Why did half my house lose power but the other half still works in Calgary?

When half your house loses power while the other half still works, the most likely cause is a lost phase — one of the two 120-volt legs supplying your home has been interrupted, either at the utility transformer, the service entrance, or inside your electrical panel. This is a common and potentially serious issue that requires prompt attention, and understanding why it happens will help you respond correctly.

Your home receives power through two hot wires (called "legs" or "phases"), each carrying 120 volts, plus a neutral wire. These two legs combine to provide 240 volts for large appliances like your range, dryer, and central air conditioning, while individual 120V circuits are split between the two legs. Your breaker panel alternates circuits between the two legs — odd-numbered breaker slots on one leg, even on the other. When one leg loses power, every circuit on that leg goes dead while circuits on the other leg continue operating normally. You will notice that roughly half your outlets and lights stop working in a pattern that does not correspond to rooms — some rooms may have lights that work and outlets that do not, because the lights and outlets are on different legs.

The most common cause in Calgary is a problem at the utility level. A blown transformer fuse on one phase, a loose connection at the utility pole, or storm damage to the overhead service line can drop one leg. During Calgary's severe weather events — chinook winds, heavy snow loads, summer thunderstorms, and ice storms — utility connections are particularly vulnerable. If you suspect a utility-side issue, contact ENMAX at 403-514-6100 (or FortisAlberta at 1-866-717-3113 if you are outside Calgary city limits). The utility is responsible for everything from your meter base to the street.

A loose or failed connection at your meter base or service entrance can also cause a lost phase. Calgary's chinook cycling — those rapid 20 to 30 degree temperature swings — causes thermal expansion and contraction at the meter base connections over time. The main service entrance cable connections and the meter jaw contacts can loosen gradually, eventually failing on one leg. If you notice the problem comes and goes, especially during temperature changes, a loose service entrance connection is a strong possibility.

Inside the panel, a failed main breaker can lose one leg while the other continues to pass. The main breaker is a double-pole device, and internal failure of one pole will produce exactly this half-house-dead symptom. Similarly, a loose connection at the main lugs — where the service entrance cables terminate inside the panel — can interrupt one leg.

There is an important safety concern with a lost phase: 240V appliances may behave strangely and can be damaged. With only one leg active, your range, dryer, or air conditioner may appear to partially work — a dryer might tumble but not heat, for example. Unplug or turn off 240V appliances until the issue is resolved to prevent damage to motors and electronics.

Do not open your electrical panel to investigate this yourself. The panel contains energized bus bars carrying up to 200 amps, and the service entrance side of the main breaker is always live even when the breaker is off. A licensed electrician with proper equipment will safely diagnose whether the issue is on the utility side (ENMAX's responsibility) or the homeowner side (your responsibility). A service call for this diagnosis typically costs $125 to $300 in Calgary. If the meter base or service entrance needs repair, the work requires coordination with ENMAX for a disconnect and reconnect, an electrical permit through the City of Calgary, and inspection by a Safety Codes Officer. A full service entrance repair or replacement typically runs $3,000 to $4,500. If half your house has lost power, Calgary Electrical Services can help you find a licensed electrician quickly through the Calgary Construction Network.