How to Wire a Transfer Switch to Your Home

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For those of you who have used a generator, chances are you have heard of a transfer switch. This is a critically important device when you are running a generator that powers certain home appliances.

A transfer switch allows you to connect a generator to your house safely without the use of any extension cords. You’ll typically see these installed around the main service panel of your home for you to easily control the power supply sufficiently.

Installing your own transfer switch will allow you to switch incoming power from the main electrical panel to a generator in case you suffer a power surge and/or blackout.

Transfer switches have their pros and cons but having one as backup is always a good idea. You can choose from two configurations which are manual and automatic and each one depends on how much power you intend to use.

You can have your switch professionally wired but this can be costly. Tackling the job yourself is surprisingly simple and we will talk you through the process below.

How to Wire a Transfer Switch to Your Home

Why do you need a transfer switch for your portable generator?

This entirely depends on the kind of electrical appliances that will be running on your generator. Power switches are not needed if you have a short power outage and the only devices being run off the generator are laptops or smartphones. 

If you intend on running larger appliances such as a furnace or a hard-wired refrigerator, you will definitely need to use a power switch to avoid complications.

The switch is not mandatory if you use your generator for recreational use either. These activities can include camping or hiking and typically requires a lot less power than your home will.

Another reason you should have a transfer wire is the law set out by the National Electric Code. According to this law, it is mandatory to use a transfer switch when using a generator in your home.

It is seen as a code violation and if not followed, it can leave your house insurance void in case of a fire or other emergencies.

These wires also make your generator more efficient. One con of using a generator is how you can be unsure what appliance will need to run going forward. As the AC is hard-wired (needing an extension cord) running this and the light can become a hassle in a blackout.

A transfer switch can take this problem away. Your generator may not be able to run a range of appliances at once and maybe you’ll need to switch these regularly. Without a transfer switch, you have to lay cords around the house which isn’t feasible. 

This can be made easier as a switch can easily send the power from each room to another without the need for any extension cords as the switch is directly connected to the mains supply circuit of your house.

Transfer wires are also the safest way of connecting your generator to your house. Extension cords can cause back feed (power of your generator is sent back into the main grid) and can possibly cause serious harm to electricians working on nearby transmission lines.

The power from the main grid and the generator can also short circuit by flowing together through varying electrical appliances resulting in possible fires and electrocutions. 

What does the transfer switch do?

A transfer switch solves many of the problems we have already listed. It does this by disconnecting the power supply from the main grid. It then connects the power from the generator to your home.

Interestingly, when the main grid power comes back on, the switch disconnects the generator. This inhibits any chances of short-circuiting.

Different types of transfer switches

There are a few things you should know before wiring your transfer switch. It’s handy to read up about open-transition, closed-transition, and delayed transition switches first. 

An open transition switch ensures the connection is running smoothly with the generator before the utility is turned off. These are then swapped quickly once the connection is deemed safe. 

Close-transition switches make connections to the new power source before the connection to the older source is broken.

This means there are no gaps between disconnections and connections so loads going downstream receive a flow of power throughout the whole transfer process.

Delayed transition switching is where the original source’s contact is opened before another contact’s source is closed. These are typically used when an automatic transfer switch supplies inductive loads.

The two main types of transfer switches today are manual and automatic switches. Let’s see the difference between the two below:

Manual transfer switch

Not surprisingly, a manual trader switch needs manual switch flipping when any lights go out. It can be quite difficult to find in the event of a blackout but is cheaper to buy than its automatic counterpart.

These also let you manage your electrical load manually in your house such as only routing power to one particular room that is using appliances.

Automatic transfer switch

An automatic transfer switch alternates the power from the grid to the generator automatically when detecting a power outage.

These can be programmed to run the most used or important appliances in your home during a power outage. These versions are more expensive than manual switches due to their added features but many are happy to pay more for the added convenience.

Things you need to know before wiring a transfer switch

One important aspect when looking to wire a transfer switch is the wattage rating. You should check the limit of a transfer switch’s wattage to make sure it can handle the right amount for what you’ll require.

A higher wattage generator that is run on a switch that can’t handle its wattage will result in a short-circuit. This is why it is important to consider how many watts of generator you have. This is easy to find within the generator’s instruction manual.

It is advised you also check the running watts of the generator too as well as its starting watts to give you a closer estimation of what you’ll need from a transfer switch.

It is advised you add the wattage values of every load you intend to power and then multiply this sum by 1.25.

This should give you the minimum wattage of power the generator has to produce. Smaller, portable standby generators usually output about 5,000 to 7,500 watts while larger, stationary generators output 10,000 to 20,000 watts.

Here is a list of approximate running wattage guidelines to help you further:

  • A refrigerator is around 750 watts
  • A forced-air furnace is about 1,000 to 1,500 watts
  • A sump pump is about 800 to 1,000 watts
  • A television is about 300 watts
  • Incandescent lights are about 60 watts (per bulb) while LED and CFA lights use far less wattage
  • A garage door opener is around 550 to 1,100 watts

Warranty is another important aspect to consider. Even the best transfer switches with the best reviews can become faulty. If it doesn’t have a decent warranty, it should be avoided.

You never know when an electrical device will fail unfortunately so having a backup will keep you safe in the knowledge that you are covered. It is also recommended you purchase your transfer switch from a reputable, well-known brand as these have a proven track record.

Parts you need to wire a transfer switch

Before you install your transfer switch properly, there are some important parts required. There are options to buy kits with every part needed which can save time. If these are not what you are looking for, you can also choose the pieces yourself and put them together individually.

Here is a list of the things you will need to wire your transfer switch:

  1. A reasonably sized portable generator
  2. A power inlet box. This attaches to the outside of your home on the opposite side of the wall to the indoor transfer switch. This lets you plug in a power cord to your generator without any fuss.
  3. A generator power cord. This is used to connect your generator to the transfer switch. Most standard cords are 20 feet long to ensure a convenient connection.
  4. A power drill to make a straight hole through your home’s wall from the outside to feed wires from your transfer switch to an electric receptacle.

The installation process

This is where the fun begins. The thought of wiring a transfer switch to your home can keep you up at night. Without any guidance, it would be a very tricky task to achieve.

Thankfully, all you need is patience, attention to detail, and some knowledge of electricals. You’ll be surprised how quickly this can be done and in a few hours, you should have your transfer switch up and running.

There are a few guidelines to adhere to before this process. You should review your local laws as well as state laws that are associated with your home’s main electrical supply. Check the code requirements before tackling this task to prevent any law violations.

If you have everything prepared and have taken all the necessary precautions, let’s crack on with the wiring process.

  1. The first thing you need to do is figure out where you want your transfer switch to be mounted. You need to have it near your panel box for the easiest installation process and in a safe place where it won’t get damaged easily.

  2. Once the location has been found, you should make sure there are no obstructions or distractions around you that could disrupt your work. Now mount the switch to the wall.

  3. Now you need to switch off the main power to your home via the main electrical panel. Double-check the power is off by testing various appliances. Be very cautious here as the terminals where any power enters the main breakers will still be fully energized.

  4. Find out which circuits in your household are the most important to use in an emergency. This is usually the refrigerator and one small appliance circuit. 

  5. Next, you need to find the wires that are from the transfer switch. Connect these to the circuits in your panel box that you want to control.

  6. Now you select the knockout at the bottom of the main service panel box and remove it. Ensure the knockout is the right size to match the connector on the conduit which comes from the transfer switch.

  7. Feed wires from the transfer switch through the knockout hole. Make sure don’t damage any insulation here. Each wire will be labeled with which circuit in the switch it feeds.

  8. Fix the flexible conduit securely from the switch box to the main service panel. Do this with a locknut and a bushing where needed.

  9. Here you will need a drill. Drill a 1 and a half-inch hole through your house’s wall from its outside. This hole will be the entrance for wires to feed through from the transfer switch to the electrical socket.

  10. Mount the outdoor electrical box above the exterior wall’s hole. (Not all switches come with an outdoor electrical box)

  11. You should now connect the electrical cable that comes from the transfer switch to the electrical box and fit it through the drilled hole.

  12. Connect the electrical plug to the electrical cable in the outdoor box. Then screw this into the box.

  13. The next step should be to test your portable generator to ensure it is working well.

  14. Make sure your main power switch is still off. Now use the generator’s power cord and connect it to the outdoor electrical receptacle.

  15. Before you turn your generator back on, attach the main power cord from the generator to the transfer switch box. You should never attach or detach any generator cord when the generator is still running.

  16. Now is the moment of truth. Startup your generator and flip that transfer switch (with a deep breath). Leave it run for a minute or two. All of your appliances that are connected should now have full power.

  17. The next thing to do is to flip each circuit switch on the switch box to the generator periodically.  Try and move back and forth between circuits on the left and right sides. You shouldn’t turn all the circuits on at the same time as this can cause damage. Make a note of the onboard wattage meters as you turn on each circuit and try to keep the wattage levels balanced.

  18. Once you have made sure everything is in working order, turn the transfer switch from the generator back to the line and shut off your generator. It is now safe to turn the main power on again.

  19. It is recommended you seal the drilled hole with some appropriate sealant in order to stop dampness getting in the house as well as insects and dirt.

A typical backup system

Backup generators are great if your main generator goes down. These supply power to a manual transfer switch. This switch disconnects the whole house from the main service wires.

It then routed power from the generator through your selected circuits within your home. Installing a backup generator is an excellent way of preparing your household for emergencies.

The simplest backup systems are gas-powered generators that are portable including one or two extension cords.

Having a backup generator allows you to keep your refrigerator running as well as some lights when there is a complete power outage. This is the least expensive way to supply backup power to your home.

If you are looking to get a suitable generator for your home, you should be able to purchase one from most home centers and depots. It can then be up and running the very same day.

If you decide to do this, make sure all loads that are being run on your generator are disconnected from the main power source.

In conclusion

So there you have it. A complete guide in how to wire a transfer switch. Of course, installing any new item, especially electrical equipment, is a daunting task.

As you can see from our process though, it doesn’t have to be difficult. As long as you take all the necessary precautions, follow your state’s laws and rules, and pay attention to detail, you should be up and running with a wired transfer switch.

The most vital factors to ensure are that your generator is capable of powering all the appliances you intend to use and has the necessary wattage.

Also making sure you have all the correct parts to do the job properly and safely is crucial along with checking its overall function at the end

Remember that using a transfer switch that wasn’t installed by a professional could also void the warranty of the switch so this is worth looking into. Please seek professional help if you feel this job is too much for you as working on electrical panels in any place can be very dangerous.