Why would you need a hand off auto, and a stop start?
- Thread starter zappy
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Wouldn't the 'start/stop' be what is used for manual control in the 'hand' position?
Tulsa Electrician
Senior Member
- Location
- Tulsa
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- Electrician
In the off position. Neither the( local) start/stop will work nor a remote location of control.
- Location
- Placerville, CA, USA
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- Retired PV System Designer
For any given motor, there are a bunch of control options:
If your goal is option 3, you can either use an auto/manual switch plus pushbuttons or a switch for on/off; or you can combine both choices in an Auto/Hand(on)/Off switch. The single switch makes it more difficult to "jog" the controlled motor than the option with buttons.
I am assuming that the green light in the photo is actually a lighted push button that doubles as a status indicator.
- One is a completely manual stop/start with no automatic control at all.
- Another is completely automatic control with no manual options.
- Or manual start/stop with the ability for the manual control to kick in later after the manual start or stop.
- Auto control only with the option of taking the automation out of the loop to do manual control.
If your goal is option 3, you can either use an auto/manual switch plus pushbuttons or a switch for on/off; or you can combine both choices in an Auto/Hand(on)/Off switch. The single switch makes it more difficult to "jog" the controlled motor than the option with buttons.
I am assuming that the green light in the photo is actually a lighted push button that doubles as a status indicator.
- Location
- Placerville, CA, USA
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- Retired PV System Designer
That is one way to do it.
But the same switch, with the same labeling, could actually implement Auto/Run/Stop with no buttons required.
In the OP's photo, there is no Stop button associated with the Auto/Hand/Off switch and the green light is probably just using the indicator function of a lighted push button or is just an indicator with no Start function in either case.
Yes it is a button.
- Occupation
- Licensed Electrician
You are correct sir.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The large switch in the first pic and the green button/light with the burned-out bulb are labeled the same, so there is a correlation, and there is a stop button below the green.
TwoBlocked
Senior Member
- Location
- Bradford County, PA
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- Industrial Electrician
The way I see it, the two cooling tower pumps are in 3-wire control with a lighted start button and an unlighted stop button. If a motor trips the overload or the power is cycled, you must push the start button again to get the motor going.
The axillary oil pump and the generator heater are in 2-wire control. With either one, if the motor or heater trips an overload or the power is cycled, the motor or heater will start back up immediately.
With the HOA control on the axillary oil pump, there is some kind of permissive and/or interlock when in Auto that will cause the pump to run or not depending on an oil level, temperature, or other equipment running, or ... When in Hand, it will run regardless of the permissives or interlocks. And of course in Off, the motor doesn't run.
For the generator heater, it is a simple on/off switch, although there could be a high temp switch to keep it from getting too hot. and a run status to turn it off when the genny is running.
There could also be a Master Control Relay for an E-stop on all the equipment. AND these controls may not be hardwired. They may be PLC controlled, although you would expect them to operate the same way.
Ugly's has some drawings on 2-wire and 3-wire control.
The axillary oil pump and the generator heater are in 2-wire control. With either one, if the motor or heater trips an overload or the power is cycled, the motor or heater will start back up immediately.
With the HOA control on the axillary oil pump, there is some kind of permissive and/or interlock when in Auto that will cause the pump to run or not depending on an oil level, temperature, or other equipment running, or ... When in Hand, it will run regardless of the permissives or interlocks. And of course in Off, the motor doesn't run.
For the generator heater, it is a simple on/off switch, although there could be a high temp switch to keep it from getting too hot. and a run status to turn it off when the genny is running.
There could also be a Master Control Relay for an E-stop on all the equipment. AND these controls may not be hardwired. They may be PLC controlled, although you would expect them to operate the same way.
Ugly's has some drawings on 2-wire and 3-wire control.
ptonsparky
Tom
- Occupation
- EC - retired
That is the total of it.
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
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- Sorta retired........
You just took all the fun out of this......
kwired
Electron manager
- Location
- NE Nebraska
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- EC
"Hand" position often runs the load regardless of what interlocks may be arranged in the auto position. Hand may not necessarily be intended to be used other than for maintenance or troubleshooting purposes as it will not be coordinated with other items to run or not run during predetermined conditions.
- Location
- Illinois
- Occupation
- retired electrician
We did that a lot, but the hand was always a spring return to off...only used for troubleshooting or to verify lockout. The hand position bypassed all interlocks with the exception of the overload relay in the motor starter. The lockout policy for non-electrical work, require that you first use the hand switch to verify that the the equipment operates, then go to the lockout point and lock the equipment out, and return to the HOA and verify that the equipment does not operate.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
When in “Hand”, you have two types of control options: 2 wire control and 3 wire control. The difference is in how it acts if there is a power failure.
In 2 wire control, the “Hand” contact of the selector switch goes directly to the starter coil and runs the motor for as long as the switch is in that position. If during that time the power goes out, when it is restored and nobody has moved the HOA switch, the motor automatically (unexpectedly) comes back on. That can be very dangerous on machinery because you will have no control of when power is restored. But sometimes that's OK, like for HVAC fans for example.
With 3 wire control, your Hand position control circuit is fed through a Start-Stop button. The Start function is sealed in through an aux contact of the starter, and stays sealed in until someone hits the Stop button, OR THE POWER FAILS. If power fails, the contactor drops out and breaks the circuit sealing in around the Start button. So when power is restored, the machine does NOT automatically restart. A human must actively press the Start button to make it come back on, ostensibly making sure everything is safe first.
In addition, the action of how it responds to an overload trip and reset is similar. In 2 wire control, as soon as you press the Reset button on the Over Load Relay, the motor immediately restarts. In 3 wire control, you press the reset and nothing happens until you also press the Start button. That can be part of a safety issue as well.
In 2 wire control, the “Hand” contact of the selector switch goes directly to the starter coil and runs the motor for as long as the switch is in that position. If during that time the power goes out, when it is restored and nobody has moved the HOA switch, the motor automatically (unexpectedly) comes back on. That can be very dangerous on machinery because you will have no control of when power is restored. But sometimes that's OK, like for HVAC fans for example.
With 3 wire control, your Hand position control circuit is fed through a Start-Stop button. The Start function is sealed in through an aux contact of the starter, and stays sealed in until someone hits the Stop button, OR THE POWER FAILS. If power fails, the contactor drops out and breaks the circuit sealing in around the Start button. So when power is restored, the machine does NOT automatically restart. A human must actively press the Start button to make it come back on, ostensibly making sure everything is safe first.
In addition, the action of how it responds to an overload trip and reset is similar. In 2 wire control, as soon as you press the Reset button on the Over Load Relay, the motor immediately restarts. In 3 wire control, you press the reset and nothing happens until you also press the Start button. That can be part of a safety issue as well.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I typically will call a spring return switch position "jog" instead of "hand". That can depend on other circumstances though.
I've had machines that have say an oil pump that must run before the main motor runs, most cases will still interlock so the switch actually starts the oil pump and then when aux contact on oil pump controller closes it allows the main motor to run. And will interlock it that way whether control switch is in hand, jog, as well as auto position.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
One advantage of stop/start is that the motor won't restart after a loss of power.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
As others have noted, 2 wire VS 3 wire control are very different and each have their advantages and disadvantages. It all depends on what the starter controls to make a good and safe choice. I'm often disappointed how many electricians don't understand the basic concepts of 3 wire control. It is just so fundamental to all the possibilities of motor control and has many applications and has been around for many decades.
At the risk of insulting some, if one does not understand these basics they should not touch motor controls.
At the risk of insulting some, if one does not understand these basics they should not touch motor controls.
Very commonly Hand will start the motor with just the overload protection in the circuit. If there's a BAS building automation system or PLC, stop start may just be inputs to the computer. So they would be hard wired only as far as the local circuit card or IO and have to go through the software layer for any effect.
No PLC or BAS, Stop Start would be hardwired to the latching aux contact as previously stated and generally there would not be a HOA switch. It's an adder. If it was spec'ed that way it would be redundant.
With a PLC or BAS, Stop Start could be for a process or array equipment and start multiple motors or the process equipment itself.
For the cooling tower, that's working in combination with other things, like a chiller and responding to condenser water temp setpoint. So there would be a PLC or BAS for the process. Hand would give you manual motor ON with just the OL's. Stop Start could have different implementations as indicated. In that case I would not expect Stop Start to give manual motor ON, and I would also not expect it to give process ON. That would be the chiller that would call the cooling towers. Call for cooling >> call for chillers >> call for towers. Chillers run when the towers prove, condenser water temp is in range.
So in that case it's not apparent how the Stop Start are implemented. There is more than one possibility. Hand would start the single motor on that starter, but Start, marked for the towers, should not start the chillers.
Most likely in that case Start and Stop would be inputs to the BAS. So they might give you manual on off, with the HOA switch in "auto".
No PLC or BAS, Stop Start would be hardwired to the latching aux contact as previously stated and generally there would not be a HOA switch. It's an adder. If it was spec'ed that way it would be redundant.
With a PLC or BAS, Stop Start could be for a process or array equipment and start multiple motors or the process equipment itself.
For the cooling tower, that's working in combination with other things, like a chiller and responding to condenser water temp setpoint. So there would be a PLC or BAS for the process. Hand would give you manual motor ON with just the OL's. Stop Start could have different implementations as indicated. In that case I would not expect Stop Start to give manual motor ON, and I would also not expect it to give process ON. That would be the chiller that would call the cooling towers. Call for cooling >> call for chillers >> call for towers. Chillers run when the towers prove, condenser water temp is in range.
So in that case it's not apparent how the Stop Start are implemented. There is more than one possibility. Hand would start the single motor on that starter, but Start, marked for the towers, should not start the chillers.
Most likely in that case Start and Stop would be inputs to the BAS. So they might give you manual on off, with the HOA switch in "auto".
I wanted to clarify the above post. Several times I have seen two of the Big 3 control companies doing it very wrong. I have seen multiple conductor 18 ga CL2 cable run in the MCC gutter and intercept the HOA switch. Just looking at it there was no way to guess what scenario they had implemented. It looked so bad. But with the MCC starter coils running at 120 or 240, there was no way they had the coil Voltage going through what they had done
At a different site another of the Big 3, their design build, had run thousands of feet of gutter with everything 480 and PLC IO in the same gutter. The separation barrier where present would do nothing for the inductive interference. Actually they knew it would be a problem and their method was to run a lot of the IO at 120 V, and they still had ghosting problems with the IO from the induced noise. 1000's of ft of EMT with IO and multiple motor 480 combined in the same pipe. Why I have no clue. But that was standard for them.
Basically they were recreating problems from the 1980's when computers were first widely deployed and induced noise on the control and computer IO was found to be a problem. Problems discovered and solved back then.
Given what I've seen them doing or trying to do, there is no way I would look at a HOA with Start Stop and PLC IO and assume it was done correctly or to some standard. The Start Stops could be just other IO inputs, and wired the way I've seen, they liked feeding the PLC as much noise as they could collect.
Other scenarios posted above assume adhering to some correct standard method. I would not assume they were wired correctly.
At a different site another of the Big 3, their design build, had run thousands of feet of gutter with everything 480 and PLC IO in the same gutter. The separation barrier where present would do nothing for the inductive interference. Actually they knew it would be a problem and their method was to run a lot of the IO at 120 V, and they still had ghosting problems with the IO from the induced noise. 1000's of ft of EMT with IO and multiple motor 480 combined in the same pipe. Why I have no clue. But that was standard for them.
Basically they were recreating problems from the 1980's when computers were first widely deployed and induced noise on the control and computer IO was found to be a problem. Problems discovered and solved back then.
Given what I've seen them doing or trying to do, there is no way I would look at a HOA with Start Stop and PLC IO and assume it was done correctly or to some standard. The Start Stops could be just other IO inputs, and wired the way I've seen, they liked feeding the PLC as much noise as they could collect.
Other scenarios posted above assume adhering to some correct standard method. I would not assume they were wired correctly.
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