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Upgrading from 100 amps to 200 amps in Cambridge: when you actually need it and when you do not

A Cambridge house needs a 200-amp service when the load calculation under the Ontario Electrical Safety Code says the house, as it is about to be used, draws more than a 100-amp service can safely carry. A panel with no empty breaker slots is a different problem, and often a cheaper one.

Last updated October 24, 2026 · Reviewed by the Cambridge Electricians team

Do I need to upgrade to 200 amps?

Only if the load calculation says so. The calculation is the code method for adding up the house's demand, counting the square footage, the range, the dryer, water heating, space heating or air conditioning, a hot tub, an EV charger and any second unit, and it produces a number in amps. If that number fits inside a 100-amp service, you do not need a service upgrade no matter how full the panel looks. If it does not, no amount of rearranging breakers will fix it. The contractor we book for Cambridge runs the calculation on the first visit and writes the result on the quote so you can see why 100 or 200 is the answer.

Signs it may be time

These are the situations in Cambridge where a 100-amp service most often turns out to be short, in rough order of how often they come up:

• Adding a second unit. Cambridge allows up to two additional residential units on a lot with a detached, semi-detached or townhouse dwelling, with a building permit from the City. A second kitchen with its own range, plus a second household's heat and hot water, is the single most common reason a Galt or Hespeler house moves to 200 amps.
• A heat pump or electric heating. Replacing a gas furnace with a cold-climate heat pump adds one of the largest loads a house can carry.
• An EV charger plus everything else. ESA describes a Level 2 charger as roughly the draw of a stove or dryer. On a house that already has an electric range, dryer and air conditioning, it can tip the calculation.
• A hot tub or a shop. A 240-volt hot tub circuit or a subpanel feeding a welder and compressor in a North Dumfries drive shed.
• The main breaker trips when the oven and dryer run together. That is the house telling you the calculation is already over.

A full panel is not a full service

Most calls that start as a 200-amp upgrade in Preston Heights or east Galt end as something smaller. The 1960s and 70s side-splits were built with 100-amp breaker panels that are original and full, and the honest fix for a full panel on a service that still has capacity is a subpanel, fed from a two-pole breaker in the main and mounted where the new load is: the garage for a charger, the basement for a finished space. Where the panel is from a maker that insurers and inspectors ask about by name, or shows heat discolouration, a same-amperage panel replacement is the right job. It is simpler than a service upgrade because the utility side does not change; GrandBridge Energy still has to disconnect and reconnect, but the mast, meter base and lateral stay. In the earlier houses with aluminum branch wiring, the panel change is also the moment every circuit is re-terminated at the breaker end.

What a full service upgrade involves in Cambridge

A true 100-to-200 upgrade replaces the service entrance as well as the panel. In order:

1. Load calculation and quote. Written, after the panel and the service entrance have been seen.
2. GrandBridge Energy service layout. GrandBridge's service request page says a service layout is required to book a service upgrade, and it names upgrading the amps, relocating the meter, adding meters, installing an EV charger and installing an automatic transfer switch as examples. The contractor submits it.
3. ESA notification. GrandBridge says you will also need to arrange an ESA permit, and that contractors should obtain the notification before commencing any electrical work. The contractor files it under their licence.
4. The disconnect and reconnect appointment. GrandBridge describes this as a free service appointment unless it falls outside regular operating hours, which it lists as 8:00 a.m. to 3:30 p.m., Monday through Friday. The crew shuts the service off so the mast, meter base, grounding and panel can be replaced.
5. ESA inspection, then power. GrandBridge states it will not reconnect your service without an ESA inspection. ESA's homeowner guidance says a service upgrade is inspected before power is restored. Expect most of a working day without power for a full upgrade, and a few hours for a same-amperage panel swap.

Century homes in Galt, Preston and Hespeler

In the three old cores the question is rarely 100 versus 200, because many of the stone and brick houses on Dickson Hill, around King and Argyle in Preston and near Queen Street in Hespeler are still on a 60-amp fuse service, sometimes behind a chain of sub-panels added over the decades. A fuse service is not dangerous in itself, but a century of oversized fuses and spliced extensions usually is, and insurers and home inspectors flag it on nearly every sale. The job there is almost always a complete new 200-amp service with grounding brought up to current requirements, because old Cambridge houses were commonly grounded to a metal water service that has since been replaced with plastic. In Blair, Dickson Hill and the Main Street heritage districts the position of a new mast or meter base on a visible wall is checked with the City's heritage staff before it is ordered.

What this means for your quote

Ask for the load calculation in writing and ask which of the three jobs you are being quoted: a subpanel, a same-amperage panel replacement, or a full service upgrade. Each is described on the panel and service upgrades page, and the Cambridge electrician cost guide explains why the same word covers three very different amounts of work. Any GrandBridge or ESA charge is shown as its own line on the quote rather than folded into the total. To start, describe the house, the panel and what you want to add and the contractor will call back.

Sources

• Service Requests - GrandBridge Energy
• Notifications and Inspections: What You Need to Know - Electrical Safety Authority
• EV Charging Systems - Electrical Safety Authority
• Additional Residential Units - City of Cambridge