Most Canadian commercial buildings are served at one of two three-phase voltages: 120/208 V or 347/600 V. Smaller buildings with mostly receptacle and light equipment loads are often served at 120/208 V. Larger buildings, and those with big motors or long feeders, usually use 347/600 V and step down to 120/208 V only where it is needed. The choice affects feeder sizes, lighting, equipment selection and safety procedures for the life of the building.
The 347/600 V system is largely a Canadian feature. Much of the commercial equipment and advice you find online is written for United States systems, where 277/480 V is the common higher voltage. That difference catches out owners and contractors who order equipment without checking the voltage on the nameplate.
What the two numbers mean
Both are wye systems: three phase conductors and a neutral connected to the centre point of the transformer's secondary. The first number is the voltage from any phase to neutral; the second is the voltage between any two phases. The second is always about 1.73 times the first, which is the square root of three, because of the way the three phases are spaced in time.
- 120/208 V: 120 V phase to neutral, used for receptacles and small loads; 208 V phase to phase, used for larger single-phase and three-phase equipment.
- 347/600 V: 347 V phase to neutral, used mainly for lighting; 600 V phase to phase, used for motors, mechanical equipment and feeders to step-down transformers.
Houses use a different arrangement, single-phase 120/240 V, which is why some equipment is rated 240 V rather than 208 V.
How each building is laid out
In a 120/208 V building, the service feeds panelboards directly, and every load runs at 120 V or 208 V. In a 347/600 V building, the service feeds motors and lighting at full voltage and uses transformers near the receptacle loads to make 120/208 V. Because the higher voltage carries the same power with about a third of the current, its feeders are much smaller.
Side by side
| Factor | 120/208 V | 347/600 V |
|---|---|---|
| Typical buildings | Small commercial, retail units, low-rise multi-unit residential | Larger commercial, institutional, industrial, high-rise |
| Current for the same power | Higher | About a third as much |
| Feeder and switchboard size | Larger for the same load | Smaller, especially on long runs |
| Lighting | 120 V or 208 V | 347 V fixtures and drivers |
| Receptacles | Directly from panels | Through step-down transformers |
| Large motors | Possible, but large currents | Well suited |
| Hazard to workers | Serious | Higher; more demanding procedures and PPE |
Practical issues owners run into
Equipment rated 240 V on a 208 V supply
Many heaters, appliances and EV chargers are rated for 240 V, the residential voltage. Some will run on 208 V, but resistive heaters deliver only about three quarters of their rated output at the lower voltage, and some equipment will not work properly at all. Check the nameplate and the manufacturer's information for 208 V operation before ordering.
Ordering equipment for 480 V by mistake
Equipment built for the United States market is often rated 480 V. It is not suitable for a 600 V system without a transformer and may not carry the Canadian approvals needed for use here. Mechanical equipment, motors and drives should be specified at 600 V for a 347/600 V building, and approved for use in Canada.
347 V lighting circuits
Lighting circuits in a 347/600 V building operate at a voltage well above what people are used to from household wiring. Fixtures, drivers, sensors and switches must be rated for 347 V, and anyone working on them must treat them accordingly. Replacing a fixture with a 120 V product on a 347 V circuit can destroy it and create a hazard.
Balancing single-phase loads
Receptacles and most lighting are single-phase loads connected between one phase and neutral. In either system, designers spread them across the three phases so each carries a similar share. When renovations keep adding circuits to whichever breaker spaces happen to be free, one phase can end up carrying much more than the others. The result is a feeder or transformer that is overloaded on one phase while the panel schedule suggests spare capacity. Measuring phase currents during a load study shows whether this has happened.
Checks before ordering equipment
- What is the voltage and phase of the circuit it will connect to?
- Is the nameplate voltage the same, or is the manufacturer's rating for 208 V or 600 V operation confirmed in writing?
- Is the equipment approved for use in Canada?
- Does the output or performance change at the building's voltage?
- Is there spare capacity and a breaker space at the right voltage near where it will go?
Safety procedures
Both systems are dangerous. At 600 V, available fault currents and arc flash hazards can be significant, and approach boundaries are larger. Work on either system is done by qualified workers following an electrical safety program based on CSA Z462, and installation is done by licensed electrical contractors under permit.
Choosing for a new or converted building
The utility decides which services it offers at a given site and size, so the first step is to ask. Beyond that, the choice comes down to the size of the building, the mix of loads and the distances involved. A small retail plaza with a few rooftop units and mostly lighting and receptacle loads may be simplest at 120/208 V. A mid-rise office with central mechanical plant, long risers and a parkade is almost always better at 347/600 V.
Take a typical case: an older two-storey building served at 120/208 V is being converted for a use with heavier mechanical loads and EV charging. A load calculation shows the existing service would need to be very large at 120/208 V. Changing to a 347/600 V service, with a transformer feeding the existing 120/208 V panels, keeps the existing branch wiring in use while giving the mechanical equipment and chargers a more economical supply. Whether that is the right answer depends on the utility's offer, space for new equipment and the cost of the change, which the design compares.
How ehZee can help
We help owners choose the service voltage for new buildings and evaluate conversions for existing ones as part of our power distribution design work. For more background, read three-phase power basics and transformers in commercial buildings.
Common questions
Why is it 208 V and not 240 V?
In a three-phase wye system, the voltage between two phases is 120 V times the square root of three, which is about 208 V. The 240 V found in houses comes from a single-phase system where the two halves of the transformer winding are in series.
Can a building have both?
Yes. Most 347/600 V buildings also have 120/208 V, made by transformers inside the building. The service voltage is the one delivered by the utility.
How do I tell which system my building has?
The single-line diagram and the nameplate on the main switchboard or service equipment state the voltage. Panel labels usually show it too. If none of these are clear, ask a licensed electrician or engineer to confirm it rather than opening equipment yourself.
Does the higher voltage save energy?
It reduces conductor losses on long feeders because the current is lower. Transformers add their own losses, so the overall saving depends on the layout. The bigger benefit is usually lower cost for conductors and equipment.