Wiring a new 240V compressor with a switch

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  #1  
Old 04-09-13, 10:20 PM
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Wiring a new 240V compressor with a switch

Long story short, new compressor, 1PH 240V 15A. Compressor will be outside. I want to put a pilot switch to control the power to the receptacle for it so that it's not left on when not needed.

I only found a couple of pilot switches that are double-pole...

Leviton 1222-PLR 120V 20A double pole

Leviton 3032-PLR 120V 30A double pole

I assume that neither of these is adequate. I would love to be wrong though, even if it's the 3032 as a more expensive unit.

Any thoughts or suggestions?
 
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  #2  
Old 04-09-13, 10:42 PM
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Possibly answering my own question...

Pass and Seymour PS20AC2-RPL

Pass and Seymour PS30AC2-RPL

Would either of these work to control a 240V single phase 15A compressor?
 
  #3  
Old 04-09-13, 11:07 PM
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Those switches are heavy enough but they aren't double pole switches and won't switch both sides of the 240 volt circuit. That's ok as long as you don't intend to use that as a service switch.
 

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  #4  
Old 04-09-13, 11:40 PM
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Don't even consider an "open" switch as PJ has shown. Run the power through a unfused safety switch prior to the receptacle. If you need an indicator light to show that the power to the compressor is on we can discuss that.

[ATTACH=CONFIG]11321[/ATTACH]

(Image courtesy of shopping.yahoo.com)

Several different styles, sizes and configurations available from around $20 and up. Even check Ebay.
 
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  #5  
Old 04-10-13, 08:07 AM
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the indicator light is the more important part actually. The subpanel is near enough to the doorway that it wouldn't be impossible to simply shut off the breaker to the device if a conventional switch is not possible or not practical.

I have some unused, unwired fused safety switches on the wall in my garage from when the previous owner had some equipment, I could pull one for use at Dad's house (where the compressor is) if we really need something that substantial. I was hoping that something a little more aesthetic could handle the fairly scant power load though. I mean, the unit only calls for 15A, and I was planning on using one of those NEMA 6-15/6-20 receptacles behind a wet-application faceplate for the power to the unit.

On Page Two of the Pass and Seymour PDF they show the two switches that I listed in my first reply as being double pole and rated up to 277V, so I figured that those would possibly work in this instance.
 
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Old 04-10-13, 05:40 PM
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The problem with the switches that you linked to is that they probably do not have a horsepower rating, or if they do it is probably less than the horsepower rating of the compressor. It may not make any significant difference as long as the switch is never thrown when the motor may be in operation but I don't think that you can guarantee that.

As for the indicator lamp, I would suggest an LED similar to the one linked below. I have used several of these in different voltages with great success. You can buy them from an American company for around $10 plus shipping or buy them from China/Hong Kong via E-bay for a few dollars and free shipping. Lots of different companies carry the same item for varying prices. Same indicator lamp regardless. The 22 mm model is about an inch in diameter and requires 1-1/2 inches behind the panel or whatever it is mounted on. Mounts in a 7/8 inch hole or a standard 1/2 inch knockout on an electrical box or cover. Reasonably bright and estimated longevity is in excess of 80,000 hours of use.

2pcs 220V 22mm Red LED Power Indicator Signal Light | eBay
 
  #7  
Old 04-10-13, 08:03 PM
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When I left my post about not being two actual poles.... I was looking at two different sides of the switch that didn't show two actual poles.....or four screw terminals. I'm not sure how the pilot light will respond in that switch on 240 vac. The switch specs say 120/277v. 120V and 277V are measured at that voltage to ground. 240v is two legs of 120v.
 
  #8  
Old 04-10-13, 08:58 PM
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It appears that they operate the pilot through the ground screw on the bottom. I'll see if I can e-mail the manufacturer and find out for sure.
 
  #9  
Old 04-11-13, 05:48 AM
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Furd
"The problem with the switches that you linked to is that they probably do not have a horsepower rating, or if they do it is probably less than the horsepower rating of the compressor. It may not make any significant difference as long as the switch is never thrown when the motor may be in operation but I don't think that you can guarantee that."
Furd, could you explain this a little further. Is it that the motor generates an inrush of current that will overload the switch even though the motor may fall within the amperage rating of the switch and circuit?

I've been using a common 240 volt switch to control a compressor(on/off) for years without a problem but now you have me wondering about that. Thanks
 

Last edited by ray2047; 04-11-13 at 09:58 AM. Reason: Add quote formatting for clarity.
  #10  
Old 04-11-13, 08:43 AM
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Doing some back-of-the-envelope conversions...

Switch MFR claims of 240V at 30A is 7200W. 7200W is about 9.6HP.

Compressor MFR claims of 240V at 15A is 3600W, which is about 4.8HP.

Wouldn't a volts x amps rating on a switch give one a ballpark horsepower rating?
 
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Old 04-11-13, 12:13 PM
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I have no idea why Leviton calls the switches you linked to "double-pole" switches, since they're clearly 120 or 277V power-to-neutral switches.

I would get either of these and add a pilot light off one of the legs on the load side:

Leviton MS302-DS AC Manual Motor Starter Switch - AC Horsepower Rating 240VAC: 5HP

Leviton MS302-DSS AC Manual Motor Starter Switch - AC Horsepower Rating 240VAC: 5HP

You should be able to pick these up at any decent supply house. You'll need neutral in the switch box for the pilot light.
 
  #12  
Old 04-11-13, 12:37 PM
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The switch I'm using below, if you look at the specifications listed for the item states: HP Rating: 1HP-120V 2HP-240V-277V. Don't these clearly state that at 240 volt it's rated at 2 hp. They are two different models however as mine is a 1222-2 versus the 1222-plr?

Leviton 1222-2 - 20A, 120/277V Toggle Double Pole AC Quiet Switch :: Industrial Grade :: AC Switches :: Wiring Devices :: Electrical :: Electrical Supplies | Lighting | Motors | - Galesburg Electric Inc
 
  #13  
Old 04-11-13, 02:00 PM
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Furd
"The problem with the switches that you linked to is that they probably do not have a horsepower rating, or if they do it is probably less than the horsepower rating of the compressor. It may not make any significant difference as long as the switch is never thrown when the motor may be in operation but I don't think that you can guarantee that."
Furd, could you explain this a little further. Is it that the motor generates an inrush of current that will overload the switch even though the motor may fall within the amperage rating of the switch and circuit?

I've been using a common 240 volt switch to control a compressor(on/off) for years without a problem but now you have me wondering about that. Thanks
Yes, there is a very high inrush current when the motor is first connected. An electric motor at rest is essentially a short circuit when the power is first applied. There is also a severe inductive "kick" when a motor circuit is interrupted and that can cause the switch contacts to arc and actually weld together. The fact that you have not had a problem for years is not sufficient to ignore the horsepower rating on a switch.
 
  #14  
Old 04-11-13, 02:08 PM
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Doing some back-of-the-envelope conversions...

Switch MFR claims of 240V at 30A is 7200W. 7200W is about 9.6HP.

Compressor MFR claims of 240V at 15A is 3600W, which is about 4.8HP.

Wouldn't a volts x amps rating on a switch give one a ballpark horsepower rating?
Unfortunately, it isn't that simple. As I previously wrote, at the point in time of power being connected to the motor load it is essentially a short circuit. The switch has to be able to handle the inrush current without failure. There is also the inductive "kick" I mentioned that has the arc on the opening contacts when the power is interrupted. The switch must be able to extinguish this arc without failing. There is no question that the steady-state ratings of the switch are probably sufficient to handle the running load, it is the starting and stopping that is the problem. Switches with horsepower ratings are made to accept the inrush and inductive kick currents without failing, something a standard (non-horsepower rated) switch is not.
 
  #15  
Old 04-11-13, 05:18 PM
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So I'm assuming since the switch I reference above does have a hp rating of 2 at 240 volts that there is no problem as the compressor motor I'm using the switch on is rated at 1 hp.

It looks like this switch would also work for T-W-X's compressor also.
 
  #16  
Old 04-11-13, 08:45 PM
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So I'm assuming since the switch I reference above does have a hp rating of 2 at 240 volts that there is no problem as the compressor motor I'm using the switch on is rated at 1 hp.
It's never a good idea to assume. In electrical work it can be dangerous.

I didn't see anything in Leviton's specs for their 1222-2 switch that said that it was constructed and rated as a Manual Motor Starter Switch. It also doesn't show up when you drill down in their site for Manual Motor Starter Switches.

The two switches I showed you earlier are constructed and rated to handle the load of starting a motor. I would only use one of those, or some other one that is rated for that.

On a side note, the image of the 1222-2 switch on the Leviton site only shows two terminals on the switch, and the voltage specs say 120/277, which are both single-conductor line-to-neutral voltages, as opposed to 240 and 208. They also say it's a double-pole switch and, as you noted, they give a HP capacity at 240V -- as well as at 120V. But not at 208V.

The whole thing just doesn't add up. Is there a particular reason you prefer the 1222-2?
 
  #17  
Old 04-11-13, 08:52 PM
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How does this Square-D switch from Grainger strike you? Is it capable of being mounted into an in-wall single-gang box with conventional metal face plate?
 
  #18  
Old 04-11-13, 09:18 PM
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Nashkat1 "I didn't see anything in Leviton's specs for their 1222-2 switch that said that it was constructed and rated as a Manual Motor Starter Switch. It also doesn't show up when you drill down in their site for Manual Motor Starter Switches."

While that's true, it does have a hp rating. Doesn't the inclusion of an HP rating signify that it is motor rated? Is the term HP used in some other context rather than a motor rating?

"On a side note, the image of the 1222-2 switch on the Leviton site only shows two terminals on the switch".

The image of the switch from the perspective offered does only show two terminal but I can attest that it does switch both hots and has terminals on both sides. It's not that I prefer this switch over another, it's just that I've been using one for a couple years without problem and was attempting to verify it was an appropriate usage.

T-W-X are you really considering a switch that lists for $180? Why not use the one Nashkat1 suggested for around $25(MS302-DS)
 
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Old 04-11-13, 09:39 PM
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While that's true, it does have a hp rating. Doesn't the inclusion of an HP rating signify that it is motor rated? Is the term HP used in some other context rather than a motor rating?
Originally Posted by Furd
As I previously wrote, at the point in time of power being connected to the motor load it is essentially a short circuit. The switch has to be able to handle the inrush current without failure. There is also the inductive "kick" I mentioned that has the arc on the opening contacts when the power is interrupted. The switch must be able to extinguish this arc without failing. There is no question that the steady-state ratings of the switch are probably sufficient to handle the running load, it is the starting and stopping that is the problem. Switches with horsepower ratings are made to accept the inrush and inductive kick currents without failing, something a standard (non-horsepower rated) switch is not.
To add to what Furd said, those switches that are designed, constructed and rated to handle everything associated with motor startup are designated as Motor Starter Switches. Those are the ones I trust for this application.

It's not that I prefer this switch over another, it's just that I've been using one for a couple years without problem and was attempting to verify it was an appropriate usage.
It may be OK. I would replace it though. If the switch fails, it might just melt down. So long as it's in an approved box with a metal cover that might just be an annoyance. The reason I would replace it is that I would prefer that my expensive equipment got everything it needed to start and operate without strain.
 
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Old 04-11-13, 09:45 PM
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How does this Square-D switch from Grainger strike you?
I started to say it looked like a chrome-plated muffler bearing to me. One reason I almost never buy anything from Grainger is their ridiculously high prices. But then I saw that it was a 3-pole switch. Is that something you need?

Is it capable of being mounted into an in-wall single-gang box with conventional metal face plate?
No, it is it's own housing.
 
  #21  
Old 04-11-13, 09:47 PM
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I'm considering a $180 switch because it has a pilot light and because it's seemingly actually rated for high horsepower (7.5HP) in a 240V application.
 
  #22  
Old 04-11-13, 09:58 PM
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I'm going to ask a stupid question...

Does one actually have to cut both legs of a 240V circuit? The compressor itself has a switch. One doesn't cut the neutral side of a 120V circuit.
 
  #23  
Old 04-11-13, 10:09 PM
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Oh, the reason why I asked about that Square D is that it's actually rated for 7.5HP at 240V 1PH. The other pilot switches are rated for 2HP at 240V 1PH.
 
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Old 04-11-13, 10:28 PM
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Does one actually have to cut both legs of a 240V circuit? The compressor itself has a switch. One doesn't cut the neutral side of a 120V circuit.
In the US, yes.

The neutral is the grounded conductor. It only has potential when the circuit is closed. Both legs of a 240V circuit are ungrounded conductors. They are both hot all the time from the panel to the switch.
 
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Old 04-11-13, 10:41 PM
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okay, finally found some good info...

Square D PDF
 
  #26  
Old 04-12-13, 06:41 AM
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T-W-X "I'm considering a $180 switch because it has a pilot light and because it's seemingly actually rated for high horsepower (7.5HP) in a 240V application. "

The link to the switches Nashkat1 posted are rated for 5 hp. In your first post you stated your needs were 240V single phase 15A so they would seem to be more than adequate.

As for the pilot light, Furd previously posted a rather simple solution to that which could be mounted most anywhere.
 
  #27  
Old 04-12-13, 08:09 AM
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I'd rather have a one-device solution, that's mainly why I'm looking at pilot switches rather than separate switches and pilot lights. Also, if I buy from a vendor other than Grainger the prices are a lot better. Since there's no hurry it's not a big deal to take my time to do the research to get the right part.
 
  #28  
Old 05-07-13, 11:10 PM
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Well, I was at a junk shop today and I found a bag of about thirty 125V 1W lamps with 22AWG pigtail wires for $6.00. I tested one and it lights up a pleasant amber color. The lamp housing is round; it's a little larger than a normal small center hole on an electrical faceplate but I can probably drill out a faceplate and figure out some kind of backing to make it stay in place.

I expect that I can tie one wire of the lamp to one of the hots, and tie the other wire of the lamp to a neutral conductor, and that would light up the lamp when a two-pole switch is turned on.

I'm also considering building some status indicator devices, basically switches on the doors that control relays that will illuminate lamps in the house if the doors are open. The controls will be lower voltage, probably 24VAC so that I can use cheap HVAC transformers and 18AWG wire. I haven't figured out if the original power will come from the main panel or the subpanel, but it might be easier to use the power close to the relay and the lamp, which would be the main. I do speculate that I could use a 120VAC circuit on 18AWG to avoid needing a relay if I can find a 2A or 3A circuit breaker, but I do not expect to find a Cutler-Hammer breaker in that small of a size.
 
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Old 05-07-13, 11:45 PM
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It might be better keeping that circuit on low voltage. Keep the shocking experiences to a minimum.
 
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Old 05-08-13, 08:05 AM
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Well, what about code and putting different circuits through the same conduit? There are two locations that I'll possibly create these door notification circuits; and Dad's he's got a low-voltage conduit but at mine I don't at the moment, and I'd also like to avoid having AC current bleedover affecting DC audio...

I had figured that if it was high voltage then it might be in-code to run it through the same conduit as the wires that supply the subpanels at each location.
 
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Old 05-08-13, 10:37 AM
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You didn't mention you needed to run the control stuff thru a conduit. Switch to DC for your controls.... no more noise.
 
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Old 05-08-13, 11:39 AM
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Low voltage can run in the same conduit as line voltage if the wire used for the LV is rated for the highest voltage in the conduit and the same insulation rating as the high voltage wires.
 

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  #33  
Old 05-08-13, 11:40 AM
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So, the "600V" rating on the outer jacket of the control wiring applies in this instance?
 
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Old 05-08-13, 12:05 PM
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I would get either of these and add a pilot light off one of the legs on the load side:

Leviton MS302-DS AC Manual Motor Starter Switch - AC Horsepower Rating 240VAC: 5HP

Leviton MS302-DSS AC Manual Motor Starter Switch - AC Horsepower Rating 240VAC: 5HP

You should be able to pick these up at any decent supply house. You'll need neutral in the switch box for the pilot light.
Which of the two do you prefer? Now that I have some pilot lamps that I got cheap this is probably the best solution.
 
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Old 05-08-13, 01:17 PM
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So, the "600V" rating on the outer jacket of the control wiring applies in this instance?
Yes. That should be the same as the rating on the conductors you're using for the 120V wiring.
 
  #36  
Old 05-08-13, 03:08 PM
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Not exactly. There are three "classes" of wiring, Class 1 is most normal wiring for power or lighting. Class 2 and 3 is for communication and control systems. One of these classes is for "power limited" control which has strict limits on voltage and available amperage. Sorry, I don't remember which class that applies to. I do know that power limited circuits generally cannot run with class 1 wiring. There are also some specifics concerning wire sizes and insulation types that need to be addressed to run the two classes together.

Now as long as the communication and control system is wired with all the requirements of class 1 systems there is no problem. That means a minimum of #14 copper conductors with insulation equal to the insulation on the class one wires. Under no circumstances can you run something like SJ flexible cord in the same conduit as THHN/THWN nor can use use twisted pair "bell wire" along with the power circuits.
 
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Old 05-08-13, 07:59 PM
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Okay, so 18-4 cables wouldn't be rated to run in a conduit along with 4AWG wires supplying a subpanel then...

Is the only difference between Leviton MS302-DS and MS302-DSS is that the DSS model doesn't stick out as far?
 
  #38  
Old 06-18-13, 11:24 PM
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Well, we ended up ordering a Leviton double-pole switch rated as a motor starter switch, and I wired a neutral from the switch panel back to the subpanel, pulling the power for the pilot lamp from one of the legs on the switched side. The distance from the switch panel back to the subpanel was only about 3' and it was in conduit the whole way, so it wasn't that big a deal.

Thanks everyone for your help. I wish that anyone had made a pilot switch capable of being used as a motor starter, but this will do.
 
  #39  
Old 06-19-13, 07:08 AM
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Thanks for letting us know how you solved it.
 
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