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NEMA L20 series devices are three-pole, four-wire, non-grounding devices for three-phase 347/600-volt devices. Designs exist for 20-ampere (L12-20), and 30-ampere (L20-30) devices, and L20-20 and L20-30 devices were commercially available from at least one manufacturer (Bryant Electric).
Three-phase transformer with four-wire output for 208Y/120 volt service: one wire for neutral, others for A, B and C phases. Three-phase electric power (abbreviated 3ϕ [1]) is a common type of alternating current (AC) used in electricity generation, transmission, and distribution. [2]
High-leg delta (also known as wild-leg, stinger leg, bastard leg, high-leg, orange-leg, red-leg, dog-leg delta) is a type of electrical service connection for three-phase electric power installations. It is used when both single and three-phase power is desired to be supplied from a three phase transformer (or transformer bank).
In Europe, three-phase 230/400 V is most commonly used. However, 130/225 V, three-wire, two-phase electric power discontinued systems called B1 are used to run old installations in small groups of houses when only two of the three-phase high-voltage conductors are used. The phase shift in Europe is 120°, as is the case with three-phase current.
The maximum voltage rating of IEC 60309 connectors is 1000 V DC or AC; the maximum current rating is 800 A; and the maximum frequency 500 Hz. Plugs are available in P+N+E (unbalanced single phase with neutral), 2P+E (balanced single phase), 3P+E (3 phase without neutral), and 3P+N+E (three phase with neutral).
Lighting and general purpose receptacles are at 120 volts AC, with larger devices fed by three wire single-phase circuits at 240 volts. In commercial construction, three-phase circuits are often used. Common 3 phase configurations within a building are 208v/120 wye, 120/240 center tapped delta and 480v/277v wye. Lighting is usually fed by 277 V ...
The IET Wiring Regulations permit an unlimited number of 13A socket outlets (at any point unfused single or double, or any number fused) to be installed on a ring circuit, provided that the floor area served does not exceed 100 m 2. In practice, most small and medium houses have one ring circuit per storey, with larger premises having more.
A three or four-pole isolator or circuit breaker is used for three-phase loads, for devices with both permanent and switched supplies (such as bathroom extractor fans) and also at the distribution board to isolate all the phases. A three-phase installation with a TT earthing system is an example where four-pole devices would be required.