Subjects UL 514A
June 30, 2006
TO: Electrical Council of Underwriters Laboratories Inc.
SUBJECT: UL Listing for Adjustable Mud Ring Relying on Friction
BACKGROUND:
UL has received a request to List an Adjustable Mud Ring that relies solely on a friction connection to provide the ground path when a “non-self-grounding“ wiring device such as a Receptacle, General-Use Switch or Dimmer Switch is installed to a conduit system employing this adjustable mud ring.
The Adjustable Mud Ring is an all steel construction and is intended for use with a 4 inch square steel outlet box. The product consists of a mud ring and an adjustable extension sleeve held in place by Type 304 stainless steel spring clips (lugs) where each clip is secured by a single #8-32 screw. It is specifically designed to properly position a flush mounted wiring device when the outlet box is mounted too deeply or when the finished wall surface is not square with the box opening. The “mud ring” adjusts outward a maximum of 1-1/2 inches, and is capable of being angled to be level with the finished wall surface. The literature for this product states that it is capable of providing the metal-to-metal contact for a reliable electrical bond. The “spring bond” lugs, when tightened, secure the extension sleeve in the desired position and are intended to provide bonding between the extension sleeve and the cover (mud ring). See Appendix A for details.
NEC CONSIDERATIONS:
NEC Sec. 314.21, Repairing Plaster and Drywall or Plasterboard, states: “Plaster, drywall or plasterboard surfaces that are broken or incomplete around boxes employing as flush-type cover or faceplate shall be repaired so there will be no gaps or open spaces grater than 3 mm (1/8 in.) at the edge of the box.”
TECHNICAL ISSUES:
The friction fit of the inner sliding ring is relied upon as the only means to provide the grounding path. This raises the following issues:
· the ring is shipped unsecured. This may result in failure to properly tighten the screws, which would defeat the grounding. Lack of proper securement, adjustment of the mud ring by numerous tradesmen, or degradation of the securement over time would all be issues that must be considered and addressed.
· defeat by users may occur by seeing the accessible spring screws and thinking they need to be loosened to remove the receptacle, cover, etc.
· the presence of overlying plaster etc. does not seem to be a reliable means to assure that the screws are set and not accessible, as the product may be installed in an installation where the screws are made fully inaccessible (e.g. wood paneling).
EVALUATION REQUIREMENTS:
If UL were to establish that there is basis for an investigation, the adjustable mud ring plate would be investigated to the requirements outlined in the Standard for Metallic Outlet Boxes, UL 514A, Tenth Edition. In addition to the testing required in UL 514A, it would also be subjected to an Electrical Resistance Test (adapted for the product from clauses 8.8, 8.10.4.1 and 8.10.6.1 of UL 514B, Conduit, Tubing and Cable Fittings) and a Receptacle Secureness Test (adapted for the product from clause 13 of UL 5, Surface Metal Raceways and Fittings).
Receptacle Secureness Test: This test is proposed to test the secureness of the adjustable sleeve against normal pull forces applied during insertion and removal of an attachment plug. The requirement in the Standard for Surface Metal Raceways and Fittings, UL 5 is considered as representative of the application stresses. The cover assembly would be assembled as intended to a listed outlet box that is securely supported. The extension sleeve would be extended to 50% of its maximum extension and positioned at its maximum angle before the securement lugs were tightened. A duplex receptacle would then be mounted and secured as intended. The attachment plug of a power-supply cord would be inserted into the receptacle and made mechanically secure. A weight exerting 25 lbf (111 N) would be attached to the opposite end of the power-supply cord. With the outlet box in the horizontal position (receptacle face directed towards the ground) and the weight initially resting on a horizontal surface, the cover assembly would be gradually raised vertically until the weight is supported by the receptacle. The weight would need to be supported for 60 seconds. The test would then be repeated with the box tilted so that a line perpendicular to the face of the receptacle makes an angle of 30 degrees with the vertical cord. The direction of the tilt relative to the receptacle would be the direction most likely to cause movement of the extension sleeve.
Electrical Resistance Test: This test is proposed to test the presence of a low resistance bonding connection after normal installation and after potential stresses exerted in normal use. The requirement in UL 514B for fittings for use with non-flexible metallic conduit and tubing are considered as a representative test method and pass-fail measurement. A direct current of 30 amperes would be passed through the assembly at the connections between the extension sleeve and cover component. Separate tests would be conducted at each attachment location at a point within 12 mm (1/2 in.), but no closer than 1.6 mm (1/16 in) of the point of contact on each component. As a result of the test the voltage drop shall not be greater than 10 mV. Following the receptacle secureness test, the electrical resistance test is to be repeated. The resistance measured shall not exceed 15 mV.
Additional Requirements: Additional requirements may be implemented based on the feedback from the Council. Additional requirements may address:
· The application and location of product markings to indicate the requirements for creating and maintaining a reliable ground path;
· The ability of a ground lead to be attached to the adjustable device mounting ring and be marked to indicate that securement to the box is required to provide a competent ground path
· Expansion of the proposed Receptacle Secureness Test parameters
· Expansion of the proposed Electrical Resistance Test parameters
UL plans to modify the QCIT Guide information to indicate any applicable marking requirements.
FEEDBACK REQUESTED:
So that we might carefully consider the implications that such a product Listing program may introduce, we ask you to consider the questions outlined in the questionnaire attached as Appendix B. Please return the questionnaire by July 24, 2006. If we do not receive your comments within this time frame, we will presume that you have no comments.
The confidential information contained herein is provided to UL’s Electrical Council members for conducting the business of the Council and should not be made available to others.
Thank you for your time and commitment to this endeavor.
Sincerely, Reviewed by:
David A. Gerstetter (Ext. 41733) George Walbrecht
Staff Engineer Principal Engineer
Power Distribution Conduit, Boxes and Raceways
(847) 664-1733
E-mail:
Ken Boyce
Staff Primary Designated Engineer North America
APPENDIX A
Expandable/Adjustable Mud Ring
Bonding of Mud Ring Base to box assured by threaded screw
Attachment and impingement under screw head.
Mud Ring Base
Adjustable Device Mounting Ring
Conductive path from device strap provided through
threaded screw attachments in Adjustable Device
Mounting Ring.
Spring-Bond Lugs (2 provided)
“Spring Bond” lugs, when tightened, intended to provide secure spring force contact on two ½ in wide surfaces of the extension sleeve and threaded attachment to the Mud Ring Base. This conductive path is relied upon exclusively for grounding when the adjustable Mud Ring is employed to mount an ungrounded switch.
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