June is when the calls for detached garage and workshop sub-panels stack up. The reno is booked, the framing crew wants power for tools next week, and the homeowner has a one-line quote from someone that says "60A sub-panel - $X." That number is almost never the real number. A sub-panel feed to a detached structure involves the trench, the feeder conductor, the conduit, the ground rod at the remote, and a neutral-handling decision that has to be made before the conductor is pulled. Here is what the job actually looks like on the ground.
Why a sub-panel is usually the right answer
The alternative is running three or four individual branch circuits out to the garage from the main panel. That works for a single-circuit shed - a light and a couple of receptacles. It does not work for a workshop. The reasons we steer almost every garage install to a sub-panel:
- One trench, one feeder. You dig once and pull one cable, not three or four separate runs. The trenching cost dominates the price on a long run - the conductor cost is secondary.
- Local disconnect. Code requires a means of disconnecting power at the remote structure. A sub-panel with a main breaker satisfies that on its own. A pile of individual circuits does not.
- Future-proofing. A sub-panel with eight or twelve spaces lets you add the welder circuit, the dust collector, the air compressor, or eventually a Level 2 charger without going back to the main house panel.
- Branch-circuit work happens at the garage. Once the feeder lands, every downstream change is local. No more pulling cable from the basement panel through a finished ceiling.
Feeder sizing - 60A is the floor, 100A is the common pick
The two sizes we install for most residential detached structures are 60A and 100A feeders. The right pick depends on what is going to live in the garage.
- 60A feeder covers lighting, general-purpose 15A and 20A receptacles, a 240V receptacle for a welder or dust collector, and a small workshop heater. Real continuous load is rarely above 30-40A. Common conductor: #6 AWG copper or #4 AWG aluminum.
- 100A feeder is what we install when the customer plans an EV charger out there, a serious workshop heater, or a future legal secondary suite. Common conductor: #3 AWG copper or #1 AWG aluminum.
- Anything bigger than 100A to a residential detached garage almost always means the project is a separate service or a true accessory dwelling. Different conversation, different permit.
Voltage drop matters past about 25 metres. For a 30-metre run on a 60A feeder we typically upsize the conductor one step so the lights at the garage aren't dimming when the table saw starts. The math is straightforward but it is math worth doing - not a guess at the truck.
Trench depth and conduit in Ontario
The OESC trench depth rules are not negotiable and they are not "deep enough is fine." The two numbers that matter:
- 450 mm minimum cover for underground cable that is either direct-burial rated or in non-metallic conduit.
- 150 mm minimum cover if you are in rigid metal conduit and you have a slab or paving above. Effectively only used at the house wall transition.
For practical work, plan the trench at 600 mm. That gives you headroom for the sand bedding, the cable, sand cover, the warning tape required above the cable, and the topsoil. A trench that came up exactly at 450 mm and then settled three inches the following spring is a finding waiting to happen - we have dug them up.
Conduit selection comes down to two real options:
- Rigid PVC conduit with RW90 conductors pulled through. Cheapest, easiest to work with, code-compliant, and what we use on most residential detached-garage runs. Use long-radius sweeps, glue every joint, and bring the conduit up at both ends with a sealing fitting against moisture migration.
- TECK90 armoured cable, direct buried. No conduit needed - the armour is the mechanical protection. We use TECK on rocky cottage runs where chasing PVC through buried rock is brutal, and on commercial runs where the spec calls for it. More expensive per metre than PVC plus conductors.
NMWU direct-buried with no conduit is permitted in some configurations but we almost never use it - re-pulling a fault later means digging the trench again, which nobody wants.
The four-conductor neutral question
This is the part the YouTube tutorials get wrong and the part the inspector will absolutely check. A sub-panel in a detached structure is fed with four conductors: two hot, one neutral, one bonding conductor. The neutral and the bonding conductor are separate at the sub-panel - the neutral bus is isolated from the cabinet, and the bonding conductor lands on the cabinet ground bus. Same as any sub-panel.
What changes at a detached structure: code also requires a grounding electrode (a ground rod, or two) driven at the remote structure, bonded to the sub-panel ground bus. So you have a bonding conductor running back to the house grounding electrode and a local ground rod at the garage. Both. Not one or the other. This catches people who learned wiring on the older three-conductor sub-panel rules from decades ago - those rules changed and any inspector under 55 will fail a three-wire feed to a detached structure on sight.
What the install day actually looks like
For a representative 60A sub-panel install to a detached garage 20 metres from the house panel, on a 200A main service with capacity available:
- Site visit and quote. Walk the route, confirm the panel has capacity, note any obstacles - septic field, gas-line locates, existing landscape lighting. Quote in writing.
- Locates and excavation. Ontario One Call before any digging - mandatory and free. Trench dug to 600 mm, sand bedding laid in.
- Conduit and cable. Rigid PVC sweep up the house wall, run the full length, sweep up at the garage. Pull RW90 conductors through. Sand cover the cable, lay the orange warning tape, backfill.
- Sub-panel install. 12-space sub-panel (Siemens, Eaton, or Schneider) mounted inside the garage on plywood backing. Main breaker matched to the feeder size. Neutral bus floated, ground bus bonded to the cabinet.
- Ground rod at the garage. Driven just outside the wall, bonded to the sub-panel ground bus with #6 bare copper.
- House-end termination. Feeder lands on a 2-pole breaker matched to the feeder size at the main panel. Existing space if available; we covered the math for when you don't have one in our panel replacement post.
- Branch circuits inside the garage. Lighting, general-purpose receptacles (GFCI where required), 240V receptacle for the welder or compressor.
- ESA permit and inspection. Permit was pulled at the start. Inspection happens once everything is energized.
Realistic time on site: one full day for the trench, conduit, and cable, plus a half-day for the sub-panel and branch work. Two days if the trench is long or the soil is rocky.
Common owner mistakes we get called to fix
- The extension cord. An outdoor-rated extension cord from the house to the garage, sometimes with three or four cords daisy-chained. We have removed these. They overheat, they crack at the connectors, and they are not legal as a permanent installation.
- The three-wire feed. Neutral bonded to ground at the sub-panel because that is what someone's uncle did in 1980. Inspector will fail it, and the parallel neutral-ground path is a real shock hazard.
- No local ground rod. Feeder run, sub-panel installed, no ground electrode at the remote. Code violation. Easy to fix during install, painful to fix once the slab is poured.
- Sub-panel rated wrong. A 100A sub-panel buswork fed by a 60A breaker is fine. A 60A sub-panel fed by a 100A breaker is not - the bus cannot handle a fault that the upstream breaker won't see. Match the bus to the feeder or oversize the bus.
- Trench too shallow. Owner dug their own trench at 12 inches because that was as deep as the rented machine got before hitting clay. Has to be redone.
What the ESA permit covers
The permit covers the feeder, the sub-panel, the grounding, and any branch circuits installed under the same job. We pull it in our name as the LEC and the inspector signs off after the work is energized. For more on what the inspector actually checks, see our ESA permit post.
When to call us
If you have a backyard workshop, a detached garage, or a future-EV-charging garage and you are scoping the sub-panel work, we do this routinely across Hamilton, Dundas, Burlington, Waterdown, Ancaster, Stoney Creek, Oakville, and across Muskoka. Service-upgrade and sub-panel work is most of what we do day-to-day. Send us a photo of your main panel and a rough trench length and we can quote the install in writing. Request a quote.