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How to Connect a Portable Generator to the Home Supply – 4 Methods

How to Wire a 1-P & 3-P Portable Generator to the Home Supply using Changeover & Without Changeover or Transfer Switch (ATS & MTS) for 230V/400V & 120V/240V

We all suffer from power failure in emergency breakdown (i.e. short circuit, overload, damage to electric transmission lines, substations or other parts of the distribution system as well as storms and other bad weather conditions etc.). In this case, emergency and portable generator can be used to restore the electric power to the home supply and other connected appliances.

In this step by step tutorial, we will be showing the portable generator wiring and connection diagram to the home supply and main distribution board according to NEC and IEC. We will be using Automatic Changeover Switch also known as  Automatic Transfer Switch (ATS), Manual Changeover Switch (MTS or Manual Transfer Switch) to connect the generator to a house for 230V and 400V (IEC) and 120V and 240V (NEC). In addition,  We will show how to wire a portable generator to home supply without a changeover switch or transfer switches.

By using the following basic electrical wiring installation diagrams for generator connection, you may restore an emergency electric supply in case of power outage by connecting a portable generator (Gas/Petrol/Diesel Generator) to the main distribution board.

How to Connect a Portable Generator to the Home NEC and IEC

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So now let’s begin.

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

Each method with wiring connection and working and operation has been explained in step by step tutorial. (Please read all cautions / warnings, user manual and care must be taken before installing a generator to the home electric power supply system. If you are not sure, contact a licensed electrician to do it properly).

Important Note:

Electricity is our friend as well as the worst 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 practical tutorial.

How to Connect a Portable Generator to the Home using Manual Changeover & Transfer Switch for 120V, 240V & 230V – NEC & NIEC

Connecting a portable emergency generator to the home power supply system  using manual or automatic changeover switches (Auto transfer Switch (ATS) is the safest and recommended method) for 230V (UK & EU – IEC) and 120V/240V (Canada, US – NEC).

Wiring an Emergency Generator Using Manual Changeover Switch 230V – IEC

Steps for Wiring & Installation of a Generator using Manual Changeover Switch

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

  1. Install a changeover switch (rated for 63-100A depending on the load) near the main distribution board in the home.
  2. Connect the main power supply (Line and Neutral) as incoming to the first upper slots of changeover Switch as shown in fig.
  3. Connect a 6 AWG (7/064″ or 16mm2)” cable wire to the lower two slots of the changeover switch.
  4. Now connect a 3-pin power socket (for small load) or 32A, 240V power socket – male (for large load) to the 6AVG wire and install onto the wall (near to the generator) and put the generator 3-pin power plug or or 32A, 240V power socket (female) into the power socket which you have installed before.
  5. You have done and are ready to supply emergency electric power to the home appliances in case of an emergency power blackout.

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Below is the generator wiring connection diagram to the main distribution board using the manual changeover switch where all the load circuits are connected to the generator supply in case of a power outage. If you don’t need to power up the specific load circuits, you may switch-OFF the related breakers and the rest breakers remain switch-ON. This way, only specific load points can be fed-up through emergency power via generator.

Click image to enlarge

Wiring an Emergency Generator Using Manual Changeover Switch 230V - IEC

If you want to connect specific load to the generator when utility power goes off i.e. some load on generator and the rest on main power supply as there may be a case where generator may not be able to handle the overall load. You may just switch-off those load points or related circuit breakers to it.

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Wiring a Portable Generator Using Manual Transfer Switch for 120 & 240V- NEC

The following wiring diagram shows a portable generator is wired to the 120V/240V main panel using manual transfer switch. Generally, you may connect a 30 amp transfer switch (like Protran or Reliance) for up to 7500 watts generator while other sizes (such as 50 amps) are also available for residential applications.

In this transfer switch, the single pole breaker is 15 amp while the double pole breaker is 30 amp having the max size of 12 gauge wire size.

To do this, just install a 30 amp (or 20 amp depending on the system requirement such as L14-30R, L14-20P) the twist lock plug for extension cord which plug into the generator.

The making of L14-30R, L14-20P plug and outlet indicates the following terminals:

  • X = Hot 1 (Black)
  • Y = Hot 2 (Red)
  • G = Ground
  • W = Neutral

Now, to wire the generator and main panel to the transfer switch, Remove the load wires from the related breakers and connect those wires to the corresponding wires from the transfer switch. Now connect the Black A and Red A from the transfer switch to the 2P breaker. Do the same for the SP breaker as shown in below wiring diagram (or according to the user manual). If not sure, contact a licensed electrician.

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Wiring a Portable Generator Using Manual Transfer Switch for 120 & 240V- NEC

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When Utility Power is not available, and Generator is ON

The breaker’s switch in the transfer switch pushes one direction and power is connected to the load appliances through Generator → Breaker in the transfer switch → to load points.

The direction of flow of power is followed through wires to the different circuits.

  • 120V = Black C1 (to transfer switch) and Black C (from transfer switch) to the load and Neutral wire.
  • 240V = Black A & Red A (to transfer switch) and Black B & Red B ( from transfer switch) to the load.

When Utility Power is available, and Generator is OFF

The breaker’s switch in the transfer switch pushes the other direction and power is connected to the load appliances through the main panel → Breaker in the transfer switch → to 120V and 240 load points.

The transfer switch won’t let go the power to energize the generator or power company wires e.g. it turns off the power supply that could come from the breaker in the panel. Keep in mind that only those breakers and load points will work which are connected according to the above (illustrated purpose) wiring diagram.

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Wiring a Generator Using Manual Transfer Switch for 240V – NEC

The following wiring diagram shows a generator connected to the 120V/240V main panel and 240V load circuits in separate subpanels using a manual transfer switch. These kind of transfer switches (like 2P, GE TC10323R / GE TC35322 / TC10424R or  3P, GE TC35362R emergency power transfer switches and safety switches or disconnectors) are used to connect the generator for power transfer operation or any other appliance for service disconnection as safety switch.

Click image to enlarge

Wiring a Generator Using Manual Transfer Switch for 240V - NEC

As shown, the generator is connected to the transfer switch through L14-30 (or L14-20) plug and power inlet. The two hot wires (Hot 1 and Hot 2) from the generator are connected to the lower main lugs in the transfer switch.

The upper two hot lugs of the transfer switch are wired to the 60A double pole breaker in the main panel. The center lugs of the transfer switch as load is connected to the 60A subpanel which is designed for 240V load circuits only. As it is a 240V load subpanel, so there is no need for a Neutral wire. Neutral is only required in case of 120V circuits or GFCI/AFCI protected circuits.

The lever operation of the transfer switch is follow:

  • UP = Main Supply = ON
  • Middle = OFF
  • Down = Generator Supply = ON

When the generator is OFF, the lever is on Down position, so the 240V load points are connected to the generator supply, When main supply is available, the lever position is changed to the Up position (manual operation) and the load circuits are fed-up through utility power.

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How to Connect a 1-Phase, 230V Generator to a Home using Automatic Changeover Switch – IEC?

In this way, We have to use a two pole (2P) automatic changeover switch to connect the generator to a home. The connection method is the same as mentioned above for method 1, but we have to use single phase 2 pole automatic changeover instead of manual transfer switch. No hesitation in this way i.e. when the power restores from the utility, the auto transfer switch automatically detects the power and redirects from the generator supply to the main supply and vice versa.

Note: You may use Three Poles (3P) Changeover instead of 2 Poles as well.

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How to Connect a 1-Phase, 230V Generator to a Home using Automatic Changeover Switch – IEC?

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How to Connect a Portable Generator to a Home without Changeover / Transfer Switch – NEC & IEC

Wiring a Portable Generator without Transfer Switch using Interlock Kit for 120V & 240V – NEC

If you want an alternative but cheaper way to connect the generator to the home panel without using a transfer switch, an interlock kit is the solution. Although you may switch off the main breaker and run the generator to power up 120V and 240V circuits via generator supply, it is still safe and recommended method to use the interlock kit to use in the main panel and generator breaker which keeps the main breaker and generator from operating at the same time.

The following wiring diagram shows how to wire an interlock kit for the generator and its operation during the power failure. The interlock kit is installed in the main panel which prevents both (the main and generator breakers at once). Only one breaker (either main or generator) can be ON or OFF at a time by sliding up or down the interlock.

As the generator is wired to the main panel through L14-30 (or L14-20) plug and power inlet and interlock kit in the main panel, let’s see the working operation.

When Utility Power is OFF = Generator is ON

When the main power supply is not available, simply switch OFF the main breaker and slide up the interlock kit (which will lock the main breaker to the ON position as shown in fig). This way, you will be able to start the generator and the interlock kit will allow you to switch ON the 2 poles breaker for the generator. Just start the generator and switch ON the 2P breaker. Now, you can switch ON the 120V or 240V breaker one by one to run the desired load circuits on power supply from the generator. The red arrow from the generator and power inlet to the 2P breaker and main panel shows the power supply to the load points.

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Click image to enlarge

How to Wire an Interlock Kit for Generator to the Main Panel

When Utility Power in ON = Generator is OFF

When the utility power is restored, just shut down the generator and switch OFF its related two-pole breaker. Now slide-down the interlock kit (it will prevent switching ON the breaker for generator) which will allow switching ON the main breaker. Just switch ON the main breaker and the supply will restore via main power to the connected load points. The red arrow from the main supply cables shows the power flow to the circuit.

Click image to enlarge

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Wiring an Emergency Generator without Changeover Switch for 230V – IEC

Caution: Please follow the local area codes as this method may be not according to the codes in case of IEC following countries. This may lead to serious injuries and hazardous fire as it may be done with special attention as there are chances someone forget to OFF the desired breaker before the operation. In short, it can be done with special care if allowed by the code.

The Installation process and operation is the same as mentioned above but without the Changeover Switch. For this method,  switch off both the main switch (MCB) in the distribution board to disconnect the power supply. Now install a separate 63 Amp breaker for the generator (same as main MCB).

Now, connect this new breaker via power inlet (3 Pin power socket or 32A, 230V male power socket) using 6 AWG (7/064″ or 16mm2)”. Finally, connect the 3 pin power plug or 32A, 230V female power plug of the generator in that power inlet or power socket (As shown in below fig). You have done it!

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Click image to enlarge

Wiring an Emergency Generator without Changeover Switch for 230V - IEC

Operation and Working

1. In case when utility power supply is not available:

To do this, first of all switch OFF the main breaker and start the generator. Now switch ON the breaker for the generator and switch ON those breakers one by one which connected to the desired load and needed to be operated via emergency power supply from the generator.

When the generator is not in use, FIRST switch OFF the breaker for the generator, switch OFF the generator and then finally, switch ON the main breaker in the distribution board or consumer unit.

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

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

Note: Please! Be Careful.

In this case, the first MCB (Main Switch which is connected to the main power supply) would be “OFF” and the second MCB switch wired for generator) should be “ON”. For extra safety purpose, switch off the 3-pin power socket or 32A generator socket and outlet by switching OFF the built-in ON/OFF button switch when generator is not in used.

Click image to enlarge

How to Wire a Generator to the distribution board without Changeover Switch using a Separate Breaker

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2. In case when power supply restores from power house:

In this case, the main electric lines supply electricity to the home appliances and power flow will continue to those connected electrical appliances in the system  through the (the Red Line i.e. wires covered in the Red rectangle box) by main power supply from the power house. Thus, the portable generator remains standby.

Keep in mind that the breaker for the generator will be at OFF position. Never ever switch ON this breaker when main supply is available. For extra safety, switch OFF the power socket by bulletin ON/OFF button or remove the 3-Pin plug for the generator.

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Wiring of Portable Generator to the Home Supply Using Separate MCB

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Note: Please! Be Careful.

In this case, the second MCB switch wired for the generator should be “OFF”. For extra safety purposes, switch off the 3-pin power socket or 230V, 32A power outlet and socket by switching OFF the built-in ON/OFF button when the generator is not in use. In addition, shut down the generator and remove the power plug. Now Switch ON the main MCB (Main Switch which is connected to the main power supply).

Cautions And Warnings:

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

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 MSB’s switch “ON” at the same time. Then;

  1. When utility power is restored from the power house , it may damage your generator or burn the whole system that can cause electric shock & hazard, 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 linesman & electricians who work/repair in other homes and utility power lines.
  3. If you don’t have enough practical experience and are not sure about the safety rules provided by the power supplier or generator user manual in your country, don’t practice this method to connect the portable generator to the home supply system. It is also recommended to contact a licensed electrician or power supply company before implementing this method.

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How to Connect a 3-Phase Generator to Home with 4 Pole Automatic Changeover Switch?

To connect a three phase portable generator to the home supply, We have to use a four pole (4P) automatic changeover or transfer switch. The connection method is the same as mentioned above for single phase generator and changeover switch, but we have to use three phase 4 poles manual changeover switch. It is the most reliable and recommended way to connect a generator to the home supply because when the power restores from the utility, the automatic transfer switch automatically detects the power and redirects from the generator supply to the main supply and vice versa.

Note: You may use Three Poles (3P) Auto changeover switch instead if Four Poles (4P) changeover or transfer switch.

Click image to enlarge

How to Connect a 3-Phase Generator to Home with 4 Pole Auto Changeover Switch?

How to Connect a 3-Phase Generator to Home with 4 Pole Manual Changeover Switch?

There is no big difference in wiring connections for automatic and manual changeover and transfer switches with portable generators. In the following wiring connection, we have used a four pole manual changeover switch to connect a three phase emergency generator to the distribution boards. The wiring connections for three phase transfer switch are same as wiring for single phase 2 pole changeover switch in method one, while there are another two slots for additional line and neutral as shown in fig below.

Note: You may use Three Poles (3P) Manual changeover switch instead if Four Poles (4P) changeover or transfer switch.

Click image to enlarge

How to Connect a 3-Phase Generator to Home with 4 Pole Manual Changeover Switch

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Wiring Color Code:

We have used the IEC and IEC wiring color codes for 230V/400V and 120V/240V circuits. You may use the local area codes or i IEC – International Electrotechnical Commission (UK, EU etc.) or NEC (National Electrical Code [US & Canada] where;

NEC:

Single Phase 120V AC:

  • Black = Hot or Line
  •  White  = Neutral
  • Green /  Yellow  or bare conductor = Ground Wire

Single Phase 240V AC:

  • Black = Hot 1 or Line 1
  • Red = Hot 2 or Line 2
  •  White  = Neutral
  • Green /  Yellow  or bare conductor = Ground Wire

Three Phase 208 AC:

  • Black = Hot 1 or Line 1
  • Red = Hot 2 or Line 2
  • Blue = Hot 3 or Line 3
  •  White  or Gray = Neutral
  • Green /  Yellow  or bare conductor = Ground Wire

Three Phase 240 AC (High Leg Delta):

  • Blue = Hot 1 or Line 1
  • Orange = Hot 2 or Line 2 (HIGH LEG DELTA)
  • Black = Hot 3 or Line 3
  •  White  or Gray = Neutral
  • Green /  Yellow  or bare conductor = Ground Wire

Three Phase 480V & 600V AC

  • Brown = Hot 1 or Line 1
  • Orange = Hot 2 or Line 2
  •  Yellow  = Hot 3 or Line 3
  •  White  or Gray = Neutral
  • Green /  Yellow  or bare conductor = Ground Wire

IEC:

Single Phase 230V AC:

  • Brown = Phase or Line
  • Blue = Neutral
  • Green /  Yellow  = Earth Conductor = Earth Conductor

Three Phase 400V – 415V AC:

  • Brown = Phase 1 or Line 1
  • Black = Phase 2 or Line 2
  • Grey = Phase 3 or Line 3
  • Blue = Neutral
  • Green /  Yellow  = Earth Conductor

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General Precaution

General Precautions while playing with Electricity.

  • Disconnect the main power source (by switching OFF the main switch in the distribution board / consumer unit and  load center / main panel) before servicing, repairing or installing electrical equipment.
  • Never try to work on electricity without proper guidance and care.
  • Troubleshooting, repairing, installation and modification work related to electricity can be done only in presence of those persons who have good knowledge and practical work and experience who know how to deal with electricity.
  • Read all the instructions, user manuals, cautions, local area codes and follow them strictly.
  • Doing your own electrical work is dangerous as well as illegal in some areas. Contact the licensed electrician or the power supply company before practicing any change in electrical wiring connection.
  • Use the suitable voltage and ampere rating of the switch with appropriate wire size and proper size MCB according to the load rating.
  • Switch off the main MCB circuit breaker to make sure the power supply is OFF before wiring an existing or new outlet or switch with an electrical/junction box.
  • Contact the authorized and licensed electrician for switch installation if you are not sure about the wiring diagrams.
  • 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 the wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

Related Electrical Wiring Installation Tutorials.

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22 Comments

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

  2. 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?

  3. 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.

    1. 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

    1. The switching is legally and safely installed by a licensed electrician who has the proper municipal work permits .
      Not some con job installed by Mr Handy Man trying to be cheap .

  4. 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.

  5. 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.

    1. 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.

  6. 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.

    1. 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.

  7. I find it amazing that no one has mentioned the PLUG from the generator!

    He states this “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 practical tutorial.” – YET

    If the generator is running and the plug in your hand and not connected, you are going to be injured or worse, killed.

    You CANNOT assume that people will “plug it in” prior to the generator being started. Humans will either forget or not read it fully.

    A far “safer” way, if there is one looking at the diagrams and comments from others (which I in general agree with where changeovers are mentioned) is to have the plug and socket termination wired as a fixed item to a fused Isolator at the appropriate amperage for the size of the load.

    The lead, which should also be sized for the load demand, can then have a plug on that will and be connected to the socket of the generator, therefore, no live ends.

    You’re going to kill somebody!

  8. Hi John,
    I normally run an extension lead, of suitable current rating and fitted with male and female plugs, from generator to the switchboard where it plugs into an inlet socket similar to the type used on caravans. There is no way to get a shock from the lead. The inlet socket has 3 male pins and if wired to the proper changeover switch/relay is impossible to become live at the input pins. I would not put a changeover switch between a meter and the main switch but rather go from meter to main switch then to the changeover with maybe some protection inline with a MCB.

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