Service Entrance & Panel Installation
Residential service types, 120/240V systems, service masts, panel clearances, main bonding jumpers, and service conductor sizing.
- Describe the standard residential electrical service in Canada
- Explain the voltage relationships in a 120/240V, 3-wire system
- State the minimum service size for a single dwelling unit
- Identify service mast height and conductor sizing requirements
- Apply panel clearance and working space requirements
- Explain the function of the main bonding jumper
Lesson 1
Residential Service Types & 120/240V Systems
The Standard Canadian Residential Service
The standard residential electrical service in Canada is single-phase, 120/240V, 3-wire. This system delivers power from the utility transformer to the dwelling using three conductors - two hot (ungrounded) conductors and one neutral (identified) conductor.
How the 120/240V System Works
The utility transformer has a center-tapped secondary winding. The center tap is the neutral point. The two ends of the winding are the hot conductors (Line 1 and Line 2).
- Hot to neutral = 120 volts (for standard receptacles, lighting)
- Hot to hot = 240 volts (for ranges, dryers, water heaters)
In a 120/240V system, the voltage that appears between the two hot conductors is 240 volts. This is because the two hot legs are 180 degrees out of phase - they add together rather than cancel.
Exam Tip
When the exam asks about voltage between the two hot conductors in a 120/240V system, the answer is always 240 volts. Hot to neutral is 120V. Hot to hot is 240V.
Minimum Service Size
According to the Ontario Electrical Safety Code, the minimum service size for a single dwelling unit is 100 amperes. Most new homes are installed with 200A service to accommodate modern electrical loads including electric heating, EV chargers, and high-demand appliances.
The standard residential service in Canada is single-phase, 120/240V, 3-wire. The minimum service for a dwelling unit is 100 amperes, and the voltage between the two hot conductors is 240 volts.