[en] A pulsed transformer septum magnet is under development for the Intense Pulsed Neutron Source (IPNS-I), 500 MeV accelerator. The septum consists of a copper sheet and a steel sheet. The copper sheet is one side of the shorted single turn transformer secondary. The steel sheet, which is on the stray field side of the septum, is part of the transformer core. External support and cooling structures, as well as the septum itself, can be grounded, which simplifies the design. The design construction and operation will be discussed. The transformer primary is driven by a condenser discharge. A reverse discharge a few ms later recharges the condenser and demagnetizes the septum. Details will be discussed