Can We Use AC Circuit Breaker for DC Circuit and Vice Versa? . Circuit breakers are integral to electrical safety, protecting systems from overloads, short circuits, and electrical faults. But when it comes to their application in AC or DC circuits, compatibility becomes critical. This article unpacks whether an AC circuit breaker can function effectively in a DC circuit, and vice versa, while highlighting the risks, differences, and best practices.
Why DC Circuit Breakers Can’t be Used in an AC Circuit and Vice Versa?
Both AC and DC are electrical energies having the same heating effects for the same RMS values but there are multiple differences between AC and DC with different parameters.
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What Is a Circuit Breaker?
A circuit breaker is an automated electrical switch designed to protect circuits from damage caused by overloads or short circuits. Its primary function is to interrupt current flow after detecting faults, preventing damage to the system or appliances.
Types of Circuit Breakers:
- AC Circuit Breakers: Engineered for alternating current systems.
- DC Circuit Breakers: Designed to handle the unidirectional flow of direct current.
While their core function remains the same, their designs cater to the specific behaviors of AC and DC electricity.
AC Breakers in a DC Circuit
For instance, the AC voltage and current may have different effect in the circuit other than the DC with the same level of voltage. For this reason, An AC circuit breaker can’t be used for circuits. Similarly, DC circuit breakers can not be used for AC circuits. Let’s see the following facts behind the scene.
We know that AC needs more insulation than DC having the same level of voltage. This way, the insulation material used in a circuit breaker and its contacts may react differently facing the opponent voltage other than the rated voltage.
In case of AC, the sine waves of current and voltage reaches to the zero about 60 times per second (in US where frequency is 60Hz while 50 time in UK and EU where f = 50Hz). In other words, AC voltage and current cross the zero after each half cycle due to frequency and they change the direction and magnitude at time interval.
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DC Breaker in an AC Circuit
In case of DC, zero crossing is not possible as there in no frequency in DC voltage and current as DC is a constant value i.e. DC voltage and current won’t change the direction and magnitude (it flows in one direction and can’t changes the polarity).
This way, DC will melt the breaker contacts faster than DC as DC is constant while AC changes it direction and magnitude 50 or 60 times a second.
How AC and DC Circuits Differ
To understand circuit breaker compatibility, you need to grasp the fundamental differences between AC and DC systems:
- Current Flow:
- AC: Alternating current reverses direction periodically.
- DC: Direct current flows in a single direction.
- Voltage Behavior:
- AC voltage oscillates, providing natural zero-crossing points that aid in arc suppression.
- DC voltage remains constant, making arcs harder to extinguish.
- Applications:
- AC circuits power homes, offices, and industrial systems.
- DC circuits dominate batteries, solar panels, and EVs.
These differences require distinct designs in circuit breakers to ensure effective operation.
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Why Arc in DC is stronger than AC in Breaker Contacts?
When we break a DC circuit via DC circuit breaker, the electrons flows are steady state and want flow through the contacts as the applied voltage pushes them forward, so the created arc is stronger as compare to the AC as DC flow of electrons have momentum.
In case of AC, the applied voltage and current are not steady state i.e. the flow of electrons are relaxed as they back and fourth changing the direction and amplitude continuously. In other words, the firstly go to the peak value and go back to the zero in the first half cycle (+ve) and then go to the peak and zero again (respectively) but in the opposite direction (-ve). This vibration distort to create the momentum, so the arc created in AC is weaker than DC voltage.
Keep in mind that you won’t be able to feel the zero crossing of AC as the effect of changing of AC is too much fast even you can’t assume that the AC at zero value at any instance. Keep again in mind that AC is more dangerous than DC
These are the reasons you should not use DC circuit breaker for AC and vise versa.
Is it still possible to use DC breaker on AC and AC breaker on DC?
If you need a favor (you did) and find a way to use AC breakers on DC, You can, but you may not.
Before going to do so, you should read all the instruction, circuit breaker nameplate data printed on it especially the voltage and current rating for both AC and DC.
There are some circuit breakers which can be used for both AC and DC with limitation. For instance, a 240V AC, 30A circuit breaker can be used for 48 to 60V DC. Similarly, a 110V AC circuit breaker can only be used for 30V DC.
To use an AC circuit breaker in a DC circuit, the proper size of circuit breaker should be used. This is because the breaker do the following two jobs when overcurrent fault occurs on the connected circuit.
The current sensing system sense and identify the overcurrent which leads to separate the breaker contact to break the circuit from power supply.
The circuit breaker then quench and distinguish the arc created safely during the contacts separation without damaging the breaker and contacts. This is only possible when we use correct size of wire and breaker according to the NEC and IEC standards and regulation for wiring installation.
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kA Capacity when using AC and DC Circuit Breakers
kA rating of a circuit breaker must be consider while using it for AC and DC circuits. It is the breaker rating in amperes based on the peak value (breaking capacity rated in RMS value of currents) which shows the making abilities in case of surge and transient voltages for very short time.
For this reason, the voltage and current rating reduced to the half of the AC voltage and current. For instance, the 10kA AC will reduce to the 5kA in case of DC circuit. Now, if a fault of 5kA occurs on DC line, the breaker will act as short path due to to melted contacts and over connected devices may damage which even leads to hazardous fire and electric shock.
Due to the above reasons and facts, we don’t recommend to use AC circuit breaker for DC and vise versa.
Note: The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.
Disconnect the power before replacing, repairing, troubleshooting, maintenance and installation electrical appliances and equipment other wise, it will kill you and you won’t be able to ask that who killed me – Current or voltage? Also, you won’t be able to ask which one roast me AC or DC? So please stay safe.
Design Differences Between AC and DC Circuit Breakers
- Arcing Phenomenon:
- AC breakers rely on voltage zero-crossings to break the arc.
- DC breakers use magnetic blowout mechanisms or large arc chutes for arc extinguishment.
- Contact Material and Separation:
- DC breakers require wider contact separation due to the absence of zero crossings.
- Trip Mechanisms:
- AC breakers utilize alternating current properties for tripping mechanisms.
- DC breakers often have more robust and specific trip units for higher reliability.
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Risks of Incorrect Circuit Breaker Usage
- Overheating: Mismatched breakers generate excessive heat, reducing lifespan and increasing fire risks.
- Electrical Fires: Arcs that fail to extinguish can ignite nearby materials.
- System Downtime: Incompatibility causes frequent tripping, disrupting operations.
FAQs About Can We Use AC Circuit Breaker for DC Circuit and Vice Versa?
Can an AC circuit breaker handle DC voltage?
Only if it is dual-rated; otherwise, it cannot safely extinguish DC arcs.
What happens if I use the wrong circuit breaker?
Overheating, system failure, or even fire hazards can occur.
Are dual-rated breakers expensive?
They cost more upfront but save money in the long run by preventing damage.
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