# Wiring for 2 HOA stations



## JRaef (Mar 23, 2009)

MWayne said:


> We've got an exhaust fan that used to be controlled from 2 places, at the MCC and also while standing near the fan. Some contractors came in and wrecked out the bucket for this fan by mistake and never wired it back, about a month ago I wired it up and thought everything was great until the second station was pointed out to me. I found 3 wires between this second station and the bucket and can't figure out how to make it work correctly. The plans i come up with have flaws such as one station being off, the other in auto and the fan turns on and catches somebody by surprise. FWIW I don't know for a fact that it ever worked correctly, just that it did work in hand. So I'd appreciate a link to a drawing or a drawing. Thanks all!


It may indeed have never worked right if there are only 3 wires coming from the remote HOA, and (assuming) a standard HOA switch in the MCC bucket. At one place or the other, you would need either additional contacts on one of the HOAs, or at least a pair of DT relays. The only way I can think of it working with just 2 standard HOAs is if both circuits were in series, which would mean it ONLY worked if BOTH switchs were in the same position. Hand 1 + Hand 2, or Auto 1 + Auto 2 in series with the Auto control device. Off on either switch would be off.

Next closest is that still using that scheme, if you tied H 2 to A 2, then in Auto 1, it would run with Switch 2 in Hand as well as Auto, which can get confusing. Still would not run if Auto if Sw 2 is not also in Auto (or Hand) though.

Can't upload my drawing from this system (blocked access to file sharing sites), sorry.


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## John Valdes (May 17, 2007)

What controls the fan when in auto? 
Need the scope before any drawing can be made. Tell us exactly what you want the fan to do.


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## Big John (May 23, 2010)

I guess the question is, what do you want it to do? Either it has to work similar to Jraefs firs description, where both stations need to be in agreement before the fan will function. Or else you've gotta wire it so one station takes priority.

Personally, I would eliminate the "Auto" function from one station and make it only HO. Which, if I had to guess, is how it was wired to begin with.


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## John Valdes (May 17, 2007)

He can wire it anyway he wants. All he has to do is tell us what he wants it to do.
This is not something you can explain.
He needs to tell us, then we can work on a drawing.
I know of no other way to accomplish this other than to draw it.

Wayne. Make sure you include any fail safes required.

Whats the going rate for engineered drawings? :laughing:


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## MWayne (Nov 8, 2010)

John Valdes said:


> What controls the fan when in auto?
> Need the scope before any drawing can be made. Tell us exactly what you want the fan to do.


SCADA now controls the fan when in auto. 

To me the important thing is that when either station is off that the fan won't run. 
Be able to run in hand from both stations. 
And the auto on the floor station can probably be done away with, like Big John said, I'll relabel it hand off off. 

JRaef, there is room in the bucket for some relays but no room at the remote station.


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## MWayne (Nov 8, 2010)

John Valdes said:


> Whats the going rate for engineered drawings? :laughing:


How about the next time I'm in SC, I drop in and buy you a few beers and politely grin and bear it while you go on and on about how you hate the Cowboys?


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## JRaef (Mar 23, 2009)

Trying a new image host that my IT dept seems to be unaware of... so far!

Nope, can't embed it. but here's a link.

http://postimg.org/image/4xhj5k5cb/


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## John Valdes (May 17, 2007)

MWayne said:


> SCADA now controls the fan when in auto.
> 
> To me the important thing is that when either station is off that the fan won't run.
> Be able to run in hand from both stations.
> And the auto on the floor station can probably be done away with, like Big John said, I'll relabel it hand off off.


So basically, you need two operator stations to start and/or stop the fan? And activated by the system control in the automatic mode? Yes? 
That the computer/PLC/ closes a contact in the logic or turns on an output. If this is a PLC application, which it is starting to sound like, I am not certain how this is programmed. 
I always just drew up a new diagram.
I hated trying to figure out what the last hack did. Just redo it. Faster and better.



MWayne said:


> How about the next time I'm in SC, I drop in and buy you a few beers and politely grin and bear it while you go on and on about how you hate the Cowboys?


I am waiting for your visit. Look forward to it. :thumbsup:

I do highly dislike the Cowboys, but I have other teams I despise even more. 

But yes. Any member is always welcome and invited! In fact I would really enjoy it! :thumbsup:


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## ScooterMcGavin (Jan 24, 2011)

MWayne said:


> SCADA now controls the fan when in auto.
> 
> To me the important thing is that when either station is off that the fan won't run.
> Be able to run in hand from both stations.
> ...


If you want it to run in hand from both stations and not run when either is off, how can you get rid of the auto on the floor? In either position your overriding the auto function.

We have a chemical pump with a similar setup. At the pump you have hand/off/auto. In the control room there is a 2 position auto enable switch. When enabled the pump will work in auto mode. When disabled it won't run in auto but you can always override it with hand at the pump itself for testing or whatever.


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## dronai (Apr 11, 2011)

One of you guys want to show a drawing ? I want to see how that would look with the PLC used as the auto. I am picturing 1 motor starter, with the hand position wiring going directly to the coil, and the auto position would have to go to PLC inputs, first, and then outputs to the same starter coil. The off would disable both before it goes to the plc. Also if more than one hands control is needed, would you add, and parallel to the coil directly ? and not have the auto available at the other stations ?

In schematic shown that operating control device shown would be the contacts from the plc I/O right ?


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## Wirenuting (Sep 12, 2010)

Here is a H/O/A for you. 
A picture of a picture.


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## LATTC (Feb 12, 2012)

You can replace Start 2 and Stop 2 with your second HOA


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## ScooterMcGavin (Jan 24, 2011)

dronai said:


> One of you guys want to show a drawing ? I want to see how that would look with the PLC used as the auto. I am picturing 1 motor starter, with the hand position wiring going directly to the coil, and the auto position would have to go to PLC inputs, first, and then outputs to the same starter coil. The off would disable both before it goes to the plc. Also if more than one hands control is needed, would you add, and parallel to the coil directly ? and not have the auto available at the other stations ?
> 
> In schematic shown that operating control device shown would be the contacts from the plc I/O right ?


This would be my ideal setup if i was designing one from scratch that was PLC controlled. All the switches would go to the PLC. 

If either of the switches are off the fan won't turn on. If the opposite control station is in either hand or auto the control station you can run the fan in hand. If both stations are in auto it gives control of the fan to the control device (a temperature switch in this example). 

If the guy at station 1 has the fan in auto he should expect that it could start at any time regardless whether it comes from the hand switch at the other station or the automatic controls.


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## MWayne (Nov 8, 2010)

I had a colonoscopy this morning and in the fog of the anesthetics came up with this:










It requires the addition of a couple of ice cube relays in the bucket and I think it does most of what it needs to. Right?


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## dronai (Apr 11, 2011)

scameron81 said:


> This would be my ideal setup if i was designing one from scratch that was PLC controlled. All the switches would go to the PLC.
> 
> If either of the switches are off the fan won't turn on. If the opposite control station is in either hand or auto the control station you can run the fan in hand. If both stations are in auto it gives control of the fan to the control device (a temperature switch in this example).
> 
> If the guy at station 1 has the fan in auto he should expect that it could start at any time regardless whether it comes from the hand switch at the other station or the automatic controls.


All switches to the PLC :thumbsup: That way the program can monitor what's working at all times. Scameron, in your drawing, it looks like hand CS-2 wont work unless hand CS-1 is made ? To energize the B3:0/1 bit. And both auto's would have to on to let that B3:1/1 relay work ? Am I reading this right ? Here's my program


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## ScooterMcGavin (Jan 24, 2011)

Take a look at the branches on hand mode. If cs1 is in hand and cs2 is in hand or auto, it will complete the rung for hand mode. 

Where is the Off input coming from? Generally you don't need an "off" input because if its not in auto and its not in hand then it must be off.


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## dronai (Apr 11, 2011)

scameron81 said:


> Take a look at the branches on hand mode. If cs1 is in hand and cs2 is in hand or auto, it will complete the rung for hand mode.
> 
> Where is the Off input coming from? Generally you don't need an "off" input because if its not in auto and its not in hand then it must be off.


I didn't know a stop wasn't needed when doing this, makes sense though. I don't program in the real world yet :laughing: Your CS-2 is in series with CS-1, and will only work if CS-1 is made right ? Damn thing is small and my eyes are straining. Mines good without the stops, and control hand from either switch right ?


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## varmit (Apr 19, 2009)

Y'all are over thinking this. It will work using only two selector switches and the contact closure from the automatic control. If both SS are in "Auto": Auto control functions. If either is "Off": Motor will not start from either SS. In any other combination, Manual function will have the local SS be the lead (the local SS would need to be in "Hand" to enable the MCC mounted "Hand" function. This scenario is common in some plants that require the local control to be primary.

I'll post a sketch later.
http://s1286.photobucket.com/user/hairyvarmit/media/skele2_zps43ff7d21.jpeg.html


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## varmit (Apr 19, 2009)

I don't claim that my post above is an ideal way to do this, but it will function with what the OP said that he had to work with.


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## JRaef (Mar 23, 2009)

Here's mine finally (had to post from my wife's PC), it was very similar except you found a way for the MCC hand Switch to work with the Remote switch in either position, well done. I'll only point out that in the original scenario, there were only 3 wires to the remote switch, your solution needs 4.


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