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Control of solid state loads with transformer isolation: 60947-5-1 AC-14: Control of small electromagnetic loads: 60947-5-1 AC-15: Control of A.C. electromagnetic loads: 60947-5-1 AC-20: Connecting and disconnecting under no-load conditions: 60947-3 AC-21: Switching of resistive loads, including moderate overloads: 60947-3 AC-22
Distribution transformers typically have ratings less than 200 kVA, [3] although some national standards allow units up to 5000 kVA to be described as distribution transformers. Since distribution transformers are energized 24 hours a day (even when they don't carry any load), reducing iron losses is vital in their design.
In electric power systems and industrial automation, ANSI Device Numbers can be used to identify equipment and devices in a system such as relays, circuit breakers, or instruments. The device numbers are enumerated in ANSI / IEEE Standard C37.2 Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations .
Types used in commercial and industrial low-voltage distribution systems are rated to safely interrupt 200,000 amperes. The rating of power circuit breakers varies according to the application voltage; a circuit breaker that interrupts 50,000 amperes at 208 volts might be rated to interrupt only 10,000 amperes at 600 volts, for example.
Single-pole circuit breakers feed 120 V circuits from one of the 120 V buses within the panel, or two-pole circuit breakers feed 240-volt circuits from both buses. 120 V circuits are the most common, and used to power NEMA 1 and NEMA 5 outlets, and most residential and light commercial direct-wired lighting circuits.
Circuit breakers with higher ratings can have adjustable trip settings, allowing fewer standardized products to be used, adjusted to the applicable precise ratings when installed. For example, a circuit breaker with a 400 ampere frame size might have its over-current detection threshold set only 300 amperes where that rating is appropriate.
A mobile substation is a substation on wheels, containing a transformer, breakers and buswork mounted on a self-contained semi-trailer, meant to be pulled by a truck. They are designed to be compact for travel on public roads, and are used for temporary backup in times of natural disaster or war .
Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker, which automatically centers the conductor inside the CT window. Current transformers can be mounted on the low voltage or high voltage leads of a power transformer. Sometimes a section of a bus bar can be removed to replace a current transformer.