Compound 90° Around a Square Obstruction
Quick answer
A compound 90° around a square obstruction uses two 45° bends joined by a straight chamfer that runs along the far side of a square turned 45° in the corner. Chamfer = 3 × the side of the square, corner to corner, exactly. Between bends = chamfer − the gain of one 45° bend, and both bends are made with the hook facing the stub end.
A compound 90 turns a corner with two 45° bends instead of one 90, cutting across the corner in front of something that sits in it. This screen is for a square obstruction turned 45° in the corner, with one of its corners against each wall.
What to measure
- Stub length: from the end of the conduit to the back of the other leg, as for a 90.
- Side of the square: the length of one side.
- Other leg (optional): from the other end to the back of the stub. With it you get the Cut length.
- First bend or Between bends (optional): when the first bend has to go somewhere in particular, or the chamfer has to be a set length, type it in and the other follows. Clearance then shows whether the conduit still clears the obstruction; leave the obstruction blank if there isn’t one.
How to bend it
- Mark the First mark from the stub end, and the second mark Between bends further along.
- Put the first mark on the arrow with the hook facing the stub end, and bend 45°.
- Slide to the second mark and bend another 45° the same way, with the hook still facing the stub end, so the two make 90°.
- Check that the stub and leg are square to each other and both bends are in one plane.
Where the numbers come from
The two 45s are joined by a straight chamfer that runs along the far side of the square. Its length from corner to corner (where the straight lines would meet) is exactly 3 × the side. The rest is the same radius math as any other bend.
chamfer = 3 × sidebetween bends = chamfer − g(45°)first mark = stub − OD/2 − chamfer ÷ √2 − setback(45°) − start of bend- Stub length
- 36"
- Side of the square
- 8"
- Other leg
- 36"
- First mark
- 16 1/2" (19" by multiplier)
- Between bends
- 23 13/16" (24" by multiplier)
- Cut length
- 61"
The chamfer doesn’t allow for the conduit’s own size, but because the stub, leg and square are all measured to the walls, the conduit still clears the square by about a fifth of its OD, a little over 1/8" for 1/2" EMT.
If it turns orange or red
Red means the stub or the leg is too short for the chamfer, so a bend would run off the end of the conduit. Orange or red can also mean the two 45s are too close together for the shoe, which only happens with a very small obstruction. Orange also shows when the conduit would touch the obstruction (a negative Clearance), or when the cut length is longer than one stick.
Get the marks for your bender
BendMate works this out from your bender’s radius and deduct, flags a bend that won’t work, and shows you every mark.
Common questions
What is the chamfer for a compound 90 around a square?
For a square turned 45° in the corner, with one of its corners against each wall, the chamfer is exactly 3 × the side, measured corner to corner where the straight lines would meet. An 8" square gives 24" between bends by the multiplier method, or 23 13/16" on a 1/2" EMT hand bender.
Where is the first mark on a compound 90 around a square?
First mark = stub − OD/2 − chamfer ÷ √2 − setback(45°) − start of bend, for the arrow. For an 8" square with a 36" stub on a 1/2" EMT hand bender it is 16 1/2" (19" by the multiplier method).
How much clearance does the conduit have around the square?
The chamfer doesn’t allow for the conduit’s own size, but because the stub, leg and square are all measured to the walls, the conduit still clears the square by about a fifth of its OD. That is a little over 1/8" for 1/2" EMT.