04 Equipment & Sizing

Electrical & sub-panel

The breaker box is one of the things that most often forces a change order on install day. Get this right at the survey and the install runs clean.

Minimum breaker space

You want at least 3 breaker spaces available in the panel.

Each breaker = 1 slot
Slots can be doubled up, so 3 slots = 6 effective slots

Three slots (six effective) is generally enough to fit the condensers without adding a sub-panel — depending on how many condensers and their amperage requirements.

When a sub-panel is needed

Sub-panels are often required, even when the box looks like it might fit. Plan for one in the quote so you don’t have to surface it as a change order on install day.

The install team always tries to fit the new circuits without adding a sub-panel. Sometimes it works. Often it doesn’t. Quote conservatively.

What to look for at the survey

Open breaker slots (count them)
Whether existing breakers can be tandem’d / doubled
Main panel amperage rating
Distance from panel to where condensers will mount
Panel condition, old fuse equipment, and any brand/type that looks unusual

If you see an old fuse panel, a Federal Pacific-style panel, or anything you are not qualified to judge, photograph it and escalate it. Do not tell the homeowner it passes or fails from memory. Electrical is one of the easiest places to create an expensive change order by guessing.

Search phrases

Federal Pacific panel, fuse panel, old breaker box, electrical panel photos, panel upgrade, MPU, main panel upgrade.

Pitfalls

Quoting without checking the breaker box. Sub-panel adders surface as change orders on install day, which homeowners hate. Always look at the panel during the survey.

Assuming “looks like enough space” = no sub-panel. Available slot count is necessary but not sufficient. The install team makes the final call based on amperage and condenser configuration.