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.
Receptacle Outlets per 20 Amp Circuit | Before: 13 | Recommended: 3 to 6 |
Neutrals | Before: Full size or downsized neutral (on 3-phase systems) | Recommended: Use double size neutral (CBEMA) or larger |
Before: One neutral shared among equipment (on 1-phase branch) | Recommended: Separate neutrals or upsized neutral back to panel | |
Phase Conductors | Before: Standard phase conductor sizing per code | Recommended: Use upsized phase conductors to minimize heating for harmonics |
Circuits | Before: Can shared among many outlets and uses | Recommended: Use separate circuits for harmonic-sensitive loads |
Grounding | Before: Can use metal conduit as grounding conductor | Recommended: Use separate insulated wire as grounding conductor |
Before: Downsized grounding conductor | Recommended: Use full size or over size grounding conductor | |
Before: (Commercial/Industrial) Must use metal water pipe and a concrete-encased electrode |
Recommended: Use a copper ground ring and multiple interconnected ground rods | |
Before: Use a second ground rod if first is over 25 ohms (no resistance measurement required) | Recommended: Use multiple rods or ring and measure to ensure very low resistance to ground | |
Before: Access floor for equipotential grid in computer mainframe room | Recommended: Use copper system for equipotential grid | |
Before: No lightning or surge protection | Recommended: Use lightning and surge protection |