A subpanel is a simple service panel used to distribute power to specified building property areas or homes. It’s a panel that acts as a secondary circuit breaker.
If you want to have a subpanel in your house, you must understand the exact number you need for the service. This way, everything will work the way it’s supposed to without overloading the subpanel.
For instance, let’s take a main panel having 200 amps. You can add as many subpanels as you need providing the combined electrical demand is below 160 amps. If all the circuitry was operating at once, the electrical service could become overloaded. However, all combined circuitry would not likely be on at any given time.
Here, we’ll explore more information about subpanels, how they are connected to the main panel, and what they’re used for. When you connect a subpanel to the main panel, ensure that you pay attention to the amount you’re adding.
The good news is that this guide will assist you through the process. Let’s get started!
What is a Subpanel
An excellent example of a subpanel is a smaller circuit panel, usually less than 200amps. The subpanel will contain about four to twelve breaker slots. It’s supplied with a 240V circuit breaker from the main panel. In this case, the main panel is referred to as the feeder breaker. However, a 200amp subpanel can be connected to a 200amp feeder panel as long as the load is 160amps or less.
There is a similarity between a main panel and subpanel since both contain two similar hot bus bars. In addition, the ground and neutral bus bars also have similarities.
The Purpose of a Subpanel
Subpanels are employed in two main scenarios:
- There’s no room for installing additional circuits to the main breaker panel. In such a scenario, the main panel is full of breakers.
- To control the area closer to where the circuit serves. This could be a workshop or apartment.
The subpanel is located closer to the main panel if it’s only needed to provide space for more circuits. Subpanels can also be used to provide power for a room addition.
How to Connect Subpanels
During the installation of a subpanel, a feeder cable connects it to the main panel. The feeder cable is a three-wire cable. It has a copper ground wire and three insulated conductors.
You need to connect two hot wires from the feeder cable to the lug located on the hot bus bar found in the subpanel. Connect the neutral wire to a neutral bus bar. You then connect the copper grounding wire to the grounding bus bar.
The hot feeder wires are connected to the 240V circuit breaker from the main panel. The ground and neutral wires are joined to the bus bars from the feeder cable.
You then snap the feeder breaker into the open double slot found inside the main panel. At this point, the subpanel is ready to have additional circuits.
Capacity of Subpanels
You should address two capacity issues once a subpanel has been installed:
- The subpanel needs to have the correct amperage capacity for the circuit and area it will serve.
- The main service should be sufficiently sized to supply the power required due to the added demand resulting from the subpanels.
If the main service is old, there is a need for a replacement before installing subpanels.
Warning Signs of an Electrical Circuit that is Overloaded
The warning signs of an overloaded electrical circuit include:
- Frequent tripping of circuit breakers
- Lights that dim, blink, or flicker
- Wall Plates are discolored or warm
- Fuses that are frequently blown out
- Switches, receptacles, and appliances giving you mild tingle or shock
- Receptacles having sizzling, buzzing, or crackling noises
- Wall switches or receptacles having a burning odor
If any of the above issues ever happen, you’ll have to disconnect some subpanels. If you overload a circuit, all the appliances connected to it stand a chance of getting damaged.
Checking if a Panel is Maxed Out
Here, you can employ a multimeter for checking the amperage of every hot wire. In such a case, you want a low amperage.
It would help if you turned on everything as possible to get the right amperage for each wire. If there are signs of an overload, but that isn’t reflected on the meter, there is a high chance that there is an overload.
How to Determine Subpanel Loads
There are various calculations that you should do to determine the safe gross load on a subpanel. The circuit load represents the total load on the subpanel.
You’ll also have to understand the subpanel’s coverage area and the appliances that your subpanel serves.
Step 1: Determine the Subpanel’s Coverage Area
To calculate the subpanel’s coverage area, you should first determine each room’s square footage. Finding the square footage involves multiplying the width and length.
You can then add together the square footage for each room. Finally, employ the calculation below:
‘Total square footage x 3 watts = general lighting and receptacle circuit load’
Step 2: Find Appliance Wattage
Here, you’ll require the appliance wattage. After totaling the appliance wattages, you should multiply by 0.75 for at least four appliances.
You can add the largest load to the total. The extra wattage is there to account for the additional load that large motors utilize while starting up.
Step 3: Determining the Subpanel Wattage
This is the time to calculate the subpanel wattage. You employ the calculation below:
‘Total wattage (square footage plus appliance calculations) x 1.25 = adjusted load’.
The adjusted load represents the safety adjustment that the National Electrical Code requires. It provides a voltage drop buffer on the feeder circuit.
After installing a subpanel, it is recommended that you inspect it. It’s a proactive approach to address any possible issues that might arise later.
If there are exposed cables connecting to the subpanel, you should attach them to the wall tightly. It would be best if you also covered open holes using a knockout plug.
Ensure that the breaker or fuse is connected to a proper gauge wire. For instance, a 20 amp breaker or fuse must be connected to a 12 gauge wire.
Is a Permit Needed to Install a Subpanel?
Minor electrical changes won’t require a permit. However, the requirements vary depending on the jurisdiction. In most areas, an electrical inspection is only required to obtain a certificate of occupancy to allow the electric company to install the meter.
It’s therefore important to check the building codes and regulations to see whether a permit is necessary before you start work. Some jurisdictions insist on electrical work being handled only by electricians and require all changes to be inspected.
Final Thoughts on Subpanels
Having subpanels on the main panel can assist you in achieving several goals, especially if there is no room for installing additional circuits on the main panel. Even though there is no limit on the number of subpanels that you can add to a circuit, it shouldn’t exceed 160 amps when you’re using a 200 amp main panel. Always follow this guide to install subpanels effectively.