Thermal Contraction and Expansion

Temperature Differential Maximum Spacing Between Expansion Joints for 1" Movement (Ft.)
° F ° C
A
M G L T
F
25 14 260 512 667
50 28 130 256 333
75 42 87 171 222
100 56 65 128 167
125 70 52 102 133
150 83 43 85 111
175 97 37 73 95

Expansion Splice Plate Installation
It is important that thermal contraction and expansion be considered when installing cable tray systems. The length of the straight cable trays runs and the temperature differential govern the number of expansion splice plates required (see table).

Proper operation of the expansion splice plates depends upon correct placement of the tray supports, hold down clamps and expansion guides as shown.

Hold Down Clamps should be used at the support point nearest to the midpoint between expansion gaps. These clamps should be installed in such a way to allow the tray to slide freely under the clamp when thermal contraction and expansion takes place.

Expansion Guide Clamps should be used at all support points other than the midpoint. These clamps should be installed in such a way to allow the tray to slide freely under the clamp when thermal contraction and expansion takes place.

Supports with expansion guide clamps should be located within 24" of each side of expansion splice plates.

Accurate gap settings between trays at the expansion joint at the time of installation are necessary for the proper operation of the expansion splice plates. Use the following procedure to determine the correct gap setting:

  • Determine what the maximum temperature will be at the installation location and plot this point on the graph on the max. temp line. (Example value = 100)
  • Determine what the minimum temperature will be at the installation location and plot this point on the graph on the min. temp line. (Example value = -30)
  • Draw a line between the maximum and minimum points.
  • At the time of installation, determine the air temperature. (Example = 50). Plot this point on the line drawn between the maximum and minimum temperatures to determine the correct gap setting at the expansion plate. (Example = 3/8").

Expansion splice plates should be placed on the outside of the cable tray on both side rails. The screw heads should be on the inside and nuts on the outside of the cable tray. Tighten the lock nuts on the screws in the slotted holes just a few turns, allowing the bolt to move freely in the slot.