Critical Load Panel Planner

Four limits, against figures you enter. The running watts of the circuits you want backed up, summed and tested against the inverter's continuous output rating. The largest single starting draw, added to everything else already running, and tested against the inverter's surge rating. The daily energy those circuits consume, tested against the battery's usable capacity. And the number of panel spaces the list needs, tested against the spaces available. A list can pass one of these and fail another, which is why they are reported separately rather than as a single verdict.

Because motors are the loads that fail a backup system on paper that looked fine. A well pump, a sump pump, a compressor or an air conditioner draws a large transient at startup and a much smaller figure while running. An inverter can be comfortably within its continuous rating and still shut down the instant that motor starts. The tool takes the worst realistic case — the largest motor starting while everything else on the list is already running — rather than assuming every motor starts at once, which would be pessimistic, or ignoring startup entirely, which is how the problem gets missed.

From the nameplate on the appliance, and from the equipment datasheet for the inverter and battery. This tool deliberately does not supply default wattages. Typical figures vary widely by model and by age, and a planner that fills in an assumption produces a confident answer to a question nobody asked. A circuit with no wattage entered is reported as missing and is excluded from the totals rather than estimated.

Because usable capacity is what the system will actually deliver, and it is normally lower than the nominal capacity printed in marketing material. Manufacturers reserve a portion of the pack, and some systems reserve more in certain operating modes. Entering the nominal figure produces a runtime estimate that is optimistic by exactly the amount of the reserve. If the proposal does not state usable capacity, that is itself worth asking about before signature.

They are the part that decides what gets built. The arithmetic establishes what is possible; the record establishes what happens. A circuit list agreed in conversation and absent from the proposal and the plan set is a list that will be reconstructed on installation day from whatever is physically reachable in the existing panel — which is how a household ends up with a backed-up hallway light and a refrigerator that is not on the list. Panel space is on that list too, because a backup panel needs a feeder from the existing main panel, and where the main panel is full that is a main panel upgrade nobody budgeted.

Indirectly, and honestly. Whole-home backup is achievable; it generally requires more inverter capacity, more storage, some form of load management, or a combination. If you list every circuit in the house and the result exceeds the continuous rating, that is the arithmetic telling you the proposal in front of you is a partial-backup proposal, whatever the conversation implied. That is a useful thing to establish before signature rather than during the first outage.

No. It is a preparation aid. It performs arithmetic on figures you supply and asks questions about where the decision is recorded. It makes no code claims, applies no derating factors, and does not size conductors, overcurrent protection or the feeder to the backup panel. The system design belongs to the licensed electrical contractor and the engineer of record, and the permitted scope belongs to the plan set the jurisdiction reviews. Use this to arrive at that conversation with a list rather than without one.