Conduit Bending Techniques and Calculations

Flashcards testing terminology, shrinkage rates, trigonometric formulas, and layout steps for electrical conduit bending.

Back-to-Back Bend

A combination of two 90° bends made on the same piece of conduit and placed back-to-back.

Offset Bend

A bend configuration consisting of two equal bends of less than 90° made at a specified distance apart, used to clear obstructions or enter junction boxes and cabinets.

Shrinkage

The reduction in effective conduit length that occurs when an offset or saddle bend is formed, requiring an allowance to be added during layout.

Distance Between Bends Formula

The formula used to calculate the spacing between offset bends: $\text{Distance between bends} = \text{depth of offset} \times \text{multiplier}$.

Offset Multiplier (CSC)

The numerical multiplier for a given offset angle representing the cosecant (CSC) of the angle, determined by $\text{Multiplier} = \frac{\text{hypotenuse}}{\text{depth of offset}}$.

Girdling

The action of drawing a narrow pencil or marker line completely around a piece of conduit when using the take-up method.

10° Offset Multiplier and Shrinkage

A 10° x 10° offset angle has a multiplier of 6.0 and a shrinkage rate of 1/16" per inch of rise.

22 1/2° Offset Multiplier and Shrinkage

A 22 1/2° x 22 1/2° offset angle has a multiplier of 2.6 and a shrinkage rate of 3/16" per inch of rise.

30° Offset Multiplier and Shrinkage

A 30° x 30° offset angle has a multiplier of 2.0 and a shrinkage rate of 1/4" per inch of rise.

45° Offset Multiplier and Shrinkage

A 45° x 45° offset angle has a multiplier of 1.4 and a shrinkage rate of 3/8" per inch of rise.

60° Offset Multiplier and Shrinkage

A 60° x 60° offset angle has a multiplier of 1.2 and a shrinkage rate of 1/2" per inch of rise.

Parallel Offsets

Offsets performed on multiple parallel conduit runs around a common obstruction, requiring centerline adjustments to prevent uneven conduit ends.

Parallel Offset Adjustment Formula

The calculation used to shift successive centerline starting points: $\text{Amount added} = \text{center-to-center spacing} \times \tan\big(\frac{1}{2} \text{ offset angle}\big)$.

Matching Bends Technique

A method used on rigid conduit where a smaller conduit (such as 1" / MD 27) is bent using a larger shoe (such as 2" / MD 53) so that both parallel runs share the same bend radius.

Torpedo Level

A hand tool used to check for plumb on vertical conduit rises.

Saddle Bend

A series of bends (typically a 45° center bend and two 22 1/2° side bends) used to route conduit around round obstructions like pipes.

Saddle Bend Shrinkage Rate

The shortening rate of 3/16" (4.8 mm) per inch of saddle depth that occurs on each side of a 3-bend saddle.

Saddle Bend Side Mark Spacing

The layout distance for outer marks B and C, which are measured 2 1/2" away from center mark A for every 1" of saddle depth.