If you size the feeder to 125% of the motor FLA, this gives you ,at 75Celsius, a #6 AWG conductor. Size feeders to panel (just like branch circuits. b) Fire Pump applications are discussed in Article 695 of NFPA 70: National Electrical Code A #6 AWG is rated for 65 Amperes. 2014 Code Language: 215.2(A)(1) General. The feeder overcurrent device must be sized not less than 125% of 184A, 184A x 125% = 230A. to get conductor size; For 480V 100HP, correct conductor size is 2/0 References: a) A fire pump motor should be in accordance with NFPA 20 9.5.1.1 which states that it must comply with NEMA Design B standards and be listed for fire pump service. Even though the heat load FLC was greater than that of the motor, we still added the 25% to the largest motor! However, choosing the next larger size motor (say 10 instead of 7.5 hp), brings greater capacity for coping with frequent starts, Starting qualities for the four basic motor designs. A typical electrical system may have many types of feeders supplying many different types of loads. For feeders with a long length, what is protecting the conductors in between the 150A feeder OCPD and the fusible disconnect(150A nontime-delay fuse)? MCP Breakers for Motors 125% or next larger size Standard breaker sizes are listed Page 70-74, 240-6 NEC Conduit Sizing 1. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load. For motor circuit conductors tapped from a feeder [430.28], determine the ampacity per 430.22. Step 1 - Size the overcurrent device in accordance with 215.3. Taps. For AC single-phase motors, polyphase motors other than woundrotor (synchronous and induction other than Code E): [1], [2] Feeder wire size is 125 percent of motor full-load (FL) current minimum.. Feeder breaker (thermal-magnetic fixed-trip type) is 250 percent of FL current maximum.. Feeder breaker … Sizing Motor-Circuit Feeders and Their Overcurrent Protection. Also, The Owner Requires An Equipment Grounding Conductor Run With This Feeder, Thus Calculate The Conduit Size … Motor Feeder Calculations By John C. Pfeiffer, P.E. Question: 1) What Size Feeder Is Required By Code That Feeds (3) 5HP Single Phase 120V Motors, A 10HP, 15HPand 25HP 3-phase/208V Wound Rotor Motor And A Lighting Load (120V) Of 27,350va. Note: The “next-size-up protection” rule for branch circuits [430.52(C)(1) Ex 1] doesn’t apply to motor feeder short circuit and ground fault protection device sizing. What size feeder overcurrent protection device and conductor (THHN) is required for a 184A continuous load on a panelboard (75°C terminals). Pfeiffer Engineering Co., Inc. First, we have taken a chart out of the National Electrical Code, Section 430, Motors and expanded the chart to better define where the various aspects of motors and motor control are located. Sizing conductors for VFDs We have a motor control center (MCC) where we removed the combo starters and landed the wire directly to the circuit breakers and then to a variable frequency drive (VFD). 80% loaded wire same size or larger than ampacity of main breaker. Example: What is the minimum size THHN feeder allowed for 1 - 3hp, three phase, 208 volt motor and 1 - 2hp, single phase 208 volt motor? The size and type of feeder conductors, as well as the rating of the feeder overcurrent protective devices, should also be included with the feeder diagram. The Conduit For This Feeder Runs Through A 42° C Ambient Area. Feeder Continuous Load Example .
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