Does the connection flex between the master and slave fixtures placed in a suspended ceiling need to be supported in any way? It is part of a listed assembly so I would think you would just need to follow installation instructions. Also, I wouldn't think you could assume 3/8 or 1/2" fmc is being used (and thus follow the corresponding codes regarding installation). The manufacturer could have there own unique wiring method not even found in the nec as long as it got the needed listing.
Tesla, your suggestion is what the inspector wanted. I just can't find an article in the nec to support his claim. Also, I would say that most of the m to s connections I come across are longer than 6'.
It has been my understanding that why whips on any lights are six feet long is because of the rules that govern flex conduit. I can't say for certain. As an inspector without specific instructions, I'd refer to the flex rules in the NEC
300.23 Panels Designed to Allow Access. Cables, raceways,and equipment installed behind panels designed to allow access, including suspended ceiling panels, shall be arranged and secured so as to allow the removal of panels and access to the equipment. _____________________________________________________
Tesla: Lithonia equips their satellite (slave) fixtures with 11' whips to connect to the master unit.
Don’t the manufacturer’s instructions usually state something along the lines of... "This equipment must be installed in accordance with the national electrical code and all local ordinances" and then go on to list any special requirements like, "this equipment must be connected to an individual branch circuit", etc.
IMO, laying horizontal runs of the whips over the grid is in essence using the grid for support, which is not permitted in 300.12. I believe the whips must still be secured within 12-inches of where they connect to the fixtures. If the whips happened to be FMC, then they would also be restricted to 360-degrees of bends between boxes or fixture. I would be almost certain that the manufacturer would use one of the wiring methods in Chapter 3, since 320, 330, 334 and 348 specifically mention special conditions regarding these wiring methods for use as fixture whips. Keep in mind that these are only my opinions, so may have all the relevance of bird crap on a park statue.
If such a beastie exists, then I'd use batwings (tm) to clip it to my own painted seismic drop wires.
Standard industry length has been 9' for at least the last 20 years for the M/S whips, though we frequently get them in 11'-15' lengths. Most manufacturers have length limitations based on the chosen ballast requirements.
I have never seen or heard of any issues from this as longs as they're supported by a means acceptable by the AHJ.
Article 410.137 (c) allows max of 25 feet of 'master/slave' and references conformance with Art 348:
348.30 Securing and Supporting. FMC shall be securely fastened in place and supported in accordance with 348.30(A) and (B). (A) Securely Fastened. FMC shall be securely fastened in place by an approved means within 300 mm (12 in.) of each box, cabinet, conduit body, or other conduit termination and shall be supported and secured at intervals not to exceed 1.4 m (41/2 ft). Exception No. 1: Where FMC is fished between access points through concealed spaces in finished buildings or structures and supporting is impractical. Exception No. 2: Where flexibility is necessary after installation, lengths shall not exceed the following: (1) 900 mm (3 ft) for metric designators 16 through 35 (trade sizes 1/2 through 11/4) (2) 1200 mm (4 ft) for metric designators 41 through 53 (trade sizes 11/2 through 2) (3) 1500 mm (5 ft) for metric designators 63 (trade size 21/2) and larger Exception No. 1 was limited for the 2008 Code to prevent fished installations of FMC where the installation of supports remains practical. In Exception No. 2, the phrase “where flexibility is required” was changed for the 2008 Code to “where flexibility is necessary after installation.” An example of where flexibility is necessary is an installation of flexible metal conduit to a motor mounted on an adjustable or sliding frame, where the frame is required to be movable to perform drive belt maintenance. Exception No. 3: Lengths not exceeding 1.8 m (6 ft) from a luminaire terminal connection for tap connections to luminaires as permitted in 410.117(C). Exception No. 4: Lengths not exceeding 1.8 m (6 ft) from the last point where the raceway is securely fastened for connections within an accessible ceiling to luminaire(s) or other equipment. Exception No. 4 correlates this permission of unsupported flexible metal conduit with other wiring methods permitting the same exception throughout Chapter 3. One such example is 320.30(D)(3) for Type AC cable. FMC fittings are not considered to be a means of cable support. (B) Supports. Horizontal runs of FMC supported by openings through framing members at intervals not greater than 1.4 m (41/2 ft) and securely fastened within 300 mm (12 in.) of termination points shall be permitted.