75 and 20 Pounds Force
75 Pounds-force, Model ZLT-F75P
For resistance to crushing on direct plug-in units, according to UL1310-2005 clause 46.5.1.
One sample of the unit shall withstand for 1 minute a steady crushing force of 75 pounds-force (334 N) applied a right angle to the mounting surfaces. The enclosure is to be tested between two parallel, flat, hardwood blocks, each not less than 1/2 inch(12.7 mm) thick.
20 Pounds-force, model ZLT-F20P
For rod pressure on direct plug-in units, according UL1310-2005 clause 46.4.2.
Weight 20 pounds, the axis of a 1/2 inch diameter metal rod, having a flat contact end with the edge rounded to a radius of 1/32 inch to eliminate sharp edges.