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NEMA (National Electrical Manufacturers Association) contactors and motor starters are rated by sizes. These sizes are grouped by rated current and power. [1] [2]
NEMA contact ratings are how much current at a rated voltage a relay or other pilot device can switch. The current rating of smaller NEMA contactors or their auxiliaries are defined by NEMA ICS 5: Industrial Control and Systems, Control Circuit and Pilot Devices [1] standard. The nomenclature is a letter followed by a three-digit number, the ...
NEMA 1-15P (two-pole, no ground) and NEMA 5-15P (two-pole with ground pin) plugs are used on common domestic electrical equipment, and NEMA 5-15R is the standard 15-ampere electric receptacle (outlet) found in the United States, and under relevant national standards, in Canada (CSA C22.2 No. 42 [1]), Mexico (NMX-J-163-ANCE) and Japan (JIS C 8303).
The service factor is typically in the 1.15-1.4 range, with the figure being lower for higher-power motors. For every hour of operation at the service-factor-adjusted power rating, a motor loses two to three hours of life at nominal power, i.e. its service life is reduced to less than half for continued operation at this level.
The SAE defines the ampacity value to be derived by a formula based on the 1 ms full cycle (of the 1 kHz signal) with the maximum continuous ampere rating being 0.6 A per 10 μs up to 850 μs (with the lowest (100 μs/10 μs) × 0.6 A = 6 A). Above 850 μs, the formula requires subtraction of 640 μs and multiplying the difference by 2.5.
A lower rating will apply if multiple conductors are in proximity, since each contributes heat to the others and diminishes the amount of external cooling of the conductors. Depending on the type of insulating material, common maximum allowable temperatures at the surface of the conductor are 60, 75, and 90 °C, often with an ambient air ...
In this system, the primary distribution network supplies a few substations per area, and the 230 V / 400 V power from each substation is directly distributed to end users over a region of normally less than 1 km radius. Three live (hot) wires and the neutral are connected to the building for a three phase service. Single-phase distribution ...
The other end of the three secondary windings and the neutral are brought down the service drop to the service panel. 230 V loads are connected between any of the three-phase wires and the neutral. Because the phases are 120 degrees from each other, the voltage between any two phases is sqrt(3) * 230V = 400V, compared to the 2 * 120V = 240V in ...