How To Connect A Portable Generator To The Home? NEC And IEC

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.

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• How to Size a Generator? Portable, Backup & Standby for Home & Commercial Applications
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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.

Table of Contents

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• How to Hook Up a Portable Generator to the Home Supply using Manual Changeover & Transfer Switch for 120V, 240V & 230V – NEC & NIEC
  • Wiring an Emergency Generator Using Manual Changeover Switch 230V – IEC
  • Wiring a Portable Generator Using Manual Transfer Switch for 120 & 240V- NEC
  • Wiring a Generator Using Manual Transfer Switch for 240V – NEC
• How to Connect a 1-Phase, 230V Generator to a Home using Automatic Changeover Switch – IEC?
• 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
  • Wiring an Emergency Generator without Changeover Switch for 230V – IEC
• How to Connect a 3-Phase Generator to Home with 4 Pole Automatic Changeover Switch?
• How to Connect a 3-Phase Generator to Home with 4 Pole Manual Changeover Switch?
• Wiring Color Code:
• General Precaution

How to Hook Up a Portable Generator to the Home Supply 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.

Related Posts:

• Single Phase Electrical Wiring Installation in Home – NEC & IEC
• Three Phase Electrical Wiring Installation in Home – NEC &  IEC

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

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.

Click image to enlarge

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• How to Wire 120V & 240V Main Panel? Breaker Box Installation
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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

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.

Click image to enlarge

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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’re looking for a more affordable alternative to a transfer switch for connecting a generator to your home panel, an interlock kit is a practical solution. While you can manually switch off the main breaker and run the generator to power 120V and 240V circuits, it is still safer and highly recommended to use an interlock kit. The interlock kit ensures that the main breaker and the generator breaker cannot be turned on at the same time, preventing backfeeding and enhancing overall safety.

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 unavailable, first switch OFF the main breaker and slide the interlock kit up (this locks the main breaker in the OFF position, as shown in the figure). This allows you to start the generator and then switch ON the two-pole (2P) breaker connected to the generator. Once the generator is running and the 2P breaker is ON, you can begin turning ON the 120V and 240V breakers one by one to supply power to the desired load circuits. The red arrow from the generator and power inlet to the 2P breaker and main panel indicates the direction of power flow to the load points.

Related Post:

• How to Determine the Right Size Capacity of a Subpanel?
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Click image to enlarge

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!

Related Posts:

• Wiring of the Distribution Board with RCD
• Wiring of the Distribution Board without RCD

Click image to enlarge

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.