1. What Is the Half-Perimeter? (Definitions)
Half-perimeter = (box width + box height) ÷ 2, the basis for calculating the number of wiring terminals in electrical budgeting. The larger the half-perimeter, the larger the box, and the more terminals it can accommodate.
2. Calculation Formula (3 Steps)
Half-perimeter = (W + H) / 2, where W = box width (mm), H = box height (mm). Example: for a 600×400 mm box, half-perimeter = (600+400)/2 = 500 mm = 0.5 m.
3. Worked Examples (3 Box Types)
| Box Type | Dimensions (mm) | Half-Perimeter | Terminals |
|---|---|---|---|
| PZ30 12-way | 300×240 | 0.27m | approx. 24 |
| XL-21 250A | 600×1600 | 1.10m | approx. 60 |
| GGD 800A | 800×2200 | 1.50m | approx. 96 |
4. How to Apply the Quota (Tiered by Half-Perimeter)
Electrical installation quotas are tiered byhalf-perimeter: ≤ 0.5 m / 0.5–1.0 m / 1.0–1.5 m / >1.5 m. The higher the tier, the higher the labor and material costs. To apply the quota, first calculate the half-perimeter, then look up the corresponding tier.
5. Relationship Between Half-Perimeter and Terminal Count (estimated)
Rule of thumb: roughly 6–8 terminal positions per 100 mm of half-perimeter. The terminal block drawing governs in the actual build.
FAQ FAQ
What is half-perimeter used for?
It is the basis for electrical estimating and unit-cost pricing — installation labor is priced in half-perimeter bands.
How is half-perimeter calculated?
(Width + Height) / 2. For a 600×400 box, half-perimeter = 500 mm.
How many half-perimeter bands does the unit-cost standard define?
4 bands: ≤0.5 m / 0.5–1.0 m / 1.0–1.5 m / >1.5 m.
How does half-perimeter relate to terminal count?
The larger the half-perimeter, the more terminals — roughly 6–8 terminals per 100 mm of half-perimeter.
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