Breaker Box Wiring | How to Wire a Main Circuit Breaker Panel?

An Electrical Service Panel or a Circuit Breaker Panel is an important part of every residential electrical system. It takes in the AC Mains supply coming from your utility and distributes it to different circuits in your home through individual circuit breakers. Breaker Panels may have different appearance or rating but essentially, they all serve the same purpose. So, their wiring is also same. In this guide, let us take a technical look at circuit breaker panel and its elements, steps involved in Breaker Box Wiring. We will also understand the importance of balanced and unbalanced load distribution.

NOTE: This discussion about the breaker box wiring is not a user guide on wiring circuit breaker panels but rather a technical informative guide. If you are planning to install a new panel or make changes to your existing panel, then definitely consult with a professional.

Circuit Breaker Panel

As mentioned earlier, the service panel (also known Circuit Breaker Panel or simply a Breaker Box) has three main purposes in a home’s electrical system.

  • It acts as a distribution hub for different circuits in a house.
  • All the circuit breakers (overcurrent protection devices) for individual circuits are present in the main service panel.
  • It contains the master switch to turn ON or OFF the electricity to your home.

The following image shows the layout of a typical circuit breaker box.

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There are knockouts for passing cables at the top, bottom and sides of the panel. Depending on your installation requirements, you can remove any knockouts.

At the top of the panel, there is the main circuit breaker that acts as the “main” or “master” switch. Selecting the main service panel is very important as it determines the maximum current your entire system can draw. Most medium sized modern homes are being equipped with at least 200A main panels. But if you need more, then you can either increase the capacity of the main panel or add subpanels.

Immediately below the main breaker, we have two hot bus or legs (usually made up of copper but sometimes aluminum is also used). They run along the center of the panel and have tabs for inserting circuit breakers from which the hot wires are distributed to individual circuits.

Each hot bus is connected to two different incoming phase (or hot) lines (black and red) and are at same voltage (120V) with respect to the neutral.

Speaking of neutral, the breaker box has two aluminum strips with screw terminals along the sides of the panel that act as neutral bus. We connect the incoming neutral to this bus and from the screw terminals, we provide neutral to individual circuits from these screw terminals. Some panels have a separate ground bus with screw terminals and it will be connected to a grounding rod.

Tools Required for Breaker Box Wiring

Here is a list of the tools and material that we require for wiring a breaker panel.

  • Screwdrivers
  • Wire Stripper and Cutter
  • Flash Light
  • Fish Tape
  • Voltage Tester
  • Utility Knife
  • Circuit Breaker Panel
  • Electrical Tape
  • Circuit Breakers

Breaker Box Wiring

It is actually very easy to wire the main service panel if you have the proper tools and you take necessary safety measures. The first step in this is to contact your power utility company and requesting them to shut off the power supply. You can confirm this with the help of a voltage tester.

  • Step 1: Take your main panel and break the knockouts for the incoming mains supply from utility. Usually, the service wires drop through a solid metal pipe (service mast) from the roof to the meter/service panel. Most breaker panels have a knockout for this service conduit at the top.
  • Step 2: Apart from the main service conduit knockout, you may also want to remove the knockouts for outgoing circuits, grounding wires etc. You can easily tear or break the knockouts using a screwdriver or a chisel.
  • Step 3: Next, you have to mount the breaker panel with the help of screws. If the incoming power supply consists of a metal conduit, then you have to carefully align the opening on the top of the panel (which we just removed the knockout for) with the conduit. Once they are aligned, you can make markings for drilling holes.
  • Step 5: Once you properly mounted the panel, we can begin the breaker box wiring starting with installing the main service wires. Using a fish tape, you can pull the service wires through the conduit. Usually, you get three wires: two hot (black and red or sometimes both black) and a neutral (white). Additionally, you will also get a grounding wire from the grounding rod.
  • Step 6: We can start the wiring by connecting this grounding wire (a bare copper wire) to the grounding bus bar. Then, start connecting the main white neutral wire to the neutral bus bar.
  • Step 7: Now, insert the main circuit breaker (usually a 200A rated breaker) at the top of the panel. This breaker acts as the main switch and monitors all the current entering your home. Now connect the two hot wires to the two lugs on the main circuit breaker. Secure them properly and make sure that no copper wire is exposed beyond the lug to avoid any accidental contact.
  • Step 8: This completes the installation of the main service wires and we are now ready to wire the individual circuits. We can do this by installing necessary circuit breakers on both sides and wiring the neutral and hot wires. Make a rough calculation of the current draw of all the circuits and properly arrange them on both the hot legs.

Image

  • Step 9: Some circuits in the home such as kitchen, bath room etc. require GFCI Breaker and/or AFCI Breakers. So, install those breakers where ever necessary and wire the hot side. Coming to the neutral wire in GFCI for example, first connect the neutral wire from the circuit to the neutral terminal on the GFCI breaker. Then connect the white neutral from GFCI to the neutral bus bar.
  • Step 10: If any circuits require grounding, then connect the copper grounding wire to the grounding bus bar.

Make a Balanced Load

This is an additional safety step you can take for a safe operation of your electrical system. In a Balanced Load, both the hot legs take up approximately the same amount of load (current).

Using the above circuit schedule, make an approximate estimation of the current draws of all the circuits. Now based on your calculation, place the loads in such a way that both the hot legs have a similar amount of current. Such balancing will ensure that the wires don’t heat up.

Conclusion

We presented a simple guide on Breaker Box Wiring. The main circuit breaker panel is an important part of residential electrical system. With proper safety and tools, you can easily wire it yourself. However, as it involves working with AC Mains Supply, you are better off with a licensed electrician for wiring the main service panel.

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