Answer / viren89desai@yahoo.co.in

During a short circuit, a high amount of current can flow through a cable for a short time. This surge in current flow causes a temperature rise within the cable. High temperatures can trigger unwanted reactions in the cable insulation, sheath materials and other components, which can prematurely degrade the condition of the cable. As the cross-sectional area of the cable increases, it can dissipate higher fault currents for a given temperature rise. Therefore, cables should be sized to withstand the largest short circuit that it is expected to see.

http://www.openelectrical.org/wiki/index.php?title=Cable_Sizing_Calculation

We have drive feeding an output contactor for a 5000 hp motor @ 5kV application. The motor FLA is 629amps x 1.25% service factor = 786.25 amps The cable that we current have in place between the drive and the output contactor is 350kcmil- MV-105 (parallel cables). Per the NEC table 310.60 (C) (69). This show the cable ampacity is at 615 amps per cable for a rating of 1230 amps. We have derated the cable for the cable tray and the multiple cables application and our calculations show that after the correction factor factor we are at 922amps. 1230 amps x .75% correction factor factor = 922.5 amps. The customer is driving us to then use another safety factor of .25% off of the already derated cable. Can you please provide a longhand calculation for your solution on this application?

0 Answers   Siemens,

---

in control scheme dc logic wiring commonly using negative loop,what is the reason?if we use positive looping what will happen?

0 Answers   DNJ Energy LLC, WI,

---

two parallel conductors are carrying the current in the same direction.which of the following statements is true? (a)there is arepelling force between the conductors (b)the force increases when the distance between the conductors is increased (c)there is an attaracting force between the conductors (d)the force increases when the distance between the conductors is decreased

1 Answers  

---

Do you know how to measure the earth resistance? if so explain it

42 Answers   ABB, BEL, BridgeStone, College School Exams Tests, Dalkia, Dalmia Group, DEC, Electrical, Genpact, HEC, IOCL, JLL, L&T, MSEB, Saraca, Sical, Telecommunications, University Exams,

---

what is the difference between ceiling fan and wall mounteed fan technically

3 Answers  

---

Why inverter rating in KVA?

3 Answers  

---

A 150KW 440V motor is need to replace in the field instead of faulty one. what are the main parameter should I need to check?

1 Answers  

---

Define the term factor of inertia.

0 Answers  

---

Write the force balance equation of ideal dashpot element.

0 Answers  

---

what is fundamental difference between voltage and current

5 Answers  

---

What is bus-bar?

1 Answers  

---

a 3 phase motor was running with delta connected, suddenly one phase winding got burnt off, what will be the effect ?

8 Answers   Bhel, RRB, SR,

---