If the site insulation is used as a means of protection against electric shock, the insulation resistance of floors and walls should be checked with an appropriate measuring instrument using a probe dedicated for this purpose. PRS-1 has the shape of an equilateral triangle and has been made according to the guidelines provided in for in the HD 60364-6 and EN 1081 standards. Legs of the probe were made with a special rubber mix – volume resistance of a single leg does not exceed 5 kΩ, and the hardness is in the range between 50 to 70 IRHD. With appropriate pressure on the probe, such a design solution will ensure approx. 900 mm2 contact surface area with the tested plane.