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Main Lug Vs Main Breaker: Differences, Uses, & Considerations

Differentiating between the main lug and the main breaker can be confusing to homeowners. These two electrical devices have similar goals, but they function differently. Even if you are not an electrician, you should be familiar with their distinctions, so you know what to do when problems arise. We did research for this post to help you distinguish the main lug from the main breaker.

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Both the main lug and main breaker are load centers for electricity distribution. The main breaker acts as an overcurrent control and provides protection over primary circuits. The main lug is only a sub-panel that helps increase the number of circuits. 

You will find the two components in the circuit breaker box. Both the lug and the breaker allow for proper electricity flow. These terms are technical, and it's okay if you need more time to understand them. Read further to learn more about the main lug and breaker. 

Difference between Main Lug and Main breaker in this two images, Main Lug Vs Main Breaker: Differences, Uses, & Considerations

Is The Main Lug The Same As The Main Breaker?

The main breaker and main lug work together for the proper electrical distribution in your home. As a homeowner, you should know the differences between the two in case there are power supply problems.

Before you can distinguish their similarities and differences, read their definitions below.

Main Breaker (MCB Panel)

The point where electricity enters the home's power system is through the main breaker. It connects to a circuit board inside the main electrical service box. You can find the box on an inside wall or outside a property.

The function of the main breaker is to control the flow of electric current from the outside to all connected branch circuits.

If you see labels or numbers, these are the branch circuits. The breaker heaps, branches, and transfers electricity within the system. 

Electrician’s Hand Turning On Circuit Breakers

Also, the main breaker is a protective device against overcurrents from all service entrances. It is the central switch to reset the home's power supply.

The breaker will automatically disconnect the electricity from the loads if the current exceeds the normal levels. Moreover, the main breaker prevents overheating and grounding issues of electrical wires.  

Main Lug (MLO Panel)

Electrical Circuit Breaker panel in new home construction

On the other hand, the main lug is not an overcurrent device. It is a primary sub-panel that supports the main circuit breaker panel in a downstream manner.

It is only secondary to the main breaker. You add the main lug if the slots in the main breaker are full or if you plan to have a remote panel.

There is no main breaker supplying the main lug. Instead, there are wires or terminals connecting to the panelboard bus. You can place the main lug adjacent to the main breaker or farther if you plan to supply for other areas in the house. 

The main lug supports the main breaker through the following:

  • Lightening the main breaker's load
  • Extending the connections to other parts of your home
  • Meeting growing electricity needs

To help you refine the distinctions, below are their similarities and differences.

Similarities

Both the main breaker and main lug have the following characteristics:

  • Both are types of load centers that enclose branch circuits and provide safety against electric hazards, such as arc and ground faults.
  • Both regulate and distribute electricity to all connected circuits in your home.
  • You can install them flush or surface-mounted.

Differences

In contrast, here are some of their differences:

  • The main lug is only an add-on and does not have a main breaker. It can have a separate disconnect from the meter.
  • The main breaker is the only service entrance of electricity to the house. 
  • There can be as many circuit breakers as the main breaker can hold. In contrast, the main lug can only have 2-6 circuit breakers.
  • You can tie neutral and ground bars together for the main breaker, but the main lug needs an isolated neutral bar and dedicated ground bar.
  • The amperage rating for the main breaker ranges from 125-600 amps, while the main lug has 125-800 amps.

Continue reading to learn which of the two you should use.

Which To Use: Main Lug Or Main Breaker?

Electrical fuse box

Choosing between the main lug and the main breaker depends on your needs. Below are some factors to consider.

Protection

In this category, the main breaker is better than the main lug. The main breaker is a safeguard against overcurrents and overheating.

In comparison, the main lug does not have a protective capacity. The main lug is good as a supplement to the main breaker if you want to add more circuits.

The main breaker is in accordance with the National Electric Code 408.36 which states that there should be an overcurrent protective device for the panelboards.

The main lug does not have an overcurrent because it only distributes the power and directly connects with the conductors.

Location

Besides protection, you can choose between the two by considering the area you plan to supply with power.

For the main breaker, you should install it in low-traffic areas, such as the basement or garage. If you are in an apartment, the main breaker will be at a central location.

Meanwhile, the common locations for the main lug are residential multi-family apartments and light commercial mixed-used spaces.

Capacity

You should match the main breaker and main lug with the acceptable voltage capacities of the circuits. Doing so can avoid overloading the circuits.

Include the voltage requirements of the electrical devices you use at home. If you need to serve many devices, the main lug is a must.

It is best to consult an electrician to help you decide what to use. 

How Much Does It Cost To Replace The Main Lug Or Main Breaker?

If you need to replace the main lug, it will cost you around $400-1,000, depending on the amperage and circuit's capacity. For circuit breakers, the standard will cost as low as $10 and up to $100. 

There can be additional costs for labor and necessary work permits.  

Can A Main Lug Be Converted To A Main Breaker And Vice Versa?

Hand turning in or off a fuse box switch.

Yes, it is possible to convert the main lug to the main breaker. However, the main lug will need to be convertible. Check the product description to find out if it is convertible.

Not all models of main lugs are convertible. If the model is convertible, buy a compatible main breaker kit (MBK).

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Normally, you cannot convert a main breaker to a main lug, but it is possible if you have a hold-down kit. 

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Here are the steps for conversion:

  1. Turn off the power supply before you start.
  2. Remove the main breaker from the panel. 
  3. Install the main lug kit by following the product instructions.
  4. Insert the hold-down retainer in the gaps between the main breaker poles. Push up and slightly twist until it snaps in place.
  5. Add the rail extension to the ends of the main lug interior. Then cover the main lug with a blank dead front.

If you are converting, you should follow the product instructions carefully or let a licensed electrician do the job. The conversion should follow the applicable local electrical codes.  

Will The Main Lug Stop If The Main Breaker Trips?

When the main breaker trips, it will disconnect the circuits at once.

However, the main lug does not require the main breaker. It requires a separate disconnect, so the main lug's power may not be cut off. 

The main breaker can trip at unexpected times. It is normal if the breaker trips because it acts as a safety device. If the electric current is too high and unsafe, the breaker trips and stops the flow of electricity to your home. 

In Summary

Difference between Main Lug and Main breaker in this two images

The main lug and main breaker work together to distribute electricity at home. The main breaker is the central entrance of power, while the main lug is an add-on to the main breaker.

When choosing between the two, you should factor in protection, location, and capacity.

It is possible to convert a main lug into a main breaker and vice versa. You need to make sure that the new lug or breaker kit is compatible with the load center requirements. Check your local electrical codes to find out if they permit conversions.

If you have problems with the power supply in the future, you won't have to worry because you know how to differentiate the main lug from the main breaker.

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