Quiz: Rotation and Discharge Codes¶
Test your understanding of rotation and discharge codes, motor position restrictions, conduit box positions and the axial and inline conventions with these review questions.
1. Which discharge position does FanPedia omit for double width, double inlet (DWDI) centrifugal fans?¶
- Upblast (UBD)
- Top Angular Down (TAD)
- Bottom Angular Up (BAU)
- Bottom Angular Down (BAD)
Show Answer
The correct answer is D. FanPedia's DWDI discharge pages list seven discharges in both rotations, UBD, TAU, THD, TAD, DBD, BHD and BAU, and omit Bottom Angular Down. BAD (225 degrees) is listed for single width, single inlet fans only. When a layout calls for a DWDI fan blowing bottom angular down, the fix belongs in the ductwork or the fan type, and the current catalog should be checked.
Concept Tested: DWDI Discharge Limits
2. How is the conduit box position coded and viewed?¶
- F1, F2 or F3, viewed from the drive side of the motor, looking at the motor shaft
- W, X, Y or Z, viewed from the drive side of the fan
- A through H, viewed from the discharge side of the fan
- L or R, viewed from the opposite drive end of the motor
Show Answer
The correct answer is A. The conduit box position is the side of the motor that carries the electrical connection, coded F1, F2 or F3 (F3 is on top) and always viewed from the drive side of the motor, looking at the shaft. FanPedia marks F1 as standard on its motor position pages. W, X, Y and Z (B) are motor positions for Arrangements 1, 3 and 3F, A through H (C) are axial motor positions, and L and R (D) are Arrangement 9 motor positions.
Concept Tested: Conduit Box Position
See: Conduit Box Position
3. On SWSI Arrangements 1, 3 and 3F, a restriction on motor position W for a clockwise fan becomes a restriction on position Z for the counterclockwise fan with the same discharge. Why?¶
- Counterclockwise fans always use larger motors that need a different position
- A CCW housing is the mirror image of a CW housing, so the outlet moves to the opposite side
- AMCA renumbers the motor positions whenever rotation changes
- Position W is never available on counterclockwise fans
Show Answer
The correct answer is B. A counterclockwise housing is the mirror image of a clockwise one: the scroll expands the other way and every discharge comes out on the opposite side. The outlet that blocks W on a CW fan therefore blocks Z on a CCW fan, and the reverse. Motor size (A) plays no part. The positions keep their names (C), and W is available on many CCW combinations (D); for CCW TAD, for example, only Z is restricted.
Concept Tested: Motor Position Restrictions
4. How is the rotation of an axial fan determined and written?¶
- Viewed from the drive side, written CW or CCW
- Viewed from the inlet side, written CW or CCW
- Viewed from the discharge side, written left hand (LH) or right hand (RH)
- Viewed from above, written up or down
Show Answer
The correct answer is C. FanPedia determines axial rotation by viewing the impeller from the discharge side of the fan and writes it as LH or RH, which must match the impeller's hand and the airflow direction. The drive side with CW or CCW (A) is the centrifugal convention. The chapter warns against converting an axial LH or RH into CW or CCW on an order, because each family keeps its own viewpoint.
Concept Tested: Axial Rotation Convention
5. A fan was ordered CW, but at startup the rotation arrow on the housing shows CCW when read from the drive side. What does this mean?¶
- The motor leads are crossed, and swapping two of them will fix it
- The arrow is only a guide, and the fan will perform the same either way
- The installer is standing on the wrong side and should read the arrow from the inlet
- The housing was built to the wrong hand, and no rewiring will fix it
Show Answer
The correct answer is D. The rotation arrow shows the direction the housing was built for. If it reads CCW from the drive side on a fan ordered CW, the housing itself is the wrong hand. Swapping two leads (A) only changes the motor direction, which would make the wheel match a wrong housing. A backward centrifugal wheel moves far less air than its rating (B), and rotation is always read from the drive side (C).
Concept Tested: Rotation Arrow
See: Rotation Arrow
6. A single width, single inlet fan turns counterclockwise from the drive side. Its outlet is at the bottom of the housing and blows horizontally toward the observer's right. What is the rotation and discharge code?¶
- CCW BHD, also written CCW 270
- CW BHD, also written CW 270
- CCW THD, also written CCW 90
- CCW BAU, also written CCW 315
Show Answer
The correct answer is A. A horizontal outlet at the bottom of the housing is Bottom Horizontal (BHD). For a CCW fan, turning counterclockwise from straight up gives left at 90 degrees, down at 180 and right at 270, so a right-pointing bottom outlet is CCW 270. A CW fan (B) cannot have a right-pointing bottom horizontal outlet. THD (C) is at the top, and BAU (D) points up at 45 degrees.
Concept Tested: Rotation and Discharge Code
7. A schedule line reads "SWSI Arrangement 3, CCW, BHD, belt drive." Which motor position is not allowed?¶
- Z
- W
- X
- Y
Show Answer
The correct answer is B. With a BHD discharge the motor interferes with the outlet opening in one position: Z for CW rotation and W for CCW rotation. This line is CCW, so W is not allowed. Z (A) is the forbidden position for CW BHD, a common mix-up when the rotation is forgotten. X and Y carry no restriction for BHD.
Concept Tested: Motor Position Restrictions
8. A belt-driven inline fan is installed with its axis vertical, the air moving downward, and a hood. Which configuration code describes it?¶
- VUH
- VRH
- VDH
- VDO
Show Answer
The correct answer is C. Vertical configuration codes read left to right: V for vertical, then U, D or R for up, down or reversible, then the support or top. Vertical down with a hood is VDH. VUH (A) is vertical up with a hood, VRH (B) is vertical reversible with a hood, and VDO (D) is vertical down with floor mount brackets on the outlet.
Concept Tested: Inline Vertical Configuration
9. A specifying engineer submits "SWSI Arrangement 1, CW, THD, motor position W." Which analysis of this line is correct?¶
- It is not allowed, because the motor interferes with the outlet opening, and W must be changed to Z
- It needs a height check, because the motor may not fit below the discharge; on Arrangement 1 a lengthened pedestal lets the motor fit
- It is allowed with no check, because THD carries no motor position restriction
- It is not allowed, because Arrangement 1 cannot be built with a THD discharge
Show Answer
The correct answer is B. FanPedia's THD restriction is a height restriction, not an outright ban: for CW rotation in position W, the motor may not fit below the discharge. FanPedia adds that on an Arrangement 1 fan the motor will fit if the pedestal is lengthened. Option A applies the BHD and TAD interference wording to THD. Option C ignores the THD restriction entirely, and THD is a standard discharge for Arrangement 1 (D).
Concept Tested: Motor Position Restrictions
10. Two supply fans stand on either side of a service aisle, with their drive sides facing the aisle. Both must blow north through Top Horizontal outlets. The west fan's observer faces west, and the east fan's observer faces east. What are the correct codes?¶
- Both fans CW THD, because they blow the same direction
- Both fans CCW THD, because their drives face each other
- West fan CW THD, east fan CCW THD
- West fan CW THD, east fan CW BHD
Show Answer
The correct answer is C. Facing west, north is on the observer's right, so the west fan's top outlet blows right and the fan is CW. Facing east, north is on the observer's left, so the east fan's top outlet blows left and the fan is CCW. The discharge code is the same; only the rotation differs, and the pair is a mirror image across the aisle. Options A and B ignore that the two observers face opposite ways, and BHD (D) is a bottom outlet.
Concept Tested: Counterclockwise Rotation