Cummins Electric, LLC.

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Arc Flash/Blast Basics!

Posted on May 25, 2012 at 9:50 PM Comments comments (175)

When a phase to ground or phase to phase short occurs at over 250 volts there is a potential for an arc flash/blast. The severity of the incident depends on a number of factors including the distance to the supply transformer, the rated fault current of that transformer, the size of the conductors coming from the transformer and the rating of the over current device. An arc flash/blast emits massive amounts of energy referred to as Incident Energy.


Incident Energy: The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. One of the units used to measure incident energy is calories per centimeter squared. (cal/cm²)


An Arc flash can reach temperatures of 35,000˚F (four times hotter than the suns surface) at these temperatures copper will expand to 67,000 times its' original mass.


1.2 cal/cm² - 2nd degree burns

1.5 cal/cm² - 3rd degree burns

4 cal/cm² - Hazard Risk Category 1 (HRC1)

8 cal/cm² - HRC2

25 cal/cm² - HRC3

40 cal/cm² - HRC4

GFCI's Save Lives!

Posted on May 25, 2012 at 9:50 PM Comments comments (0)

Did you know a 60 watt light bulb has a current of 0.5 amps? (500 milliamps) From 200 to 500 milliamps, the heart clamps tight. At only 1.5 amps tissue and organs start to burn!

Ground Fault Circuit Interrupter (GFCI). A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device. [NEC 2011]

Informational Note: Class A ground-fault circuit-interrupters trip when the current to ground is 6 milliamps or higher.

The GFCI senses the fault current and trips (de-energizes the circuit) in less then 0.1 second to save lives!