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Building or Electrical Inspector

steveray said:
what if the ceiling was designed for the weight of the fixture?
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2 wires required on a 2x4 fixture. The ceiling is designed to support the light fixtures. The wires are required for seismic zones and firefighter protection during an event. So basically everywhere in the USA
 
classicT said:

2021 IBC​

808.1.1.1 Suspended Acoustical Ceilings​

Suspended acoustical ceiling systems shall be installed in accordance with the provisions of ASTM C635 and ASTM C636.

I do not have access to these ASTM (they are not available via the ASTM Reading Room). Appears that ASTM C636 would be the applicable standard.

ASTM C636 - Standard Practice for Installation of Metal Ceiling Suspension Systems for Acoustical Tile and Lay-In Panels
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Of course...why would we make the law available to the public.....Of course with no language provided I would argue that is a ceiling standard, not a light standard....
 
If I remember correctly (and if I haven't missed a recent code change), additional support is required only when the fixture exceeds a certain weight. Older fluorescent fixtures with magnetic ballasts were almost always heavy enough to require this, but I don't think that most LED lights would be heavy enough. I also remember a provision that an alternate method was to provide additional grid support wires so there was one near each corner of the fixture. NEC 410.36(b) requires fixtures to be securely fastened to the ceiling grid. Virginia is a low seismic area, so it's likely that there are additional requirements for higher seismic design categories.
 
Don't know if the requirements can be found in todays vast codes and standards we use. It was in the legacy codes and I may not remember what I ate for breakfast but I knew at one time they where required

1997 UBC Volume 3 Standard 25-2

When heavy-duty systems are used, supplemental hangers are not required if a 48-inch (1219 mm) modular hanger pattern is followed. When cross runners are used without supplemental hangers to support lighting fixtures, these cross runners shall provide the same carrying capacity as the main runner. Lighting fixtures weighing less than 56 pounds (25.4 kg) shall have, in addition to the requirements outlined above, two No. 12 gage (2.7 mm) hangers connected from the fixture housing to the structure above. These wires may be slack. Lighting fixtures weighing 56 pounds (25.4 kg) or more shall be supported directly from the structure above by approved hangers. Pendant-hung lighting fixtures shall be supported directly from the structure above with No. 9 gage (3.8 mm) wire or approved alternate support without using the ceiling suspension system for direct support. SECTION 25.214 -

MECHANICAL SERVICES Ceiling-mounted air terminals or services weighing less than 20 pounds (9.07 kg) shall be positively attached to the ceiling suspension main runners or to cross runners with the same carrying capacity as the main runners. Terminals or services weighing 20 pounds (9.07 kg), but not more than 56 pounds (25.4 kg), in addition to the above, shall have two No. 12 gage (2.7 mm) hangers connected from the terminal or service to the ceiling system hangers or to the structure above. These wires may be slack. Terminals or services weighing more than 56 pounds (25.4 kg) shall be supported directly from the structure above by approved hangers. SECTION 25.215 - PARTITION
 
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