to the equipment and no neutral conductor is used. These cases generally use a grounding conductor which is separated from the safety grounding conductor specifically for the purposes of noise and "hum" reduction. Another specialized distribution system was formerly specified in patient care areas of hospitals. An isolated power system was furnished, from a special isolation transformer, with the intention of minimizing any leakage current that could pass through equipment directly connected to a patient (for example, an electrocardiograph for monitoring the heart). The neutral of the circuit was not connected to ground. The leakage current was due to the distributed capacitance of the wiring and capacitance of the supply transformer. Such distribution systems were monitored by permanently installed instruments to give an alarm when high leakage current was detected. Shared neutral A shared neutral is a connection in which a plurality of circuits use the same neutral connection. This is also known as a common neutral, and the circuits and neutral together are sometimes referred to as an Edison circuit. Three-phase circuits In a three-phase circuit, a neutral is shared between all three phases. Commonly the system neutral is connected to the star point on the feeding transformer. This is the reason that the secondary side of most three-phase distribution transformers is wye- or star-wound. Three-phase transformers and their associated neutrals are usually found in industrial distribution environments. A system could be made entirely ungrounded. In this case a fault between one phase and ground would not cause any significant current. Commonly the neutral is grounded (earthed) through a bond between the neutral bar and the earth bar. It is common on larger systems to monitor any current flowing through the neutral-to-earth link and use this as the basis for neutral fault protection. The connection between neutral and earth allows any phase-to-earth fault to develop enough current flow to "trip" the circuit overcurrent protection device. In some jurisdictions, calculations are required to ensure the fault loop impedance is low enough so that fault current will trip the protection (In Australia, this is referred to in AS3000:2007 Fault loop impedance calculation). This may limit the length of a branch circuit. In the case of two phases sharing one neutral and the third phase is disconnected, the worst-case current draw is one side has zero load and the other has full load, or when both sides have full load. The latter