Is it safe to test IT equipment with the IT setting on my tester?

The earth continuity test is carried out using a 200mA test current, in accordance with the requirements of IEC 61557-4. The risks associated with accidently passing a high test current through parts of the appliance, not intended to carry high currents, are therefore eliminated.  The insulation resistance measurement is carried out at a voltage of 500V (or 250V when available) in accordance with the requirements of IEC 61557-2. During the test, Seaward instruments make a temporary link between both live conductors (line and neutral) and the test voltage is applied between live conductors and protective earth/insulation test probe. The test voltage is used to measure the insulation between live parts and protective earth/insulation test probe and cannot be applied across the mains input of the appliance under test. An appliance that is compliant with the relevant product standard, for example IEC 60950 in the case of IT equipment, should not be damaged by this measurement.