Many of us will take the electrics in our house completely for granted. Basically all the appliances and plug sockets in our homes will connect back to a main panel where you can access the circuit breakers for them.
When you want to add new circuits to your home for powering items such as, electric car charging ports, high-powered compressors or other items, it may become necessary to expand your main circuit panel.
But what do you do when the main service panel in your home doesn’t have room for another circuit breaker?
Well, in these instances you may need to install a secondary subpanel that gives you the room for adding new circuits to your home.
Subpanels, or main lugs, are connected back to the main service panel and are a great way for installing new electrical appliances that may need more power than the sockets in your home can provide.
Installing a new electrical panel can be a complicated process.
In order to get started, you’ll need to determine where to put the panel, whether to run circuits through a conduit or bury them underground, as well as what kind of voltage you want the panel to supply.
Installing a new electrical panel is a big job.
The good news is that you don’t have to do it alone. In this article we will be telling you everything you need to know about installing a new subpanel, or main lug in your home.
What Is A Subpanel?
To understand what a subpanel/ main lug is, it will help to understand the main panel and the role it plays in your home.
All the electrics in your house from plug sockets to lighting fixtures are connected to circuits which are located inside your walls.
These circuits all feed back to the main panel, which is a metal box where you can access vital safety features.
If a circuit becomes overloaded, or otherwise damaged, it will often trigger one of the trip switches in your main panel.
When these switches are activated, it will shut off the flow of electricity to that specific circuit to prevent further damage.
As such, the main panel is where you have the most direct access to the electronics in your home.
It allows you to shut off, or reactivate specific branch circuits as well as access their individual fuses, so you can replace them when necessary.
The main panel is connected to the distributor transformer, which takes energy off the grid and provides it to your home, by a feeder cable.
The cables are made up of four different wires, including two live ones colored black and red, a neutral one that is white and a bare brown grounding wire.
The hot wires are connected to the positive and negative terminals in your main panel, while the neutral is connected to the neutral terminal.
Finally, the ground wire is connected to a special metal bar at the bottom that takes excess power to safely dispose of it before it can damage the circuit.
A subpanel is an electrical box that connects to a main panel by means of a three wire cable.
This allows you to tap into the main panel’s electricity and attach new circuits for powering different appliances to your home’s main source of electricity.
Subpanels can be useful for extending existing circuits in your home or for supplying power to an external location such as a garage, guest house, or utility shed.
You can buy subpanels that are designed to be fitted inside or outside your home, offering you a lot of versatility when it comes to where you install them and how you use them.
Common Uses For Electrical Subpanels
As we said above, subpanels can be used to extend branch circuits in certain areas of your home.
As such, they can be used to add new sockets, light fixtures or other appliances that can’t fit on the circuits that run to the main service panel.
Subpanels are also very useful for power areas that you don’t want connected to your home’s main trip switch.
If you have a workshop in your garage, you could end up with power tools tripping your circuit breakers.
If they were connected to the main panel, this could shut off the electricity for your whole house, so connecting them to a localized subpanel can be a great way to handle this issue.
They are also a very convenient way to add new circuits when you don’t have room for another circuit breaker in your main service panel.
This makes them useful for electric car owners who want to install a charging port in their garden or garage.
Normally, connecting this to your main circuit breaker would over-power it, but you can equip your subpanel to up the voltage via a transformer to provide enough juice for powering your car.
Tools You Will Need For Installing A New Subpanel
If you want to install a new subpanel in your home, you will need some specialist equipment to do so.
Remember, when handling life electronics, it is vital to take the proper safety precautions to ensure you don’t injure yourself.
The first thing you will need is a good set of electricians tools, including screwdrivers, pliers and clippers. It is worth buying a set that is made for electrical work, since these will most likely be insulted.
Insulated tools will help to protect you from electrical shocks while you work and will be the right size for stripping and working with wires.
Depending on where you want your subpanel and the location of your main service panel, you may also need a flashlight for navigating dark enclosures.
A hammer can also be a helpful tool, as well as a drill for mounting the subpanel where you want it.
Finally, it is vital to have a voltage meter, so you can test the input and output voltage going into your panel.
This tool will help you to isolate any problems as they occur and will give you a clear idea of whether your new subpanel is working or not.
It will help to have a multi-meter that can measure voltage, amperage and resistance. This way you will be able to test all aspects of your new system, so you know exactly what is working, and what isn’t.
Choosing The Right Materials For Installing Your Subpanel
When adding a new subpanel to your home by yourself, you will need to pick the right materials for the job.
You can’t just use any kind of wire for this job, and if you try to do it with the wrong materials you will risk your new system not working, or being unsafe.
Remember you will be dealing with high voltages and high amperage as well depending on what you want to use your panel for.
If anything does go wrong, it could lead to an electrical fire that could cause extensive damage to your home. As such, here are some tips for finding the right materials for installing your new subpanel.
The Subpanel
The most important component is the actual subpanel itself. This will often come in the form of a metal box, with fixtures inside it for attaching circuit breakers, and buses.
The type of subpanel you buy will depend greatly on where you want to place it and how many amps you want it to provide.
There are subpanels built for being installed outside and inside your home. The main difference between the two is that one will be watertight and highly weather resistant, while the other will not.
Often you will need different circuit breakers and components for installing inside an outdoor subpanel to protect them from moisture or other environmental risks.
Subpanels come in a range of different sizes, and which one you select will depend on how many amps you want it to supply.
Larger 150A subpanels will hold more circuit breakers, allowing you to set up more circuits and power more appliances.
You don’t want to buy a panel that has too much room, as it will only take up space on your wall and won’t be able to supply more power than it has been allocated from the main breaker.
Circuit Breakers
These components serve the vital function of controlling the flow of power from your subpanel to the appliances it is connected to.
In the past, when a short circuit or voltage spike occurred, it would blow a fuse, which would then have to be replaced.
Circuit breakers serve a similar function, but don’t need to be replaced nearly as often.
They act as a type of electrical fuse that will automatically shut off power to their respective circuit when it has been overloaded.
As such, breakers are one of the most important pieces you will need when installing a subpanel.
They will allow you to turn off the flow of power to a specific appliance, or turn it back on again after a short circuit or voltage spike.
There are different types of circuit breaker that you can buy, each of which serves different functions.
Double Pole And Single Pole Breakers
For a start, there are double pole and single pole breakers, which are differentiated by their capacity.
Single pole breakers are used for low-power 120V appliances and typically handle between 10 and 20 amps. These are useful for standard electrical outlets, and lighting circuits.
Double pole circuit breakers are for much larger appliances such as washing machines (see also ‘How to Fix a Washer Machine Drain Backing Up?‘) and tumble dryers.
They can handle between 20 and 60 amps as well as voltages of up to 240V, which makes them the go-to choice for any appliance that is going to need a lot of juice.
You will often need at least one double pole breaker for adding to your main service panel to supply your subpanel with the power it needs.
GFCI Breakers
There are also GFCI circuit breakers, which are specifically designed for powering circuits that are in proximity to water.
These units have special waterproof casings to prevent moisture getting to the wires in your subpanel.
You will often see GFCI units used for circuits in kitchens, laundry rooms and near swimming pools.
Tandem Breakers
You can also get tandem circuit breakers that are as large as a single pole but capable of powering two circuits.
These are useful if you have a limited number of slots in your subpanel and want to connect two low amperage circuits to the same breaker.
Choosing The Right Breakers
When choosing breakers for your subpanel, the first thing you will need to do is think about how much power you want it to supply.
If you want a small 60amp subpanel for powering a guest house, then you will need at least a 60amp circuit breaker for adding to your main service panel.
This breaker is where you will connect your cable running from the main service box to your subpanel.
The first rule of choosing circuit breakers is that it is better to have too many amps than too little.
If you connect a device like a washing machine to a 15 amp circuit breaker, then you will quickly end up with a broken unit at best and an electrical fire at worst.
Therefore, once you have chosen the breaker for powering the subpanel itself, you will want to choose the breakers for putting inside it.
This means taking the total amperage of your box and allocating it amongst the appliances you want to power.
Use small breakers for simple circuits that don’t require much power, like lighting circuits, and larger ones for appliances that need a bit more juice.
Just make sure the total amperage of the breakers in your subpanel isn’t greater than the total amperage of the breaker supplying it.
It is also important to note that you can’t use every single amp that a breaker has to offer. Most breakers are only rated to handle 80% of their labeled output.
As such, a 200A circuit breaker can supply up to 160A of power, allowing it to handle up to three 50A breakers in a subpanel.
Cables And Wires
The final material you need for setting up your own subpanel is lots of wiring and cables for connecting it to your main service panel.
There are lots of different thicknesses and types of wires that you can buy from most hardware stores, and which one you pick will depend on what you are trying to do.
It is essential when installing a subpanel to only use 600V wire that is made from copper.
Aluminum wire will expand and contract more as it gets hot, which could cause it to come loose from the connector in the box, posing a fire risk.
All wires will get hot when carrying an electrical current, and this is why it is vital to choose the right wires for the right job.
If they generate too much heat, your wires may burn through their plastic casing and touch one another.
This will lead to a large voltage spike that will shut down your whole circuit and require you to replace the wires, which is fine if they are above ground, but much trickier if they are buried.
As you can see you want to choose the right thickness, or gauge of wire for your particular job. As the gauge of a wire goes up, its size goes down, so a 12 gauge wire will be significantly thinner than an 8 gauge one.
Below you will find a list of the different gauges of wire and what breakers they will be best suited for.
- 14 gauge – should be to 15 amp circuit breakers. This is the smallest gauge of wire and therefore is only suited for low power appliances.
- 12 gauge – connects to a 20 amp circuit breaker. Again, this type of wire is best suited for low power appliances that don’t require more than 120V
- 10 gauge – Can be connected to 30 amp circuit breakers.
- 8 gauge – This thickness of wire is designed for 40, or 50 amp circuit breakers and is suitable for powering larger devices such as washing machines or other white goods.
- 6- gauge – this wire is strictly only for circuit breakers that are connected to high-powered equipment. It can only be used on 50 amp circuit breakers.
It is very important to choose the right type of wire for your chosen circuit breakers.
If you are laying down wires over a long distance, or burying it underground, then you will need to use a lower gauge than you normally would.
Burying cables will insulate them, so you want them to be able to handle the extra heat without becoming damaged.
As such, if you are putting any cables underground, then you will want to make sure they are 1 or 2 gauges up from what you would normally use.
The same applies if you are laying cables for over 100 inches. At around 150 inches, it will become necessary to choose a lower gauge of wire to prevent too much power being lost to resistance.
Wire Connectors
Wire connectors are small housing units with a screw and a hole for feeding in the end of a wire.
They are the main means by which you can connect your main service panel to your subpanel and the appliances you want it to power.
Push-in wire connectors are easier to use, but far less secure than traditional screw on ones.
They only require you to push the wire into the hole, and you’re done, which makes them very easy for amateur electricians to use.
That said, if you are an amateur electrician, you probably shouldn’t be installing a subpanel by yourself.
Screw on terminals can be tightened with the screw on the top, which allows you to make sure they are firmly gripping the end of the wire.
You are far less likely to get a poor connection with one of these terminals, which is why they are the better choice for wiring up your subpanel.
The best option is a combination of both of the above terminals, which are push-on connectors that have tightening screws on the top.
With these, you will have an easy time installing your wires and terminals, as well as having the option to tighten them and prevent a loose connection.
Conduits
You will also need some sort of housing for protecting your wires, especially if you are installing a subpanel outside.
These come in many forms, and some will be better than others for certain jobs.
If you are burying wires underground then it will be essential to have an armored cable made from metal.
These offer great heat dissipation to prevent your wires from overheating and offer protection against somebody chopping through the cable if they try to dig it back up.
Other conduits are often made of plastic housings, and they are vital for keeping wires safe and out of reach.
How To Install A Subpanel
Now that we have gone through all the different components required for installing a subpanel, this section will tell you how to go about doing it.
We will include instructions for installing three different types of subpanel depending on how many amps you want it to deliver and the desired output voltage that you want from it.
Afterwards, we will include some helpful tips and tricks for dealing with certain types of installation that are a little more complex.
Warning
It is vital to point out that handling live electronics is incredibly dangerous and should only be done by those who know exactly what they are doing.
One wrong move could lead to nasty electric shock, and that is the best case scenario.
Dealing with any high voltage wiring could easily result in death, so it bears repeating, only install a subpanel by yourself if you have the right equipment and are confident in your abilities.
In some states, it may be actually illegal to undertake this kind of work. You should always check the laws in your local area to make sure that you are allowed to install your own subpanel before you try to do so.
If at any point in the process you are unsure about what you are doing, STOP!
Do not be afraid to call a professional electrician to help you or offer advice. It is worth it to prevent the possibility of an electrical fire or worse.
Installing Your Subpanel
Before you reach for any cables, you will need to install your subpanel in your chosen location. It is important to install your panel in a place that is secure, where it won’t easily come off.
When installing a panel inside your home or another enclosed space, you will want to install it between 2×4 studs.
It will help to install your studs where they can attach to the wooden supports that make up the infrastructure of your house.
Doing this will make sure that the subpanel can’t easily come off the wall, which is something you need to avoid at all costs.
Never attach a subpanel to thin sections of drywall or plaster, as these will not provide enough support.
Main lugs installed in this way could easily be pulled off the wall, exposing live electronics and potentially causing a fire.
When installing a subpanel outside, it is very important to attach it securely to a wall and make sure that it is at least 12 inches above anticipated snowfall.
Doing this will prevent your panel being inaccessible after heavy snowfall. When installing a panel outside, it is vital that it is grounded.
If you want to locate your subpanel far away from the main service panel, then it will help to install a grounding rod near the other structure that you want to supply power to.
Handling Wires
Before you start connecting anything to live electronics, it is a good idea to know how to handle wires.
It is vital that you buy solid wires for installing a new subpanel, as wires with frayed ends won’t provide as solid a connection. As we said before, only ever use copper wires and never the aluminum variety.
In some situations, you may need to join two wires together and insert them into the same connector.
When doing this, twist the ends of the wire together before you insert them into the connector. Of course, before you can do this, you will need to strip the wire of its plastic casing.
When stripping wires, it is important to use insulated stripping pliers and try not to push down too hard in case you sever the whole wire.
You only need to strip roughly 1-2 inches of plastic sheathing off the wire, so don’t overdo it and risk leaving exposed copper wiring that people could accidentally touch.
When placing wires in your subpanel it is important to follow some basic rules to prevent them from overheating. These rules have been listed below:
- Try to keep wires along the edge of the box so that they are overlapping as little as possible.
- Wires should never be placed over the top of busbars or circuit breakers
- Never place wires over breakers or busbars either.
- It is okay for wires to overlap a little, but they should never do so at the point where they connect to a circuit breaker.
Red and black wires are traditionally used as the live wires, with white ones being reserved for neutral.
You can connect a white wire to a hot busbar and use it for carrying 240V power, but if you do so, you should wrap a small piece of black electrical tape around it.
This will act as a warning for future electricians that the wire is live.
Green or bare copper wires are used for grounding and can only be used for this purpose. You should never connect one of these wires to a hot bus bar, as it is not properly insulated for carrying this kind of current.
You should always clean wires before connecting them to any bus bars. This will require sanding them down to remove corrosion. This will help to prevent loose connections or your connector corroding over time.
Installing A 60A Subpanel With For Both 120V And 240V
When installing a 60A subpanel, the first thing you will want to do is find a 240V circuit breaker on your main service panel that you can replace.
It is often better to find one near the top of the box, but it doesn’t need to be, so long as you can find the space.
Once you have found a space, you can insert a 60A double pole breaker into it. Some breakers will hook over a thin metal rod, while others will just click into place.
You should connect your cable to the breaker first before adding it to your main service panel.
Warning
At the top of your main service panel, you will see screws from the main circuit breaker that supplies power to the hot bus bars.
These screws are always hot, and touching them can risk giving you a very nasty electric shock, or worse.
The only way to safely touch these screws is to pull the meter, but most of the time you won’t need to do this. Just be careful when going near these screws with any metal tools.
Once it is inserted, you will need to feed your cable out of the main service panel to your subpanel.
If you are running the wire over any considerable distance, then you will need to enclose it in a conduit of your choice.
Once you have reached your subpanel you need to feed all of your wires into the main lug, or subpanel.
Next, you will need to identify the two hot bus bars in your subpanel. These are metal bars that carry the current to your circuit breaker and supply them with electricity.
They have wire connectors located at the end for linking up your wires. There are four connectors that will often have screws on them, so you can tighten them onto the wire.
At the top of the area where you can insert breakers, you will find the two hot busbars.
Often to the side of this arrangement you will find a long metal bar that isn’t connected to the main hot bars, this is the neutral bar.
The ground bar is normally placed at the bottom of the service panel, although sometimes you will have to add your own, which is a simple enough task.
Once you have located and identified all of the busbars it is time to connect your wires to them.
For connecting the 60 amp circuit breaker in the main service panel, to the hot busbars in your subpanel you will want to use 6-gauge wire.
Take the two live wires and connect them to both of the hot bus bars in your subpanel.
Make sure when connecting wires to tighten the screws on the connectors to make sure that they can’t easily come loose.
Wires will expand and contract as they get hot, so you don’t want there to be any leeway that will allow the wires to come out and potentially cause an electrical fire.
Connect your white neutral wire to the neutral bus bar and the bare copper ground wire to the ground bar.
Provided you are patient, the wiring shouldn’t be too difficult, but there are some significant issues you will want to avoid, which we will cover later on.
Either hot wire can connect to either hot bus bar, so don’t worry about mixing them up, provided you have kept the neutral and ground wires separate.
Adding Appliances To Your Subpanel
Once you have done this, you are ready to add circuit breakers to your subpanel.
These circuit breakers will need to be connected to their respective branch circuits so that the subpanel can supply power to all the appliances you want it to.
Remember to choose the correct gauge of wire for hooking your appliances to the circuit breakers in your subpanel.
It is also important to feed the wires into your subpanel correctly; the neutral wire from your branch circuit must be connected to the neutral busbar.
The ground wire must be routed back to the grounding bar, while the live wires must be connected to the circuit breakers on the hot bus bars.
Most of the time, you will only have neutral wires for 120V circuits that are connected back to small single pole breakers below 20A.
For the larger circuit breakers, you will only have to connect two live wires to the breaker itself and the copper ground wire back to the grounding busbar.
For single pole breakers, you will only need to connect one live wire to it. When using double pole breakers, you will need to add two hot wires.
240V appliances coming into the subpanel won’t require a neutral wire, as these are only necessary for GFCI breakers and those supplying 120V circuits.
Installing A 150A Subpanel For Only 240V
This section of the guide will take you through the steps for setting up a larger subpanel for powering bigger appliances that need more juice.
You would choose this option for supplying power to a workshop full of power tools. If you want to install smaller circuits for lighting, then you will need to have a 120V outlet as well, so bear that in mind before you start.
For the most part, this installation will work similarly to the last one, so your first step will be swapping out a 240V circuit breaker in your main service panel for a double pole 200A breaker.
This breaker then needs to be connected to your subpanel in much the same way as we did last time. The crucial difference is that since your subpanel is only for 240V, you won’t need to have a neutral wire.
For this installation, you will want to use a 3/0 gauge wire for handling the larger current.
With a 200A breaker in the main service panel, you will be able to connect three 50A breakers to your subpanel or any other combination that adds up to less than 160A.
Note
You will still need to have a neutral wire if you want to install any GFCI breaker into your box.
In these instances, you will need to run a neutral wire from the appliance or circuit coming into the subpanel, and connect it to the neutral connector on the GFCI breaker.
This breaker will have its own short neutral wire that can be routed back to the neutral bus bar. GFCI breakers are the only 240 volt circuit breakers that will require a neutral wire.
Installing A 100A subpanel For Only 120V
This will be a useful configuration for setting up a subpanel for powering a small guest house.
Provided you don’t have any large, power hungry appliances you won’t need to have a 240V output and as such you may not need as large of a breaker in your main service panel.
For this set up, you can use a single pole 100A breaker in your main service panel, which means you will only need to feed one live wire into your subpanel.
This wire is shared between both hot busbars, and as such you will need a jumper wire for connecting the two.
Feed in your single live wire and connect it to the closest hot bus bar, then prepare your length of jumper cable and run it from the same busbar over to the second hot connector.
This will require you to have two wires feeding into the first connector, and to do this you should twist their ends together to prevent a loose connection.
You should set up different outlets for standard 120V power and GFCI 120V power. This is due to the slightly different way that the neutral wires need to be connected when working with 120V breakers.
In this configuration you can set up multiple smaller, single pole breakers which will be great for supplying low-power branch circuits for lights or plug sockets.
You can use GFCI circuits for any utilities that are commonly exposed to water, such as kettles or lights next to a kitchen sink.
Switching A 120V Subpanel To A 240V Subpanel
It is possible to convert a 120V subpanel to a 240V one, although it is best to do so carefully to prevent damaging any electronics.
Firstly, you will have to find the main breaker that supplies power to the subpanel and find out what it powers.
For a 120V only panel, this breaker will likely be a single pole one, so you will want to make sure that you are able to swap it out for a 240V double pole circuit breaker.
This will entail checking there is enough space for the double pole breaker and ensuring that the subpanel is the only thing powered by the single pole breaker.
If there are any other circuits connected to the subpanel’s single pole breaker, then they will not be able to handle the larger current delivered by a double pole breaker.
If the single pole breaker does service more than just the subpanel, then the first thing you will need to do is create a dedicated circuit breaker for the subpanel.
Once you have ensured that swapping out your single pole breaker won’t damage any other circuits, you can start work.
It will be a good idea to turn off your subpanel and remove some of the wiring that won’t be necessary. The first thing you can take out is the jumper wire that travels between the two hot busbars.
Then you can swap out the original breaker in your main service panel for a double pole 240 V one.
This should be connected to a cable with two live wires, a neutral and a grounding wire.
You can then configure the box similarly to our guide for setting up a 200A subpanel for only 240V. Remember, you won’t need a neutral for this set up unless you are going to be using GFCI breakers.
Top Tips For Installing A Subpanel
We have now covered most of the things you need to know about installing a new subpanel. In this section, we will provide some top tips and safety precautions to bear in mind while you are working.
Some of these tips will simply make the job a bit easier, while others will be almost essential for preventing serious injuries.
Don’t Connect Ground And Neutral Wires
Some people may consider the ground and neutral wires to be interchangeable, but this is far from the case.
The purpose of the ground wire is to provide a resistance free route for excess power to escape the circuit and flow into the ground.
This is essential for mitigating damage caused by short circuits or voltage spikes.
Inside the main service panel the neutral and ground bars are often connected together, but doing this for your main lug, or subpanel could greatly impede their performance.
Yes, both wires will still perform as intended, but it will increase the resistance of both wires, which is not what you want.
More resistance will lead to more heat produced by each wire, which could lead to overheating and electrical fires.
If your subpanel is far away from the main service panel, then it will probably have its own grounding rod.
If this is the case, then you can connect the neutral and ground bus bars together without it having a negative impact. In all other circumstances, keep these two bus bars separated.
Other Tips
- Always disconnect the power to your main service panel before servicing, repairing or installing a subpanel.
- Never touch wet, or metal components with your bare hands.
- Check with your electricity supplier or a professional electrician before installing a subpanel to make sure it is safe and legal to do so.
- If unsure about what you are doing at any point, then stop and call a professional. Playing with live electronics is dangerous and potentially lethal.
Final Thoughts
You now know everything you need to know for installing a new subpanel or main lug. Doing this will help massively with providing power to a garage, shed or other external location outside your home.
It will also allow you to create a separate power supply for specific circuits so that you can turn them on and off without having to go to your main service panel.
Provided you are careful and follow all the necessary safety precautions, then you should be able to install your own subpanel with a few materials and a bit of time.
