rupturing capacity fuses (HRC) have an interrupting capacity of _________
100,00 amps
Two forms of HRC fuses:
Form 1: provides both short circuit and ________ protection
Form 2: provides for short circuit protection _____
form 1: overload
form 2: only
The CEC defines a _________ as an electromechanical device designed to open a current carrying circuit under both overload and short cct conditions
circuit breaker
CEC also requires circuit breakers be ___ free
trip
Name three types of circuit breakers:
thermal
magnetic
thermal magnetic
solid state
thermal circuit breakers are connected in ______ with the load it controls and its function is to protect the circuit against overloads
series
Magnetic breakers have a magnetic connected in series with contacts and it protects against short _____
circuits
The thermal magnetic breaker has a thermal element and electromagnetic in series with the contacts, it protects against both _______ and _________
short circuits and overloads
GFCI detect a difference between the current flowing in the conductor to the load, and the current returning to the ______
device
Relays are normally used to carry less than ___A of rated current flow through the contacts
20A
Contactors are larger versions of a relay and normally carries between 20-60a through the _______
contacts
Motor starters have built in means of ________ protection
overload
Contactors and motor starts can control inductive and ________ loads
resistive
Overload protection in a motor starter is rated at not more than ____% of the motor RLA
125%
(motor starter) For over current protection with fuses on single phase or three phase it is required that all hot legs be ________
protected
(motor starter) For overload protection only the two hot legs must be ______
protected
Motor starter contacts are normally made of ______ or cadmium
silver
Overload protection on motor starters may be magnetic, thermal or ______-________
thermal - magnetic
Overloads respond _______
slowly
standard code fuse interrupting capacity is _________Amps
10,000amps
High rupturing capacity fuse is ________ amps
100,000amps
Form 1 HRC provides for both _______ and short circuit protection
overload
Form 2 HRC provides for ___________ only
short circuits only
Standard plug fuse colours and ratings?
B - 15a
P - 20a
R - 25a
G - 30a
plug fuse max volt rating?
150v to ground
Thermal breakers are for ________ only as they are slow response
overloads
Magnetic breakers protect against _________ only
short circuits
Thermal-Magnetic breakers protect against _______ and ________
overloads and short circuits
Are HRC fuses available in plug type
No
A current larger than normal, but flowing within its normal current path is referred to as an __________
overload
A current larger than normal but flowing outside its normal current path is referred to as a ________
short circuit
The ________ rating refers to the ability of a fuse/breaker to extinguish an arc after opening
voltage
Standard code fuses have a _______ interrupting capacity than HRC fuses
lower
HRC stands for?
high interrupting capacity
Time delay fuses marked with “__” and Non-time delay marked with “__”
D
P
Time delay fuses allow for temporary _______
overloads
Ferrule type fuses rated for up to ___amps
60 amps
Knife type fuses rated for 60-____amps
60-600amps
