# Residual Current Circuit Breaker (RCCB)

New article from Manish, one of the members of the EEC! In his last article he told you about Miniature Circuit Breakers (MCBs). Today he will take a look at another important type of circuit breaker called Residual Current Circuit Breaker (RCCB).

#### Introduction

A Residual Current Circuit Breakers is another different class of Circuit Breakers. A Residual Current Circuit Breaker (RCCB) is essentially a current sensing device used to protect a low voltage circuit in case of a fault. It contains a switch device that switches off whenever a fault occurs in the connected circuit.

### Purpose of RCCB

Residual Current Circuit Breakers are aimed at protecting an individual from the risks of electrical shocks, electrocution and fires that are caused due to faulty wiring or earth faults.

RCCB is particularly useful in situations where there is a sudden earth fault occurring in the circuit.

e.g. A person accidentally comes in contact with an open live wire in the circuit.

In such situation, in absence of an RCCB in the circuit, an earth fault may occur and the person is at the risk of receiving an electrical shock.

However, if the same circuit is protected with RCCB, it will trip the circuit in fraction of a second thus preventing the person from receiving an electrical shock. Therefore, it is a good and safe practice to install RCCB in your electrical circuit.

### How does it Protect?

As explained above, RCCB is meant for protection from earth faults and associated risk to human life such as electrical shocks.

The underlying fundamental principle behind operation of RCCB is that in ideal situations the current flowing in to the circuit through live (hot) wire should be same as the returning current from the neutral.

In case of an earth fault, the current finds a passage to earth through accidental means (such as accidental contact with an open wire etc.). As a result the returning current from neutral is reduced. This differential in the current is also known as “Residual Current”.

RCCB is designed such way that it continuously senses and compares for difference (residual current value) in current values between the live and neutral wires. Any small change in the current value on account of such event would trigger the RCCB to trip off the circuit.

### Types of RCCBs

• 2 Pole RCCB: It is used in case of a single phase supply that involves only a live and neutral wire. It is as displayed in image below. It contains two ends where the live and neutral wires are connected. A Rotary switch is used to switch the RCCB back to ON or OFF positions. A test button helps to periodically test the RCCB functionality.
• 4 Pole RCCB: It is used in cases of a three phase supply connection involving three phase wires and a neutral. It is as displayed in image below. It consists of two ends where the three phases and neutral wire is connected. Besides this it is similar in construction and operation as 2 Pole RCCB.

RCCBs come in different ratings like: 30 mA, 100 mA, 300 mA

### Residual Current Sensitivity

RCCB is primarily designed for protection from earth fault and its consequence to human life such as electrical shocks.

As per studies, a person is able to sustain electrical shocks only to the magnitude of 30 mA.
Thus, RCCBs in low voltage protection are designed such a way that they will trip off the circuit even for small change in residual current value of up to 30 mA. The response time is usually within 40 mSec, thus ensuring that the person is fully protected from electrical shocks at all times.

Higher values of 300 mA are used in cases where a protection from fire hazard is sought. This is useful in places where a lot of flammable material is stored.

#### Conclusion

RCCB is an essential protective device in your electrical circuit that helps to prevent electrical hazards in cases of earth faults. A properly set RCCB will ensure that there is no fatal injury caused to human being in case of an accidental touch to live wires.

• RT. Prof. Nazar M. Karyar says:

You must be aware of the fact that there are billions people living without electricity out of USA in this 21st century. For Example: In Afghanistan, only 6% people have access to home electrical power though, Americans’ presence in this country had been since 13-years (2001-2014). They have capitalized several un-literate Afghan most corrupted individuals in the country to easily rule Afghanistan by force that is impossible. Afghanistan with several millions Muslim inhabitants live in this Islamic State of Afghanistan. I love the people of USA but not the politicians. They have not invested a penny in generation of Hydropower Energy where we have many Rivers, read your Geography. We have the potential to generate 23,000 MGW Hydropower in Afghanistan. We engineers all around the world are not serving humanity that is out of being human being. We are functioning under wrong- doing Politicians. Send some good article in grid design so that I can share it with my college Afghans students. I am a USA- educated but idle because of the wrong politics of USA in this 21 first century around the world specifically, in most poor countries. Lesson; never, and never touch somebody ideology by force. We are now all citizen in this globalization world so, why touch peoples ideology???.
Prof. Nazar M. Karyar Kabul-Afghanistan. E-mail: nazarmkr@yahoo.com

• In any (2 OR 4 pole)rccb out put side neutral wire contact with earth, then rccb become trip(fault) neccesory. Remove neutral wire from earth contact. It is helthy (safe)condition.

• anil says:

Dear sir
we have 10 nos sldb and 10 spdb’s
in each sldb one main incoming 40A 4 pole MCB after that 3no’s rccb sub incomers each phase respectively
now i connect R,Y,B phases to sub incomer rccb inputs
and the main neutral tapped to 3 RCCB neutrals
and sub incomer output phase connectd to another sub incomers like 10A MCB’S
all 3 sub incomer RCCB output neutrals and After RCCB OUTPUT sub incomer neutrals are connected to one neutral link connected
now at a time 3 RCCB switch on after even put any light load are fans loads 3 RCCBS tripped
same proble comes on SPDB (POWER DB ALSO)
SORRY SIR if any english grammer mistakes please excuse me sir

• Shaiju says:

First you have to understand about residual means different between live wire and neutral wire it will connect 1 circuit

Hi,

RCCB: Stands for Residual Current Circuit Breaker. It is also known as Residual Current Device (RCD). RCCB senses the difference between current values in phase and neutral and breaks the circuit in case of an imbalance. In ideal situations, the current flowing through phase (hot) wire equals the returning current in the neutral. However, in case of fault conditions such as an earth fault the current flowing through neutral would not be same as flowing through phase and hence it trips the circuit.

ELCB: Stands for an Earth Leakage Circuit Breaker, is used to protect the circuit from an earth fault. It is an old protection system based on voltage based protection device. It is nowadays replaced by RCCB.
ELCB is connected between the circuit and the system earthing system. It is a voltage operated device and detects any rise in potential between the circuit and the system earth and trips the circuit.

RCBO: Residual Circuit Breaker with Overload. Is a circuit breaker that offers both Residual Current and Overload protection in one single device.

GFCI: Stands for Ground Fault Circuit Interrupter. It is another name for RCCB/RCD. This term is used in USA whereas RCCB/RCD term is used in UK and Europe. Functioning of both is much the same.

• Sitthichai P. says:

Thank you. It is cleared explain.

• BIPIN KUMAR says:

dear mr. manish & other respected engineer’s
my name is bipin kumar and i’m working as an sr.electrician in u.a.e in a very reputated bank for electrical maintance…from few days i’m suffuring a problem that i’m sharing with u all. some time RCCB trip and somebody bank staff reset the rccb it will work till one week or months without any problem. but when its trip my supervisor ask me the reason of tripping but i can’t tell somthing to him,,,,,,,coz some body has reset without my proper checking & its also working,,,,,
i hope that u’ll be understand well my probs,,,so plz give me the bettre solution……,,,,,thnx

• Vijay Saini says:

Dear Manish please make sure that no connection should be loose in this circuit.

• Loganathan says:

Mr.Bipinkumar , I would like to share my experience in RCCB tripping problem. Please ensure the type of loads connected to the distribution board. Please be aware that any type of HARMONIC LOADS CONNECTED TO the distribution system will result in spurious tripping of RCCB. HARMONIC TYPE OF LOADS IN A SYSTEM ARE SOMETHING LIKE COMPUTORS , MONITORS etc which uses rectifiers and switch mode power supplies. In a HARMONIC TYPE OF LOADS , EVEN IF YOUR LOADS ARE BALANCED YOU WILL COME ACROSS HUGE NEUTRAL CURRENT (TRIPPLEN HARMONICS) . THERE ARE SEPERATE RCCBs MEANT FOR SUCH LOADS.

• ABHISHEK SHARMA says:

When connecting RCCB (2p or 4p). What to do with earth connection at DB, all earth wire should be removed from link at DB or it should remain connected.

• rashid says:

any one can expkain, why RCCB is trip when neutral and earth touch in secondary side, since RCCB sence only difference in neutral current comparing with phase?

• Loganathan says:

Mr. RASHID IT IS VERY SIMPLE.WHEN YOUR NEUTRAL WIRE IN THE OUTPUT OF THE RCCB IS TOUCHES (OR) COMES IN CONTACT WITH EARTH , REMEMBER YOU ARE CREATING A PARALLEL PATH TO THE RETURN CURRENT ( IT IS SOMETHING LIKE A LEAKAGE CURRENT THROUGH EARTH) SUPPOSED TO BE THROUGH NEUTRAL. NATURALLY THE SENSOR SEES THE DIFFERENCE IN SUPPLY CURRENT(THROUGH PHASE ) AND RETURN CURRENT (THROUGH NEUTRAL) AND HENCE IT TRIPS THE RCCB.

• binoy says:

Why RCCB is tripping during lightening and which type of RCCB is suitable for invertor out let.

• Loganathan says:

When lightening strikes a distribution (OVRHEAD) line , lightening induced ovrvoltage (resulting a current) which will not be returned through neutral. This current passes through earth , trips the RCCB>

• sowjanya says:

in this RCCB what type of sensors are used ??

• Loganathan says:

There is a CORE BALANCED CURRENT TRANSFORMER (otherwise called CBCT) in the RCCB. The phase wire from the input passes through the CBCT and connected to output of the RCCB. The neutral wire from the input side passes through the CBCT and connected to the output terminal of RCCB. There is another secondary winding in the CBCT connected to an electronic circuit and activates a link to the trip bar of RCCB . When the phase current and neutral current in the RCCB is same , the CBCT is balanced. When there is a diff in the phase and neutral current (Defined by the rating of RCCB) there is a current in the secondary winding of CBCT.

• s says:

Hi, Can RCCB be installed on the mains even if there is no earthing in the house. In such a case, will it provide protection?
Will it protect against neutral wire failure or disconnection in case of 3 phase connection?
Which is the best way to protect the house in case of neutral failure in three phase connection?

• Shakthi says:

In my home I have 3 phase supply. Regular ELCB is installed on each single phase.
But I had a problem of power surge inside my home possibly due to neutral connection in the distribution transformer. During short period, possibly single phase load experiences full phase to phase voltage.
During this time, my single phase ELCB trips but before that there is a equipment damage also.

For neutral cuts/loose contacts of three phase supply in 4 pole RCCB is the solution to protect the equipments in my home?

• shubham says:

Dear sir,
For welding activity leakage current will be more than 30mA and above that value of current will be harmfull to human.
so which RCCb should be prefered a30mA or 100mA and why?
Plz guide

• oscar migani says:

Hi , i have real gained alot from the RCCB explaination, i went to the haouse of my customer where electric shock happen, RCCB connected was Havells made in India. The RCCB switched off the power but did not operate again we discovered that the switch could not hold at on position even if the load side was removed . now my customer wants a thoroughly explanation why the RCCB got destroy instaaedy of switching off and remain safe. Please help

• anil says:

sir we have 3nos 32A rccbs 30ma in each phase respectively incoming is 40A 4pole mcb now i can on three rccbs even one light on three rccb are tripped but single single rccb can operate full load it takes please solution sir
if any grammer mistakes please excuse me sir

• Learning says:

Hello

we have a 3 phase connection in our recently purchased house in Belgium.
There is a 4 P/40A/300mA RCCB that is, I assume, put in the incoming electricity phases (3P for the 3 phases and the 4 Pole connected to the Neutral) and a 4P/40A/30mA RCCB that is, I assume, 3 poles in the 3 phases and 1 pole in the Neutral that goes into the circuits for the internal wiring.

Normally, one needs a 300mA RCCB as what we have, a 30 mA for all the circuits that are in damp areas (like kitchens, bathrooms, gardens, cellar) and for grounded sockets and not necessarily for light bulbs/switches in the dry areas)

The electricity attestation that was done on the house prior to our purchase, indicates that there is need for an additional 30mA RCCB, and we do not understand why, please can someone explain the need for this.

thanks

• saka sateesh kumar says:

Dear friends,
The trippig value set at 100ma means when 100ma or more current is flow in nutral / earthing it may be trip. You aware that fatal current is 5 mA to 10 mA.
It is advisable to set 30 mA when in your home or industry you use 24 hours duty i.e continuous duty.
For higher capacity it i.e 100mA or more is apply where more current rated single apparatus is use. It is advisable to fit rccb with refrigerator, single phase water sump motor or pump and heater use in your house. In those house where small kids advisable to fit rccb.

• Srikanth says:

Dear sir,
at a home having one submersible motor , one fridge, at a kitchen mixture grinder. how many rccbs used?

• Mathikrishnan says:

Have a good day!

My question is, can 3 phase RCCB works on single phase circuit?

• james says:

Hi. Our house is old and we dont have ground wire. Will the RCCB be able to save me if I touch one electrical case (Like Microwave 2600W) without ground wire from High Shocks?

• steven789 says:

I like to discuss about type of RCCB, in term of their built-in (switch) pole. I know from Wiki
1.Single-pole / SP / one-pole – the RCD will disconnect the energized wire only.
2.Double-pole / DP / two-pole – the RCD will disconnect both the energized and return wires.
but onother type “1P+N” comes in. I see some RCCB specification put 2P and 1P+N on the same RCCB products. Why？ Also is 1P+N short for 1 phase + neutral ? or 1 pole + neutral..Thanks

• sujal patel says:

Dear,

I have RCCB in my home by standard company. i installed it in the year of 2009.from last few days it is tripping sometimes in a day. i filled this tripping is due to newly installed Inverter AC in bed room.
Can you please guide me the reasons for tripping.
Regards’

• Abhijeet says:

The Mains supply is three phase supply. What will happen if the three phase wires are connected in a single pole and the neutral on the other pole of a 2 pole RCCB? Will it work fine?

• ravindra says:

hi. in my home RCCB is tripping as soon as electricity board power resumes. if we switch on after sometime it works normally. what can be the root cause for this. I have changed the RCCB with new one and checked but still the problem persists.

• prashant says:

sir, I connect 3ph-N ( 4 wires) to 4 pole RCCB incomer. my load is 3phase motor ( without neutral), my question is will RCCB trip when any of motor phase gets earthed?

• sachin says:

whether ELCB or RCCB can be used for 3 phase 4 wire over head distribution network with unbalance voltage and unbalance load? so that person comes in contact with the line or snapping of conductor on earth will interrupt the supply so as to avoid further hazards… needs help for better understanding

• Srikanth says:

please show line diagram of Rccb. How to connect rccb? how to protect rccb? i

• Srikanth says:

Dear sir,

please show line diagram of Rccb. How to connect rccb? how to protect rccb?

• Gloucester Electrician says:

Hi, the whole thing is going nicely here and ofcourde every one iis sharing facts, that’s actually fine, keep up writing.

• Mojtaba says:

Hi, in some RCCB ( up 40A) I see a capacity, what is this? and it’s function?

• Christopher says:

I was asked a question that if a neutral connection fails on the rccb breaker, will the device still protect from an earth fault. I assume that an imbalance greater than the trip level say 30ma would be detected immediately and the device would trip or even fail to reset on. Would the current balance transformer work in these circumstances? I am a retired engineer and really cannot answer this person. Can you please send me f/b on Such a situation
Regards Chris