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Old 07-27-2012, 10:31 PM   #1
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Remote switch for air compressor


I have a 240V air compressor with a motor starter. I am moving it out of my shop to a add-on room on the back side of the building. At present it is located close to the door and I turn it off and on with a two pole disconnect switch mounted on the compressor. Once it is moved, I don't want to have to go around the shop to the compressor room to turn it on or off. I want to wire a toggle switch in series with the pressure switch, and mount that switch close to the door, so I can turn it on or off as I come and go. I have no problem with how to wire the toggle switch in series with the existing pressure switch. My question concerns circuit protection for the switch loop. There is a note in the cover of the starter stating that "control circuits may need circuit protection". Right now the control circuit consists of about 12" of two wire cord to the pressure switch, no circuit protection. I will be adding a 40' run of conduit (metal building) for the remote switch. What is a practical method of adding a circuit breaker to protect that switch loop?
Also, if I am going about this the wrong way, I can be guided in the right direction.
Thanks in advance, jp

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Old 07-27-2012, 10:37 PM   #2
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr View Post
I have a 240V air compressor with a motor starter. I am moving it out of my shop to a add-on room on the back side of the building. At present it is located close to the door and I turn it off and on with a two pole disconnect switch mounted on the compressor. Once it is moved, I don't want to have to go around the shop to the compressor room to turn it on or off. I want to wire a toggle switch in series with the pressure switch, and mount that switch close to the door, so I can turn it on or off as I come and go. I have no problem with how to wire the toggle switch in series with the existing pressure switch. My question concerns circuit protection for the switch loop. There is a note in the cover of the starter stating that "control circuits may need circuit protection". Right now the control circuit consists of about 12" of two wire cord to the pressure switch, no circuit protection. I will be adding a 40' run of conduit (metal building) for the remote switch. What is a practical method of adding a circuit breaker to protect that switch loop?
Also, if I am going about this the wrong way, I can be guided in the right direction.
Thanks in advance, jp

Here is an even easier solution, buy a correctly sized contactor with a 120v coil, and a lutron Pico switch and remote, install the contactor at the panel location along with the lutron switch to energize the coil, and you can wirelessly turn on the compressor anywhere in the shop.

Just dont buy the dimmer version, they make a non dimmable switch.

This contactor will go near the panel and turn on/off power going to the compressor via the wireless remote.


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Old 07-27-2012, 10:37 PM   #3
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Remote switch for air compressor


What about either a Safety Disconnect or Safety Switch? http://www.grainger.com/Grainger/saf...071&sst=subset Mount it in the main space basically between the panel & compressor. I take it that you have a breaker already in the panel in the shop that would stay I take it, so you could use it, then the Secondary being the disconnect switch.
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Old 07-27-2012, 11:13 PM   #4
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What about either a Safety Disconnect or Safety Switch?
I already have a safety disconnect. It is mounted on the compressor right now. It was mounted on the wall at my former shop. The compressor was in a separate room there, with no line of sight to the breaker box. I just mounted it on the compressor when we moved to the new house/shop. IF I was just moving the compressor to an outside room, I could just get an additional safety switch and wire through it, and mount it close to the door, and use it to turn the compressor on or off. I could also use the circuit breaker, but I do NOT like using circuit breakers for switches, it is not their intended purpose. But there is more to the story that makes using a disconnect not practical for what I want to do. In conjunction with moving the air compressor, I am adding a 100A sub panel on the back side of the shop to feed the compressor and other new loads on that side of the building. I feel like using the control circuit of the magnetic starter (smaller wires, 1/2" conduit) would be the most cost effective way of doing what I want to do. I am just not aware of how I would need to add a circuit breaker to the loop. The only thing I know of is a "circuit breaker enclosure", but that seems like overkill for what I am doing. I just don't think I should have a 40' loop of 14G wire with only the 40A compressor circuit breaker for protection. Am I wrong on that?

Also, before someone suggests I need to go to the compressor room to drain the tank, so I can just turn it on/off when I do that, the compressor is equipped with an automatic tank drain.
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Old 07-27-2012, 11:18 PM   #5
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Remote switch for air compressor


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Originally Posted by ArTrvlr View Post
I already have a safety disconnect. It is mounted on the compressor right now. It was mounted on the wall at my former shop.
So that's your answer, isn't it? Move the disconnect back to the wall you choose and be done with it. You already have the wiring expertise.
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Old 07-27-2012, 11:59 PM   #6
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So that's your answer, isn't it? Move the disconnect back to the wall you choose and be done with it. You already have the wiring expertise.
Not quite. Did you miss the part about the new sub panel? I am adding a new sub panel 40 feet away from the main panel. Also about 40 feet from the door where I want to mount the switch. The compressor will be fed out of the new sub panel. So to use the disconnect, I would have to run 80 feet of 8G, 40 feet from the sub panel to the door, 40 feet back to the compressor. More like 100 feet, since the 80 feet doesn't take into account the vertical portion of the run.

It just seems so simple to just add a switch in series with the pressure switch (14G instead of 8G), I just don't know about providing circuit protection. That is my question, what is a cost effective (also known as cheap) way to add a circuit breaker outside of a main or sub panel? Or, do I even need to add one?
jp
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Old 07-28-2012, 12:07 AM   #7
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Remote switch for air compressor


Circuit breaker in what ever panel. From there to a Safety disconnect where ever. Then to the compressor. If it was me, I would want a means to be able to have one disconnect or the other as close to the compressor as I could. It is up to you as to where you place the secondary, so get planning.

For our wood shop in high school, the shop teacher would go to the panel and shut everything down if it was the last class for the day, then during the first class, would flip the breakers back on. At the compressor, there was a disconnect right there. That was it. If it was me, I would be doing the same thing, or have a main disconnect that shuts all power to everything but the lighting circuit, that I could flip as I get ready to exit out the door when I am done.
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Old 07-28-2012, 12:10 PM   #8
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr
I have a 240V air compressor with a motor starter. I am moving it out of my shop to a add-on room on the back side of the building. At present it is located close to the door and I turn it off and on with a two pole disconnect switch mounted on the compressor. Once it is moved, I don't want to have to go around the shop to the compressor room to turn it on or off. I want to wire a toggle switch in series with the pressure switch, and mount that switch close to the door, so I can turn it on or off as I come and go. I have no problem with how to wire the toggle switch in series with the existing pressure switch. My question concerns circuit protection for the switch loop. There is a note in the cover of the starter stating that "control circuits may need circuit protection". Right now the control circuit consists of about 12" of two wire cord to the pressure switch, no circuit protection. I will be adding a 40' run of conduit (metal building) for the remote switch. What is a practical method of adding a circuit breaker to protect that switch loop?
Also, if I am going about this the wrong way, I can be guided in the right direction.
Thanks in advance, jp
In answer to your question, the control circuit conductors are considered protected by the motor branch circuit over current device as long as the conductors are sized in accordance with art 430.
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Old 07-28-2012, 05:09 PM   #9
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Remote switch for air compressor


Don't know why this didn't occur to me before. It just came to me in a flash, from out of nowhere.

I can just use something like this.

At present the cord to the pressure switch comes out of a knockout in the bottom of the starter box. I can just mount a handy box there, put a little "push to reset" breaker in it (probably mounted through a hole in the cover) and wire from there to my remote switch and the pressure switch, all in series.

So simple, and I was trying to complicate it.
jp
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Old 07-28-2012, 05:33 PM   #10
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr
Don't know why this didn't occur to me before. It just came to me in a flash, from out of nowhere.

I can just use something like this.

At present the cord to the pressure switch comes out of a knockout in the bottom of the starter box. I can just mount a handy box there, put a little "push to reset" breaker in it (probably mounted through a hole in the cover) and wire from there to my remote switch and the pressure switch, all in series.

So simple, and I was trying to complicate it.
jp
Did you read my last post? What size is the compressor breaker?
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Old 07-29-2012, 01:15 AM   #11
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Did you read my last post? What size is the compressor breaker?
Yes, I read it. It is on a 40A breaker, 8GA wire. I took your reference to art 430 (I don't have a copy of the NEC) to mean that for any wiring to be protected, they would all have to be the same size. I assume 14GA control wiring would get pretty hot before tripping a 40A breaker, and 8GA in a 100 foot loop to a disconnect switch is out of the question, might even require 6GA to avoid voltage drop.

Is there some reason my mini breaker won't work?
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Old 07-29-2012, 01:45 AM   #12
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr View Post
Yes, I read it. It is on a 40A breaker, 8GA wire. I took your reference to art 430 (I don't have a copy of the NEC) to mean that for any wiring to be protected, they would all have to be the same size. I assume 14GA control wiring would get pretty hot before tripping a 40A breaker, and 8GA in a 100 foot loop to a disconnect switch is out of the question, might even require 6GA to avoid voltage drop.

Is there some reason my mini breaker won't work?
There is couple issue that will get the DIY's in hot water pretty fast first of all I know you say magatic starter that is fine due you have pretty decent sized unit.

The first part do meet the NEC code but for some reason you did not mention how many CV ( HP ) this motour is I know you say 240 volts so let not worry about this part for a second but it will come up in second when I get to the control circuit.

I know say about 100 foot from the new subpanel if so that is correct.

Now for the remote switch this get tricky due you posted a single pole mini breaker if you are useing the 240 volt contractor coil this WILL not fly at all you will need two pole to order meet the code.

My methold I useally use to this all the time is use small control transfomer ( 240 X 24 volt ( 24 volt secondary ) and use single fuse on secondary that part will meet the code very easy.

I have to find the excat NEC number related to this one I know it is in 430 area but specfic number plus there is couple other items will show up so one of the reader can post specfic number they can do that as well.

The key issue that anytime you have something shorted out on control circuit you should able disconnet both pole at the same time that the reason why it will not fly with single pole mini breaker as you posted.

Is the automatique drain valve is hooked up to the motour circuit ? That part may change the game plan a little as well ( if you can find out what voltage the automatique drain valve do run on )

Merci,
Marc
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Old 07-29-2012, 10:11 AM   #13
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr

Yes, I read it. It is on a 40A breaker, 8GA wire. I took your reference to art 430 (I don't have a copy of the NEC) to mean that for any wiring to be protected, they would all have to be the same size. I assume 14GA control wiring would get pretty hot before tripping a 40A breaker, and 8GA in a 100 foot loop to a disconnect switch is out of the question, might even require 6GA to avoid voltage drop.

Is there some reason my mini breaker won't work?
Let's start at the beginning. Since you are relocating the unit a new branch circuit has to be installed. What is the hp rating of the motor? Phases? Then we can proceed from there.

Mini breaker not necessary.
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Last edited by electures; 07-29-2012 at 11:21 AM.
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Old 07-29-2012, 12:48 PM   #14
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Remote switch for air compressor


Thanks to electures and frenchelectrican for your thoughtful comments and interest. As suggested, let's start all over from the beginning.

This is the compressor I have.

Motor is a 7.5HP Baldor, nameplate states:
Volts: 208 - 230
Amps: 32 - 29
Just so there is no confusion, it is single phase.

It is on a 40A branch circuit, 8GA wire.

At present, in it's temporary location, just inside the man-door of the shop, it is convenient to turn it on or off as I enter or leave for the day. Once I move it to an outside room on the other side of the building, I don't want to have to go back there, unlock a door and flip the switch. All my light switches and exhaust fan switch are already right at that door, so I thought a compressor switch there will help me to remember to turn it off when I leave for the day.

Part of the plan for the relocation of the compressor includes a new sub panel on that wall of the shop, to feed the compressor, a dust collector (5HP), a future paint room with lights, outlets and exhaust fans. I am maxed out in the present main panel.

There is a piece of extension cord, SJOOW, 16/2 going from the magnetic starter to the pressure switch on the tank. In my feeble little, non-electrician mind, I reasoned that a simple switch added to that control circuit, could be mounted anywhere. But I also felt that since it would be extended all the way across the building, circuit protection would/should be required. Then I saw the note inside the cover of the starter: "CONTROL WARNING: Control circuit conductors installed by the user may require additional overcurrent protection to comply with applicable electrical codes.", which confirmed my thinking.

The automatic drain valve is on a separate, 110V circuit. It is this one. It opens every 45 minutes, for 1/2 second, it stays on 24/7.

So now my question is, why won't a single pole breaker, in series in that control circuit, protect those wires if they were to be shorted? Do I need one on each leg of the circuit? If so, does it have to be common trip?
jp
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Old 07-29-2012, 02:07 PM   #15
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Remote switch for air compressor


Quote:
Originally Posted by ArTrvlr View Post
Thanks to electures and frenchelectrican for your thoughtful comments and interest. As suggested, let's start all over from the beginning.

This is the compressor I have.

Motor is a 7.5HP Baldor, nameplate states:
Volts: 208 - 230
Amps: 32 - 29
Just so there is no confusion, it is single phase.

It is on a 40A branch circuit, 8GA wire.

At present, in it's temporary location, just inside the man-door of the shop, it is convenient to turn it on or off as I enter or leave for the day. Once I move it to an outside room on the other side of the building, I don't want to have to go back there, unlock a door and flip the switch. All my light switches and exhaust fan switch are already right at that door, so I thought a compressor switch there will help me to remember to turn it off when I leave for the day.

Part of the plan for the relocation of the compressor includes a new sub panel on that wall of the shop, to feed the compressor, a dust collector (5HP), a future paint room with lights, outlets and exhaust fans. I am maxed out in the present main panel.

There is a piece of extension cord, SJOOW, 16/2 going from the magnetic starter to the pressure switch on the tank. In my feeble little, non-electrician mind, I reasoned that a simple switch added to that control circuit, could be mounted anywhere. But I also felt that since it would be extended all the way across the building, circuit protection would/should be required. Then I saw the note inside the cover of the starter: "CONTROL WARNING: Control circuit conductors installed by the user may require additional overcurrent protection to comply with applicable electrical codes.", which confirmed my thinking.

The automatic drain valve is on a separate, 110V circuit. It is this one. It opens every 45 minutes, for 1/2 second, it stays on 24/7.

So now my question is, why won't a single pole breaker, in series in that control circuit, protect those wires if they were to be shorted? Do I need one on each leg of the circuit? If so, does it have to be common trip?
jp
Based on the information provided the branch circuit conductors need to be sized for 50A and the branch circuit overcurrent device (breaker?) should be sized at 100A. This will allow the motor to start and run. #8 romex is rated for 40A. However, #8 THWN in conduit is rated for 50A as long as all terminations are 75 degree listed.

The feeder to the subpanel has to be sized for the largest motor FLA x 125% plus all other motors @ 100% plus 125% of all continous loads plus 100% of any noncontinous loads. So just for the compressor and dust collector = (40A x 125%) + (28A x 100%) = 78A. The feeder conductors need to be sized for 78A + all other loads as mentioned earlier. I'm guessing at a 100A to 125A feeder.

The feeder breaker has to be sized for the largest motor OCPD (compressor) + the FLA's of all other motors + other loads as mentioned earlier. 100 + 28 + all other motors + other loads. Again I'm guessing at 150A to 175A feeder breaker.

As for the control circuit conductors, they are permitted to be protected by the motor branch circuit overcurrent device in accordance with 430.72(B). #14 control conductors are rated for 45A. #12 control conductors are rated for 60A. Since the compressor breaker can be as large as 100A you can install an in line fuse or the mini breaker you mentioned earlier. If you reduce the motor compressor breaker to 45A or 60A then the control conductors mentioned earlier respectfully can be used, but this could lead to nuicance tripping.

You did not mention whether or not this is a home shop or a business. Some posters will argue that if this is a home shop that these calculations are obsurd, but the NEC does not differentiate between home shops and commercial shops. Motors are motors - code is code.

Smaller breakers can be used on the motors, but can lead to nuisance tripping. Without knowing all the motor loads and other loads, these calculations are to be considered estimates. You may want to consult a professional electrical contractor or engineer.

Good luck!!

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