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Sub panel: when and how to add one
What a sub panel solves, what it doesn’t, the three cases where we install one, what the Code asks for a detached building, and the installed price.
In short
A sub panel is a secondary panel, fed by the main panel, installed close to the area it serves.
- Installed by STM-Électrique, its price is in the written quote, free of charge.
- It adds breaker spaces, not amps: if capacity is what’s missing, it solves nothing.
- In most cases, it doesn’t require a Hydro-Québec disconnection.
- For a detached building, the 2026 Code says how to ground each building supplied by the same service.
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Sub panel or main panel: the difference
The main panel is the one that receives Hydro-Québec’s supply and holds the main breaker; there is only one per dwelling. The sub panel is fed by that main panel and serves a specific area: a garage, a workshop, a finished basement.
“Distribution panel”, finally, is the generic term: any box that splits electricity into circuits is one, the main panel as well as the sub panel. A sub panel is also called a secondary panel.
It’s useful when the main panel still has capacity but no more room for new breakers. We then install it close to the new circuits, which connect to it.
A secondary panel costs less than replacing the main panel, partly because it doesn’t require redoing the service entrance. The terms are explained on our page electrical distribution panel.
Garage, basement, detached building: the three cases
The basement being finished. The new rooms need new circuits, and the main panel has no free slots left: a sub panel installed in the new area often settles it.
The attached garage or workshop. Same logic: a sub panel close to the garage’s tools and outlets, fed by a feeder from the main panel.
The detached building. It’s the most complete case, and in Mirabel, our most frequent request: double garage, workshop, shed, stable, greenhouse, machinery garage. We first calculate the load of the building to supply, based on what you plan to do in it; we then choose the cable size based on the distance, because a long run needs a bigger cable to limit voltage drop. The cable runs underground in a trench, or overhead, depending on the property; the sub panel is installed in the outbuilding with its own protection, and the building is grounded.
One point we make before the job: we don’t dig the trench. You have it dug, or you dig it yourself, and we run the wiring afterwards.
For a panel installed outdoors rather than in the outbuilding, see our guide outdoor electrical panel.
A sub panel doesn’t add amps
It’s the point we explain most often: one more box creates no amps, it shares the ones the main panel already receives.
If your house lacks room for breakers but not capacity, a sub panel is often enough. If it lacks capacity, for example a 100 amp house that’s getting an EV charger and a heat pump, the main panel needs replacing instead, and often the service entrance with it. In other words: short of room, a sub panel; short of amps, a new main panel.
To know which of the two you’re short of, looking at the panel isn’t enough: the load calculation decides, and we do it before any work.
What the Code requires for a detached building
Chapter V of Québec’s Construction Code, in its 2026 version (decree 236-2026), incorporates the Canadian Electrical Code, Part I, 25th edition (CSA C22.1:21), with Québec’s own amendments.
Québec added section 10-120, for at least two buildings or structures supplied by a single service. It provides two ways to do it: at each building, connect the circuit’s grounded conductor to a grounding electrode and to the non-current-carrying metal parts; or ground the metal parts of each building with a bonding conductor run with the feeder or branch circuit.
A building housing livestock, supplied by distribution equipment, can only be supplied the second way.
The decree also set a transition period for work started under the old text; the RBQ extended it to October 17, 2027.
On the manufacturer’s side, Siemens Canada’s instructions for a Type 1 (indoor) main breaker panel say to remove the bonding strap of a main breaker panel that isn’t used as service equipment, such as a sub panel; that’s its instruction, not a section of the Code. The same instructions point out that a permit and an inspection may be required to energize the equipment. See our guide Siemens electrical panel.
Who is allowed to install a sub panel in Québec?
The Corporation des maîtres électriciens du Québec puts it plainly: no one may carry out electrical work of any kind, in their own residence or elsewhere for others, unless they are an electrical contractor (translated from French).
Québec’s Régie du bâtiment specifies that electrical installation work requires a licence that includes subclass 16, Electrical contractor; the CMEQ qualifies its members as the government’s mandatary.
The CMEQ points out that anyone who violates the Master Electricians Act and the Building Act faces a fine of $5,000 to $200,888. STM-Électrique is a CMEQ member and holds RBQ licence 5815-0137-01.
How much does an installed sub panel cost?
At STM-Électrique, the price of an installed sub panel is in the written quote, free of charge. It depends on the distance, the number of circuits and the building to supply.
A main panel replacement, for its part, is a bigger job. Adam Chirola sums it up in one sentence: secondary panels are cheap.
In most cases, a sub panel doesn’t require a Hydro-Québec disconnection, which makes it faster than replacing the main panel.
Basement unit: sub panel or second meter?
For a unit set up in the basement, Adam Chirola, our master electrician, answers: a second Hydro-Québec meter.
What a secondary suite requires on the electrical side is explained in our guide secondary suite: the electrical side.
Frequently asked questions
What is an electrical sub panel?
It’s a secondary panel fed by the main panel, installed close to the area it serves: a garage, a workshop, a finished basement, a detached building. It adds breaker spaces where they’re needed, without changing the house’s capacity.
What’s the difference between a main panel and a sub panel?
The main panel receives Hydro-Québec’s supply and holds the main breaker; there is only one per dwelling. The sub panel is fed by it and serves one area. It redistributes the main panel’s amps, it doesn’t create any.
How much does it cost to install a sub panel?
At STM-Électrique, the price of an installed sub panel is in the written quote, free of charge. The exact price depends on the distance to cover, the number of circuits and the building to supply; it’s in the written quote, free of charge. In most cases, no Hydro-Québec disconnection is needed.
How do you install a secondary electrical panel in Québec?
Through an electrical contractor: in Québec, the law reserves this work for electrical contractors, even in your own home, and the RBQ requires a subclass 16 licence. We do the load calculation, install the sub panel and its circuits, and label each one.
Can you use a 200 amp panel as a sub panel?
A Siemens Canada document provides for it for its Type 1 (indoor) main breaker panel: if the panel isn’t used as service equipment, its instructions say to remove the neutral bonding strap. But a 200 A panel used as a sub panel doesn’t add 200 A: it shares the amps the main panel leaves it.
A garage, workshop or basement to supply?
We do the load calculation, tell you whether a sub panel is enough, and the price is written in the quote, free of charge.
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Sources
Consulted on November 3, 2026.
- Gazette officielle du Québec, decree 236-2026 (Construction Code, Chapter V, Electricity) (in French)
- Corporation des maîtres électriciens du Québec, Attention : licence obligatoire (in French)
- Régie du bâtiment du Québec, Licence (electricity) (in French)
- Siemens Canada, Loadcentre, Type 1 enclosure for indoor application, Installation instructions