5.2. ERMUSR 03-11-2008/j
Elk River -~
Municipal Utilities
13069 Orono Parkway • P.O. Box 430
Elk River, MN 5330-0430
March 4, 2008
To: Elk River Municipal Utilities Commission
Jerry Takle
Jerry Gumphrey
John Dietz
From: Bryan Adams
Subject: Arc Flash Assessment
Phone: 763.441.2020
Fax: 763.441.8099
The arc flash issue has raised its head again. Approximately 20 years ago arc flash became a
discussion point with the adoption of OSHA ] 910.269. Arc flash is the light and heat energy
given off in an unintentional electrical contact between two energized conductors or an energized
conductor and ground. This is analogous to the light and heat energy given off as in arc welding
only much more intense due to the higher voltage involved. This is not electrical burns from
contact to an energized conductor where the current flows through the body.
OSHA 1910.269 states that the clothes worn by linepersons camlot make the injuries worse from
arc flash. At this point, linepersons could only wear clothes of natural fabrics such as cotton,
silk, wool, etc.; not synthetic materials like rayon, nylon, etc. that can melt and cause further
injury from burning fabric.
Section 410 of the National Electric Safety Code (NESC) requires employers to do an arc flash
assessment by January 1, 2009. The employer shall require employees to wear clothing or a
clothing system that has an effective arc rating not less than the anticipated level of arc energy.
The NESC has an exception which states that for secondary systems below 1000x, applicable
work rules required by this part and engineering controls shall be utilized to limit exposure. In
other words, we are not required to follow the arc flash assessments below 1000x. Unfortunately
this is the area where many hazards are. The National Electric Code (NEC) which generally
applies to voltages less than 600v (covers electricians, not electric utilities) and the National Fire
Protection Agency (NFPA) do not include the NESC exception. The NFPA does not apply to
electric utilities.
The level of energy from an arc flash is a function of distance from the arc flash, clearing time of
fault (how quickly the fuse or disconnection device reacts and opens the circuit) and magnitude
of fault current available. These three variables make a detailed engineering analysis very
difficult and only generalized conclusions can be made.
The dilemma we have is there are three codes (NESC, NEC, and NFPA) that do not agree, yet
the code we fall under excludes the area that contains the real hazards, an imperfect engineering
analysis with only general conclusion. The end result is that we may have to change our work
practices and the protective clothing we provide to our employees.
Attached please find the following information for your review:
1) Arc flash analysis completed by USG.
2) Copy of our current Fire Retardant Clothing Policy.
3) Section 31 of our Employee Handbook titled Employee Clothing. The clothing we now
provide satisfies Hazard Risk Category 1 per the arc flash analysis.
Staff is currently reviewing our Fire Retardant Clothing Policy and work rules and will make a
recommendation at our meeting.
ELK RIVER MUNICIPAL UTILITIES
FIRE RETARDANT CLOTHING POLICY
Attached to this policy are the ARC/Flash Assessment, Requirements for Personal
Protective Equipment, and Clothing Flammability Assessment Table for electrical work.
'vb'~ yen working on or near energized equipment the operational personnel of the Eik River
Municipal Utilities shall wear clothing [underwear, outerwear (pants, shirt) weatherwear
jacket, coveralls, etc.)] not containing acetate, nylon, polyester or rayon. The outer layer shall
be a minimum of 14 oz. 100% cotton pants or coveralls and a minimum of 7.5 oz. 100%
cotton shirt, jacket or coat. Under the following circumstances a nomex or equal fire retardant
switching coat shall be worn as the outer layer.
~) In Substations while operating Line or By-pass fuses, disconnect blades, air switches or
any live line work on 15 Kv and above.
2) Performing live line work on the secondary side of any 3 phase transformer bank. (/f
only taking line voltage readings; cotton clothes with rubber gloves are
adequate).
3) Removing/ Installing direct 3 phase metering on energized meter banks greater than
270 volts.
If clothing becomes ripped, frayed, etc. it shall be replaced. In regard to clothing
appearance to our customers, no cut-off shirts, muscle shirts, or white safety shoes shall be
worn.
---~r-- ~ -------
30. EMPLOYEE SAFETY
All regulations and laws of the State of Minnesota and rules of the Utilities Commission
governing the safety of employees and the public shall be complied with by the employee
and the Utilities Commission.
The Utilities will provide one pair of safety glasses at the time of employment. The
employee shall provide the correct prescription for the safety glasses.
The 1~itilities ~4-ill nay the pct of r1eiA, Safet" lenses ,~„ .~ ,~- ~
r- ~ },on a c„angc in ~„e prescr;ptron. I~
needed, frames will be replaced every four years.
Safety glasses that are broken or darnaged while the employee is on the job will be
replaced by the Utility.
31. EMPLOYEE CLOTHING
The Utilities will, after an initial issue of five long sleeved shims and five short sleeved
shirts per outside employee, replace annually. The Utilities will also replace as needed:
Nomex ILIA lined bib overalls, Nomex IIIA lined parka and hood, Nomex IIIA lined
bomber jacket, and hats with the appropriate emblems and identification. The policy also
includes the following additional items: lineman's climbing boots, summer work boots or
shoes, rubber boots, rubber overshoes, insulated ~~-inter boots, and coveralls (used for
maintenance on trucks). It is expected that the employee wear these ~~ork items during
~ti~orking hours. Worn out items to be turned in. The Utilities ~~~ill issue a check to the
supplier for the covered items. For outside operational employees whose job duties do
not require Nomex clothing, non-Nomex clothing items will be furnished.
32. EXPOSURE TO HALARllOUS SUBSTANCES
Any employee routinely exposed to hazardous substances or harmful physical agents as
defined in the Minnesota Employee Right to Know Act of 1983 (Laws 1983, Ch. 316,
1`~1inn. Stat. ] 82.675) shall be trained before being assigned or reassigned work exposing
the employee to such substances or agents and shall be given training annually thereafter.
Training shall include an explanation of how and where information about hazards is
stored in the work place, how the hazards are labeled, and where to obtain specific
information. The supervisor (or other designated official) shall provide for such training
and for compliance with the "Minnesota Employee Right to Know Act of 1983",
including the establistunent of specific policies to insure compliance with the state law
and regulations. An employee acting in good faith has the right to refuse to work under
conditions ~a~hich the employee reasonably believes present an imminent danger of death
or serious physical harm to the employee.
ARC FLASH ANALYSIS
FOR
ELK RIVER
MUNICIPAL UTILITIES
Respectfully submitted,
UNITED SERVICES GROUP
Prepared by~------~~
,~ nne Parent
Approved by
n, r.
I hereby certify that this plan or report was
prepared by me or under my direct supervision
and that I am a duly Registered Professional
Engineer under the laws of the State of
Minnesota.
Q~
ed Newton, P.E.
Date 2 2, C~ Reg. No. 45430
nited
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THREE-PHASE TRANSFORMER ARC FLASH ANALYSIS FOR
ELK RIVER MUNICIPAL UTILITIES
2i22io8
Arc flash hazard analysis is important to determine the PPE required for personnel
when working with energized equipment. This hazard analysis focuses on three-phase
padmounted and substation transformers at various working distances and operational
voltages. In addition, time-current curves (TCCs) with the arc flash hazard category
superimposed on the TCC are provided for various system fuses and protective
devices.
The bolted fault current was calculated using an infinite bus calculation and input into
the IEEE 1584 arc flash analysis spreadsheet. The resultant arcing fault current was
calculated within the spreadsheet through a formula derived from experimental analysis
of the relationship between the bolted fault current and the anticipated arcing fault
current. Using the calculated arcing fault current value, the total clear time of the
transformer high-side fuse or upstream protective device was determined and input into
the spreadsheet. The time in which a fault is cleared is by-large the largest factor in the
calories emitted during a fault event. In the case of substation transformers, the total
clear time was determined using the protection settings proposed in the 2007
Sectionalizing Study. For transformers less than 500 kVA, arc flash hazard analysis was
performed for both 208V and 480V bus voltages. For all transformers, working distance
of both 381mm (15") and 2440mm (8') were used, which correspond to the distance
between the chest/torso and the energized equipment while working with your hands
(381 mm) and a hotstick (2440mm). Analysis results include an arc flash hazard risk
category classification and arc flash boundary distance, or the distance in which a
second degree burn to the face and torso does not occur.
Also provided is a table relating transformer secondary current to transformer primary
current. This table illustrates that for many transformers a value close to the infinite bus
bolted fault current and/or calculated arcing fault current is obtainable given the location
of the transformers and the available primary fault current at that location.
The following table defines the PPE requirements for each of the arc flash hazard
classifications:
PPE Ratin Table from NFPA 70E -Table 130.7 C 11 - 2004 Edition
Min. Cal/cm Ratin of PPE Max. Cal/cm Ratin of PPE Risk Cate o
0 1.2 0
1.2001 4 1
4.001 8 2
8.001 25 3
25.001 40 4
40.001 No maximum X
Exposure to Risk Category X equipment is not recommended.
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Arc Flash Hazard Category Descriptions
from NFPA 70E -Table 130.7 C 10 - 2004 Edition
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i
t Hazard /Risk Cate o
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ve
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0 1 2 3 4
Non-melting T-shirt short-sleeved : X X X
(according to: Shirt Ion -sleeved : X
ASTM F 1506-
X
00) or Untreated Pants (long): X X Noted X
Natural Fiber: Note 1
Long-sleeved shirt: X X Note6 X
Fire-Resistant Pants: X
FR
Cl
hi N t 1 N t 3 Note6
(
)
ng:
ot
Coverall: Note2 Note4 Note6 Note2
Jacket, arka, or rainwear: AN AN AN AN AN
Flash suit ~acket multila er : X
Flash suit ants multila er : X
Hard hat: X X X X
Head
protection: FR hard hat AR AR
liner: ~
Safet lasses: X X AL AL AL
Eye protection:
Safet o le: AL AL AL
Fire Resistant Arc-rated face X
(FR) Protective shield or flash Notes
Equipment: Face & head suit hood:
area protection: Flash suit hood: X X
Hearing X X X
rotection: Notes
Hand protection -leather gloves AN X X X
Note?
Foot protection -leather work AN X X X
shoes:
AN = As needed
AL =Select one in group
AR = As required
X =Minimum required
*Categories 2, 3, & 4 -require cotton underwear
Note1: Regular weight (minimum 12 oz/yd2 fabric weight),
blue jeans are acceptable in lieu of FR pants. The FR pai
Category 1 shall have a minimum arc rating of 4.
Note2: Alternate is to use FR coveralls (minimum arc rating
and FR pants.
Note3: If the FR pants have a minimum arc rating of 8, lone
untreated natural fiber are not required beneath the FR pants.
Note4: Alternate is to use FR coveralls (minimum arc rating
untreated natural fiber pants and T-shirt.
untreated, denim, cotton
its used for Hazard/Risk
of 4) instead of FR shirt
pants of non-melting or
of 4) over non-melting or
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Notes: A faceshield with a minimum arc rating of 8, with wrap-around guarding to
protect not only the face, but also the forehead, ears, and neck (or, alternatively, a flash
suit hood), is required.
Note6: Alternate is to use two sets of FR coveralls (the inner with a minimum arc rating
of 4 and outer coverall with a minimum arc rating of 5) over non-melting or untreated
natural fiber clothing, instead of FR coveralls over FR shirt and FR pants over non-
melting or untreated natural fiber clothing.
Note7: If voltage-rated gloves are required, the leather protectors worn external to the
rubber gloves satisfy this requirement.
3 of 3
ELK RIVER MUNICIPAL UTILITIES
Summary of Incident Energy Calculations
Results ftom IEEE Std. 1584-2002 -IEEE Guide for Performing Arc-Flash Hazard Calculations
PPE Calculated
Incident Working Arc Flash Hazard Arcing Fault
Voltage Energy Distance Boundary Category Current
Location (cal/cm2) (inches) (inches) (amps sec.)
2/29/2008
Reduced Reduced
Calculated Calculated Calculated
Arcing Fault Arcing Fault Arcing Fault
Current Current Cunent
(amps pri.) (amps sec.) (amps pri.)
45 kVA xmfr - 358C03 fuse 208 0.7 15.0 10.21 0 3,031 98 2,577 73
45 kVA xmfr - 358C03 fuse 480 0.3 15.0 5.18 0 2,120 376 1,802 207
45 kVA xmfr - 358C03 fuse 208 0.0 96.0 10.21 0 3,031 98 2,577 73
45 kVA xmfr - 358C03 fuse 480 0.0 96.0 5.18 0 2,120 376 1,802 207
75 kVA xmfr - 358C05 fuse 208 3.1 15.0 28.66 1 4,293 122 3,649 94
75 kVA xmfr - 358C05 fuse 480 0.5 15.0 8.65 0 3,245 445 2,758 273
75 kVA xmfr - 358C05 fuse 208 0.2 96.0 28.66 0 4,293 122 3,649 94
75 kVA xmfr - 358C05 fuse 480 0.0 96.0 8.65 0 3,245 445 2,758 273
112.5 kVA xmfr - 358C08 fuse 208 20.7 15.0 103.81 3 5,222 140 4,438 109
112.5 kVA xmfr - 358C08 fuse 480 2.3 15.0 23.45 1 4,123 505 3,504 323
112.5 kVA xmft - 358C08 fuse 208 1.3 96.0 103.81 1 5,222 140 4,438 109
112.5 kVA xmfr - 358C08 fuse 480 0.2 96.0 23.45 0 4,123 505 3,504 323
150 kVA xmfr - 358C08 fuse 208 20.1 15.0 101.48 3 5,540 146 4,709 114
150 kVA xmfr - 358C08 fuse 480 2.3 15.0 23.24 1 4,433 526 3,768 341
150 kVA xmfr - 358C08 fuse 208 1.3 96.0 101.48 1 5,540 146 4,709 114
150 kVA xmfr - 358C08 fuse 480 0.1 96.0 23.24 0 4,433 526 3,768 341
225 kVA xmfr - 358C10 fuse 208 106.7 15.0 315.71 X 6,196 158 5,267 125
225 kVA xmfr - 358C10 fuse 480 9.5 15.0 61.03 3 5,083 571 4,320 377
225 kVA xmfr - 358C10 fuse 208 6.9 96.0 315.71 2 6,196 158 5,267 125
225 kVA xmfr - 358C10 fuse 480 0.6 96.0 61.03 0 5,083 571 4,320 377
300 kVA xmfr - 358C10 fuse 208 90.6 15.0 282.43 X 7,537 184 6,406 146
300 kVA xmfr - 358C10 fuse 480 9.0 15.0 58.94 3 6,459 666 5,490 452
300 kVA xmfr - 358C10 fuse 208 5.9 96.0 282.43 2 7,537 184 6,406 146
300 kVA xmfr - 358C10 fuse 480 0.6 96.0 58.94 0 6,459 666 5,490 452
500 kVA xmfr - 358C12 fuse 208 462.9 15.0 854.85 X 9,745 226 8,283 181
500 kVA xmfr - 358C12 fuse 480 27.5 15.0 125.73 4 8,844 827 7,517 579
500 kVA xmfr - 358C12 fuse 208 30.0 96.0 854.85 4 9,745 226 8,283 181
500 kVA xmfr - 358C12 fuse 480 1.8 96.0 125.73 1 8,844 827 7,517 579
750 kVA xmfr - 353C14 fuse 480 6.2 15.0 45.60 2 11,239 985 9,553 702
750 kVA xmfr - 353C14 fuse 480 0.4 96.0 45.60 0 11,239 985 9,553 702
1000 kVA xmfr - 353C16 fuse 208 3473.3 15.0 3358.14 X 13,421 295 11,407 239
1000 kVA xmfr - 353C 16 fuse 480 12.8 15.0 74.81 3 13, 082 1,104 11,119 796
1000 kVA xmfr - 353C16 fuse 208 225.3 96.0 3358.14 X 13,421 295 11,407 239
1000 kVA xmfr - 353C16 fuse 480 0.8 96.0 74.81 0 13,082 1,104 11,119 796
1500 kVA xmfr - 353C16 fuse 480 11.6 15.0 70.04 3 16,939 1,348 14,397 988
1500 kVA xmfr - 353C16 fuse 480 0.8 96.0 70.04 0 16,939 1,348 14,397 988
2000 kVA xmfr - 353C 17 fuse 480 21.2 15.0 105.28 3 20,021 1,539 17,017 1,138
2000 kVA xmfr - 353C17 fuse 480 1.4 96.0 105.28 1 20,021 1,539 17,017 1,138
.2500 kVA xmfr - 353C17 fuse 480 19.6 15.0 99.81 3 24,110 1,788 20,492 1,334
2500 kVA xmfr - 353C17 fuse 480 1.3 96.0 99.81 24,110 1,788 20,492 1,334
ELK RIVER MUNICIPAL UTILITIES
Summary of Incident Energy Calculations
Results from IEEE Std. 1584-2002 -IEEE Guide for Performing Arc-Flash Hazard Calculations
PPE Calculated
Normal Working Arc Flash Hazard Arcing Fault
Voltage Operation Distance Boundary Category Current
Location (cal/cm2) (inches) (inches) (amps sec.l
Station 14 TR#3 & TR#4 12.47 21.0 15.0 283.53 3 8,449
Station 14 TR#3 & TR#4 12.47 3.4 96.0 283.53 1 8,449
West TR#1 12.47 20.4 15.0 275.19 3 8,082
West TR#1 12.47 3.3 96.0 275.19 1 8,082
West TR#2 12.47 16.9 15.0 227.74 3 6,629
West TR#2 12.47 2.8 96.0 227.74 1 6,629
Otse o TR#1 12.47 22.4 15.0 303.44 3 6,630
Otse o TR#1 12.47 3.7 96.0 303.44 1 6,630
North TR#1 12.47 6.0 15.0 78.67 2 4,231
North TR#1 12.47 1.0 96.0 78.67 0 4,231
Waco TR#1 12.47 22.7 15.0 308.50 3 7,897
Waco TR#1 12.47 3.7 96.0 308.50 1 7,897
Fdr 71 - SG302/303 12.47 1.0 96.0 80.80 0 3,760
Fdr 82 - SG98/99 12.47 0.9 96.0 68.57 0 2,932
Fdr 52 - SG501/502 12.47 1.3 96.0 104.79 1 5,078
Fdr 63 - SG202/203 12.47 0.5 96.0 41.93 0 1,769
r 5 - 50 12.47 96.0 63.35 2,401
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ARC FLASH HAZARD TIME-CURRENT CURVES FOR
ELK RIVER MUNICIPAL UTILITIES
Zi2oios
The following arc flash hazard time-current curves (TCCs) illustrate the arc flash hazard
category at .various points on the TCC for selected fuses and protective devices.
Analysis was performed at both 15" (381 mm), equivalent to doing work with ones
hands, and 8' (2440mm), equivalent to doing work with a hotstick /shotgun stick. In
creating these curves, defined fault current values were used as opposed to the infinite
bus bolted fault calculations and the resultant calculated arcing fault current. Given the
selected fault current value, the protective device's total clear time was input into the
IEEE 1584 spreadsheet resulting in arc flash hazard category for the given fault current.
For current values between that shown on the TCC, the arc flash hazard category
should be assumed to be the higher of the two hazard categories.
It can be seen that many fuses have an arc flash hazard category greater than 2. While
these results are accurate for the illustrated fault currents, for many protective device
locations a fault with a magnitude less than 500A is uncommon. In many cases,
especially with underground conductor, fault currents that we have seen are at least
50% of the maximum available fault current at a given location.
When consulting arc flash hazard TCCs to deduce the arc flash hazard risk category at
a given location, remember that it is the fuse upstream of the arcing point that will likely
clear the fault. For example, if replacing an 80T fuse reference the TCC for the
protective device upstream of the 80T fuse.
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30T Fuse Arc Flash Hazard
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