H-6 Fuses And Breakers Flashcards
What is overload protection ?
overload: A moderate increase in current to an above normal level over a short period time .
What is over current ?
overcurrent : A current much larger then normal , momentarily
One advantage and one dis advantage of a fuse
Faster , more reliable , Only used once
One advantage and one dis advantage of a breaker
resetable, may have poor repeatability
two injurious effects that short current causes
mechanical , thermal stress
What determines how much current flows through when a fault occurs
IMPEDENCE
A fuse with HRC means
HIGH RUPTURING CAPACITY (FAST)
maximum current for plug fuse
30 A
Max voltage rating for plug fuse
150v to ground
2 other reasons a fuse may open
High Ambient temperature , vibrations , poor connection
what do “tamper resisting” plugs do ?
Prevent overfusing
Name 2 different style of cartridge fuses
Bolt on , ferrile , blade
A fuse is marked with the letter d
Marked as TIME DELAY
Example of a fast speed response fuse
Electronics - fast
Example of a slow speed response fuse
Breakers - motor protection
significance of the voltage rating in fuses
Maximum voltage fuse may operate at
significance of continuous current rating in fuses
Maximum current fuse may operate at
Significance of interrupting capacity
Maximum fault current fuse can handle without destroying itself
A fuse is marked with the letter P
Marked as LOW MELTING POINT
Max current ratings for cartridge fuses
600A
Max voltage ratings for cartridge fuses
600V
One adv , one disadv of “One Time” and “Renewable” cartridge fuses
Used One time ,cant tamper with fuselinks
renewable , can be spiked
What is meant by the term code fuse
Class H (10 000 AIR)
Maximum interrupting rating for code fuses
10 000A
What is a dual element fuse ?
Two elements , protecting against shorts and overloads
Cartridge Fuse
Ferrule - contacts , knife , bolt on
Type C fuses :
Rejection Ring must be used
Type S fuses :
Rejection adapter must be used
Standard low voltage ratings for Fuses
125v , 250v , 300v , 600v
What kinda base does a plug fuse have?
Screw Base , Edison Base
What does a fuse do?
Protects the Conductor in a circuit
How does a Bi metallic fuse work ?
An insulated tube containing metal strips that melt if too much current passes through ( short circuit )
Are type C AND S interchangeable?
NON INTERCHANGABLE
Proper voltage rating is required …
To prevent the arc from re striking.
What do the letters HRC mean when refering to a fuse ?
High Rupturing Capacity
What is the essential difference between HRC1 AND HRC2 fuse ?
HRC2 Does not protect against overload , it is used with overload heatres
what is a rejection holder?
Rejects a standard H fuse
Usual interrupting capacity of HRC fuses
200 000A
What is difference about HRC fuses then cartridge fuses ?
Silver links ( lower resistance) , ceramic body , sand filler
Are HRC1 AND HRC2 fuses interchangeable ?
No
Does code let HRC fuses be used instead of cartridge fuses
Yes
what are HRC1 used for
General Purpose Motors
HRC2 is used for what?
Motor circuits that use seperate overload protection
Explain Trip Free
The breaker cannot be held ON . It is free to trip.
Explain Thermal Trip
Trips on bending bi metallic strip ( time delay )
Explain Magnetic trip
Taps in magnetic Coil
Explain Thermal - magnetic trip
combination of metal strip and magnetics.
what do the letters GFCI mean?
Ground fault circuit interrupter
If a two pole breaker is not available , it is permissible to use a two single pole breaker?
Yes, as long as the poles are together using a tie bar
