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# Designing Low Voltage Non-Motor Industrial Feeder Circuits

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## Calculating ampacity ratings of feeders conductors

### Factors Affecting Ampacity Ratings

Although there are many factors that affect the ampacity ratings of conductors, this ModuleÂ will restrict the discussion to the following three factors:

• Continuous Current
• Short Circuit Current
• Voltage Drop

### Continuous Current

The National Electric Code (NEC) defines the continuous current rating of a conductor asÂ ampacity, which means â€śthe current in amperes that a conductor can carry continuously underÂ the conditions of use without exceeding its temperature ratingâ€ť.

The NEC recognizes that the maximum continuous current carrying capability of a conductorÂ varies with the different conditions of use and the insulation temperature rating of theÂ conductor itself.

For example, ambient temperature is a condition of use. A 75Â°C conductorÂ installed outdoors in Saudi Arabia would have very little ampacity capability compared to theÂ same temperature-rated conductor installed indoors in an air-conditioned space.

AnotherÂ example of condition of use is the number of conductors that are installed in a racewayÂ (conduit).

### Short Circuit Current

The short circuit current rating of a conductor is the maximum current that a conductor canÂ carry, for a specific and very short time interval, without reaching temperatures that willÂ permanently damage the conductor insulation.

Note –Â The next Information Sheet will discussÂ in detail the calculation of the short circuit ratings of conductors.

### Voltage Drop

Because most electrical equipment is voltage-sensitive, it is very important to have withinÂ equipment and design standard tolerances, the proper voltage at the terminals that are servingÂ the equipment. Any excessive voltage drop could possibly damage the equipment and impairÂ its proper operation.

Note – Calculating the voltage drop of feeder conductors will beÂ discussed later in this Module.

 Title: Designing Low Voltage Non-Motor Industrial Feeder Circuits – Saudi Aramco Format: PDF Size: 0.38MB Pages: 86 Download: Right here | Video Courses | Membership | Download Updates

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