What is a Sub Panel in a Residential Electrical System?

By JDFerris | Electrical

Oct 04

What is an Electrical Sub Panel?

An electrical sub panel is essentially a separate hub at a midpoint between the main service panel, and whatever branch circuits the wiring is going to. An electrical sub panel can also be known as a service sub panel or circuit breaker sub panel. In essence, an electrical sub panel can be considered a tiny service panel.

Though not as common, even some manufactured homes make use of sub panels for the differentiation of their electrical service and circuitry.

Electrical Sub Panels Differentiate the Home’s Circuitry

Electrical panel picture from an sps inspections home inspection

For the sake of differentiation of electrical circuitry within a home, an electric sub panel will service one different area that has a discrete function, such as a cooking area, shop, workplace, or addition.

The setup of a sub panel should rarely ever be your first option when you need more space inside of your main panel. First, you should search for any slots that might be filled with available circuit breakers. Second, even if a slot is loaded, you can purchase a tandem breaker that shares one slot, however, deliver the same quantity of electrical output.

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By setting up a breaker sub panel, you make it clear that circuit breakers and branch circuits apply to which parts of your home. It is simple to segregate the responsibilities of all of the branch circuits by keeping them sequestered within the electrical sub panel.

If you have abnormally large power requirements in your home, you may even want to think about looking at something like the Plug on Neutral 225 Amp Breaker Main 42-Space 42-Circuit Indoor Load Center with Cover and Ground Bar

When the Service Panel is Inaccessible

It can become serious when a tenant in one of your rentals overloads a circuit and the circuit breaks in the central area that is inaccessible to the tenant.

Such incidents are a common scenario with any property leases where the property owner’s location is locked and inaccessible to the tenant. If the tenant’s breaker trips and the property owners are not home, the occupant has no choice but to wait until the proprietor returns.

Electrical subpanel in a garage during a home inspection by SPS Inspections
Electrical sub panel in a garage during a home inspection by SPS Inspections

With an electrical sub panel, though, the tenant can control the circuit breakers in the sub panel to reset their circuitry.

Main Service Breakers Can Shut Off

Although an electrical sub panel has its collection of circuit breakers, all running power to a specific sub panel, the sub panel is still fed from just one circuit located in the primary circuit box. A double-pole circuit breaker protects that feeder circuit itself, and this breaker can shut itself off. Most likely, the sub panel’s breakers would close down first, but if you are receiving a large volume of requests from your network or fixtures and receptacles, the possibility still does exist.

200 amp main service breaker
200 amp main service breaker

Electrical Sub Panels Can Differentiate Service

A typical factor for setting up any sub panel system is the need to separate different areas’ circuitry from each other. If perhaps, you are the owner and landlord of a duplex, or maybe if there is a mother-in-law residence on the property, it is advantageous to keep those circuits separate from the circuit that feeds into it, or the primary circuit.

The fundamental structure of an electrical sub panel is the same as a service panel, with the primary feeder wire leading into ground bus bars and neutral bus bars and circuit breakers. Sub panel wiring is the same as any other; red and black wires are your hot wires, green is ground wire, and white goes to the neutral bar. Branch wire circuits lead off of the sub panel breaker into various parts of the home, such as for new lighting or new light fixtures.

A standard amperage and voltage for a sub panel are maybe 30 amps, 240 volts. Keep in mind that a breaker sub panel does not provide extra electrical power to your home; it is merely taking energy off of the main service panel.

Sub Panels For New Light Fixtures

One of the major uses many people have for sub panels in their electrical systems, is to bring new lighting and light fixtures to a new or separate part of the home. In doing this, you are able to, as a homeowner, essentially section off your home into different electrical zones. You could have a zone for your outdoor lighting, a living room zone, heck, even a dining room zone! This way, it becomes much easier to watch and also diagnose electrical problems, or issues with wiring!

This is a picture of an ungrounded outlet found during a home inspection by sps inspections olympia
This is a picture of an ungrounded outlet found during the electrical portion of the home inspection by SPS Inspections of Olympia

Electrical Sub Panels Allow for More Space

If the main breaker box does not have adequate space to hold circuit breakers for the new circuits that you intend to set up, the electrical sub panel can produce a new area for breakers to be installed, however, in a physically separate place.

Setting up an electrical sub panel near the remodel location allows for the section of the home to be fed with a single cable from the main service panel. Many times, that cable and its routing path may already exist, given that the area having renovations might still have viable wires running to it you can reuse for your sub panel wiring.

Installing a subpanel solely for the sake of clarity is seldom an efficient means of accomplishing the differentiation you might want in your home’s circuitry. Clarity is but a favorable outcome of installing a subpanel for other reasons.

Electrical Metering Not Separate

Electrical Sub Panel Resource – Wiring Branch Circuits: How to wire a subpanel

Electrical use from the accessory residence can not be separated from the main residential area just by installing an electrical sub panel. Even when this happens, all metering still runs by the house’s main electrical meter before actually being metered.

Instead, to discern separate energy use, set up a residential renter submeter. These small systems help individually keep an eye on electrical sub-usage in 120/240V systems for rental occupants, workplace suites, and workshops.

Roof view picture of a not-so-good service drop which supplies power to the main service panel in the home
Roof view picture of a not-so-good service drop which supplies power to the main service panel in the home

Submeters do not instantly deduct energy usage info from the primary energy meter; in the majority of cases, this needs to be calculated by hand.

Electrical Sub Panels Relieve Wire Routes

For home remodel work, particularly for energy-hungry locations such as bathrooms and kitchens where you have light fixtures and appliances etc. eating up your power, several brand-new cables will many times need to be run from the primary service panel to the project location to provide power. With older homes, it can be very tough to route numerous brand-new cables and electrical wires through already closed walls, floors, and ceilings.

This is where the beauty of sub panels really begins to shine! Rather than needing to run several messy wire pigtails through different new holes you have to open up in your walls and home in order to properly run all of the wire harnesses, you can have a sub panel installed near to where you need power extended.

Now, all you need to do is connect the main electrical panel to the sub panel to supply it with the necessary electricity to run the lighting, appliances, and the rest of this electrical system section, and other items in that area of your home directly from your new sub panel location. Once this is done, wiring everything else on this branch circuit becomes much easier to deal with, and will likely require SEVERAL fewer holes in your walls to boot!

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