Flexible metal conduit is used as a fixture whip in an accessible suspended ceiling, running from a junction box to a luminaire. Measured from the last point where the raceway is securely fastened, what length is permitted before further support is required?
- A18 inches
Eighteen inches is not one of the flexible-raceway allowances. It is close to the 12 inch securing distance at boxes and fittings, which is a different measurement entirely.
- B3 feet
Three feet is the allowance for a length where flexibility is necessary at a termination, such as the final connection to a vibrating motor, and it is the wrong allowance for a luminaire whip in an accessible ceiling.
- C4-1/2 feet
Four and one-half feet is the ordinary securing interval for this raceway along a run. It is not the unsupported length permitted for a tap to a luminaire.
- 6 feet
Why D is correct
Fixture whips exist because luminaires get moved when ceiling grid changes. The Code allows 6 feet of unsupported flexible raceway from the last securing point when that raceway is a tap to a luminaire in an accessible ceiling, which is enough to reach a fixture two or three grid squares away without adding a strap in the middle of the plenum.
What this question is testing
This item tests whether you can keep three different numbers straight in one article: the distance to a box, the general securing interval, and the special allowances for flexibility and for luminaire taps.
On the job
On tenant improvement work the ceiling grid is full of whips, and the inspector counts them. The two mistakes that show up are a whip longer than the allowance, usually because the electrician tried to feed two fixtures off one drop, and a whip in a ceiling that is not actually accessible, such as a hard-lid gypsum ceiling. In a hard ceiling the allowance does not apply and the raceway has to be secured on the normal interval, which is why hard-lid areas take so much longer to rough in.
Memory technique
Six feet to a fixture, three feet for flexibility, one foot to a box.
Exam tip
Read the securing section of a flexible raceway article all the way through the exceptions before answering. The exceptions carry the numbers the exam wants.
Where to look it up
Securing and supporting is the .30 section of every Chapter 3 raceway article. The luminaire tap allowance is one of the exceptions listed under it.