The WRU-10 differs from the RGU-10 in one decisive respect: the toroidal transformer is built into the unit, a Ø28 mm aperture through which the circuit conductors are passed directly. Relay and transformer are a single three-module device, so there is no separate toroid to size, order, mount or wire — the reason it is usually the cheaper and faster choice wherever the cable will physically pass through 28 mm. It is a self-reclosing device. After a trip it can re-close the circuit automatically, on a programmed number of attempts, which is what keeps an unattended or remote installation running through a transient earth fault instead of losing it until someone drives out to reset it — while still locking out and staying open on a genuine persistent fault. Sensitivity and delay are adjustable. A backlit LED display shows the trip current, the number of reclosures performed and the protection status. Three programmable output relays are provided, one change-over and two simple, on pluggable terminals. Supply is 230 V AC and the operating range is -20 to 70 °C. It is a type A device: it responds to sinusoidal AC residual currents and to pulsating DC residual currents. Circutor specify it as superimmunised, with high-frequency filtering and true RMS (TRMS) measurement, so that the harmonic leakage normal in an installation full of switch-mode loads does not read as a fault. Manufactured by Circutor (Spain) and supplied under the Function brand; the Circutor catalogue reference is WRU-10. Supplied by cBallast on quote-to-invoice terms; lead time and freight are quoted per RFQ against the destination Incoterm.