Liquidtight flexible metal conduit is installed as a fixed run to a piece of rooftop equipment. Under the general rule, how must that run be secured and supported?
- Fastened within 12 inches of each box or fitting and supported at intervals not over 4-1/2 feet
- BFastened within 3 feet of each box or fitting and supported at intervals not over 10 feet
Three feet from a box and ten feet between supports are the figures used for threaded rigid raceways. Applied to a flexible product they would let the run sag and would put pulling strain on the liquidtight connectors.
- CFastened within 12 inches of each box or fitting and supported at intervals not over 6 feet
Six feet between supports is the interval used for metal-clad cable, not for liquidtight flexible metal conduit, which is a heavier and far more flexible product that needs closer support.
- DFastened within 8 inches of each box or fitting and supported at intervals not over 3 feet
Eight inches and three feet are not the values used anywhere in this article. Over-supporting is not a violation in itself, but this answer shows the candidate is guessing rather than reading the support section.
Why A is correct
The article covering liquidtight flexible metal conduit sets two separate numbers: a fastening within 12 inches of every termination, and support along the run at no more than 4-1/2 feet. Both must be met. Because the product is flexible, the close fastening at terminations is what keeps strain off the connector and keeps the liquidtight seal intact.
What this question is testing
The item tests whether the candidate keeps separate support intervals straight for different wiring methods rather than remembering one generic number. It also tests reading a support section as two rules at once: the distance from terminations and the distance between supports along the run.
On the job
Rooftop work is where this gets caught. A liquidtight run from a disconnect to a condenser is easy to strap once at each end and call it done, and then the middle of the run pools water, sags into the roof membrane, and the connector at the equipment works loose from vibration. Inspectors on commercial jobs routinely fail rooftop liquidtight for missing intermediate supports. Getting the two numbers right also matters at pumps, motors, and any place a flexible whip crosses open space.
Memory technique
Flexible products get short leashes: twelve inches at the ends, four and a half feet between.
Exam tip
Support intervals differ by wiring method. Learn them as pairs: distance from the box, then distance along the run.
Where to look it up
Turn to the support section near the beginning of the installation part of the liquidtight flexible metal conduit article, roughly two-thirds of the way into Chapter 3.