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Electrical

Wiring for Power Quality

The table below illustrates some of the new wiring practices recommended to achieve a high level of power quality. Many of the "before" practices are still reflected in building codes today.

	Old Practice or Code Minimum	Helpful Procedures or Current Recommended Practice
Receptacle outlets per 20 amp circuit	13 maximum	3 to 6 maximum
Neutrals	Shared neutral, or even downsized neutral (on 3-phase systems)	Use double-size neutral or larger on 3-phase systems
Neutrals	One neutral shared among equipment (single-phase branches)	Use separate full-size neutral for each phase, back to panel
Phase Conductors	Standard phase conductor sizing per Code	Use upsized phase conductors to minimize voltage fluctuations
Circuits & Panelboards	Can be shared among many outlets and uses	Use separate branch circuits for sensitive loads, emanating from separate panelboards, supplied by separate feeders (from separate K-rated transformers, if possible)
Grounding	Can use metal conduit as grounding conductor	Use separate insulated copper wire as grounding conductor
	Downsized grounding conductor	Use full-size or upsized grounding conductor
	Grounding electrode system can consist of as little as a metal underground water pipe and an 8-foot ground rod	Use a copper ground ring (4/0 or larger ) and multiple interconnected ground rods to supplement the required electrodes in new construction
	Use a second ground rod if first measures over 25 ohms (no resistance measurement or further action is required)	Use multiple rods with a ground ring and measure before and after installation to ensure low resistance to ground (10 ohms or less is desirable, even less for certain sensitive applications, such as telecommunications facilities)
	Access floor used for equipotential grid in computer mainframe room	Use a copper grid system for equipotential grid
	No lightning or surge protection required	Use adequately sized lightning and surge protection systems
Other Equipment	Standard-rated transformers, circuit breakers, and panels	Use harmonic-rated transformers and panels where electronic loads are present
Other Equipment	Use standard-size neutral and ground buses in panel boards	Use 200% rated neutral and ground buses where electronic loads are present
Circuit Breakers	Can use bolt-in or snap-in circuit breakers	Use bolt-in circuit breakers for more secure, reliable connections

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Useful Resources

Busbar section includes AC and DC ampacity tables, mechanical properties, sources, and additional engineering information.

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