Downward Facing Receptacles for Perimeter Raceway
The use of perimeter raceway has historically been limited by opposition from designers and end-users to the obtrusive and "boxy" nature of raceway. Contributing to the utilitarian appearance is the presence of highly visible power and data connections on the raceway surface. Other objections include the fact that these outward facing connections are susceptible to damage and prevent furniture and peripheral equipment from being located adjacent to the wall.
A new-generation perimeter raceway from Wiremold/Legrand employs a downward facing configuration for receptacles and data jacks to reduce visual and spatial impacts. This configuration also improves connection reliability and provides more space inside the raceway to meet cable bend radius requirements.
Design
The vast majority of perimeter raceway systems consist of a three sided enclosure that is mounted on a base that is attached to the wall. In profile, the unit is a rectangle (Fig. 1). Receptacles and data ports have traditionally been incorporated into the front of the raceway, facing away from the wall.
Figure 1: Cross section of standard raceway. Note, optional divider is not shown.
A new raceway profile, developed by Wiremold/Legrand, provides the option to locate the receptacles and data outlets on the downward facing bottom of the raceway (Fig. 2).
Figure 2: Cross section of Wiremold® Designer Series raceway. Note integral divider and dual covers.
This downward facing configuration offers several advantages over traditional raceway designs.
The raceway profile is less visually intrusive, and cords do not protrude into the room. Power and data cords fall directly against the wall where they do not interfere with equipment or furniture, and are less susceptible to damage.
The downward direction expands available space for data cables within the raceway and allows a cable bend radius capability up to 4.5". This is especially important for new and emerging technologies, such as augmented Category 6 cable with a .335" diameter. To maintain maximum system performance, the recommended bend radius is 10X the cable diameter, or 3.35".
This raceway incorporates a "crossover" feature, a steel enclosure that shields power and data devices from interference (electro-magnetic, cross-talk, & noise) and allows for adjacent downward power and data installations.
Testing
While data ports can be located in any position due to the "locking" nature of jacks, the ability of receptacles to perform in a downward facing position required testing. Receptacles were subjected to tests to determine whether the downward facing configuration meets standards for load security, and blade retention and release.
Receptacle security testing assures that the downward activation bracket assembly will successfully hold a receptacle under a UL defined 25 lb static load test. This test is performed in both a vertical and 30 degree angle orientation. Further, Wiremold/Legrand performs a more severe internal test that employs a 50 lb. dynamic load. Again, this test determines whether the device bracket and receptacle will become dislodged from the raceway under extreme cord pulling conditions.
Receptacle assembly security testing is performed to assure the strap will not separate from the face of the device under rugged use. The UL test employs a 50 lb. static load on the receptacle assembly in face-up and face-down positions.
Receptacle blade retention and release testing determines the ability of the receptacle to hold the plug in place against a specified force, and also whether the plug will disengage, again with a specified amount of force.
- Blade retention uses a polished steel 2-bladed plug gage. After ten insertions into the receptacle, the gage must retain the plug gage against a 3-lb. force for one minute.
- Blade release employs a polished three-blade plug. After ten insertions it must release the plug gage at 15-lb. of force or less.
The results indicate that the downward facing configuration exceeds load and retention and release standards. Based on the release test standards, caution is suggested when plugging older, heavier device transformers into downward facing receptacles. These units may exert sufficient force to disengage the blades. Most new transformers are lighter, however, and easily meet the blade retention standard.
Further comments
The design of the downward facing receptacle and test results were forwarded to a sampling of "authority having jurisdiction" (inspectors, fire marshals, etc) officials. No objections were reported. This configuration is also an acceptable method per NEC and UL code.
The downward facing configuration should not adversely impact user convenience. Raceway systems are typically installed at "chair rail" height (approx. 36"), which allows users to easily locate the receptacles and plug in cords. This will hold true for most people down to about 28" above the floor. To meet ADA requirements, receptacles must be at least 18" from the floor.
Conclusions
With proven performance, downward facing receptacles offer designers a way to reduce the visual impact of wire and cable management, afford additional protection against damage, and provide more freedom to locate furniture and peripherals adjacent to the raceway. For installers and users, this innovation will increase the space behind power and data devices for terminations, and allow a greater area for communication cable bend radius recommendations, thus maintaining the performance of the cable.