Service Entrance Design: Utility Coordination That Makes or Breaks Your Project Timeline
The utility doesn't care about your construction schedule. A service entrance application takes 4–12 weeks — and if your load letter is wrong or your CT cabinet doesn't match the LDC's approved list, you restart the clock.
Service Types in Ontario
| Service Type | Voltage | Typical Application | Metering |
|---|---|---|---|
| 120/240V 1Φ | 240V single-phase | Residential, small retail | Self-contained meter (200A max) |
| 120/208V 3Φ | 208V three-phase wye | Small commercial, offices | Self-contained or CT metering |
| 347/600V 3Φ | 600V three-phase wye | Industrial, large commercial | CT metering required |
| 4.16kV / 13.8kV | Medium voltage | Large industrial, campus | VT/CT metering, customer substation |
The Load Letter
Every service application starts with a P.Eng-sealed load letter specifying connected load, demand load (CEC Section 8), service size in amps, voltage, and 20–25% future allowance.
CT Cabinet & Metering
| Service Size | Metering Type | CT Ratio |
|---|---|---|
| ≤ 200A | Self-contained meter base | N/A |
| 201–400A | CT metering | 400:5 |
| 401–800A | CT metering | 800:5 |
| 801–1200A | CT metering | 1200:5 |
| 1201–2000A | CT metering | 2000:5 |
Critical: CT cabinets must be from the LDC's approved equipment list. Hydro One, Toronto Hydro, and Alectra each have different approved models. Wrong CT cabinet = rip out and replace at your cost.
Service Conductor Sizing (CEC Rule 4-006)
| Service Size | Min Conductor (Cu, 90°C) | Conduit |
|---|---|---|
| 200A | 3/0 AWG | 2" |
| 400A | 500 kcmil | 3" |
| 600A | 2 × 3/0 AWG per phase | 2 × 2" |
| 800A | 2 × 350 kcmil per phase | 2 × 3" |
| 1200A | 3 × 350 kcmil per phase | 3 × 3" |
| 2000A | Bus duct | Bus duct |
Grounding Electrode System (CEC Rule 10-700)
- GEC — sized per CEC Table 17
- Ground rod — 3m driven copper-clad, 16mm diameter
- Water pipe bond — within 1.5m of building entry
- Ufer ground — 6m of #4 AWG bare copper in footing
Utility Coordination Timeline
| Phase | Duration | Action |
|---|---|---|
| Load letter submission | Week 0 | P.Eng sealed load letter + site plan |
| Offer to connect | Weeks 4–8 | LDC reviews and issues conditions |
| Accept + pay contribution | Week 8–10 | Capital contribution if required |
| LDC installs transformer | Weeks 10–16 | Pad-mount or pole-mount transformer |
| Service connection | Week 16+ | After ESA inspection, LDC energizes |
Pro tip: Submit the load letter as early as possible — even before detailed design. Use conservative estimates. Easier to reduce later than increase after transformer is sized.
Disclaimer: This article provides general engineering guidance. Verify against current CEC, OESC, and your LDC's conditions of service. Consult a P.Eng for project-specific applications.
Download the Service Entrance Checklist
Load letter requirements, CT cabinet selection, conductor sizing, and utility coordination timelines.
Need Service Entrance Engineering?
ETEM Engineering handles complete service entrance design — load calculations, P.Eng load letters, single-line diagrams, CT cabinet specs, and coordination with Hydro One, Toronto Hydro, and Alectra.
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