PanelDexHow a 42-space panel is numbered
Forty-two spaces make 21 rows. Circuit 1 is top left and circuit 2 is top right; circuit 41 is bottom left and 42 is bottom right. On a 120/240 V split-phase panel the rows alternate between the two legs:
1 ─┤ L1 ├─ 2 3 ─┤ L2 ├─ 4 5 ─┤ L1 ├─ 6 … … …
Row 21, with circuits 41 and 42, is on L1, because the odd-numbered rows are all on L1 and the even rows on L2. On a three-phase 42-space panel the 21 rows cycle A, B, C, giving each phase exactly 7 rows, and circuits 41 and 42 land on phase C.
Why 42 is such a common size
For many years, the electrical code limited some panelboards to 42 overcurrent devices, so 42 spaces became a standard size for both residential load centres and commercial lighting panels. Larger panels are common now too, but a great many existing panels have 42 spaces, which is why “42 circuit panel schedule” is one of the most searched sizes.
The tool doesn't limit you to 42. The quick picks cover 12, 20, 24, 30, 40, 42, 54, 60 and 84 spaces, and you can type any even number from 12 to 84. A 30-space panel, for example, has 15 rows, 1 to 29 down the left and 2 to 30 down the right.
Filling in a 42-space schedule quickly
- Start a new blank panel, set 42 spaces and the system, and fill in the header fields.
- Select space 1. Choose the breaker type, type the description and the rest, then press Next. The editor moves to space 2, then 3, in panel order, skipping spaces already taken by a 2-pole or 3-pole breaker.
- Leave unused positions as Empty space, and mark breakers with nothing connected as Spare.
- Check the totals card. Each leg's VA and approximate amps update as you type.
If you already have the circuits in a spreadsheet, download a CSV from PanelDex to see the column layout, paste your data into it and use Import CSV.
2-pole breakers near the bottom
A 2-pole breaker takes two spaces one above the other in the same column, so it needs a free space two numbers higher. In a 42-space panel, a 2-pole can start at 39 (taking 39 and 41) or 40 (taking 40 and 42), but not at 41 or 42. The editor tells you why when a placement doesn't fit, and it also refuses one that would overlap a breaker that's already there.
The Excel version
The .xlsx download lists all 42 spaces in number order with the side, the leg or phase, and the load per pole. The totals at the bottom are SUMIF formulas over the leg column, so if you change a load in the spreadsheet, the leg totals, the approximate amps and the imbalance all recalculate. These are totals of the loads you entered — not a code load calculation. For sizing a service, feeder or panel, a licensed electrician does an NEC Article 220 load calculation.
Labelling tool only. Turn power off and follow local code; have a licensed electrician do electrical work.
Frequently asked questions
How many rows does a 42 circuit panel schedule have?
21 rows of two spaces each: 1 and 2 on the top row down to 41 and 42 on the bottom. Odd numbers run down the left, even numbers down the right.
Can a 42-space panel have more than 42 circuits?
Only with tandem breakers, and only if the panel's label allows tandems in those spaces. Each tandem space holds two circuits, numbered like 13A and 13B on the schedule.
Why can't I put a 2-pole breaker in space 41?
A 2-pole breaker needs the space below it in the same column, which would be 43. A 42-space panel stops at 41 on the left, so the editor blocks it. Spaces 39 and 41 work.
Do you have a 30 circuit panel schedule too?
Yes. Pick 30 under Spaces (or 12, 20, 24, 40, 54, 60 or 84, or type any even number from 12 to 84). A 30-space panel has 15 rows, 1 to 29 on the left and 2 to 30 on the right.
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Last updated · Written by the Rooh Sites team. General information, not electrical advice.