miniature circuit breaker sizing _ electrical engineering centre

HomeAboutVideoGlossaryElectrical FormulasSearch ResultsSite map

04 February 2011 ~ 6 Comments

Circuit Breaker 0

When we design or build a electrical installation,wemust know how to choose the suitable circuitbreaker for the any application that we design.Forelectrician,this is compulsory knowledge.So here iwant share my little knowledge about circuitbreaker sizing method.

This calculation for sizing the miniature circuitbreaker.For other circuit breaker likesMCCB,ACB,VCB,OCB and etc,it have a additionalfactor and calculation that we must consider.Forthat i will discuss it in my next post…so this time iwant explain the simple way how to sizing theminiature circuit breaker.

Ads by Google HVAC Sizing MCB Panel Sizing 2 Pole MCB ABB Motor

Circuit Breaker Lockouts www.reecesafety.co.uk

Complete range of locking devices to fit MCB,Circuit Breakers

3 Phase Power Monitor www.london-electronics.com

Windows touch-screen power monitor and datalogger with 4Gb capacity

Electric Power Blogs www.energyblogs.com

Read (and contribute) blogs about electric powerindustry.

motor soft starter wwww.wanzhou.com.cn

high quality soft starter supplier 10 yearsexperiences on motor start

Miniature Circuit Breaker Sizing | Electrical Engineering Centre http://www.electricneutron.com/circuit-breaker/miniature-circuit-break...

1 of 9 8/3/2011 2:42 PM

Why it so important? Ok..it have many reason as below :

For electrical safety purposeTo not over cost to purchase circuit breaker when we over sizing it. or not suitableTo prevent the equipment from damage before it can use it.To easy when we want purchase the mcb,because we have all detail information about it.To make the design matter more effective and faster to complete.

How to select a suitable MCB for the application?

we must focus in 3 main points to choose a right MCB for electrical circuit :-

1) Ampere rating ( In )

2) Short circuit breaking capacity ( If )

3) Application type

Calculation for Miniature circuit breaker ( MCB ) sizing

Example : We want install 1 unit single phase motor.full load ampere is 20 ampere. Power supply240VAC,50 Hz

1) Ampere Rating ( In )

Formula : In = 0.25 x Iz

In = ampere rating Iz = Load ampere

Calculation :

In = 0.25 x 20 ampere

In = 25 ampere x 0.25 ( safety factor )

In = 31.25 Ampere

Refer the ampere rated in technical data for MCB from manufacture

From the technical data,we selected the ampere rated for MCB is : 32 ampere


2 of 9 8/3/2011 2:42 PM

2) Short circuit breaking capacity ( If )

Formula : If = V / 0.276 (R cable)

If = short circuit breaking capacity

V = Voltage

R cable = resistance cable ( 0.276 )

Calculation :-

If = 240 / 0.276

If = 870 ampere

From the answer,we can decide to select rating for one ( 1 ) kA

3) Application type.

From application,it state the single phase motor,so we can choose TYPE C for MCB.It for generalapplication and for small motor.Please refer the table below for MCB type for the application.

* For more detail,please refer the manufacture Technical data / user manual or contact the supplier.

ABB MCB Technical data

MCB Type,Instant trip and Application table

—————————————————————————-

1 2.7 – 4 In Domestic and commercial

B 3 – 5 In

—————————————————————————

2 4 – 7 In

C 5 – 10 In General use,small motor

3 7 – 10 In

—————————————————————————

D 10 – 20 In High in rush equipment

4 10 – 50 In

—————————————————————————-

K Frequent short duration

—————————————————————————-

Z Semiconductor devices

—————————————————————————-


3 of 9 8/3/2011 2:42 PM

So…the conclusion from the calculation,we get the specification for MCB to install on our application :-

1) Rated ampere is : 32 ampere

2) Short circuit breaking capacity is : 1 kA

3) Type of MCB is : Type C

For more detail,please contact the electrical engineer for their suggestion.This is a simple way to sizing thecircuit breaker.Please refer the IEE manual for electrical guideline.

Circuit breaker specific features for main switchboardVacuum circuit breakerMolded case circuit breaker maintenanceTypes of motor overload relayCriteria for cable design

Tags: abb, ampere, clipsal, mcb, mccb, safety, schneider, voltage

Sinnadurai Sripadmanaban 24 April 2011 at 11:41 PM Permalink

Please give an example for selection of MCB(type C or D)for a 3phase induction motor,say10HP,15Amp- if started using an across the line(DOL)as well as wye-delta starter.

Reply

1.

lemau 25 April 2011 at 1:34 PM Permalink

from your example :-10 hp;15 ampere

2.

PCWI Australia www.pcwi.com.au

for Clamp Meters (Tong Testers) for Current andVoltage measurement

Relays, Switches & Sensor www.comus.be

Manufacturer Reed Relays & Switches Solid StateRelays, Sensors

LTspice IV www.linear.com/ltspice

Free Circuit Simulation Tool & Schematic Capture -Learn More!

AC Power Sources www.elgar.com

California Instruments, Elgar, AC ProgrammablePower /current Sources


4 of 9 8/3/2011 2:42 PM

the calculation is :

15 ampere x 0.25 = 3.75 + 15 ampere = 18.75 ampereSo we can choose the MCB ampere rating = 20 ampereFor induction motor with DOL stater,the suitable type is C or D

Reply

Sinnadurai Sripadmanaban 3 May 2011 at 11:13 AM Permalink

As the starting current is not the same for DOL and star-delta starterscan we use smaller MCB for star-delta starting?. Is it correct if I say 20A for star-delta and25A for DOL starting

Reply

lemau 4 May 2011 at 9:42 AM Permalink

U can use a smaller MCB but make sure it not below from the full load ampererating.One more important thing is the TYPES of MCB must suitable with yourapplication.Example MCB type C or D for motor stater.For more safety about overloadprotection,we still have the overload relay :D

Reply

Sinnadurai Sripadmanaban 5 June 2011 at 10:11 AM Permalink

For frequent start/stop or DOL starting, OL relay won’t protect. MCB will trip for inrush current.Sowe used MCB type C rated 2xFLA for DOL and 1.5xFLA for star delta starting. Another importantaspect is the rating and type of MCB should match the duty of motor -AC1,2,3 etc. For frequentstart/stop like pressure switch operated water boosting pumps should be use type C duty AC3 ortype D AC1?. Therefore the formula 1.25xFLA is for which duty class and will the tripping andcontact wear problem will be solved for some class of duty by using class D MCB?. Pleaseelaborate.Manufacturer’s literature will be a useful guide.

Reply

3.

saouita 18 June 2011 at 9:18 AM Permalink

stl

Reply

4.

Name (required)

Mail (will not be published) (required)


5 of 9 8/3/2011 2:42 PM

Website

Please tick to confirm you are NOT a spammer

Search This Site

Translation Tool

High VoltagePowerCables, accessories &installation 66kV,132kV & 400kV.XLPE,gas & oilwww.elmeridgecableservices.co

Crane OverloadProtectionCranegard,DynaSwitch, loadlimiting deviceswww.dqplus.com

高速同軸ケーブル高周波帯域に優れた特性を示す同軸ケーブル、その他各種ケーブルwww.sanyu-tempflex.com

vacuum circuitbreakerAir type Vacuum typewww.Panickker.com/vcb.htm

Prevent CurrentDamageG&W Electric Co. -Current LimitingProtectorwww.gwelec.com


6 of 9 8/3/2011 2:42 PM

Powered by Translate

Latest post sent to your Email?

Enter your email address:

Delivered by FeedBurner

Categories

AutomationCircuit BreakerDo It Your SelfEarthing SystemElectric MotorElectrical SafetyGeneralGeneratorHand ToolsHVACLightingMeasuring instrumentsMotor ControlTheorywire & cableWiring Techniques

Popular Posts

Star delta starterStar delta motor connectionElectrical FormulasTypes Of Earthing SystemsDirect on line starterVideoTerminal connection for induction motorConductor splicesSearch ResultsInduction motor fault findingMotor Overload ProtectionMiniature Circuit Breaker SizingMiniature Circuit BreakerElectric motor testing


7 of 9 8/3/2011 2:42 PM

Recent Posts

Types of Molded Case Circuit Breaker MCCBMCCB protection for induction motorWhat is electric shock?How to servicing the magnetic contactor?Electrical installationHow to select the best location for install split unit air-conditioner?How calculate ampere for electric motor?How to choose speed controllers for AC motor?Vacuum circuit breakerHow to install lug for electric cable?

Archives

August 2011 (1)July 2011 (17)June 2011 (19)May 2011 (25)April 2011 (11)March 2011 (20)February 2011 (21)January 2011 (11)December 2010 (2)October 2010 (15)September 2010 (26)August 2010 (4)

Related Pages

Hand Tools Review

Electrotechnik

HVAC Tutorial

solar pv systems

General Info

Technology blogs

HomeAutomationCircuit BreakerDo It Your SelfEarthing SystemElectric MotorElectrical Safety


8 of 9 8/3/2011 2:42 PM

GeneralGeneratorHand ToolsHVACLightingMeasuring instrumentsMotor ControlTheorywire & cableWiring Techniques

© Electrical Engineering Centre. (2010 - 2011) email : [email protected]

This page took 3.0 seconds to load.


9 of 9 8/3/2011 2:42 PM

miniature circuit breaker sizing _ electrical engineering centre

Documents