By the Solar X Engineering Team, ESA/ECRA Certified. Published . Updated .
Solar X is an ESA/ECRA licensed electrical contractor headquartered in Toronto, operating since 2017 and serving Ontario, Alberta, Nova Scotia, and New Brunswick.
If you are comparing battery quotes right now, you have probably noticed that two quotes for the same battery can describe two very different systems. The difference usually is not the battery. It is the wiring. We install whole home battery backup, and in this guide we explain exactly why the connection type matters more than most spec sheets suggest, and what to ask every bidder before you sign.
How does a home battery connect to your electrical panel?
There are two ways a residential battery gets wired into an Ontario home, and every quote you collect uses one of them.
A whole home connection is made at the service entrance, after the utility meter, through a whole home disconnect. The battery system then feeds your entire existing panel through hardware commonly rated for 200 amp residential services. Nothing about your panel layout changes. Every circuit in the house can draw from the battery.
A backup subpanel connection adds a second, smaller panel, usually rated between 30 and 60 amps, and an electrician moves a handful of selected breakers into it. Only the circuits on that small panel can ever receive battery power. You may hear this called a critical loads panel in some quotes. A subpanel also claims wall space beside your existing panel, while a whole home connection adds only the disconnect at the service entrance and leaves your panel wall untouched.
| Aspect | Whole home connection | Backup subpanel |
|---|---|---|
| Where it connects | Service entrance, after the meter | Small second panel beside the main panel |
| Circuits it can power | Every circuit, up to 200 amps | Only the breakers moved to the subpanel |
| Changing what is backed up | At the breaker panel, any time | Electrician revisit and rewiring |
| Inverter size limit on a 100 amp panel | Escapes the busbar cap | Subject to panel constraints |
| Offsets whole home usage while grid connected | Yes, by design | Only if the system is wired and configured for it |
What can you keep running during an outage?
With a whole home connection, the outage decision stays in your hands. You can run the entire house if your battery is sized for it, or walk to the panel and switch off heavy loads to stretch the runtime. Furnace fan, fridge, internet, and lights sip power. An electric range or a dryer drains a battery fast. Being able to choose in the moment is what makes the runtime flexible.
With a backup subpanel, that choice was made on installation day. Whatever breakers were moved to the subpanel are what you get. If you later want your heat pump or your EV charger backed up, that is an electrician revisit and more rewiring, not a switch flip.
How does the connection type change your savings?
Rate arbitrage means charging a battery when electricity is cheap and using that stored power when electricity is expensive. Ontario makes the opportunity unusually clear. Under the Ultra Low Overnight price plan in effect from November 1, 2025 to October 31, 2026, electricity costs 3.9 cents per kWh overnight from 11 p.m. to 7 a.m. and 39.1 cents per kWh during the weekday on peak window from 4 p.m. to 9 p.m., according to Alectra Utilities. That is a spread of roughly 35 cents on every kWh you shift, before delivery charges and round trip losses. You can see how the plans compare in our guide to Ontario electricity rates.
Here is the part the spec sheets rarely spell out. That spread only turns into real savings when the battery can offset your whole home's draw during the expensive window. A whole home connection ensures that, because the battery sits ahead of the entire panel. Wiring that lets the battery discharge only into a small subpanel caps the offset at whatever happens to run on those few circuits, which guts the savings math no matter how large the battery is.
To be fair to every configuration: some grid interactive systems back up only part of the home during an outage yet still offset whole home consumption while the grid is up. The wiring is the question, not the size of the backup. So put it to every bidder, in writing:
- While my home is grid connected, does this battery offset my whole home's consumption, or only the circuits on a subpanel?
- Show me where in the design that happens.
If the answer is vague, the savings projection deserves the same skepticism.
Can your panel support a bigger inverter with whole home wiring?
Yes, and on older services the difference is large. When an inverter is connected through a breaker inside your panel, the busbar rule in Section 64 of the Canadian Electrical Code limits the total supply feeding a dwelling panel's busbar to 125 percent of its rating. On a typical 100 amp panel with a 100 amp main breaker, that leaves room for about a 25 amp backfed breaker, which works out to an inverter around 5 kW.
A whole home connection is made at the service entrance, ahead of the busbar, so that cap does not apply. Inverter sizing then runs up to Ontario's micro embedded generation ceiling instead. As of May 1, 2026, the Ontario Energy Board's Distribution System Code amendments define a micro embedded generation facility as 12 kW or less, and Alectra Utilities confirms that projects at or below 12 kW use the simpler micro connection process while larger projects go through the fuller connection process, which includes a Connection Impact Assessment. We covered the change in detail in our post on Ontario's new 12 kW residential limit.
The practical takeaway: on a 100 amp panel, whole home wiring can more than double the inverter headroom available through a panel breaker. Your utility still has to approve the connection, and no approval is ever guaranteed, so treat every sizing number as design headroom rather than a promise.
What does a whole home battery installation involve?
The honest version, because you should hear it before you sign anywhere.
Connecting at the service entrance means working on the supply side of your panel, so we schedule what many utilities call a disconnect and hold: your utility disconnects power at the meter first. Our crew then installs the whole home disconnect, mounts the inverter and battery, and completes the wiring. The utility reconnects the home, typically the same day the work is done, and in our experience reconnection often follows within about four to six hours, though the utility always controls the schedule. An ESA inspection applies, as it does for any work of this kind in Ontario.
The variable is scheduling. Utility disconnection and reconnection windows depend on the utility's own calendar, and that can add lead time before installation day. Permits, ESA inspection, and utility approvals are never guaranteed, and we do not commit to install dates until every approval is complete. Any installer who promises a firm date before approvals exist is promising something they do not control.
What happens if the inverter fails?
This is the one whole home consideration almost nobody explains at quote time, and it separates system architectures more than brand names do.
A bypass is the path that lets grid power keep reaching your panel when the inverter is out of service. Systems built around a grid gateway keep your home connected to the grid and only island during an outage. In that architecture, grid power keeps flowing to the panel automatically even if the battery inverter goes offline. Tesla's published Powerwall 3 documentation describes its Backup Gateway detecting outages and transferring automatically, with a manual override available for service events, and Sigenergy's published gateway specifications list a built in bypass circuit.
Other systems wire the hybrid inverter in series between the meter and your loads. If that inverter fails while the grid is up, the home can stay dark until an electrician attends and operates or installs a manual bypass. That is a meaningful difference in how a bad day plays out.
Whichever brands appear in your quotes, ask the same question in writing: if the inverter fails while the grid is up, does my home still get grid power automatically? Then ask for the spec sheet page that says so.
Why we install whole home battery backup in Ontario
We are an ESA/ECRA licensed electrical contractor, and after years of installing residential solar and battery systems across the province, we standardized on whole home connections because they hold up on all three fronts that matter to a buyer comparing quotes. You keep outage flexibility instead of locking your choices in on installation day. The battery can offset your whole home's consumption, which is what makes the overnight rate math work. And the supply side connection gives your system sizing headroom that a panel breaker on an older service simply cannot.
It is the premium configuration, and we think it is the one worth quoting properly. You can see the equipment we work with on our battery and solar solutions page, and if you already have quotes in hand, we are glad to walk you through what each one actually wires in.
Whole home battery backup in Ontario is a wiring decision first and a product decision second. Get the wiring right and everything else follows.
Solar X, ESA/ECRA licensed electrical contractor, Headquartered in Toronto, Operating since 2017
Frequently asked questions
How long does a whole home battery installation take?
The on site work is typically completed within a single day once equipment, permits, and approvals are in place. Total project time depends on utility scheduling for the disconnection and reconnection, ESA inspection, and approval timelines, all of which vary by utility and season. No installation date is guaranteed until every approval is complete.
What happens during the utility disconnection and reconnection?
Your utility disconnects power at the meter so the crew can safely install the whole home disconnect at the service entrance, then connect the inverter and battery. Reconnection typically happens the same day the work is done, but the utility controls the schedule. Your home is without grid power during the work window, so plan around it.
Does a 100 amp panel support whole home battery backup?
Usually yes, through a supply side connection at the service entrance. Connecting through a breaker inside a 100 amp panel is limited by the electrical code's busbar rule to an inverter around 5 kW, but a supply side whole home connection is made ahead of the busbar, so that cap does not apply, and inverter sizing can then run up to Ontario's 12 kW micro embedded ceiling. A site assessment confirms what your service supports.
How much more does whole home backup cost than a backup subpanel?
It is quote dependent. Whole home wiring adds the disconnect hardware, service entrance work, and utility coordination, while a subpanel adds a second panel and breaker relocation. The fair comparison is total cost against total savings, because subpanel only wiring caps how much of your bill the battery can offset. Ask every bidder for an itemized quote covering both options.
What happens if the battery inverter fails?
It depends on the system architecture. Systems built around a grid gateway keep your home connected to the grid and only island during an outage, so grid power keeps flowing automatically if the inverter goes offline. Systems wired in series between the meter and your loads can leave the home dark until an electrician operates a manual bypass. Get the answer for your specific system in writing.
Can I still save money on overnight rates with a backup subpanel?
Only if the system is wired and configured to offset your whole home's consumption while it is grid connected. Subpanel only discharge caps the savings at whatever happens to run on those few circuits, no matter how large the battery is. A whole home connection removes that cap by design, because the battery sits ahead of your entire panel. Ask every bidder, in writing, which one their design does.
Sources
- Alectra Utilities, Ultra Low Overnight Pricing: alectrautilities.com
- Alectra Utilities, Connecting Generation: alectrautilities.com
- Tesla, Powerwall 3 Datasheet (North America): energylibrary.tesla.com
- Tesla, Backup Switch Datasheet: digitalassets.tesla.com
- Sigenergy, Sigen Energy Gateway product specifications: sigenergy.com