Cable Tray Fill Calculator

How it works

Each round cable occupies a cross-section of π × (OD ÷ 2)², where OD is its outside diameter from the manufacturer's data sheet. The page adds up the areas of every cable you enter, in up to three groups of the same diameter.

In the United States, cable tray fill is addressed in NEC section 392.22, which, as commonly described, compares the summed cross-sectional areas of certain multiconductor cables in ladder or ventilated-trough tray with an allowable fill area that depends on the tray's inside width. Which cables and trays that comparison covers, and the allowable area itself, are set by the code edition your jurisdiction adopts; its table is copyrighted and is not reproduced here. You enter the allowable area, and the page reports the share used, the margin and how many more cables of the largest diameter entered would still fit.

Formula

area of one cable = π × (OD ÷ 2)²
total area = Σ count × π × (OD ÷ 2)²
share of allowable = total area ÷ allowable fill area
within ⇔ total area ≤ allowable fill area
more cables that fit = ⌊(allowable − total) ÷ area of the largest cable⌋

Example

Twelve cables of 0.86 in OD and six of 0.50 in OD: one 0.86 in cable is π × 0.43² = 0.5809 sq in and one 0.50 in cable 0.1963 sq in, so the total is 12 × 0.5809 + 6 × 0.1963 = 8.149 sq in. Against an allowable fill area of 10 sq in (a placeholder; enter the value for your tray) that is 81.5 %, within, with 1.851 sq in to spare: room for 3 more 0.86 in cables.

Assumptions and limitations

• The allowable fill area is a value you enter from the code your jurisdiction adopts; this page does not supply or check it, and no NEC table value is reproduced. The default 10 sq in is a placeholder.
• Cables are treated as round with the outside diameter you enter; the area is the geometric cross-section of a circle of that diameter. Manufacturing tolerance on OD is not included.
• Only the sum-of-areas comparison is made. Single-conductor cables, cable sizes or mixes that the code handles under other rules, solid-bottom trays, tray depth and cable weight, and any derating are outside this calculator.
• This is an arithmetic aid, not an electrical code determination. The adopted code and the authority having jurisdiction govern; a licensed electrician determines a compliant installation.

Frequently asked questions