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 MinimumHelpful 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
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
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