Conduit Offset Bend Calculator
Use this calculator to determine the travel and shrink for an offset bend in conduit. An offset bend is used to move conduit from one plane to another, often to clear an obstruction or align with a box or panel.
Understanding Conduit Offset Bends
An offset bend is a fundamental technique in conduit installation, allowing electricians to navigate around obstacles or transition between different depths or surfaces. It involves two identical bends in opposite directions, creating a parallel shift in the conduit's path.
Key Terms Explained:
- Offset Height: This is the vertical or horizontal distance you need the conduit to shift. For example, if you need to clear a 3-inch beam, your offset height is 3 inches.
- Bend Angle: The angle at which each of the two bends is made. Common angles include 10, 15, 22.5, 30, 45, and 60 degrees. The choice of angle often depends on the available space and the desired appearance. Smaller angles result in longer, gentler offsets, while larger angles create shorter, sharper offsets.
- Travel: This is the distance along the conduit between the start of the first bend and the start of the second bend. Knowing the travel distance is crucial for accurately marking your conduit before bending.
- Shrink: When you bend conduit, its overall effective length shortens. This reduction in length is called "shrink." It's vital to account for shrink when cutting conduit to ensure the final piece is the correct length. If you don't account for shrink, your conduit run will end up too short.
How to Use the Calculator:
- Enter Desired Offset Height: Input the total distance you need the conduit to move (e.g., 6 inches to clear a pipe).
- Select Bend Angle: Choose the angle you plan to use for your bends. This is typically determined by your bender's capabilities and the specific requirements of the job.
- Click "Calculate Offset": The calculator will instantly provide the "Travel" and "Shrink" values.
Practical Application:
Let's say you need to create a 6-inch offset using 30-degree bends:
- You would mark your first bend location on the conduit.
- From that first mark, you would measure the "Travel" distance (e.g., 12 inches) and make a second mark.
- You would then make your first 30-degree bend.
- Next, you would align your bender with the second mark and make the second 30-degree bend in the opposite direction.
- Finally, when cutting your conduit to length, you would add the "Shrink" amount (e.g., 3 inches) to your total desired straight length to compensate for the shortening effect of the bends.
Accurate conduit bending is a skill that improves with practice. Always double-check your measurements and consider making practice bends on scrap pieces, especially when working with unfamiliar angles or complex offsets.
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function calculateOffsetBend() {
var offsetHeightInput = document.getElementById("offsetHeight");
var bendAngleInput = document.getElementById("bendAngle");
var resultDiv = document.getElementById("result");
var offsetHeight = parseFloat(offsetHeightInput.value);
var bendAngleDegrees = parseFloat(bendAngleInput.value);
if (isNaN(offsetHeight) || offsetHeight <= 0) {
resultDiv.innerHTML = "Please enter a valid positive number for Offset Height.";
return;
}
if (isNaN(bendAngleDegrees) || bendAngleDegrees <= 0) {
resultDiv.innerHTML = "Please select a valid Bend Angle.";
return;
}
var bendAngleRadians = bendAngleDegrees * (Math.PI / 180);
// Calculate Travel
// Travel = Offset Height / sin(Bend Angle)
var travel = offsetHeight / Math.sin(bendAngleRadians);
// Calculate Shrink using common electrician's multipliers
var shrinkMultiplier;
switch (bendAngleDegrees) {
case 10:
shrinkMultiplier = 0.0625; // 1/16" per inch
break;
case 15:
shrinkMultiplier = 0.1875; // 3/16" per inch
break;
case 22.5:
shrinkMultiplier = 0.375; // 3/8" per inch
break;
case 30:
shrinkMultiplier = 0.5; // 1/2" per inch
break;
case 45:
shrinkMultiplier = 0.75; // 3/4" per inch
break;
case 60:
shrinkMultiplier = 1.0; // 1" per inch
break;
default:
shrinkMultiplier = 0; // Should not happen with dropdown
}
var shrink = offsetHeight * shrinkMultiplier;
resultDiv.innerHTML =
"
Calculated Travel: " + travel.toFixed(2) + " inches" +
"
Calculated Shrink: " + shrink.toFixed(2) + " inches";
}
// Calculate on page load with default values
window.onload = function() {
calculateOffsetBend();
};