What a subpanel is
A subpanel is a second, smaller panel fed from your main panel. A large two-pole breaker in the main panel feeds a set of conductors, called the feeder, out to the subpanel. The subpanel then splits that power into its own branch circuits, each with its own breaker.
Think of it as a branch office for your electrical system. It puts breakers closer to where the circuits are used and gives you more spaces for new circuits.
When a subpanel makes sense
- Detached garage or shop. One feeder to the garage is neater than several long circuits, and lets you add a heater, workbench circuits and an EV charger later. See garage and workshop wiring.
- Basement development or secondary suite. A subpanel in the basement keeps new circuits short. For a legal suite, occupants generally need access to the breakers that serve their unit, which often means a subpanel inside the suite. Confirm the requirement with your electrician and the permit office.
- Additions. A new wing far from the main panel is easier to wire with a local subpanel.
- A full main panel. If the service has capacity left but there are no spaces, a subpanel adds room. Compare the options in when your panel is full.
A subpanel is also handy when circuits have to travel a long way. Long runs of small wire lose voltage, which shows up as dim lights or tools that bog down. A feeder sized for the distance, with short circuits from a local subpanel, solves this neatly.
For a business, the same idea applies to a tenant space, a shop floor or a rooftop equipment area.
A subpanel does not add power
This is the most common misunderstanding. A subpanel gives you more breaker spaces and shorter circuits, but every amp it supplies still comes through your main service. If your service is already near its limit, adding a subpanel will not fix that.
Before a subpanel is added, a licensed electrician should do a load calculation to confirm the service can carry the new loads. If it cannot, the answer is a service upgrade, possibly with a subpanel as part of the plan.
How a subpanel differs from the main panel
Inside, a subpanel looks much like a main panel. One important difference is how the neutral and ground are handled. In the main service panel they are bonded together at one point. In a subpanel they are kept separate, with the feeder bringing both back to the main panel.
Getting this wrong can put current on metal parts and water lines where it does not belong. Detached buildings can have extra grounding requirements of their own. These details are why subpanels are installed by licensed electricians under a permit.
Installing a subpanel means working in the main panel and sizing the feeder, breaker and grounding to the Canadian Electrical Code. It needs a permit and an inspection in Alberta.
Planning a subpanel
A little planning makes the subpanel useful for years. Things to think about before your electrician quotes:
- What you will run there, now and in five years: heaters, tools, an EV charger, a hot tub, a kitchen.
- Location. The panel needs clear working space in front of it, and should not be in a bathroom, clothes closet or over stairs.
- Spaces. Choose a subpanel with more spaces than you need today.
- The route. Distance and whether the feeder runs through finished walls or underground affects the cost more than the panel itself.
Your electrician will also ask a few practical questions: is the area finished or unfinished, will the subpanel ever feed a suite or a business use, and is there room in the main panel for the feeder breaker. If the main panel is old or full, replacing it at the same time is sometimes simpler than adding a subpanel to it.
For businesses, the same planning applies to a new tenant area, a shop floor or a mechanical room. A subpanel close to the equipment shortens circuits, makes maintenance easier and keeps a fault in one area from affecting others. See tenant improvements.
Alberta Electrical designs and installs subpanels for garages, suites and commercial spaces, including the permit and inspection.
Common questions
Will a subpanel let me add an EV charger on a 100 A service?
Only if the service has capacity to spare. The subpanel adds spaces, not power. A load calculation, and possibly EV load management, decides whether it works.
What size subpanel do I need?
It depends on the loads it will serve and the capacity of your service. Your electrician sizes the feeder and breaker from a load calculation.
Can a subpanel go in a detached garage?
Yes, it is one of the most common uses. The feeder usually runs underground, and the garage typically needs its own grounding arrangement.
Can I put a subpanel in my basement for a future workshop?
Yes. Many homeowners add a subpanel during a basement development so future circuits are easy to add. Size it for the tools and heaters you expect to use.
Does a basement suite need its own panel?
Suite occupants generally need access to the breakers serving their unit, so a subpanel in the suite is common. Your electrician and the permit authority will confirm what applies.
Codes and permit rules change and every building is different. For work on your system, talk to a licensed electrician and your local permit authority.