Explain principle of operating test on the vigilohm fault locator XD312 for checking.
Please keep in mind that detecting of a fault by XD312 depends on the IMD (IM400, IM20, XM300C, XML308/316 and XM200) settings. Such XD312 locators use the 2.5 Hz signal injected by the IMD to determine through which circuit the fault current is flowing. When IMD see a fault, the output level of its electrical signal is higher to ease the detecting of fault with XD312.
Attached a slides having the principle of operating test on the XD312 for checking. You can refer this.