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How to Connect Portable Generator to Home Supply System (3 Methods)

How to Connect an Emergency Portable Generator to Home Supply System (Three Methods)

Hi folks! I am here with a new tutorial as most of you guys sent me lots of mails as well as messages on our Facebook page about the portable generator wiring and connection diagrams for home supply system. So I have prepared this article for (in case of) emergency (i.e. short circuit, overloading, damage to electric transmission lines, substations or other parts of the distribution system and  bad weather etc.) power failure and all these electrical installation wiring diagrams given below are useful in emergency power failure (electric main power supply failure).

In simple, you can restore electric supply in emergency (power outage) by connecting an Emergency Portable Generator (Gas/Petrol/Diesel Generator) to home power supply system with no hesitation.

So now let’s begin.

We can connect a portable generator to our home supply system by three methods.

Below are the details of each method. (Please read all cautions / warnings and care must be taken before while installing a Generator to home electric power supply system.)

Important Note:

Electricity is Our Enemy, if you give it a chance to kill you, Remember, they will never miss it. Please read all caution and instruction while doing this tutorial in practical.

Method #1. Connection of Portable Generator to Home Supply with Separate MCB

First of all, switch off both the main switches (MCB) of main power supply and the Secondary MCB where generator to be connected. Connect a Power inlet to the second MCB. Now connect the 3 pin power plug of generator in that power inlet (As shown in below fig). You have done!

The Blue Line (In fig 2, 6 & 7) and arrows () shows the power flow in the circuit.

Click image to enlarge

How to Connect Portable Generator to Home Supply System (Three Methods)

Operation and working of Method #1.

1. In case when power supply available from power house.

In this case, the main electric power supplies electricity to home appliances and power flow will continue to those connected electrical appliances and devices this way  (The Red Line in the Blue rectangle box) by main power supply from the power house. Thus, portable generator remains standby.

The Blue Line and arrows () shows the power flow in the circuit.

Click image to enlarge

How to Connect Portable Generator to Home Supply System (Three Methods)

2. In case when power supply is not available from Power House

In this case, generator supplies electricity to home appliances and power flow will continue to those connected electrical appliances and devices this way  (The Red Line in the Blue rectangle box) by generator (as shown in below image).

The Red Line in the Blue rectangle box) and arrows () shows the power flow in the circuit.

Click image to enlarge

How to Connect Portable Generator to Home Supply System (Three Methods)

Note: Please! Be Careful.

In this case, the first MCB (Main Switch which is connected to main power supply) would be “ON” and the second MCB switch (which is connected to generator) should be “OFF”.

Cautions And Warnings:

Only 1 MCB should be “ON” at a time. If the second MCB is “ON” in the above shown figures and operation, i.e. Both MSBs switch “ON” at the same time. Then;

  1. When power supply restores from the power house , it may damage your generator or burn the whole system that can cause dangerous fire and explosion at once.
  2. When main electric supply is not available, generator will send electric supply back into main cables and lines which may overload the generator and may electrocute those electricians who work/repair in other homes and utility power lines

Method #2. Connection of Emergency Generator to Home Supply with Change-Over Switch

It is the safe and recommended method to connect a portable emergency generator to home power supply system.

Steps for Wiring & Installation of a Generator with Changeover Switch

To connect a portable generator with home supply system by changeover switch, follow the steps below:

  1. Install a Change-Over switch (about 65A) near main distribution board in the home.
  2. Connect the main power supply to the one end of Change-Over Switch.
  3. Connect a 7.029 (or 4mm)” or 7.044” (or 6mm) flexible wire to the other end with Change-Over switch.
  4. Now connect a 3-pin power socket with flexible wire and install it near the generator onto the wall. Now put the generator 3-pin power plug into that socket which you have installed in step (4).
  5. You have done and ready to supply emergency electric power to the home appliances in case of emergency power blackout.

Click image to enlarge

generator connection with change over system to home supply

Method # 3

Method #3. Wiring of Emergency Generator to Home Supply with Power Wall Socket Not Recommended.

  • Please read all the given notes, warnings, instructions and cautions before go to this method as it is not legal in some countries due to safety. Also, It is not recommended for beginners and only for practical engineers and experienced technicians in case of very emergency (i.e power supply failure in hospitals during serious operations) and there is no alternative to restore the power supply.

Connecting a generator to the 3-Pin Power wall socket in home you have already installed.

This is quite simple (as well as dangerous) method to connect a portable generator to home power supply system and you will be able to quickly restore electric power supply in case of power cut.

In case of power supply failure, just switch “OFF” the main switch and simply plug the Generator 3-pin plug into 3-Pin power inlet/ wall socket which is already installed in the home wiring system as shown in the below wiring diagram.

Click image to enlarge

generator connection with change over system to home supply

Operation and working of Method #3.

The working and operation of method #3 is same like method #1.

1. In case when power supply available from power house.

In this case, the main electric power supplies electricity to home appliances and power flow will continue to those connected electrical appliances and devices this way  (The Red Line in the Blue rectangle box) by main power supply from the power house. Thus, portable generator remains standby.

The Red Line in the Blue rectangle box) and arrows () shows the power flow in the circuit.

Click image to enlarge

How to Connect Portable Generator to Home Power Supply System

2. In case when power supply is not available from Power House

In this case, generator supplies electricity to home appliances and power flow will continue to those connected electrical appliances and devices this way  (The Red Line in the Blue rectangle box) by generator (as shown in below image).

The Red Line in the Blue rectangle box) and arrows () shows the power flow in the circuit.

Click image to enlarge

How to Connect a Portable Generator to Home Power Supply System

Note: Please! Be Careful.

In this case, the first MCB (Main Switch which is connected to main power supply) would be “ON” and the second MCB switch (which is connected to generator) should be “OFF”.

Cautions And Warnings:

Only 1 MCB should be “ON” at a time. If the second MCB is “ON” in the above shown figures and operation, i.e. Both MSBs switch “ON” at the same time. Then;

  1. When power supply restores from the power house , it may damage your generator or burn the whole system that can cause dangerous fire and explosion at once.
  2. When main electric supply is not available, generator will send electric supply back into main cables and lines which may overload the generator and may electrocute those electricians who work/repair in other homes and utility power lines. If you don’t have enough practical experience and not sure about the safety rules provided by the power supplier in you country, don’t practice this method to connect the portable generator to home supply system. It is also recommended to contact a licensed electrician or power supply company before to do so.

General Precaution

General Precautions while playing with Electricity.

  • Disconnect the power source before servicing, repairing or installing electrical equipments.
  • Never try to work on electricity without proper guidance and care.
  • Work with electricity only in presence of those persons who has good knowledge and practical work and experience who know how to deal with electricity.
  • Read all instruction and cautions and follow them strictly.
  • Contact the licensed electrician or the power supply company before practicing any change in electrical wiring connection.
  • 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.

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19 comments

  1. nice post sharing information related to electric supply

  2. The only one that's legal is the one with a change over switch. All others are illegal in the U.S. by OSHA

  3. Read the Description as will as cautions. Thanks

  4. The second method which uses change over switch is safer than methods 1 and 3. Thank you<br />for the information.

  5. Thanks for sharing useful information.

  6. A.O.A.
    Q1.Why inductors are not fabricated in the IC?
    Q2.P=VI=V^2/R=I^2R
    On what occasion,these formulas are used?

  7. This is so good , thank

  8. All of these diagrams are dangerous and illegal and shouldn’t be published here. No one should ever connect a generator to the house in these ways. The only way is to use a changeover switch so that the mains is isolated whilst the generator is in use and visa versa. In other words, the switchboard is connected to the common side of the changeover switch and the mains connected to the input 1 and the generator to the input 2.

    • i totally agree with Alan the way to go is either a auto change over or a mechanical change over either way it is no possible to have both supplies on at once

  9. alan u are 100% correct

  10. please sir how can one make interswich connection between solar, generator and grid supply for residential use

  11. Method 2 is almost right but there should be no wiring or connections to the top MCB’s.
    The mains power should come into the top of the changeover switch only and no wiring to anywhere else.
    Basicly you are interupting the mains power to the MCB’s by the changeover switch, when you switch it over, the power will flow from the generator to the MCB’s. Only one set of MCB’s is needed.
    In Australia, if you published or told a non qualified person how to wire up electrical equipment like this, you could be prosecuted if they were injured. Please remove all other methods, there is only one method, the manual or automatic changeover swith.

  12. I use 2 high power relays switching both L and N and have it so they are wired to automatically switch power source. This is wired with delay timers in the circuit to ensure clear separation of power supply when changing over and prevent accidentally making the Mains line live. You don’t want to kill the electrician working down line trying to fix the reason for the power cut in the first place. If you are going to have it manually switched you need to consider making it physically impossible to have both on.

    • Tim, you don’t need a delay you need to electrically interlock each relay coil with each other so only one can energise as well as mechanicaly interlocking them so it is impossible to energise both.
      They do fail and I have worked on cranes with forward reverse contactors for years (relays) they do stick and jam on sometimes. Mechanical interlocks prevent this happening. The better way is to get a changeover contactor which is energised with the mains on with 2 normaly open contact and 2 normaly closed contacts. When the power fails, it drops out and the auxillary input is connected.

  13. thank you brother you are giving very best information about electricity.

  14. Hi, I have a query / feedback. Hi, In relation to this link and the generator connection ? https://www.electricaltechnology.org/2013/11/how-to-connect-portable-generator-to-home-supply.html In the diagrams. The switch board has a socket and the generator has a male 3 pin plug which is alive when the generator is running ? Sorry kids your not allowed to run past, play or touch the end of the lead when the generator is running, especially now that the ground is wet from that storm we just had. Kids will be kids… This is not very good practice and dangerous / illegal. Safety… My suggestion is to fit a standard 15a (or special 30a) caravan male plug socket with circuit breaker and a 3 position switch. The whole switchboard is re-wired through this switch. The concept is to have the switchboard connect to the main circuit breaker coming in from meter OR the c/van plug socket. The c/van socket can never be alive at any one time and the generator lead can use a standard lead. If the mains come on it won’t short out or blow anything because you had forgot and flipped all circuit breakers to ON. Rgs Michael large

  15. Bhai Generator relay lagany ka tricka
    bata day plzzz

  16. Hi,

    Thank you very much for the information, By the way I have a question regarding the portable generators that I always power up my store unfortunately some times I found that when I switch on many things my generator sims to sound loudly and suddenly Shut down and offline. Please can you help me to rectify the fault.

    • In my Case, (When I face this problem) I check the generator oil (engine lubricant) if they need to change, Check the spark plug if they need to clean/replace, Check the load (especially overload), make sure the gas/oil as input is connected and sufficient to run the generator. Finally contact the generator mechanic for overhauling.

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