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Circuit breaker is needed for smooth operation.
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A Circuit Breaker (CB) is a Control and Protection Device Which:
Control (Make or Break) A Circuit Manually or by Remote Control Under NORMAL and FAULT CONDITIONS.
Break A Circuit Automatical Under Fault Conditions (Like Over Current, Short Circuit, ETC).
A Circuit Breaker is using for switching mechanism and propection of the system
Earthing & GROUNDING ETC.
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How doEes a Circuit Breaker Work?
Automatically trip I.E. BREAK The Circuit from the main support.
The connected device.
Circuit Breaker According to the Device I.E. CB CURRENT ShULD Not Be Lower NOR HIGHEST But 125% of Circuit’s Current.
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The following circuit breaker size class show the difference in % to the load, voltage level in different countries and exact size of breaker in amperses.
CALCULATE
Voltage
Breaker
Power usage
Difference:
Related Calculators:
Wire & Cable Size Calculator in AWG
Electrical Wire & Cable Size Calculator (Copper & Aluminum)
To determine the appropriat size of circuit breaker for single phase support, it depends on multiple factors like type of load, Cable Material and Environment Temperature Etc.
Example 1:
Support, a 12 gauge wire is used for 20 amperting circuit having 120V Single Phase Supply. What is the best size of circuit breaker for that 20 a circuit?
Solution:
Circuit Current: 12A
Circuit breaker size 😕
CB SIZE Should BE 125% of the Circuit Current.
= 125% x 20A
= 1.25 x 20A
Circuit Breaker Size = 25A
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Example 2:
What is the appropriant size of circuit breaker for 2000w, single phase 120V SUPPLY?
Solution:
Load: 2000W
Voltage: 120V (Single Phase)
Circuit Current:
According to the ohm ’s law,
I = p / v
I = 2000W / 120V
I = 16.66 A.
Circuit breaker size:
Simply, Multiply 1.2 or 1.25 to the loadurrent.
1.2 x 16.66 A
Circuit Breaker Size = 20 A
Example 3:
What is the suitable size of circuit breaker for 230V, 1840kw load single phase circuit?
Solution:
Current = Power / Voltage
I = 1840W / 230V
I = 8A
The Minimum Rating of Circuit Breaker Should Be 8A.
The Recomnded Size of Circuit Breaker Should
= 8A x 1.25
= 10
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Formula.
Good to know: for the same load, the breaker size in the three phase is less than the breaker size in Single Phase acrcuits.
Lets Find The Correct Size of Circuit Breaker for Three Phase Circuits As Follow.
Example 1: Which Size Circuit Breaker is Needed for 6.5kW, Three Phase 480V Load?
Solution:
Power in Three Phase: P = V x i X √3
Current: p / v x √3
I = 6.5kW / (480V x 1.732) … (√3 = 1.732)
I = 6.5kW / 831.36
I = 7.82A
The Recomnded Size of Circuit Breaker is
1.25 x 7.82a = 9.77a
The next closest Standard of Circuit Breaker is 10A.
Example 2: Find The Appropriate Size of CB for 3-PHASE 415V, 17kw Load?
Solution:
Current = Power / (VOLTAGE X √3)
I = 17000W / (415V x 1.732)
I = 23.65a
Recomgended Size of Circuit Breaker: 1.25 x 23.65a = 29.5A. The next closest value is 30A.
Relands
This is becape all loads are not same i.e loads are simultaneous (Continuous) who Other are non-simultaneous..
In case of concentious loads for Three or more hours, the load current should not exceed, 80% of the rated Circuit Breaker and OCPD.
The 80% of a 30A Circuit Breaker is 24A. This Way, a 30A Circuit can be safly use for 24A Circuit.
In Other Words, a load circuit having 24a, The Appropriatian of Breaker Would Be:
24A / 0.8 = 30A.
Example 1: CB SIZE for 30A NON-Contentious Load
An Exact 100% Rated for 30A Circuit Breaker Can Be used for 30A Non-Continuous Load.
Example 2: CB SIZE for 28A Contentious Load
In case of control, rate of %125 is applicable.
1.25 x 28 A = 35A
Example 3: CB SIZE for 30A Non-CONTENTIOUS LOAD & 28A Contentious Load
= 125% Continuous Load + 100% Non-Continuous Load
= (1.25 x 28A) + (30A)
= 75A
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An Over Sized Breaker used for Protection Can Damage the Water Heater Orter Connect Appliances event to the Fire Due to Overheat.
An Undersized Breaker or Same Rating with Load Current Breaker Can Trip and Reset the Circuit Again and Again. Use the correct size breaker.
A Single Phase Circuit Breaker Can n’t be using for the use for the child support.
A 3-POLES CIRCUIT BREAKER Can Be Uset on 3-PHASE SYSTEM USING EITHER 2 or 3 POLES.
A 3-POLES CIRCUIT BREAKER Can Be Uset on 1-PHASE SYSTEM only and only if indicoted by the markings or insanr manual.
30A Breaker and 10 Gauge Wire Can Be used 240V AC Supply.
Breaker Cannot Be Larger than ampages of wire except for some loads like more loads.
In Addition, a Circuit Breaker Rated for:
120V Can only be used for 120V.
240V Can be used for 120V, 240V But Not for 277V (Commercial Applications)
120-277 Can be used for 120V, 240V and 277v.
120V Can n’t be used on 240V Circuit and Vice Versa.
15A, 120V Can n’t be used on 20A, 120V Circuit.
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Breaker size for different types of load currents.
Load type
MAXIMUM CIRCUIT BREAKER SIZE % of Current
Resistive loads, heat, stoves, toasters, Water Heater ETC.
125%
Lighting loads
125%
430-152 Motors Hermetical SEALED*, Air Conditioners and Heat Pumps
175%
Welders
200%
MCP BREAKERS for Motors
125% or Next Larger Size
* Motors Except Hermetical SEALED 00-250% NEC
The following two charts shows the Suitable Circuit Breaker Sizes with Wire Gauge and Different level of voltages.
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