European relay practice treats insulation as a design discipline rather than a final test, and this document is the one that supplies the rules. It supports the whole family of relay product standards in Europe, so a manufacturer will usually meet it indirectly, through the part that governs the particular protection device being developed, and will then apply the coordination method it contains during design review rather than only at the test stage. The method ties the assumed overvoltage of the installation to the physical separation between circuits, so the choice of overvoltage category and pollution degree is made once and then governs the dimensions of the product. For a protection relay this matters more than for most equipment because the device sits between a high voltage measuring circuit and a low voltage control circuit. The document also states how a specimen is prepared and what constitutes a breakdown, points on which European laboratories are audited.