Electrical Load & Wire Size Calculator

In Ontario, most electrical work requires an ESA notification and inspection. Typically, the licensed electrical contractor files it. If you’re hiring an electrician, ask for the notification number.

• New circuits, panel changes, service upgrades, garage feeds, basement wiring: usually yes.
• Minor swaps may still have rules depending on what’s being altered.

Best practice: assume it needs ESA unless your electrician confirms otherwise.

Most new-build timelines follow a predictable sequence:

• Underground/trench (if you’re burying a feeder).
• Service (meter base / mast / grounding / bonding as applicable).
• Rough-in (wiring installed, before insulation and vapour barrier).
• Final (devices, panel, labeling, cover plates, lights, equipment connected).

Your electrician coordinates the scheduling, but you can plan your build around those checkpoints.

Rough-in failures are usually simple “misses,” not dramatic disasters:

• Missing/incorrect protection (nail plates, damaged cable, unsupported runs).
• Box fill issues (too many conductors/devices in a box).
• Wrong cable routing through studs/joists or unprotected penetrations.
• Bonding/grounding not done as required at that stage.

Builder tip: don’t let anyone cover walls until rough-in is signed off.

Ontario has strict rules around who can perform electrical work, and ESA has requirements that often make DIY impractical for most real projects.

• Even if some homeowner work is allowed in limited cases, it still must meet code and inspection requirements.
• Insurance and resale implications are real—buyers and insurers may ask for proof of ESA inspection.

Practical advice: for anything beyond very minor tasks, hire a licensed electrical contractor and get an ESA inspection trail.

Yes, underground feeds typically require a trench/underground inspection before backfilling.

• Depth, protection, conduit type, warning tape, transitions, and bonding/grounding details may be checked.
• If you bury it and hope for the best, you may be digging it up again.

Final inspection goes smoother when everything is visible and complete:

• Panel labeling, breaker types (AFCI/GFCI where required), and panel cover installed.
• All devices installed (switches, receptacles, lights, fans) with cover plates.
• Equipment connected and ready to test (range, dryer, HVAC controls, etc.).
• Access to all areas: attic hatches, crawlspaces, utility rooms, garage, exterior receptacles.

Most modern custom homes land at 200A as the “normal” baseline—especially if you’re adding EV charging, hot tub, electric ranges, or future shop power.

• 100A can work for smaller/simple homes with limited electric loads.
• 200A is common for today’s typical custom home.
• 400A becomes relevant with heavy electric heating, multiple EVs, big shops, or very large homes.

Do a proper load calculation early so you don’t redesign mid-build.

A panel is “functionally full” when you’re out of safe breaker spaces or you’re stacking too many loads into too few circuits.

• Subpanel often makes sense when you need more spaces and your service size is adequate.
• Service/panel upgrade makes sense when the service capacity is the limiting factor.

Don’t let someone solve a capacity problem with a “creative” breaker arrangement. Do it properly.

A service upgrade is not just swapping a panel. It can involve:

• Meter base, service entrance, mast, weatherhead and clearances.
• Grounding electrode system and bonding details.
• Utility coordination (temporary disconnect/reconnect).
• ESA inspections at defined stages.

Timing matters: do it early enough that it doesn’t stall drywall/insulation schedules.

This is the classic “long run” question—wire size is driven by two things:

• Ampacity (what breaker size you’re feeding it with).
• Voltage drop (distance—especially long underground runs).

Use the calculator on this page in Check a Wire Size mode to verify a copper/aluminum option at your exact distance and load.

Start by listing the largest loads (welder/EV/heater) and whether they run simultaneously. Then:

• Reserve dedicated circuits for high-demand equipment.
• Leave spare breaker spaces (future-proofing is cheap at rough-in time).
• Don’t forget lighting, receptacles, door openers, and exterior plugs.

Most shop regrets come from undersizing the subpanel and running out of spaces later.

Yes, but it must be installed in a code-compliant way that prevents back-feeding the grid and protects line workers.

• Transfer switches/interlocks must be compatible with your panel and installed correctly.
• Generator sizing, neutral/ground bonding, and outdoor inlet details matter.

Bottom line: this is not the place for “YouTube engineering.” Get it inspected.

Spacing rules are intended to avoid extension cords becoming permanent decor. People get caught on:

• Long wall runs with “just one plug” planned.
• Hallways, landings, and small wall sections that still count.
• Furniture layouts: the “required minimum” isn’t always the “practical minimum.”

Kitchens are the circuit-hog of the house. Plan for:

• Counter receptacle circuits (often multiple).
• Dedicated circuits for dishwasher, microwave, fridge, and any specialty appliances.
• Range/oven requirements (often 240V).

Best practice: plan it like a workshop, not like a 1978 bungalow.

Bathrooms have special rules because water and electricity are a bad marriage.

• GFCI protection is typically required for bathroom receptacles.
• Dedicated circuits may be required depending on layout, number of bathrooms, and loads.
• Heated floors, towel warmers, and fancy mirrors can complicate things.

Future-proof it while walls are open:

• Run extra circuits to likely future rooms (bedroom, rec room, kitchenette).
• Plan a mechanical/utility zone (furnace, HRV/ERV, pumps, dehumidifier).
• Consider rough-ins for a future bar or suite (where permitted).

Adding circuits later is always more expensive than doing it now.

Modern homes need “IT closet thinking.” Consider:

• Dedicated circuit for office/tech loads (printers, computers, monitors).
• Surge protection and clean power considerations.
• Low-voltage wiring routes (Ethernet, coax, access points) before insulation.

Anywhere water is involved or likely. GFCI is required in defined locations and strongly recommended in others:

• Bathrooms, kitchens (counter areas), outdoors, garages, unfinished basements are common examples.
• Think “wet hands + electricity” = GFCI territory.

Exact requirements depend on the current OESC and your application.

AFCI rules are a frequent source of confusion. In general, many residential branch circuits require AFCI protection, but there are exceptions depending on circuit type and location.

• People get tripped up (pun intended) when adding a circuit and discovering it now needs AFCI.
• Some specialty loads may have different requirements.

When in doubt, assume AFCI is required and confirm with your electrician/ESA inspector.

• GFCI: protects people from shock (ground-fault).
• AFCI: helps prevent fires from arcing faults (damaged cords, loose connections).
• Dual-function: does both AFCI + GFCI in one breaker.

Choosing the right one depends on where the circuit is and what it serves.

Common causes include:

• Shared neutrals, wiring errors, or poor terminations.
• Problem devices (some motors, older appliances, damaged cords).
• Loose connections that create arcing signals.

Best approach: isolate the circuit systematically (loads off, inspect connections, test devices). Don’t just swap breakers and pray.

Whole-home surge protection is increasingly common because modern homes are packed with electronics (appliances, controls, heat pumps, smart systems).

• It’s typically installed at the main panel (or service equipment) by your electrician.
• It works best combined with good grounding/bonding practices.

Voltage drop matters most when runs get long or loads get heavy:

• Garage/subpanel feeds, well pumps, far-end bedrooms, long outdoor runs.
• Symptoms: dimming lights, motors struggling to start, nuisance tripping.

Use the calculator on this page to test different distances and wire sizes with a 3% or 5% planning target.

Aluminum is common for larger feeders because it’s lower cost, but it requires correct methods:

• Correct lugs/terminations rated for aluminum conductors.
• Proper torque, anti-oxidant paste where required, and correct connector types.
• Good workmanship matters more with aluminum.

There isn’t one universal answer—equipment ratings and installation conditions control it. But the sizing process is consistent:

• Use the nameplate rating (amps/watts) and voltage.
• Determine if it’s continuous (often yes for EV/baseboards).
• Select breaker and wire size accordingly, then check voltage drop if the run is long.

For big loads, always size to the manufacturer specs and code requirements.

Continuous loads are loads expected to run for extended periods (often 3+ hours). Many heating loads and EV charging fall into this category.

• The circuit must often be sized so the continuous load does not exceed 80% of breaker rating.
• That’s why the planning factor is commonly shown as 125%.

Different areas call for different protection levels:

• NMD90 is common for typical residential concealed wiring.
• Armoured cable or conduit is often used where wiring is exposed or subject to damage.
• Garages, unfinished basements, mechanical rooms and outdoors may need more robust methods.

Your electrician chooses based on code and the physical realities of the space.

The intent is to keep wiring protected from nails/screws and structural damage:

• Proper hole placement in framing members (and avoid weak drilling patterns).
• Nail plates where cable is too close to the face of studs.
• Secure supports and avoid sharp edges.

This is one of the areas inspectors look at closely during rough-in.

Bonding and grounding are about safety: ensuring metal systems don’t become energized hazards and that fault current has a safe path.

• Main bonding conductor and grounding electrode system must be done correctly.
• Metal water piping and other conductive systems may require bonding depending on configuration.
• Details vary with service type and building systems.

This is not a place for “close enough.” Get it right and get it inspected.

Common causes include:

• Loose neutral or poor terminations (panel, meter, device connections).
• Undersized conductors on long runs (voltage drop).
• Large motor starts (compressors, pumps) causing brief inrush sag.
• Utility-side issues (less common, but possible).

If it’s consistent or getting worse, treat it as a real electrical issue—not a “quirk.”