Ammeter through a wire which expands as it heats. Although these instruments have slow response time and low accuracy, they were sometimes used in measuring radio-frequency current. These also measure true RMS for an applied AC. In much the same way as the analogue ammeter formed the basis for a wide variety of derived meters, including voltmeters, the basic mechanism for a digital meter is a digital voltmeter mechanism, and other types of meter are built around this. Digital ammeter designs use a shunt resistor to produce a calibrated voltage proportional to the current flowing. This voltage is then measured by
Electrical room enclosures of electrical equipment to prevent stray voltage and danger of electric shock, even during faults in the electrical system. Lightning protection requires different measures than protection from power-frequency faults. Electrical rooms may have electromagnetic shielding to prevent interference to nearby sensitive audio or video equipment. In large facilities access control systems may control admission to the room. Layout details and construction of electrical rooms will be controlled by local building code and electrical code regulations. Requirements for an electrical room relate to fire safety and electrical hazards. An electrical room is usually required to be secured from access by