Cal Haines
Diamond
- Joined
- Sep 19, 2002
- Location
- Tucson, AZ
Problems with the starting circuit are one of the common difficulties that a new owner of a 10EE faces. What follows is an explanation of the 10EE motor-generator (MG) starter circuit for machines equipped with the standard Cutler-Hammer model 9586 contactor.
I’m providing this drawing mostly for historical reasons; you don’t need to bother with it if you’re just trying to understand the starting circuit. To create the drawing I deleted some things (like the speed control rheostats) that don’t pertain to the starting circuit, cleaned it up and added some annotations. I don't know about everyone else, but I found the non-standard symbols used on the drawing very confusing. For example, the contactor's coil is shown by a circle with two terminals (the same symbol is used elsewhere for a light bulb). The transformer symbol looks like two resistors sitting side-by-side, etc. It took me the longest time to make sense of the diagram, so I've annotated the coil, overload heater (one of two) and overload switch (if that's the correct term for it) for reference.
Here is a drawing that I have modified to what I believe is a “typical” circuit as the machines were actually wired:
The blue lines on the diagram indicate the changes from EE-2674. Again, this diagram is provided solely for reference. You don’t need it for purposes of this discussion. Most MG-driven 10EEs appear to have been wired at the factory with the left side of the coil wired to L1; the other side of the starting circuit and terminal 3, at the top of the contactor, usually connects to L3. The starting circuit should be essentially the same for all 10EEs with MG drive.
Unfortunately, the typical AS-BUILT 10EE starting circuit is not compatible with most Rotary Phase Converters (RPC). RPCs tend to supply most of the power via the two “real” phases which connect directly to the incoming 240 VAC circuit. It’s very important that the “real” phases connect to the L1 and L2 terminals of the of the Cutler-Hammer contactor, since these are the only lines that have over-current protection. The problem with the AS-BUILT configuration of a 10EE starting circuit is that the coil is powered by incoming lines L1 and L3. Since the voltage of an RPC’s “wild” or artificial leg can vary significantly at startup, having it connected to the starting circuit’s coil via L3 can result in the machine failing to start or dropping out under load. The fix for the problem consists of moving a single wire from L3 to L2.
This diagram shows a typical MG starting circuit that has been modified for use with an RPC by moving the jumper that connects the top, right terminal of the contactor from L3 to L2:
As before, the blue lines show the connections that differ from drawing EE-2674. The magenta line shows the change made for RPC compatibility. The coil, overload heater and overload switch are also identified. Since this circuit functions equally well for true 3-phase power and for RPC-powered systems, it will be the basis for further discussions.
Note the following changes from EE-2674: 1) the left terminal of the coil connects to L1, not to the overload switch; 2) the right terminal of the coil connects to the right terminal of the overload switch rather than the STOP switch; 3) the left terminal of the overload switch connects to the STOP switch; 4) terminal 3, top right on the contactor, connects to L2.
One thing that is helpful to know about the diagram is that the relative positions of the terminals on the contactor are the same as those on the actual unit. Here is a photo of a 10EE Cutler-Hammer contactor with the same annotations, for reference:
Some contactors label the upper right terminal 1 instead of 3. I am using 3 here for consistency with drawing EE-2674.
Here is another photo of the same contactor, showing the overload section in more detail:
Terminals T1, T2 and T3 provide power to the MG. Terminals T1-1, T2-1 and T3 are typically used for connecting the coolant pump (if the machine is so equipped); this keeps the coolant pump from tripping the overloads when the machine is operating at full power, but also means that the coolant pump operates without overload protection.
Now we turn our attention to how the starting circuit operates. Below is an version of the above diagram, showing the coil circuit at startup, when the (momentary contact) START button is pressed:
Tracing the magenta wires, we see that the startup circuit is completed as follows: AC input L2 (and terminal 3, upper right) connect to the center position contacts of the drum switch in the headstock (which must be in the center position to allow the MG to start). The headstock switch is connected to terminal 3 of the START/STOP station (located on the right side of the "bump out" on the base); the START switch is a normally open, momentary contact switch and must be pressed by the operator to initiate startup. START switch terminal 1 is wired to STOP switch terminal 1. The STOP switch is normally closed and must be closed to allow startup. Terminal 2 of the STOP switch is, in turn, wired to the overload switch on the bottom of the contactor. If an over-current occurs on either L1 or L2, the thermally-operated overload switch will open and must be manually reset by pressing the overload reset button on the contactor; the overload switch must be closed/reset to allow startup. The other side of the overload switch is wired to one terminal of the coil. The other terminal of the coil is connected to L1, completing the circuit. Note that if there is an interruption in any portion of the red and magenta lines, above, the coil will not be energized and the MG will not start.
A lot of people are intimidated by 3-phase power and controls; don’t be. If you understand basic circuits, such as household wiring, you can understand the 10EE starting circuit. Think of it as a lighting circuit with the coil as the light bulb. All four (series connected) switches must be closed in order for the “light bulb” to operate. The four switches are: 1) headstock center-position switch; 2) START button; 3) STOP button; and, 4) overload switch.
When the coil is energized by completing the starting circuit the large 4-pole main relay at the top of the contactor closes. The contacts on the right end (terminals 3 and 1) now provide voltage directly to terminal 1 on the START/STOP station, bypassing the START and headstock switches and keeping the coil energized, as shown in the diagram below. If either the overload switch or the STOP switch open, the circuit is interrupted, the coil looses power, the contactor will open and the MG will shut down. This diagram shows the coil circuit with main contacts closed:
Using the household circuit analogy again: now the “light bulb” (coil) is powered by three switches in series: 1) the contacts on the right end of the main relay; 2) the STOP button; and, 3) the overload switch. Pressing the STOP button interrupts the circuit, the “light bulb” looses power, and the MG shuts down.
The starting circuit for a MG-equipped 10EE with an Allen-Bradley contactor is shown in this thread: 10EE starting circuit with Allen-Bradley contactor
As always, corrections, clarifications and questions are very welcome.
Cal
This is a revised version of a thread that I posted a year ago:
10EE MG Starter Circuit with Cutler-Hammer Contactor
It turns out that the “Typical” or AS-BUILT drawing that I used as a basis for my discussion there wasn’t very typical at all. Rather than create confusion by adding to that thread, I’m reposting the thread here, with updated illustrations and some additional information.
Here is a modified section of the wiring drawing for a round-dial 10EE, drawing EE-2674:10EE MG Starter Circuit with Cutler-Hammer Contactor
It turns out that the “Typical” or AS-BUILT drawing that I used as a basis for my discussion there wasn’t very typical at all. Rather than create confusion by adding to that thread, I’m reposting the thread here, with updated illustrations and some additional information.
I’m providing this drawing mostly for historical reasons; you don’t need to bother with it if you’re just trying to understand the starting circuit. To create the drawing I deleted some things (like the speed control rheostats) that don’t pertain to the starting circuit, cleaned it up and added some annotations. I don't know about everyone else, but I found the non-standard symbols used on the drawing very confusing. For example, the contactor's coil is shown by a circle with two terminals (the same symbol is used elsewhere for a light bulb). The transformer symbol looks like two resistors sitting side-by-side, etc. It took me the longest time to make sense of the diagram, so I've annotated the coil, overload heater (one of two) and overload switch (if that's the correct term for it) for reference.
Here is a drawing that I have modified to what I believe is a “typical” circuit as the machines were actually wired:
The blue lines on the diagram indicate the changes from EE-2674. Again, this diagram is provided solely for reference. You don’t need it for purposes of this discussion. Most MG-driven 10EEs appear to have been wired at the factory with the left side of the coil wired to L1; the other side of the starting circuit and terminal 3, at the top of the contactor, usually connects to L3. The starting circuit should be essentially the same for all 10EEs with MG drive.
Unfortunately, the typical AS-BUILT 10EE starting circuit is not compatible with most Rotary Phase Converters (RPC). RPCs tend to supply most of the power via the two “real” phases which connect directly to the incoming 240 VAC circuit. It’s very important that the “real” phases connect to the L1 and L2 terminals of the of the Cutler-Hammer contactor, since these are the only lines that have over-current protection. The problem with the AS-BUILT configuration of a 10EE starting circuit is that the coil is powered by incoming lines L1 and L3. Since the voltage of an RPC’s “wild” or artificial leg can vary significantly at startup, having it connected to the starting circuit’s coil via L3 can result in the machine failing to start or dropping out under load. The fix for the problem consists of moving a single wire from L3 to L2.
This diagram shows a typical MG starting circuit that has been modified for use with an RPC by moving the jumper that connects the top, right terminal of the contactor from L3 to L2:
As before, the blue lines show the connections that differ from drawing EE-2674. The magenta line shows the change made for RPC compatibility. The coil, overload heater and overload switch are also identified. Since this circuit functions equally well for true 3-phase power and for RPC-powered systems, it will be the basis for further discussions.
Note the following changes from EE-2674: 1) the left terminal of the coil connects to L1, not to the overload switch; 2) the right terminal of the coil connects to the right terminal of the overload switch rather than the STOP switch; 3) the left terminal of the overload switch connects to the STOP switch; 4) terminal 3, top right on the contactor, connects to L2.
One thing that is helpful to know about the diagram is that the relative positions of the terminals on the contactor are the same as those on the actual unit. Here is a photo of a 10EE Cutler-Hammer contactor with the same annotations, for reference:
Some contactors label the upper right terminal 1 instead of 3. I am using 3 here for consistency with drawing EE-2674.
Here is another photo of the same contactor, showing the overload section in more detail:
Terminals T1, T2 and T3 provide power to the MG. Terminals T1-1, T2-1 and T3 are typically used for connecting the coolant pump (if the machine is so equipped); this keeps the coolant pump from tripping the overloads when the machine is operating at full power, but also means that the coolant pump operates without overload protection.
Now we turn our attention to how the starting circuit operates. Below is an version of the above diagram, showing the coil circuit at startup, when the (momentary contact) START button is pressed:
Tracing the magenta wires, we see that the startup circuit is completed as follows: AC input L2 (and terminal 3, upper right) connect to the center position contacts of the drum switch in the headstock (which must be in the center position to allow the MG to start). The headstock switch is connected to terminal 3 of the START/STOP station (located on the right side of the "bump out" on the base); the START switch is a normally open, momentary contact switch and must be pressed by the operator to initiate startup. START switch terminal 1 is wired to STOP switch terminal 1. The STOP switch is normally closed and must be closed to allow startup. Terminal 2 of the STOP switch is, in turn, wired to the overload switch on the bottom of the contactor. If an over-current occurs on either L1 or L2, the thermally-operated overload switch will open and must be manually reset by pressing the overload reset button on the contactor; the overload switch must be closed/reset to allow startup. The other side of the overload switch is wired to one terminal of the coil. The other terminal of the coil is connected to L1, completing the circuit. Note that if there is an interruption in any portion of the red and magenta lines, above, the coil will not be energized and the MG will not start.
A lot of people are intimidated by 3-phase power and controls; don’t be. If you understand basic circuits, such as household wiring, you can understand the 10EE starting circuit. Think of it as a lighting circuit with the coil as the light bulb. All four (series connected) switches must be closed in order for the “light bulb” to operate. The four switches are: 1) headstock center-position switch; 2) START button; 3) STOP button; and, 4) overload switch.
When the coil is energized by completing the starting circuit the large 4-pole main relay at the top of the contactor closes. The contacts on the right end (terminals 3 and 1) now provide voltage directly to terminal 1 on the START/STOP station, bypassing the START and headstock switches and keeping the coil energized, as shown in the diagram below. If either the overload switch or the STOP switch open, the circuit is interrupted, the coil looses power, the contactor will open and the MG will shut down. This diagram shows the coil circuit with main contacts closed:
Using the household circuit analogy again: now the “light bulb” (coil) is powered by three switches in series: 1) the contacts on the right end of the main relay; 2) the STOP button; and, 3) the overload switch. Pressing the STOP button interrupts the circuit, the “light bulb” looses power, and the MG shuts down.
The starting circuit for a MG-equipped 10EE with an Allen-Bradley contactor is shown in this thread: 10EE starting circuit with Allen-Bradley contactor
As always, corrections, clarifications and questions are very welcome.
Cal
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