PCX Arc Flash Study

What is an Arc Flash study?

An arc flash study is a risk analysis that is performed by an electrical engineer. A correctly executed study can help improve plant safety by identifying the specific arc flash hazard at a given piece of equipment. It identifies the Arc Flash Protection Boundary, which is the closest approach allowed before PPE must be worn. Proper clothing or Personal Protective Equipment (PPE) must be worn once a worker steps inside the Arc Flash Protection Boundary. The main goal of arc flash PPE is to minimize burns to the body resulting from an arc flash incident. The only way to determine the proper PPE when working on a certain piece of electrical equipment is to have an Arc Flash Study completed. Qualified workers determine the proper PPE through the labeling from the study.

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Information about Arc Flash

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PPE Category Chart

01

Minimum Arc Rating of 4 cal/cm²

  • Hard hat
  • Arc-rated face shield
  • Safety goggles
  • Hearing protection
  • Leather gloves
  • Arc-rated long sleeved shirt
  • Arc-rated pants
  • Leather footwear
02

Minimum Arc Rating of 8 cal/cm²

  • Arc-rated face shield
  • Safety goggles
  • Hearing protection
  • Arc-rated balaclava
  • Leather gloves
  • Arc-rated long sleeved shirt
  • Arc-rated jacket
  • Arc-rated pants
  • Leather footwear
03

Minimum Arc Rating of 25 cal/cm²

  • Arc-rated flash suit hood
  • Safety glasses
  • Hearing protection
  • Arc-rated balaclava
  • Arc-rated flash suit jacket
  • Arc-rated long sleeved shirt
  • Arc-rated flash suit pants
  • Arc-rated pants
  • Leather footwear
04

Minimum Arc Rating of 40 cal/cm²

  • Arc-rated flash suit hood
  • Safety glasses
  • Hearing protection
  • Arc-rated gloves
  • Arc-rated flash suit jacket
  • Arc-rated long sleeved shirt
  • Arc-rated flash suit pants
  • Arc-rated pants
  • Leather footwear

What codes and standard
dictate Arc Flash Safety?

There are four different standards that dictate practices for the prevention of arc flash incidents in the United States:

NFPA 70 NEC (National Electric Code) – Mandatory by state law to comply with the NEC for all new construction. Versions 2014 and prior editions contain requirements for general arc flash warning labels:

110.16 (A)
“Electrical equipment, such as switchboards, switchgear, panelboards, industrial control panels, meter socket enclosures, and motor control centers, that are in other than dwelling units, and are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field or factory marked to warn qualified persons of potential electric arc flash hazards. The marking shall meet the requirements in 110.21(B) and shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.”

The 2017 edition requires detailed arc flash warning labels as specified in NFPA 70E.

110.16 (B)
“In addition to the requirements in (A), service equipment shall contain the following information:

1. Nominal system voltage
2. Arc flash boundary
3. At least one of the following:
a. Available incident energy and the corresponding working distance
b. Minimum arc rating of clothing
c. Site-specific level of PPE”

IEEE Standard – Serves as a guide for performing Arc Flash Hazard Calculations.

NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces– Provides a guide for safely working in hot electrical equipment. In regards to Arc Flash, it is guidance for making risk assessments (Arc Flash Studies), it details the requirements for arc flash boundaries, it serves as guidance for selecting appropriate PPE, and also guidance for establishing electrically-safe working conditions and employee training. NFPA 70 requires arc flash risk assessment. The NFPA 70E Section 130.5 states the following:

An arc flash risk assessment shall be performed and shall:

1. Determine if an arc flash hazard exists. If an arc flash hazard exists, the risk assessment shall determine:
a. Appropriate safety-related work practices
b. The arc flash boundary
c. The PPE to be used within the arc flash boundary

2. Be updated when a major modification or renovation takes place. It shall be reviewed periodically, at intervals not to exceed 5 years, to account for changes in the electrical distribution system that could affect results of the arc flask rick assessment.

3. Take into consideration the design of the overcurrent protective device and its opening time, including its condition of maintenance.”

OSHA – Addresses standards for work practices and has referenced compliance to NFPA 70E in the “general duty clause” as their basis for implementation. The general clause duty states that employers “shall furnish to each of its employees employment and a place of employment which are free from recognized hazards that are causing or likely to cause death or serious physical harm to his employees.” It considers NFPA 70E an industrial consensus standard and it intended for use by employers, and employees. OSHA expects employers and employees to comply with the provisions of NFPA 70E regardless of whether or not it has been “adopted” as an OSHA requirement.

What is included in a PCX Arc Flash Study?

PCX Corporation provides total NFPA 70E arc flash compliance as a service. An arc flash study for your facility includes the following:

  • Field surveys of new and existing equipment to obtain information necessary for an analysis
  • Evaluation of applicable OSHA, NFPA, and IEEE requirements that pertain to facilities
  • One-line diagram of existing electrical distribution
  • Short Circuit Study
  • Protection/Coordination Study
  • Protection Boundary Distance Calculations
  • Report with recommendations and stamped by a professional engineer registered in all 50 states
  • Printing labels and provide to EOR for each location

What do PCX calculations include?

  • Arcing Fault Currents
  • Protective Device Operating Time
  • Arc Fault Duration and Decay
  • Incident Energy
  • Arc Flash Protection Boundary
  • High Incident Energy Areas

Scope of services

The following services shall be provided by PCX

1. Initial meeting and data collection

2. One-line diagram

  • PCX shall generate a one-line diagram based on information from the data collection for each store.

3. Short Circuit Study

  • The information will be entered into ETAP modeling software by PCX.
  • A short circuit study shall be performed which gives the momentary and interrupting duties on each fault bus shown on the one-line diagram. A computer model will be used to sequentially place a bolted three-phase fault at each of the selected locations and perform accurate calculations of total fault current available at each location as well as the contribution from each adjacent bus.
  • PCX will evaluate the results of the ETAP program. The short circuit program’s evaluation of protective devices within the scope of this study will be analyzed for interrupting ability by comparing their interrupting rating with the maximum interrupting duty as determined from the above calculations. Protective devices will be tabulated, showing their interrupting ratings along-side their interrupting duties for ready evaluation of their capabilities.
  • The study will be run at normal operations.

4. Protection/Coordination Study

  • PCX will produce a report showing the results of the study (protective device evaluation; existing vs. recommended relay settings, motor protection settings, circuit breaker settings, etc.) and any other recommendations. This information will be used in the Flash Protection Boundary Distance Calculations.

5. Arc Flash Evaluation

  • PCX will use the information collected and the results of the short circuit study to provide the necessary input data required for the Arc Flash Hazard study. The specific information needed includes the calculated three-phase bolted fault currents at all system buses and all protective devices’ trip settings. Opening times can be obtained from the settings and the calculated fault currents.
  • The results of the study will include the calculated Incident Energy (in cal/cm2) and the calculated Arc-Flash Boundary at key system points within the scope of the short circuit study that have arc-flash hazards.

6. Arc Flash hazard labels

  • PCX will provide labels and each label will provide its Bus ID from the short circuit study, the calculated incident energy at the specified working distance, the arc-flash protection boundary, the bus voltage, the shock hazard boundaries, a description of the required combined PPE for both arc-flash hazard and shock hazard, the date of the study, and a disclaimer in regards to changes in equipment settings. As an additional service, PCX can install these labels as well as set device coordination according to the report

7. Final Report consisting of

  • Report Summary
  • ETAP One Line diagram
  • Input data and assumptions
  • Descriptions of the scenarios evaluated and identification of the scenario used to evaluate equipment ratings
  • Short circuit results

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