January 2009

Q: Where does the term "Old Style Locking Device" come from?

A: Locking wiring devices were invented and introduced by Hubbell Inc. in 1938. These devices covered dozens of different amperages and voltages to cover the types of devices used in commercial and industrial markets. These configurations were developed and introduced by Hubbell and eventually copied by other manufacturers.

In the 1960s NEMA, the National Electrical Manufacturer's Association, decided to develop industry standards for wiring device configurations. These configurations were based on the original Hubbell configurations but changes were made.

One of the most significant changes was to the 2P3W 20 Amp 125 Volt configuration. The existing configuration was commonly sold for both 2P3W and 3P3W applications. This was not an ideal situation because if the two configurations were wired differently in the same plant it could result in an energized ground conductor, which is a safety hazard.

NEMA chose to go with a new configuration for 2P3W grounding. The NEMA L5-20 configuration with an inward-facing dogleg for the ground blade.

The "Old Style" configuration did not go away, however, Although it is not a NEMA configuration, it still carries a UL Listing "For Replacement Use Only." The Hubbell catalog carries the following safety notice regarding the use of "Old Style" devices:

CAUTION: To avoid electric shock, review premises carefully and do not use if slot or blade configuration (design) is already in a circuit having a rating different from the rating of this device.