Building Electrical Systems

• Introduction
• Understanding Electric Power
• Power System Modeling
• Electrical Wiring
• Conduit Systems
• Electric Power
• Electric Power Quality
• Electric Motors
• Lighting
• Lighting - Part 2
• Grounding
• Summary
• References and Resources

Introduction

Three issues dominate the design, construction and operation of electrical systems in educational facilities:

1. Fire safety.   The modern way of fighting fires is with electrical power present so parallel and auxiliary systems are conceived to ensure occupant egress and to provide power to fire fighters.  One of the leading practice documents is The Life Safety Code© (NFPA 101) which, along with documents prepared by the International Code Council (ICC), are either adopted as a whole or used as resource documents for variants in the building codes promulgated by individual states.   Both NFPA and ICC documents refer to the National Electrical Code© (The NEC, or NFPA 70) for prescriptive requirements for actually wiring the emergency lighting systems, elevator and fire pump power.
    
2. Energy efficiency.  Many organizations are addressing energy standards; the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) is one of the leaders establishing national standards to meet federal energy efficiency objectives asserted by the Environmental Protection Agency and the Department of Energy.  ASHRAE has traditionally prepared leading practice documents for the energy efficiency of installed HVAC mechanical systems but in recent years has moved into lighting efficiency.  Since the NEC is principally a fire safety document — with wiring rules that have evolved for the safe use of electricity in the built environment — many have observed that the NEC is out of step with the national effort to conserve energy.  Wire sizing rules — and particularly the rules for sizing transformers — may result in the production of waste heat that must be removed by the systems classically governed by ASHRAE leading practice documents.
    
3. Electrician's safety. The rise of leading practices in limiting the effect of electrical arc flash originated in the early conception of the Occupational Safety and Health Administration (OSHA).  The NFPA prepared a document entitled, NFPA 70E - Electrical Safety in the Workplace, for use by OSHA in promulgating rules for reducing fatalities among electrical professionals working on live equipment.  In recent years, many in the electrical industry have tried to translate the rules of NFPA 70E — an operation and maintenance document — into NFPA 70 — a design and installation document.  The effort has not been successful so far.  One of the reasons, which facility managers may appreciate, is that design and construction budgets are rather different from operations and maintenance budgets.

In this chapter we shall illustrate the broad contours of these issues with a numerical example of a typical building power system.  The numerical example should put into relief the parts of a power system design that is focused on fire safety; how electrical engineers conform to the thermal limits of wiring systems.  The numbers shall show how the fire safety requirements of the NEC may not agree with the energy efficiency objectives of ASHRAE.  Finally, the numbers will be run for a typical flash hazard calculation to show how the least expensive moment to meet OSHA’s workplace safety requirements is when a building’s internal electrical distribution system is commissioned and accepted.