If your contractor installed a subpanel in your home, you probably noticed that it did not have a main breaker. But is this safe? The main panel has a breaker. Doesn’t the subpanel require one as well?
Does A Subpanel Need The Main Breaker?
The subpanel doesn’t need a main breaker because the subpanel gets power from the main panel. Therefore, deactivating the power in the main panel using the main breaker will cut the power to the subpanel. The NEC also doesn’t force consumers to add main breakers to the subpanel.
Electricity enters your home through two lugs that connect to the power lines at the top of the meter. The breaker completes the circuit by sending the current to the bus bars, which distribute the electricity to the circuit breaker.
Every main panel requires a device that can disconnect the power. Most houses use main breakers. They respond to electrical failures, malfunctions, and overloads, preventing fires by tripping.
However, even though people expect to see main breakers in the main panels, some houses don’t have them. This is especially true for older properties built before the 1980s.
A panel with six breakers or less can get by without a main disconnect switch. This is also called the ‘Six Breaker Throw’ rule.
The rule relies on an NEC regulation that expects contractors to ensure that electrical services require six switch throws or less to disconnect the power. However, the 2020 edition of the NEC eliminated that particular clause.
Every main panel requires the main breaker. But that only answers part of the question. If the main panel requires the main breaker, what about the subpanel?
Subpanels get electricity from the main panel. People use them when they need additional branch circuits and breakers, but the main panel doesn’t have the space.
They also use subpanels to extend the reach of their electrical service to a new location within the same building or a separate building. Subpanels are smaller than the main panels that provide their power.
In fact, many subpanels look like miniature main panels. Therefore, you can equip them with main breakers. Like the main panel, you need a means of cutting the power to the branch circuits in the subpanel. The main breaker can accomplish this objective.
The main breaker in a subpanel is not a necessity. The feeder breaker in the main panel is more than adequate.
You’re not breaking any rules by installing a subpanel that doesn’t have a main breaker. However, if the subpanel and main panel are located in different buildings, you are better off giving the subpanel the main breaker because this simplifies the process of switching the power to the subpanel off.
The last thing you want during an emergency is to run from structure B to structure A in search of the main breaker in the main panel because an electrical problem occurred in structure B.
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What Does The NEC Say About It?
The NEC doesn’t have anything to say about the presence or absence of main breakers in subpanels. Some people use the ‘Six Breaker Throw’ rule to determine whether or not main breakers in subpanels are necessary. But the NEC eliminated the clause that created that rule.
It doesn’t encourage homeowners to add main breakers to subpanels, but neither doesn’t prohibit them from doing so. Rather than consulting the NEC, look at your local code.
The local code supersedes the NEC. You should obey the local code if it expects homeowners to use main breakers in subpanels. If it doesn’t say anything about this issue, consult a professional. They will advise you accordingly. Ultimately, the main breaker on a subpanel is convenient.
How To Add Main Breaker to A Subpanel?
A subpanel doesn’t require a main breaker. But if you’re determined to install a main breaker, these are your options:
You are better off installing a disconnect switch. It is the cheaper option.
Ask your contractor to buy a panel with a breaker or disconnect switch. This is the most convenient solution. Some subpanels won’t let people install main breakers. A contractor can customize the panel to accommodate a breaker or disconnect switch. However, it is easier to buy a subpanel that includes these features.
The only disadvantage is the fact that you don’t have as much control over the size of the breaker. The advantage of buying a subpanel with a main breaker is that you have room to add extra functions such as GFCI technology.
If your panel has room for a breaker, find the lugs where the red and black wires connect. Remove the lugs and screw a breaker into place. Connect the lugs on top of the breaker to the red and black wires.
Subpanel VS Main Breaker – What’s The Difference?
The main panel creates the initial connection between your house and the grid. It is also the first barrier that surges and spikes will encounter. The main breaker provides electricity to the rest of your house. Turning the main breaker in the main panel to the off position will deprive the entire house of power.
Subpanels are smaller versions of the main panel. People use them to direct electricity to a different section of the house or a structure separate from the main house.
Subpanels have many of the same features and functions found in the main panel. However, the subpanel gets power from the main panel. It does not have direct access to the grid.
You can install subpanels next to the main panel. Some people use subpanels because they don’t have enough space for additional breakers in the main panel.
Subpanel Main Breaker Size
Look at all the equipment the subpanel will serve. Find the wattage of each device and add them all together to identify the total wattage. The size of the breaker is quantified in amps. Therefore, it isn’t enough to identify the total load in watts. You must change the watts into amps. This is a simple matter of dividing the total wattage by the voltage.
- A home with a total wattage of 8540W. Dividing 8540 by 240V (Voltage) gives you 35.6A. But you’re still not done.
- 35.5A is not an adequate breaker size for a subpanel. You have to multiply this figure by 125% to get 44.84A. But again, you’re not done. You have to leave room for future expansion. This means boosting the amperage by 20 percent.
- Multiplying 44.48A by 20% gives you 53.38A. But that raises an obvious question. Do they make breakers in sizes like 53.38A? No, they don’t. You need to round off. Aim for 60A breakers.
The breaker size should match the size of the panel.
For instance, if you have a 200A subpanel, you have to buy a 200A breaker. If the subpanel is 50A, get a 50A breaker.
You can use a breaker that is smaller than the subpanel. For instance, you could pair a 200A subpanel with a 100A breaker. However, this will prevent you from using the breaker’s full capacity.
Using the example above, you cannot run a 150A load on a 200A amp service because the breaker will trip the moment you exceed 100 amps. Therefore, the breaker size should match the amperage of the panel.
Does A Subpanel Need To Be Grounded To The Main Panel?
You bond the neutral and ground at the main panel, not the subpanel. Otherwise, you will create multiple paths for the neutral return current.
How Far Can A Subpanel Be From The Main Panel?
There is no maximum or minimum distance between the main panel and subpanel. But you should consider the voltage drop. It affects the size of the feeder cable. The longer the distance, the thicker the cable.
Consult an electrician. They can calculate the voltage drop on your behalf, taking factors like the breaker size and wire type into account.