This part applies only to resistive voltage detectors used in contact with the part to be tested, as a single unit or as a separate device completed by an adaptable insulating pole covered in IEC 855 or IEC 1235. Other types of voltage detectors are not covered by this part of standard. Capacitive voltage detectors are covered in IEC 1243-1. The upper voltage limit is in accordance with the tests described in this part of IEC 1243. Some restrictions on their use are applicable in the case of factory-assembled switchgear and on overhead systems of electrified railways (see annex 6). NOTES 1 Except when otherwise specified, all the voltages defined in this standard refer to phase-to-phase voltages of three-phase systems. Resistive detectors may be used in other than three-phase systems, but the applicable phase-to-phase or phase-to-earth (ground) voltage shall be used to determine the operating voltage. 2 Although this standard does not cover d.c. voltage detectors, some detectors may respond to d.c. voltage.