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How to Install an Electric Sub-Panel to Main Panel

An electric sub panel is installed for many reasons. Adding additional breakers to a workshop for your power tools or lighting is a common one. Or you want to convert your unfinished basement into a home-theater. A Sub-Panel installed in the basement will give you the flexibility beyond the one GFI outlet and one pull-string light you have. For instance, you can add additional breakers to the sub-panel. These breakers can be designated for outlets, lighting, powered incline theater seating, a projector or even building out a retro arcade area.

What’s Covered in this Article

  • Recommendations
  • Tools and Materials
  • The sub-panel installation as shown in the video
  • Addresses some misconceptions and frequently asked questions
  • National Electric Code (NEC) Links
  • Safety First

Safety Recommendations

I’ll state this again at the end but it is very important that you consult a licensed electrician. It is equally important that you review your plans with your city or town’s code enforcement officer. And if at any point you feel uncomfortable working on electric you should stop. Consult a licensed electrician to perform the installation for you.

Tools and Materials

The electrical tools used in my installation are available here: https://amzn.to/4016OjF

The general contractor tools used in my installation are available here: https://amzn.to/3CHXveu

The materials used in my installation are available here: https://amzn.to/3mYrI4h

Electrical and General Contractor Tools Used

  • A circular saw to cut OSB (Oriented Strand Board) or Plywood
  • Construction gloves
  • A straight edge or angle iron for reference line
  • Ridgid Power Tools Drill / Driver
  • Clamps
  • Ramset .22 Caliber Fastener
  • Ladder
  • Wire Cutter for 2-o wire
  • Romex cable ripper
  • Tape Measure
  • Hammer
  • #2 Robertson Screw Driver or #2 Combination Tip Screwdriver like Klein Tools 32378

Materials Used

  • 4×8 Sheet of 7/16″ thick OSB or 1/2″ Plywood
  • Ramset Nails with washers
  • Ramset Power Loads Rounds (yellow or red)
  • Siemens PL Series 100Amp Load Center P2020B1100CU
  • Anti-Oxidation Compound
  • 14 feet 2-0 gauge 4-Wire
  • Siemens AFCI/GFCI Dual Function 20 Amp Breaker Q120DFP
  • Wirenuts or Push in Wire Connectors
  • Siemens Q2100 2P 100A Circuit Breaker

Sub Panel Installation Video

These are the chapters within the Sub-Panel installation video:

Installation of Sub-Panel Overview

In my Load Center (main panel) I have two free adjacent slots. This means I can install a double pole breaker that will occupy both slots. Then I can install the sub-panel in that space to the right of the main panel. To give me an strong surface to mount the sub-panel to I install a half sheet of 7/16″ OSB over the drywall. To install the OSB I secure it with a few screws and double up by using my Ramset. This secures the OSB to the wall without worry of it falling off.

Next I install the sub-panel onto the OSB securing it with some screws. Lastly I remove the bonding screw as it is required to separate the neutral bus bars from the ground bus bars within the sub-panel. For more information on this you can find a reference to the NEC on Objectionable Current by Mike Holt.

Mounting of Romex Connectors

It is best to use conduit between the sub-panel and main load center. I used service cable but it is not the best approach. Many experts suggested other ways, which is why I am suggesting the use of large conduit and 2-o wire. You will also want to choose an optimal path for your wire and/or conduit. My path was not optimal. Those who are waste conscious brought this to my attention as I bought more wire than I needed. But, this is a general concern for DIYers as you’d rather have more than you need and make one trip.

Installation of 2-o Wire

Please note that 4 wire is required to connect a sub-panel to a main panel. The 4 wire consists of a Line 1 (L1), a Line 2 (L2), a neutral and an earth ground wire. You’ll see in my video that I connect the earth ground wire to the ground bar within the sub panel and I connect to the neutral to the neutral bar within the sub panel. This means that the neutral and the ground bars are floating from one another to avoid ground loops. If you are using aluminum wire please be sure to properly coat the bare aluminum with anti-oxidation compound. If you fail to do this then this could become a hot-spot over time and could potentially cause a fire.

Misconceptions and Frequently Asked Questions

Why is it necessary to remove the bonding screw in the sub-panel?

The Bonding Screw in a sub-panel bonds the neutral bus bars to the ground. It is necessary to remove it so that the neutral and ground paths remain independent back to the main panel where they are combined. This way, in the event a fault, current will not find it’s way through the metal surfaces of appliances and equipment. Have you ever felt a tingling sensation when you touched an appliance? Don’t try this but this is current finding its way to the grounded surface of the appliance. This can be very dangerous. By keeping the neutral and ground isolated within the sub-panel current will not find its way through the grounded surface of appliances.

Why is it necessary to separate the neutral and ground wires in a sub-panel?

See above.

Does adding a sub-panel increase or decrease my service?

The short answer is no but it is important that you understand why. Adding a sub panel does not increase the current capacity of your service. Adding a sub-panel only allows you to segment your existing circuits or add additional branches. It does NOT permit you to add an addition onto your home or build a kitchen in your basement.

Adding a sub-panel doesn’t increase your capacity. For instance, if you add a 50Amp sub-panel to a 100Amp Load Center you did not gain 50 additional Amps of capacity. Similarly, you do not suddenly lose 50Amps of capacity by adding a sub-panel. It is best that you see the question below “Why do you want to install a sub-panel?”

Why do you want to install a sub-panel?

You need to first answer this question. “Why do you want to install a sub-panel?”

Segment Circuits

If you want a sub-panel merely to segment existing branches that perfectly fine. For instance, you have a branch where the outlets from your hallway, are on the same branch as your bedroom and foyer. When you plug in your vacuum in the hallway the breaker trips because you have your computer, a gaming console and a box fan all running at the same time. This is a great opportunity to rewire your home and separate the hallway and foyer from the bedroom. You do this by installing another breaker and routing the bedroom wiring into the new breaker. Please be aware that it is not always that easy. A licensed electrician needs to evaluate your wiring to make sure you can isolate the other rooms onto separate circuits.

Add a Kitchen to your Basement

You want a sub-panel because you want to build another kitchen in your home. Then you are exceeding the capacity of your main panel. A load calculation was performed when your home was designed prior to being built. This is based on the square foot of the home multiplied by a 3VA, the number of bathrooms, appliances, HVAC units, bathroom fans, electric dryer, washing machine, etc. This load calculation certainly did not include the appliances required for a second kitchen.

You will need a licensed electrician to help calculate your new load requirements and determine if a larger service is to be installed. In the end you may not need a sub-panel and may just need to install a larger service. You may have a 100Amp service now and determined that you need a 200Amp service. If you have the physical room for a larger panel then this will naturally give you more available slots.

Building an Addition or Adding a Workshop

Building an addition is a similar problem. The additional comes with a VA multiplier of 3VA per additional SQFT. You also have to consider the purpose of the new space.

  • Are you adding another laundry room?
  • Are you simply providing additional living space?
  • Will you need an additional HVAC system or one or more mini-split units to be added?
  • Is the purpose of the addition for a workshop?
  • What size machinery do you expect to operate?
  • Will you be operating a 100 gallon compressor at the same time as a plasma CNC while working on another project welding?

If so, you will need to provide all of this information to the electrician who can perform the new load calculations for you.

Depending upon your situation, you may still want a sub-panel installed to give you remote connection points. Running one long larger gauge wire is easier than running 10 12AWG or 14AWG wires back to the main panel.

Why are you using aluminum wire?

Aluminum wire is not permitted in some states. Check with your code enforcement officer and also consult with a licensed electrician. As of the installation of my sub-panel in 2016 aluminum wire was permitted in New Jersey. This is a controversial subject among experts. It’s even controversial among the inspectors where they will demand that you rip out the aluminum wire and replace it with solid copper wire. New Jersey contractors have reported that has happened to them. And whether or not you use an Anti-Oxidation compound on the aluminum wire is equally as controversial. The inspector required an anti-oxidation compound to be used on my aluminum wire.

Safety First

You are responsible for following safe practices when working. Safety is a mindset that needs to be applied to all areas and not just electricity. Yes, electricity is dangerous. You can get shocked or electrocuted by it. But you could also fall off of a ladder or trip on something on the floor and get seriously injured. Be aware of your surroundings in your workspace as even turning around could result in hitting your head on something. Always be thinking about safety.

Please ensure proper electrical bonding by torquing all setscrews and lugs down to the proper torque. Proper electrical bonding helps to ensure a good flow of electricity with negligible resistance impeding the flow.

Consult a Licensed Electrician

Please consult a licensed electrician before you attempt any of this on your own if you do not have detailed knowledge of electricity. An improper installation could result in ineffective GFI protection, shock, electrocution, or fire. Please follow all safety precautions when working with electricity. If you are not comfortable performing this work then please hire or consult a licensed electrician. This is not something that you can take an approach where you’ll just wing it. A slight misstep could result in shock or electrocution. But don’t consider the only hazard the electricity. Your work area could be equally as dangerous. Observe all reasonable safety precautions from every level from standing on a ladder to installing the panel to landing the wires. Even improperly handling a knife or wire cutters could result in injury.

The National Electric Code (NEC)

Remember to read the NEC (National Electrical Code) prior to installation to verify that all is being installed according to the code.

The National Electrical Code is Free

The National Fire Protection Association is more concerned with your safety than charging for the National Electrical Code standard. To access the NEC for free, create an account here on the NFPA’s NEC page. If that link fails to load, visit the NFPA.org site. I suggest reading through the NEC. I also suggest consulting a licensed electrician and as well as your building code enforcement official.

Please follow your local and state ordinances and electric and building codes when installing a sub panel. Consult the latest National Electric Code guidebook and read the relevant sections. The NEC book contains a standard for wiring in residential, commercial, and industrial applications. Follow the appropriate section and take all codes seriously. These were created for the safe operation and maintenance of your electrical distribution system.

This demonstration shows half-way through that it would be nearly impossible to tie in the sub-panel with the bundle of wires that occupied the right half of the panel. It was necessary to short all wires and reroute them for a better layout to avoid any obstructions to the 2-0 wire that needed to be landed in a 2-pole 100 Amp breaker. Skip ahead of this section if it does not apply to your panel setup.

If you are interested in other U Do It™ articles you can see them here.

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