Sizing an electrical board for a new office fit-out

Key Takeaways

• The starting point for board sizing is total connected load, the sum of every circuit's rated capacity, but that figure is a ceiling, not the design target, since it assumes every device draws its full rated power simultaneously.
• Demand factor, the ratio of actual peak load to theoretical maximum load, is what converts the inflated connected-load total into a realistic design figure; a worked reference shows a load rated to 6,000W peaking at only 3,000W in practice, a demand factor of 0.5.
• Spare capacity for future growth is a deliberate design decision, not a rounding error, and should be sized as an explicit percentage on top of the demand-factored load, not folded invisibly into an oversized board chosen "to be safe."
• A board sized without applying a demand factor at all isn't a conservative choice, it's an expensive one: bigger boards, heavier feeders, and a larger DEWA connection all cost more without buying protection against a scenario (full simultaneous load) that doesn't occur in normal office operation.

The instinct when sizing a board for a new office fit-out is to list every socket, light fixture, and piece of equipment, add up the rated wattage, and size the board to match. That number is real, but it's not the design target, it's the theoretical ceiling that almost never gets reached in practice, and sizing directly to it produces a board that's larger and more expensive than the office actually needs.

Start with connected load, but don't stop there

Total connected load is the sum of every circuit's rated capacity on the board, and it's a legitimate first step, the ceiling that establishes what could theoretically be drawn if everything ran at once. What it isn't is a realistic estimate of what the office will actually draw, because normal office operation never puts every socket, every light, and every piece of equipment at full rated draw simultaneously.

Applying a demand factor to get the real design number

Demand factor is the ratio of maximum load actually observed in a given period to the maximum possible load, a fraction always between 0 and 1 (Wikipedia, demand factor, retrieved 2026-09-10). The reference example: equipment rated for up to 6,000W but observed peaking at only 3,000W has a demand factor of 0.5 (Wikipedia, demand factor, retrieved 2026-09-10). Applied to an office fit-out, this is the step that turns "sum of every nameplate" into "realistic peak the board actually needs to supply," and it's the single biggest lever in getting board size right rather than oversized.

Run the fit-out's connected-load schedule through the electrical load calculator with an appropriate demand factor for office use, rather than sizing the board to the raw connected-load total, since the gap between the two figures is usually substantial.

Why "size it generously to be safe" isn't actually the safe choice

A board sized to the full connected-load total, skipping the demand factor step entirely, isn't a conservative design decision in any meaningful sense, it's an expensive one that doesn't buy real additional protection. The scenario it protects against, every circuit drawing full rated power at the same instant, essentially never happens in office operation, so the extra board capacity, heavier incoming feeder, and larger DEWA connection that come with an unfactored sizing are cost without a corresponding safety benefit.

Where growth headroom belongs, and where it doesn't

Future growth capacity is a legitimate reason to size a board above the current demand-factored load, but it should be an explicit, stated percentage added deliberately, not an implicit buffer created by skipping the demand-factor calculation altogether. The difference matters: a board sized at demand-factored load plus a declared 20% growth margin is a documented, defensible design decision. A board sized at full connected load "to be safe" is the same oversizing achieved accidentally, without anyone having actually decided how much spare capacity is appropriate or why. A licensed engineering fit-out partner can turn that stated growth percentage into an actual board and feeder spec, rather than leaving it as an unwritten assumption.

Frequently asked questions

Is there a standard demand factor for a typical office fit-out?

Recognised design guidance provides typical demand factors by space and load type, which a licensed electrical consultant applies to the specific fit-out. There isn't a single universal number, since it depends on the mix of equipment, occupancy density, and how the space is actually used.

Does skipping the demand-factor step ever make sense?

Rarely. The only case where connected load and realistic demand converge is a space with unusually synchronized full-load operation, which is not typical office use. For almost any standard office fit-out, applying a demand factor produces a meaningfully smaller, cheaper, and still fully adequate board.

How much growth headroom should a new office board carry?

There's no universal figure, it depends on expected headcount growth, planned equipment additions, and how far ahead the fit-out is meant to serve. The key discipline is making it an explicit percentage decision on top of the demand-factored load, not an unstated assumption baked into an oversized board.

The bottom line

Connected load tells you the ceiling; demand factor tells you the realistic design number, and the gap between the two is usually the difference between an oversized, overpriced board and a correctly sized one. Any growth margin belongs on top of the demand-factored figure as a deliberate, stated decision, not folded invisibly into a board sized off the raw nameplate total.

Figures were verified on 10 September 2026 against Wikipedia's demand factor reference article. This session's live web search was unavailable, so UAE-specific demand factor tables by office space type could not be independently verified here; confirm applicable factors and DEWA connection sizing requirements with a licensed UAE electrical consultant before finalising a board spec.