Circuit breakers
Circuit breakers
Embedded Files
molded case circuit
breakers
high voltage breakers
miniature, equipment breaker
Molded case breaker parts
Molded case breakers have separate mechanisms to deal with overloads and short circuits.
The heater and bi-metal spring operate un der overload.
Electromagnets operate under short circuits.
Short circuit operation
If the current is very high, the electromagnet has enough power to trip the breaker.
Overload operation
If the current is an overload - above the breaker rating but under rated percentage the thermal function operates.
The heater causes the bimetal spring to bend and trip the breaker.
Breaker
Breaker
Parts
Parts
Actuator lever - used to manually trip and reset the circuit breaker.
Actuator mechanism
Contacts –
Terminals
Bimetallic strip
Calibration screw
Solenoid
Arc divider/extinguisher
Positions
Positions
If the breaker handle is
towards the panel's centre, it is “ON”
away the centre of the panel, it is “OFF”
between these 2 position, it is “TRIPPED”
To reset a tripped breaker:
move the handle all the way off
then on
Is that breaker tripped?
Try pushing it to the panel's centre.
If it won’t move, it’s not tripped
If it moves to the centre but springs back, it’s tripped.
FPE
FPE
FPE (Federal Pacific Electric) was a company manufacturing electrical panels and circuit breakers for homes in 1950s-1980s; but, the panels are now considered bad due to safety concerns as they may not reliably trip in overloads, maybe causing electrical fires.
Exception Note the position of the breaker handles in the graphic.
Note they are “ON”
Federal Pacific – FPE breakers are on when they • are away from the centre of the panel.
Why FPE boxes are dangerous? [1]
Many done on breakers since 1980s showed 1/4 stab-lok breakers are defective and won't properly trip off.
As test started in 1930s, a new Jersey court exposes FPE of testing fraud and a coverup, labeling breakers as meeting standards set by the UL, but in truth they weren't.
14-302 Construction of Circuit Breakers
14-302 Construction of Circuit Breakers
Where circuit breakers are given for the apparatus protection or ungrounded conductors, or both, they open the circuit in all ungrounded conductors by one handle's manual operation and by the overcurrent's action, aside where single-pole circuit breakers are allowed by Rule 14-010(b); or
4-010 Protective and control devices needed
4-010 Protective and control devices needed
Ungrounded conductors shall be given with (b) manually operable control devices that safely disconnect all the circuit's ungrounded conductors at the point of supply simultaneously, except for multiwire branch circuits that supply only fixed lighting loads or non-split receptacles, and that have each lighting load or receptacle connected to a neutral and one ungrounded conductor.
14-010 (b): The Exception
What if we close the top breaker and open the bottom one?
Will the heater work?
Is it safe to work on?
The orange indicates live parts
Why 14-010 (b) (2)
What happens if we use a 2-pole
breaker?
Now we have a safe system.
How many poles does the breaker need to be?
The number of poles must correspond to the circuit.
If one conductor of the circuit overloads, all the lines must open
Circuit Breaker Characteristics
Pros
Pros
a fault de-energises all circuit conductors
can be easily reset when tripped
Cons
Cons
inaccurate tripping
high interrupting are hard
higher maintenance than fuses
expensive relative to fuses
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