A subpanel adds capacity to a home — either because the main panel is full or because new circuits go to a remote area (basement renovation, garage, addition, ADU). The work involves heavy-gauge feeder wire, a subpanel enclosure, breakers, and grounding/bonding. In Ontario, this is licensed-electrician work — homeowners can do their own electrical with an ESA homeowner permit, but most go through a licensed electrician to avoid mistakes.
This guide explains the typical scope, code requirements, and what's involved. It's not a how-to for unlicensed work — the safety and legal stakes are too high. Use as understanding for planning.
Before you start
Three things to settle:
1. Sized to load. Subpanel size: 60A, 100A, 125A, 200A typical. Sized to the connected loads. Basement subpanel for a renovation: typically 60A or 100A. Whole-addition subpanel: 100A or 200A. Right-sizing prevents future capacity issues.
2. Three-wire feeder + ground. Subpanel feeder is 4 wires: 2 hot (red and black), 1 neutral (white), 1 ground (bare or green). Older 3-wire feeder (no separate ground) is no longer code-compliant for new subpanels.
3. ESA permit + inspection mandatory. Ontario: any electrical work requires ESA permit. Subpanel installation includes panel-side connections — inspector signs off after inspection. Without permit/inspection: insurance issues, sale issues, code violations.
What you'll need
Tools
- Drill with bits (for cable routing)
- Wire strippers and crimpers
- Voltage tester
- Multimeter
- Adjustable wrench
- Screwdrivers
Materials
- Subpanel (matching capacity)
- Subpanel feeder wire (typically 6 AWG for 60A, 4 AWG for 100A, 2 AWG for 125A — gauge per electrician)
- Bonding bushings (for connecting ground)
- Breakers (matched to subpanel manufacturer)
- Conduit (if running through unfinished space)
- Wire connectors (split-bolts, twist-on for circuits)
- Disconnecting means at the main panel (breaker)
Subpanel ground is separate from neutral
In a subpanel, the neutral bus and ground bus are NOT connected — bonded only at the main panel.
This separation prevents ground-loop issues and keeps neutral current off the ground path.
Older homes sometimes incorrectly bond neutral and ground at subpanel — code violation; correct during renovation.
Step-by-step instructions
Calculate subpanel capacity needed
Sum the loads going on the subpanel: lighting, outlets, appliances.
Add 25% margin.
Match to nearest standard subpanel size: 60A, 100A, 125A.
If unsure: hire electrician for load calculation.
Plan feeder route from main panel
Direct route from main panel to subpanel.
Through finished walls: requires opening drywall and patching.
Through unfinished basement/joists: easier.
Length: feeder wire gauge depends on length and subpanel size. 100A subpanel at 100 ft: typically 4 AWG copper or 2 AWG aluminum.
Pull permit through ESA
ESA online portal for homeowner permit OR electrician pulls.
Specify scope: subpanel install, sizing, location.
An ESA permit fee applies; check the current schedule on the ESA portal.
Shut off main and verify dead
Main breaker off.
Verify with voltage tester at main panel — no voltage anywhere.
Even with main off, the line side (utility side) of main breaker is still live. Don't touch.
Mount subpanel enclosure
Install subpanel on wall in planned location.
Bolt to wall studs through pre-drilled mounting holes.
Verify level.
Run feeder wire
Feeder wire from main panel to subpanel.
Through conduit in unfinished space, or through walls.
Pulling wire: lubricant helps for long runs.
Leave 12-18 inches extra at each end for connections.
Connect feeder to subpanel
Two hot wires: to subpanel main lugs.
Neutral wire: to neutral bus.
Ground wire: to ground bus (separate from neutral in subpanel).
Verify all connections firm with proper torque per panel manufacturer.
Install branch circuits in subpanel
Each new circuit gets a breaker in the subpanel.
Standard breaker types per manufacturer (Square D Homeline, Eaton CH, etc.).
Connect circuit hot to breaker, neutral to neutral bus, ground to ground bus.
Connect feeder breaker at main panel
Feeder breaker at main panel: matched to feeder wire gauge.
Two-pole breaker (covers both hot conductors).
Verify all connections firm.
Re-energize main breaker after all work complete.
Schedule and pass ESA inspection
Inspector verifies: sizing, grounding, bonding, breaker selection, all connections.
Pass: signed inspection.
Fail: fix issues, then book a re-inspection (a re-inspection fee applies).
Common mistakes that cost you
- Bonding neutral and ground at subpanel. Code violation; ground loop. Separate bus.
- Wrong feeder gauge for length. Voltage drop at distant subpanel. Calculate per length and size.
- DIY without ESA permit. Insurance won't cover; code violation. Always permit.
- Working live. Real risk of injury. Always main off, voltage-test before contact.
- Wrong breaker brand for panel. Wrong breakers don't fit/work properly. Match manufacturer.
Frequently asked questions
Can I install a subpanel myself in Ontario?
Yes, with ESA homeowner permit and inspection.
Most homeowners hire a licensed electrician for this scope — too easy to make mistakes.
The trade-off is electrician labour versus hours of your own time plus the risk of a code violation.
What drives the cost of a subpanel install?
DIY means materials plus the ESA permit. Hiring an electrician adds labour for the feeder run and termination.
Cost varies with feeder length, panel size (amperage), and complexity — a long run to a detached garage costs more than a short run to an adjacent room.
What size subpanel for a basement renovation?
Typical basement: 60-100A. Lights, outlets, occasional plug-in appliance.
With electric heat or AC: 100-150A.
ADU/secondary suite: often 200A separate panel.
Calculate based on actual loads.
When to call us instead
Subpanel work is part of every basement renovation and addition we run. Licensed electricians handle the panel-side work; we coordinate the entire project.
Book a free 60-minute site visit →Related Ottawa services
If your renovation needs added electrical capacity, our team coordinates with licensed electricians and handles permits. Book a free 60-minute consultation.