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.
Frequently Asked Questions
What is the difference between 100A and 200A service?
100A is the older standard. 200A is the current Ontario minimum for new homes, supporting modern loads like EV chargers, electric ranges, and A/C.
When is a service upgrade required?
When calculated demand exceeds existing capacity. A P.Eng load calculation determines if an upgrade is needed.
How long does utility coordination take?
10-16+ weeks total. Load letter review: 4-8 weeks. Transformer installation: 4-8 weeks. See our Toronto Hydro guide for LDC-specific timelines.
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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