Cable Tray Support Span Calculator

Method & Assumptions

Maximum support span is governed by the L/100 deflection limit defined in NEMA VE 1-2017 §4. For a uniformly distributed cable load on a simple span, midpoint deflection is:

δ = 5wL⁴ / (384EI)  ≤  L/100

Normalising against the tray's rated conditions at the class test span gives:

max_span = L_rated × (w_rated / w_actual)^(1/3)

Variables:

  • w_actual — total cable weight per linear foot of tray (lbs/ft)
  • w_rated — NEMA load-class working load (lbs/ft)
  • L_rated — class test span identified by the numeric class prefix

Citations: NEMA VE 1-2017

Applicability: aluminum and steel ladder trays, solid-bottom trays, and wire-mesh trays with standard NEMA load classes. Fiberglass trays (NEMA FG 1) use identical load-class designations and the same formula.

See also: Cable Tray Fill, Raceway Schedule.

Tray Load Class

Select the load class stamped on the tray or specified by the manufacturer. In traditional NEMA classes, the number is the rated span and A/B/C correspond to 50/75/100 lbs/ft. For example, 12A is 50 lbs/ft at 12 ft.

Input Mode
Cable List

Add cables below and the total weight per foot will be computed automatically, or type a value directly in the field beneath the table.

Conductors Conductor Size Quantity Weight (lbs/ft) Remove
Total Cable Weight

Summed automatically from the cable list above, or enter a value manually. Include all cables sharing this tray section.