Change Summary

• New requirements were added for power inlets used with optional standby generators to ensure that disconnection of the power inlet does not occur under load. Optional standby equipment containing power inlets rated 100-amperes or more for the connection of a generator source are to be listed for the intended use and be equipped with an interlocked disconnecting means.

Expert Analysis

Optional standby systems are those backup systems that are utilized when normal power failure can cause physical discomfort, serious interruption of an industrial process, damage to process equipment, or disruption of business, but the power failure does not cause lifethreatening conditions or impose any safety hazards. Optional standby systems typically consist of one of two types of systems — those that are permanently installed in their entirety including prime movers, or those that are arranged for a connection to a premises wiring system from a portable alternate power supply.

It is not uncommon to find power inlet boxes serving as a gateway for the outside power source, typically installed near the main service electrical panelboards and wired to a manual transfer switch, which restores power to the entire main electrical panelboard or selected branch circuits.

For the 2017 NEC, optional standby equipment containing power inlets rated 100-amperes or more for the connection of a generator source be “listed for the intended use” and be equipped with an interlocked disconnecting means. This new provision will ensure that disconnection of the power inlet does not occur under load conditions. A portable generator can be located outside “line of sight” from the point at which it electrically connects to the building through a permanently installed power inlet. If a person cannot visibly see the generator to which it is connected, disconnecting under load can present a safety hazard if the inlet is not rated for load break or the “intended use.”

Two new exceptions were also added following 702.12(C). The first exception gives an exemption from the requirements for being listed for the intended use and having an interlocked disconnecting means if the power inlet device is rated as a disconnecting means itself. Power inlet devices rated up to 60-amperes that are also rated as a disconnecting means are readily available. There are also load-break solutions available that possess load-break capabilities up to and above 100-amperes. The second exception pertains to supervised industrial installations where permanent space is identified for the portable generator to be located within line of sight of the power inlets. If a supervised industrial installation meets the conditions of this exception, the power inlet box or device is not required to be an interlocked disconnecting means nor be rated as a disconnecting means.

The new language at 702.12(C) is intended to require either that the power inlet devices used with portable outdoor generators be load break rated or that the power inlet be interlocked with a disconnecting means to ensure that the disconnect is opened before disconnecting the portable generator.

Several products within the Leviton Powerswitch® line of Mechanical Interlock Devices comply with Article 702.12(C) and incorporate a safety disconnect switch and IEC 60309-1 and 60309-2 pin and sleeve receptacle in a non-metallic watertight enclosure. The interlock mechanism prevents making and breaking of power under load. The switch cannot be actuated to the ON position until the IEC compatible plug is fully inserted. The plug cannot be removed until the switch is in the OFF position. The color-coded receptacle cover indicates the voltage rating of the device (matching the plug) and seals against water and dirt when not in use. There are many different ratings within Leviton’s mechanical interlock line. Article 702.12(C) is specific to 100-Amps, so this product reference relates to that rating. There are several 100-Amp devices within the line and they are available from 125- to 600-Volts AC.