Tech Tip #16

Arc Flash Hazard Analysis and NFPA 70E

This Tech Note is provided by Phil Hamilton of Hargrove And Associates Inc. For additional information, visit Hargrove's web site at http://www.hargrove-associates.com

Introduction

You are probably aware of recent developments in workplace safety for the electrical worker.  Your insurance provider is probably asking how you are addressing the requirements of NFPA 70E which OSHA has recently endorsed.  While Arc Flash is a new buzzword in industry today, power distribution system analysis has always been a part of good electrical system design.  Unless you have an arc flash expert on staff, you will need a qualified firm  to assist in evaluating plant electrical power systems and recommending procedures that meet the requirements of NFPA 70E.

Independent Advice

You will need  a firm that can provide independent advice and recommendations not dependent on any specific manufacturer’s equipment.  While many of the electrical equipment manufacturers have experts qualified to provide the analysis, they tend to offer solutions that require purchasing their equipment.

Starting Point

A Short Circuit Study with Protective device coordination analysis is the starting point for understanding your power distribution system characteristics and capacity.  Among other things, these studies will determine the incident energy available at worker exposure points in your electrical system.  From this information, limits are established on the unprotected approach distances and the proper level of PPE required while working on equipment.  This analysis is based on the NFPA 70E and IEEE Standard 1584.

Benefits of Arc Flash Hazard Analysis

In order to determine the impact of NFPA 70E within your plant, you will need to answer these questions:

1. What safety requirements of NFPA 70E will impact my plant operations?

2. What procedures must be developed for worker safety?

3. What type of safety clothing and equipment will be required?

4. Are there practical alternatives to reduce arc flash hazard?

5. Will fault currents be safely interrupted in the event of a short circuit?

6. Will plant outages be confined to the smallest possible areas of the plant?

7. What are the safe distances from exposed electrical components?

8. Can power factor improvement decrease my power bill?

9. Is harmonic content affecting system performance?

10. Can my electrical distribution system handle a proposed plant expansion?

Power System Analysis Results

A power system analysis can:

1. Determine proper interrupting capability of electrical equipment

2. Determine proper protective device coordination, isolating electrical power at the proper point

3. Indicate opportunities for power factor correction, lowering electrical power bill

4. Indicate excessive harmonic content and recommend solutions for mitigation

5. Help coordinate electrical load flow, assuring available power for expansions

6. Determine the calculated incident arc energy

7. Recommend electrical energy monitoring hardware based on existing equipment

8. Improve the Plant Electrical documentation

Typical Power System Study Components

System Fault Study   Perform a three-phase and line-to-ground fault analysis of the electrical distribution system from the utility ties to the lowest level to be documented.  The case study calculations illustrate the worst case short circuit currents for the switching configuration, including interrupting equipment duty evaluation.  A one-line diagram is generated to illustrate the system components, configuration, and impedance data.  The device and bus nomenclature used in the model, fault calculation prints and coordination curves are included.

Protective Device Coordination Study   This is performed for the electrical system for both phase and ground protection devices. The relay coordination study extends from the utility inter-tie downstream, to the 480V switchgear feeder breakers serving motor control centers and continues to the lowest level to be documented.  Recommended low voltage settings are provided for 480V switchgear main and feeder breakers, and fuses to allow proper coordination.  The study includes recommendations for protective device settings which allow the optimum coordination.

Arc Flash Hazard Study  A flash hazard analysis includes the calculation of the flash protection boundary limits and the incident energy exposure for the maximum arc producing flash expected from a piece of electrical equipment.  The study determines incident energy exposure level and arc-flash protection boundaries for electrical equipment in accordance with IEEE-1584 and NFPA-70E.  The study is based on the protective device settings and the interrupting device clearing times.  The study makes recommendations for improvements to lower the incident energy levels.

Load Flow Study The results predict power flow magnitudes, voltage levels and losses in branches of the system based on the operating conditions.  The results are useful for planning future expansions.

Harmonic Measurement Service This evaluation is to identify harmonic content of electrical parameters at the facility load centers.  Recommendations will be made for mitigation, if required. 

Power Factor Study. The study is based on actual load measurements. The results are evaluated and specific recommendations made for power factor improvement. This often lowers the plant power bill.

Why Hargrove and Associates? 

Our engineers have been performing plant electrical system analysis to determine available short circuit current, safe circuit interrupting capacity and proper coordination of protective devices for a combined total  of over 100 years.  We are currently assisting customers in meeting the requirements of NFPA 70E. We do not represent any equipment manufacturer and can provide independent advice to meet your goals at the minimum cost.

 Founded in 1995, Hargrove and Associates provides comprehensive engineering, technical support and project management services to industrial and commercial customers throughout the Southeast. 

We function as an extension of our customers’ plant engineering or facility management team.  Our experienced engineering and project management staff can assist with:

• Developing innovative process solutions or facility plans

• Design and construction management services to deliver the facility solution

• Engineering support for continuous facility improvements

• Technical support for maintenance, planning and inspection

• Consulting and site management for plant relocations, asset sales or facility demolitions.