Comply with the grounding requirements of the NEC and Canadian Electrical Code. Provide grounding recommendations that are compatible with other power grounding criteria. For more information or if ...

through the green equipment grounding conductor or metal conduit system, back through the electrical panel and to the utility ...

The National Electrical Code (NEC) generally does not apply retroactively, so you're not obligated to replace non-grounding-type receptacles. However, if you do replace them, the new ones must be ...