Click Here for
Your Service Guide

This example is a continuation of the short circuit analysis described in the example 3. The arc flash study will be conducted using IEEE 1584 procedure from the IEEE 1584 Guide for Performing Arc Flash Hazard Calculations implemented in the online arc flash calculator presented on this web-site. Incident energies and flash protection boundaries at nodes a) to j) of the power distribution system shown below will be determined.

Arc flash analysis requires 3 phase bolted short circuit current value and system line-line voltage at each of the potential fault points. These can be obtained by running online short circuit calculator. System's radial representation in terms of database records programmed in the calculator is shown below. The system "tree" is broken into levels, with each level being more focused than the last [more ..]:

• PSE[ 2000.00 (7.00X/R) +  17.13 (13.05X/R) =  2017.10 (7.03X/R)]
  • TX-1[ 222.33 (17.97X/R) +  18.40 (12.67X/R) =  240.72 (17.41X/R)]
    • C-5[ 229.13 (11.94X/R) +  0.00 (7.00X/R) =  229.13 (11.94X/R)]
      • TX-4[ 7.27 (3.79X/R) +  0.00 (7.00X/R) =  7.27 (3.79X/R)]
        • PNL-1[0.00(0.0X/R)]
    • C-1[ 231.10 (13.50X/R) +  4.13 (5.27X/R) =  235.20 (13.14X/R)]
      • TX-2[ 15.55 (5.93X/R) +  5.49 (5.15X/R) =  21.04 (5.71X/R)]
        • M-1[1.47(14.2X/R)]
        • C-2[ 15.66 (3.17X/R) +  1.48 (4.50X/R) =  17.14 (3.26X/R)]
          • MCC-2[1.48(4.5X/R)]
        • C-3[ 14.95 (3.29X/R) +  2.67 (4.50X/R) =  17.61 (3.43X/R)]
          • MCC-1[2.67(4.5X/R)]
    • C-4[ 222.85 (14.13X/R) +  14.31 (21.45X/R) =  237.16 (14.42X/R)]
      • TX-3[ 60.64 (12.98X/R) +  17.28 (25.10X/R) =  77.91 (14.54X/R)]
        • M-3[5.96(25.0X/R)]
        • M-4[8.94(28.4X/R)]
        • M-2[2.38(17.6X/R)]

ID	LABEL	DESCRIPTION	UP STREAM MVA	DOWN STREAM MVA	RES MVA	NODE
1	PSE	PSE-SOUTH 2000MVA S.E.	2000	17.3	2017	a
2	TX-1	TX-1 20 MVA Z=8% D-YRG	222.3	18.4	240.67	b
3	C-4	1-1/C-4/0 AWG 210 FEET CU	222.9	14.3	237.1	c
4	C-5	1-1/C-2/0 AWG 400 FEET CU	229	0	229	d
5	C-1	1-1/C-4/0 AWG 300 FEET CU	231.1	4.1	235.1	e
6	TX-3	TX-3 5 MVA Z=6% D-YRG	60.6	17.3	77.9	f
7	TX-4	TX-4 0.3 MVA Z=4% D-YG	7.27	0	7.27	g
8	TX-2	TX-2 1 MVA Z=6% D-YG	15.6	5.5	21.04	h
13	C-3	2-1/C-350 MCM 125 FEET CU	14.9	2.7	17.6	I
14	C-2	2-1/C-350 MCM 125 FEET CU	15.7	1.5	17.1	j

Table 3. Tabulated positive sequence short circuit current values in MVA.

ID	LABEL	BUS KV	UP STREAM KA	DOWN STREAM KA	RESULTING KA	NODE
1	PSE	115	10.1	0.1	10.1	a
2	TX-1	13.8	9.3	0.9	10.1	b
3	C-4	13.8	9.3	0.6	9.9	c
4	C-5	13.8	9.6	0.0	9.6	d
5	C-1	13.8	9.7	0.2	9.8	e
6	TX-3	2.4	14.6	4.2	18.8	f
7	TX-4	0.48	8.8	0.0	8.8	g
8	TX-2	0.48	18.8	6.6	25.3	h
13	C-3	0.48	17.9	3.3	21.2	I
14	C-2	0.48	18.9	1.8	20.6	j

Table 4. Tabulated bolted three phase short circuit current values in kA.

Also, the equipment configuration, namely gap between conductors, equipment class, grounding type, working distance, and the protective device operating time is needed for arc flash study.

The calculator uses bolted short circuit current values and the equipment configuration to calculate arcing current. The operating / arcing time is determined based on the arcing current, which can be considerably lower than the bolted fault current. The operating time can be obtained from the time-current characteristic of the upstream protective device of the faulted bus and the arcing current value estimated by online arc flash calculator.

If a main breaker or fuse protects the bus and this breaker or fuse is connected to the bus, then the arcing time would be equal to the trip time for this main device. This applies when a worker is working on the bus or on the load side of the main breaker/fuse. However, if energized work is required on the line side of the main breaker/fuse, the tripping effect of the main breaker must be excluded and the upstream trip device characteristic is used to calculate the arcing time.

Arc Fault Bus Name / Node	Arc Fault Bus, kV	Equip Type	Arc Gap, mm.	[1] Bolted SCC, kA	Arcing Current, kA	Arcing Time, sec.	Arc Flash Limit, ft.	Work Dist, inch	Incident Energy, cal/cm2	Risk Cate gory
PSE / a)	115	Open Air	178	10.1	10.1			38
MAIN SWITCH / b)	13.8	Switch gear	152	9.3	9.0	0.4	12.8	18	9.7	#3
BUS-7 / c)	13.8	Open Air	152	9.9	9.6	0.2	2.6	26	1.8	#1
BUS-9 / d)	13.8	Open Air	152	9.6	9.4	0.2	2.6	26	1.7	#1
BUS-3 - e)	13.8	Open Air	152	9.7	9.6	0.2	2.6	26	1.8	#1
REFINER - f)	2.4	Switch gear	102	14.6	14.1	0.54	30.1	18	22.3	#3
BUS-10 / g)	0.48	Switch gear	32	8.8	5.6	0.2	3.4	18	3.5	#1
BUS-4 / h)	0.48	Switch gear	32	18.8	10.6	0.34	8.3	18	15	#3
MCC-1 / i)	0.48	MCC	25	17.9	10.8	0.19	4.7	18	7.8	#2
MCC-2 / j)	0.48	MCC	25	18.9	11.2	0.19	4.6	18	7.7	#2

Table 5. Results of Arc Flash Hazard Analysis
^[1] - Bolted fault current the upstream protective device is subject to (see UPSTREAM KA column from table 4 above). This value is used to determine arcing current and arc duration the upstream protective device is subject to. Total short circuit current consists of current contributed both by upstream and downstream equipment (see RESULTING KA column from table 4 above).

Table 5 above shows the equipment configuration, arcing current determined by the calculator for the given configuration, system voltage and bolted fault current. Arc flash boundary, incident energy at specified working distance and risk category are determined based on IEEE 1584 procedure described in IEEE 1584 Guide for Performing Arc Flash Hazard Calculations and implemented in the online arc flash calculator.