Full is not the same as overloaded
A panel can be full in two different ways. It can run out of spaces, with every slot holding a breaker. Or it can run out of capacity, with the service close to its limit. These are separate problems with different fixes, and confusing them is how people end up paying for the wrong job.
Many Edmonton homes with 100 A panels installed in the 1970s and 80s run out of spaces long before they run out of capacity, especially after a basement development. Others have spaces left but are near their limit once a heat pump or EV charger arrives.
Tandem breakers
A tandem (or twin) breaker fits two 120 V circuits into one space. They are a legitimate solution, but only where the panel's label says tandem breakers are allowed, and only in the specific positions and quantities it lists. Many panels allow none, or only a few.
If your panel already has several tandems, it is a sign it has been stretched. Adding more where the label does not permit it is a code violation and can overheat the bus.
Installing any breaker means working inside the panel next to live parts. A licensed electrician will check the panel label, the breaker listing and the load before adding anything.
Your options
| Option | Fixes | Good when |
|---|---|---|
| Tandem breakers | Spaces (a few) | The panel allows them and you need one or two circuits |
| Subpanel | Spaces | Capacity is fine and new circuits are in one area, like a garage or basement |
| Larger panel, same service | Spaces | The panel is old or awkward anyway and capacity is fine |
| Service upgrade | Spaces and capacity | You are adding big loads like an EV, heat pump or suite |
| Load management | Capacity | One big new load, usually an EV charger, can share capacity |
Read more in subpanels explained and 100 A vs 200 A service.
How to tell which you need
- List what you want to add, now and in the next few years: circuits, appliances, a suite, a charger.
- Count spare spaces and note any tandems. Our guide to reading your panel shows what to look for.
- Get a load calculation. It tells you whether capacity is the problem. See load calculation basics.
- Check the panel's condition and type. An older panel or one insurers ask about may be worth replacing regardless. See obsolete and problem panels.
Be wary of quick fixes. Two wires under one breaker screw, a circuit tapped off another in a junction box, or a breaker borrowed from a different panel brand all appear in older Edmonton homes, and all of them tend to show up on inspection reports and insurance questionnaires.
With those answers, the choice is usually clear. If capacity is fine, add spaces. If capacity is short, upgrade or manage the load. If the panel itself is tired, replace it and size it for the future.
For businesses
Commercial panels fill up the same way, usually one tenant change at a time. Before a fit-out, ask for an updated panel schedule showing what each breaker feeds and how much load is on each phase. A load calculation and a tidy schedule often show that spaces can be freed by removing circuits for equipment that left years ago.
If the panel serves several tenants or a mix of old and new equipment, a new distribution panel or subpanel near the new loads is often cleaner than squeezing in more breakers. See three-phase power basics.
Planning for the future
Whichever option you choose, leave room. A new panel or subpanel with plenty of spare spaces costs little more than one that is full on day one, and saves the next round of this problem.
- Choose a panel with more spaces than you need today.
- If you think an EV, heat pump or hot tub is coming, size the service for it now.
- Ask for the new panel to be clearly labelled. See how to label your panel.
Alberta Electrical provides panel replacements, subpanels and service upgrades, with permits and inspections handled for you. What drives cost is the option you choose, the number of circuits to move and the distance between panels.
Common questions
Are tandem breakers safe?
Yes, when the panel is designed for them and they are installed in the positions the label allows. They are not safe in panels that do not permit them.
Will a subpanel fix my tripping main breaker?
No. A tripping main means the whole service is near its limit. A subpanel only adds spaces. You need load management or a service upgrade.
Can two circuits share one breaker?
Generally no. Each breaker terminal is designed for a specific number of conductors, and doubling up can overheat. An electrician will find a proper solution.
Do I need a permit to add a subpanel or replace a panel?
Yes. Both need an electrical permit and inspection in Alberta. Your electrician arranges them.
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.