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Brett M. Wilbur CSI, CDT, AIA
Senior Member
Username: brett

Post Number: 78
Registered: 12-2004
Posted on Friday, December 09, 2005 - 03:07 pm:   Edit PostDelete PostPrint Post

Anyone know where I can find how many wires are required to hang a 2x4 fluorescent fixture in a non-rated drop-in ceiling system?

Yes, UL is for rated ceilings, but I can not find anywhere in IBC or NEC that states that one #12 wire is required at each fixture corner in a non-rated ceiling, or do the ceiling hangers support the fixtures?
Ronald L. Geren, RA, CSI, CCS, CCCA, MAI
Senior Member
Username: specman

Post Number: 206
Registered: 03-2003
Posted on Saturday, December 10, 2005 - 12:22 am:   Edit PostDelete PostPrint Post

The IBC in Section 803.9.1.1 requires that suspended ceilings be installed per ASTM C 635 and ASTM C 636. Have you checked these?

I'd look it up myself, but I have a limited specifier's library here in Kuwait.
Posted on Monday, December 12, 2005 - 06:27 pm:   Edit PostDelete PostPrint Post

I believe that either ASTMs or CBC (and maybe IBC)address number of wires depending on weight of fixture and duty rating of grid.
Lynn Javoroski
Senior Member
Username: lynn_javoroski

Post Number: 270
Registered: 07-2002
Posted on Tuesday, December 13, 2005 - 12:25 pm:   Edit PostDelete PostPrint Post

ASTM C635 - "1.1 This specification covers metal ceiling suspension systems used primarily to support acoustical tile or acoustical lay-in panels.

1.2 Some suspension systems incorporate locking assembly details that enhance performance by providing some continuity or load transfer capability between adjacent sections of the ceiling grid. The test methods included in this specification do not provide the means for making a complete evaluation of continuous beam systems, nor for assessing the continuity contribution to overall system performance. However, the test methods can be used for evaluating primary structural members in conjunction with secondary members that interlock, as well as with those of noninterlocking type.

1.3 While this specification is applicable to the exterior installation of metal suspension systems, the atmospheric conditions and wind loading require additional design attention to ensure safe implementation. For that reason, a specific review and approval should be solicited from the responsible architect and engineer, or both, for any exterior application of metal suspension systems in the construction of a new building or building modification."

ASTM C636 - "This practice covers the installation of suspension systems for acoustical tile and lay-in panels. It is applicable to contractors whose services are utilized for installing acoustical ceilings and to other trades if their activities are responsible for interference with ceiling components or performance as defined in this recommended practice."

I found no ASTM which addressed the fixture hanging. But if you stated that system performance should meet ASTM C635, which establishes tolerances for the suspension system, (deflection, loading, etc.), you could be OK.
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 444
Registered: 03-2002
Posted on Tuesday, December 13, 2005 - 03:03 pm:   Edit PostDelete PostPrint Post

Normally the fixture is supported by the ceiling suspension system, but small chains (with some slack) are installed to support the fixtures in the event of a suspension system failure. I think the chains are part of the electrical code.
Ralph Liebing, RA, CSI
Senior Member
Username: rliebing

Post Number: 270
Registered: 02-2003
Posted on Tuesday, December 13, 2005 - 03:38 pm:   Edit PostDelete PostPrint Post

Direct quote from MasterSpec-- any help?

A. Support for Lighting Fixtures in or on Grid-Type Suspended Ceilings: Use grid as a support element.
1. Install a minimum of four ceiling support system rods or wires for each fixture. Locate not more than 6 inches (150 mm) from lighting fixture corners.
2. Support Clips: Fasten to lighting fixtures and to ceiling grid members at or near each fixture corner with clips that are UL listed for the application.
3. Fixtures of Sizes Less Than Ceiling Grid: Install as indicated on reflected ceiling plans or center in acoustical panel, and support fixtures independently with at least two 3/4-inch (20-mm) metal channels spanning and secured to ceiling tees.
4. Install at least one independent support rod or wire from structure to a tab on lighting fixture. Wire or rod shall have breaking strength of the weight of fixture at a safety factor of 3.
Posted on Tuesday, December 13, 2005 - 06:35 pm:   Edit PostDelete PostPrint Post

What was I thinking? In Calif., lateral forces are an issue. UBC Std 25-2 which are modified versions of C635 & C 636, is more definitive (than C 636) in addressing separate hangers for light fixtures depending on weight (<56# or 56#) and (inter or hvy) duty rating of grid.

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