ArcFlash 2 (30)

Question 1

What is 1584.1?

Answer 1

Guide for specifying performance of an arc-flash study.

Question 2

How does 1584.1 treat the question of how many cases to study?

Answer 2

Engineering judgment.

Question 3

Does 1584.1 have content that affects our calculation?

Answer 3

Not really.

Question 4

What voltage range does 1584 cover?

Answer 4

208V - 15 kV

Question 5

How does 1584 treat single-phase and DC?

Answer 5

They’re not included.

Question 6

What does 1584 mean by a ‘one-bus-away run’?

Answer 6

We need current through the first upstream device, not total fault current at a point.

Question 7

What if we have only the melting time and not clearing time for fuses?

Answer 7

1584 gives percentages to add.

Question 8

What about time for relay instantaneous operation and breaker clearing time?

Answer 8

1584 says you have to add them.

Question 9

What is the flash-protection boundary?

Answer 9

Distance at which a second degree burn could occur.

Question 10

Do I need to remember anything about the arc-flash boundary equation?

Answer 10

Not really. It’s partly empirically based. Just put in the right numbers.

Question 11

The flash-protection boundary is based on what incident energy?

Answer 11

5.0 J/cm2

Question 12

What is 5 J/cm2 in cal/cm2?

Answer 12

1.2 cal/cm2

Question 13

Describe the 1584 equation for calculating arc-fault magnitudes.

Answer 13

Complex logarithnic equation with several terms.

Question 14

What two values of arc-fault are required?

Answer 14

100% and 85% (for slower clearing time)

Question 15

What is the first step in determining incident energy?

Answer 15

For the calculated arc-fault, the incident energy for ‘normalized’ time and distance.

Question 16

What is the ‘normalized’ time and distance?

Answer 16

Clearing time of 0.2 seconds and a distance to the person of 610 mm.

Question 17

What is the second step in determining the incident energy?

Answer 17

Adjusting the normalized energy to the actual clearing time and distance.

Question 18

What are the methods available for determining arc-flash levels?

Answer 18

NFPA 70E table, theoretical (Lee) method, 1584

Question 19

What effect does arc-time have on incident energy?

Answer 19

Linear

Question 20

What effect does distance from the arc have?

Answer 20

Inverse exponential affect, with the exponent depending on the enclosure size.

Question 21

What effect does X/R ratio, frequency, and electrode material have?

Answer 21

Little or no effect on arc current and incident energy, so they are neglected.

Question 22

How much impact does bus spacing have?

Answer 22

Incident energy depends primarily on calculated arc current. Bus gap is a small factor.

Question 23

How does 1584 characterize grounding?

Answer 23

Solid or ungrounded (everything else but solid).

Question 24

What kind of fault is 1584 based on?

Answer 24

3-phase. These produce the greatest energy, and anything less quickly escalates to 3-phase anyway.

Question 25

What is the 2 second rule?

Answer 25

It allows assuming a 2-sec max clearing on the basis that a person will move away quickly.

Question 26

In ETAP, what is the ‘X Factor’?

Answer 26

The is the exponent to be used in determining the effect of distance.

Question 27

What is the Limited Approach Boundary?

Answer 27

The distance from an exposed energized circuit part within which a shock hazard exists.

Question 28

Is LAB related directly to arc-flash?

Answer 28

Not that I can tell.

Question 29

What are the two options for ETAP arc-flash analysis?

Answer 29

Quick (local) and Global.

Question 30

How do deal with the 85% arcing current cases in ETAP?

Answer 30

ETAP runs the analysis with both values, and reports the worst one.