Wiring a 3-way switch for a 240v compressor

[Don1357]

I have wired 3-way switches to regular 120v lights. The question is, would a 240v circuit be any different? I would like to put my 2HP/9amp on a 3-way switch so I can turn it on from either upstairs or downstairs.

The other option would be to wire one of these on the compressor, and use the remotes:

https://www.ebay.com/itm/AC220V-240...623321?hash=item46badaf859:g:J5sAAOSwaspfxwnl

Which being so dirt cheap makes me wonder. Is there a better version of the above I could use?

 

[Bad Habit]

Use a contactor with 120v coil, then do a typical 3 way switch set up to energize the coil

 

[jdm5]

I did kind of both - contactor to a 'standard' home automation 120v switch, then can use the same home automation technology to turn my compressor on anywhere (phone, Alexa, remote switch location, even programmatic).

In my case I use Insteon but I'm sure ZWave or other technologies would work fine.

I get txt notifications if it's on, and I automatically turn it off after 4 hours if I forget (I'm a home hobbyist).

 

[Don1357]

Use a contactor with 120v coil, then do a typical 3 way switch set up to energize the coil

Do I really need a contactor for a 240v/9amp? There are 240v rated pole switches.

 

[Wrench97]

Do I really need a contactor for a 240v/9amp? There are 240v rated pole switches.

Have you found one for 3 way?

 

[Don1357]

this guy says 120v~277v, 20 amp:

https://www.homedepot.com/p/Leviton...Handle-Toggle-Switch-Clear-1223-7LC/301447188

Then again I have been told here that just because it is available I may not want to do it, like wiring a 3+ HP engine to an outlet even if outlets of the correct amperage exist. On this case is just a 2HP, 9 amps.

 

[Don1357]

Sweet baby Jesus I keep saying compressor, this is for my dust collector.

 

[Wrench97]

Problem is that single pole switches only break 1 leg of the 230v the other leg remains hot through the motor back out to the switch when the switch is off.
A contactor allows you the break both legs.

 

[Don1357]

Problem is that single pole switches only break 1 leg of the 230v the other leg remains hot through the motor back out to the switch when the switch is off.
A contactor allows you the break both legs.

Correct. This will still shut off the machine as in a 240v system one power leg is the return of the other...

I may be coming from an ignorant place but, would it be that evil? I mean if I need to work on that machine I would unplug it anyways.

 

[Wrench97]

Bigger concern is the switched leg shorts to ground after the switch the motor runs on 1/2 voltage. I'm not positive but I'm pretty sure it's against code.

 

[Don1357]

Bigger concern is the switched leg shorts to ground after the switch the motor runs on 1/2 voltage. I'm not positive but I'm pretty sure it's against code.

Nah, it doesn't work that way. Here is what I know about 240v power.

On a 240v service you have two 120v power cables coming from the transformer on the post outside. If you are taking power out of a single leg, 120v, you need a return path, the neutral wire, for the circuit to complete. When you are talking about the two 120v power cables they come from the transformer out of phase, meaning that one cable is indeed the return of the other. So if you break one leg, the circuit is broken.

This works on 3 plug devices. Some devices have 4 plugs, because they have both 240v and 120v components inside: the 240v can do its own return path, but the 120v device (think the clock on an electric oven) needs that neutral cable to work as the return path.

I still don't know if you can safely 3-way a three wire 240v...

 

[Wrench97]

3 terminal plug has a ground, the ground is bonded to the neutral in the panel so one leg to ground is 120v. And believe me you can get zapped on the live leg after it comes through the motor and out to the switch box. I used to have a pressure switch on a well pump that was wired like that.

 

[Crazyjake8493]

Do I really need a contactor for a 240v/9amp? There are 240v rated pole switches.

It's less about being able to handle the switched load amperage, and more about being cheaper and easier for a 3-way switch circuit on the 120V coil circuit.

 

[The Cobbler]

Do I really need a contactor for a 240v/9amp? There are 240v rated pole switches.

It's less about being able to handle the switched load amperage, and more about being cheaper and easier for a 3-way switch circuit on the 120V coil circuit.

you could switch both lines with double pole double throw switches, but as Jake said, in the long run you're cheaper to do it with a contactor

 

[Norcal]

Use a proper contactor rated for the HP of the the equipment you wish to control, a 3-way switch is not rated for motor loads, but will switch the contactor just fine.

 

[wyliesdiesels]

this guy says 120v~277v, 20 amp:

https://www.homedepot.com/p/Leviton...Handle-Toggle-Switch-Clear-1223-7LC/301447188

Then again I have been told here that just because it is available I may not want to do it, like wiring a 3+ HP engine to an outlet even if outlets of the correct amperage exist. On this case is just a 2HP, 9 amps.

The biggest issue here is using a switch rated for the same or greater HP as the motor. The amp rating is meaningless...

Doubt youll find a 3-way snap switch rated for 2HP

The one you linked is 1HP

https://www.leviton.com/en/products/1223-7lc

 

[Citation]

I have wired 3-way switches to regular 120v lights. The question is, would a 240v circuit be any different? I would like to put my 2HP/9amp on a 3-way switch so I can turn it on from either upstairs or downstairs.

The other option would be to wire one of these on the compressor, and use the remotes:

https://www.ebay.com/itm/AC220V-240...623321?hash=item46badaf859:g:J5sAAOSwaspfxwnl

Which being so dirt cheap makes me wonder. Is there a better version of the above I could use?

In addition to the concerns about switching motor power, that ebay find might not switch both legs. Note that it says 220V L and N. I take that to be Line and Neutral. While the Line should be switched, Neutral may not be. This could be a device intended for other countries which have ~220V between line and neutral vs our 240V line to line.

The part that is confusing about AC motors is their running current, even at full load, is typically significantly lower than the starting inrush current. The other problem is once running motors act like large inductors. If you turn them off while they have full current running through them you will get a big voltage spike that can result in a spark across the switch contacts. This is why people get worked up over using dryer plugs to run air compressors. If you unplug that thing while it's running the spark at the outlet is likely to be big. Perhaps significant emotional event big. Thus people are saying you need to find a relay rated for the HP rating of your collector motor.

I agree with the others that the best way to do this is get a motor contractor/relay and switch it with a 120V 3 way circuit.

 

[sberry]

If I was fussing with it would get a contactor too. You could do it other ways, not sure its all worth it. But as a control wire circuit to the machine does it need to be 2 hp? Calculated load would be 1 hp? ha

 

[larry4406]

I put a switched 120V outlet on my 3-way lighting circuit. I plan on plugging in a full port ball valve to open/close the air line at the compressor vs switching the 240V power. RapidAir and others make a slow open/close full port valve for this.

 

[dogdog]

Not sure why opwanted to resist in getting a proper contactor to control your 2HP blower/cleaner. Even the "fine" print on your original Ebay item says if powering anything motor greater than 800W use a relay... in that case a 220V relay... not sure, the mind set in the thoughts.

https://i.ebayimg.com/images/g/HhQAAOSwL5xfvdCg/s-l1600.jpg

 

[Don1357]

Not sure why opwanted to resist in getting a proper contactor to control your 2HP blower/cleaner. Even the "fine" print on your original Ebay item says if powering anything motor greater than 800W use a relay... in that case a 220V relay... not sure, the mind set in the thoughts.

https://i.ebayimg.com/images/g/HhQAAOSwL5xfvdCg/s-l1600.jpg

Is ignorance on my part, plain and simple. I have never worked with anything like this so I post, get to learn something about this, those who know get to be amused at the 'wtf is he thinking?'. It works all around.

Speaking of helping... Could somebody look at amazon and find me a contactor that would work for my evil plans? 240v/20 amp capable with a 120v input for the on/off? The only thing I'm sure of is that if I try to pick it I would get the wrong one

 

[Wrench97]

The contactor is the easy part > https://www.amazon.com/dp/B001KGSJ74/?tag=atomicindus08-20

You'll need a box to put it in I have repurposed old metal timer boxes, disconnect boxes etc.

Or something like this> https://www.amazon.com/dp/B00AAU5D5W/?tag=atomicindus08-20

 

[Don1357]

Actually this is pretty awesome, even cheaper than buying the outlet and plug as I can just hard wire with romex on a metal conduit (if I just said something stupid I just want to apologize in advance).

If the box is big enough, would it be kosher to put two actuators in there? that way I can do a single toggle switch for my compressor and the 3-way for the dust collector.

 

[wyliesdiesels]

Is ignorance on my part, plain and simple. I have never worked with anything like this so I post, get to learn something about this, those who know get to be amused at the 'wtf is he thinking?'. It works all around.

Speaking of helping... Could somebody look at amazon and find me a contactor that would work for my evil plans? 240v/20 amp capable with a 120v input for the on/off? The only thing I'm sure of is that if I try to pick it I would get the wrong one

motor contactors are rated by HP not current and you would need a 120v coil....

 

[Don1357]

motor contactors are rated by HP not current and you would need a 120v coil....

Will the one suggested work?

 

[wyliesdiesels]

Will the one suggested work?

dont think so. I dont see a HP rating on it

 

[dogdog]

I think you will be fine at worse you'll be replacing it with the contacts pitting and some weird thing.

https://www.packardonline.com/products/c230b/

I think but not too sure, if your motor have LRA rating and it doesn't exceed the rating of this contactor..LRA 240V @180AMP

I have some 24V coils contactor (not c230B) I will be using for the 2HP HF dust collector... pretty sure it will be fine.

 

[wyliesdiesels]

Its rated for a resistive load only.

if were not gonna do things right then why bother even coming on here and asking questions? just cobble some BS together....

 

[Don1357]

Its rated for a resistive load only.

if were not gonna do things right then why bother even coming on here and asking questions? just cobble some BS together....

There you go again overestimating the knowledge of people. I wouldn't even be able to cobble some BS together without a lot of asking

Looks like thus one is rated to 3hp: https://www.amazon.com/dp/B07YVMYBL8/?tag=atomicindus08-20

 

[Wrench97]

The one I linked flipped from A/C compressor contactor, here the Eaton alternative > https://www.amazon.com/dp/B07GSD1YN8/?tag=atomicindus08-20 FLA 40a Restive 30A

 

[dogdog]

Its rated for a resistive load only.

if were not gonna do things right then why bother even coming on here and asking questions? just cobble some BS together....

Do educate me on the LRA rating of that contactor ? Not sure how you have determined that this is a restive load contactor only.

 

[wyliesdiesels]

Do educate me on the LRA rating of that contactor ? Not sure how you have determined that this is a restive load contactor only.

No HP rating and it says resistive load right on the contactor

 

[dogdog]

No HP rating and it says resistive load right on the contactor

what is that LRA (lock rotor amp) for ?

https://view.publitas.com/d610e5d1-a2a3-4ef6-84f5-233716235532/2018-packard-catalog/page/368

It has UL508 specification on all of their contactors, not that I know what they mean. but a quick google says it has something to do with start / stop electric motors. Not too updated on those mumble jumbo stuff... if some one knows and explains would be good educational material. A lot of us do have amateur use of relays sometimes and it is a good stuff to know. I am not sure if this is Packard's thing not listing HP ratings.. I have the EATON C240 equivalent ( C25BNB240T) series and they do print HP rating, while the packard's C240 one doesn't. I don't have the C230 to compare, pretty sure a quick google would shows the same thing.

What does UL 508 mean?
Standard for Safety For Industrial Control Equipment
UL 508, the Standard for Safety For Industrial Control Equipment, covers industrial control and related devices rated 1500 volts or less used for starting, stopping, regulating, controlling, or protecting electric motors. ... These components are intended only for end-use products that may be eligible for UL certification.