Switch for a 230v compressor

[jonlb]

I'm currently planning my shop and I have a room for the compressor. I would like to have a switch to turn it on and off that is easily accessible. my question is I know they make 30 amp switches but with 230v I would have to use two of them so that wouldn't work. does anyone have any suggestions or am I going to have to break down and buy a full disconnect box. Thanks, Jon

 

[mrb]

cheapest thing would be an air conditioner disconnect. They do make double pole toggle switches, since its for a compressor it needs to be HP rated.

With normal toggle switches you wont gain anything with a 30a over a 20a since they are both only rated at 2HP @ 240v.

Leviton makes the MS302 which is good for 5HP @ 240v. Will cost you between $20 and $30. They also have a nifty enclosure for it which allows the switch to be locked out.

I like it better than an air conditioner disconnect, but that will be cheapest.

 

[Norcal]

I'm currently planning my shop and I have a room for the compressor. I would like to have a switch to turn it on and off that is easily accessible. my question is I know they make 30 amp switches but with 230v I would have to use two of them so that wouldn't work. does anyone have any suggestions or am I going to have to break down and buy a full disconnect box. Thanks, Jon

Use a circuit breaker in a 2 circuit loadcenter, a cheap air conditioner pullout disconnect switch can be bought for less then $10.00 (the pullout type) , either type will work, or just spring for a safety switch.


They do manufacture 2 pole toggle switches in 30A but are not cheap...

 

[mrb]

Use a circuit breaker in a 2 circuit loadcenter

thats another good suggestion

 

[mrb]

They do manufacture 2 pole toggle switches in 30A but are not cheap...

i dont know about other manufacturers, but Leviton gives a 2HP @ 240v rating to both their 20a double pole toggle switches as well as the 30a version. I guess the 30 might last a little longer, but if you need more than 2hp the normal toggle switches wont cut it.

 

[jonlb]

Wow, that was fast. Three posts in 10 minutes. I really would like to use the switch for aesthetics but I guess I will have to go the A/C disconnect route. The compressor is just over 3HP if I remember correctly. thanks guys.

 

[mrb]

Wow, that was fast. Three posts in 10 minutes. I really would like to use the switch for aesthetics but I guess I will have to go the A/C disconnect route. The compressor is just over 3HP if I remember correctly. thanks guys.

look at the leviton MS302 its rated for 5hp @ 240v. its not THAT much more than a AC disconnect....$10-$15 more....

 

[Gary S]

My compressor has a switch built into it. The pressure switch has two positions, OFF and AUTOMATIC. Take a look at yours. It might already have the switch built in.

 

[jonlb]

look at the leviton MS302 its rated for 5hp @ 240v. its not THAT much more than a AC disconnect....$10-$15 more....

Thanks mrb found a used one on the internet for $15. Will probably look for a new one though.

 

[torqueman2002]

I have a NOS Safety Switch 60 AMP 240 VAC Square D; D222NCP; left over from installing a 2-stage 230 V compressor last summer.

I found 2 on eBay and have this one left over.

It takes Fuse Type: Cartridge (Class H, K, J or R) - I'm using Fuse Cylinder 60A Class J Cartridge - available at my local HW and Big Box stores.

It will need an Equipment Grounding Bar Kit - GTK03; again available at my local HW and Big Box stores.

It is yours for the cost of shipping UPS ground or what ever you choose.

If you'd like better pics, eMail me and I'll see if they're archived on my external hd.

 

[D KRAGER]

I have one that looks like a regular light switch, but switches both phases. I think it's called a single pole double throw or something like that.

 

[torqueman2002]

<...single pole double throw ...>
Yup, "single throw, double pole" or "double pole, single throw". can never remember; one flip opens/throws 2 separate circuits.

Probably the least expensive way to go.

 

[mrb]

double pole single throw switch is the one that switches both phases for 240v. The regular lightswitch type are only available up to 2hp, over that you have to use a motor starting switch like the one I posted.

 

[jonlb]

Thanks mrb. The leviton MS302 it is.

 

[shocksystems]

Thanks to the original poster and to those who replied.

Found this thread in a search of the forum and it was exactly what I was looking for. FWIW I bought the Leviton MS302-DSS Switch and the Leviton N13NC-TDS Enclosure on Amazon (links below)

http://www.amazon.com/gp/product/B003AUCWIA/?tag=atomicindus08-20

http://www.amazon.com/gp/product/B003I86HFI/?tag=atomicindus08-20

I am very happy with the result. Nice to know I will use a bit less energy now and I won't wear out the breaker.

Cheers!

Jim

 

[Jim Johnstone]

Does that pressure switch not have an off setting?

 

[tig]

And if you want to do it remotely, a Hunter PSR-52 (http://sprinklertalk.com/manuals/hunter/psr_broch.pdf) pump-start relay, controlled by a 24VAC signal works really well.

There are tons of home automation controllers that can drive a 24VAC line enabling you to do what I've done for my compressor that is in the attic: Automatically turn it on/off based on detected occupancy of the workspace:

More details here.

 

[Falcon67]

I use these on 3 hp/20amp
http://grizzly.com/products/h8238

 

[1500hd]

Why not just use a single pole switch to break the coil circuit? Would not have to worry about HP ratings.

 

[mrb]

I use these on 3 hp/20amp
http://grizzly.com/products/h8238

while thats a nice switch, its not UL listed (its a recognized component) and should not be installed in building wiring.

 

[Jim Johnstone]

Why not just use a single pole switch to break the coil circuit? Would not have to worry about HP ratings.

That would be fine, if it had a coil.

Most compressor 5hp and under don't have magnetic starters. I am looking to add one to my compressor for that exact reason. So I can switch it on and off with a light switch from my workshop area.

 

[shocksystems]

tig - That is a very interesting idea. Thanks for posting. Cheers! Jim

 

[shocksystems]

Does that pressure switch not have an off setting?

Amazing isn't it? No switch to keep the compressor from kicking on when it senses low pressure.

Cheers!

Jim

 

[scoutkid]

I have been beating my head against a wall on this for a long time!! Glad this thread came up.

I'm not even worried about having a switch in line (used to have one from previous owner, SPST, must of had a mag starter, i don't...) but every time my compressor goes to restart (basic 80 gallon Craftsman oilfree Pro '5hp' compressor) it trips the breaker.

It will start fine when the tank is empty, and the pressure switch on the compressor works to turn it off when pressurized, then it TRIES to turn it back on when the pressure drops, but the breaker kicks off.

Does the BREAKER need to be rated for HP, too?! Thanks in advance!

 

[Jim Johnstone]

What is the amp draw of the motor, and what is the breaker size?

 

[scoutkid]

So, pics speak more than my words. You can see the one UNLABELED breaker (twin 20A) is for the compressor, which is in a shed on the other side of the cinder block wall.

You can see I have a massive cable for the compressor, and all the wiring is the appropriate gauge for a 20A breaker.

So last time i checked, 15A was less than 20A?

 

[Jim Johnstone]

If I were you, I'd have that on a 30 amp breaker. Don't forget that starting amps can be about double the running amps, so I wouldn't be surprised to find out that the motor pulls 30 for a brief period of time at start up.

http://www.eatoncompressor.com/AMPDRAWBREAKERSIZE.html

Have a look at that chart. A motor with 15 amps running, is recommended to have a 30 amp breaker.

 

[scoutkid]

If I were you, I'd have that on a 30 amp breaker. Don't forget that starting amps can be about double the running amps, so I wouldn't be surprised to find out that the motor pulls 30 for a brief period of time at start up.

http://www.eatoncompressor.com/AMPDRAWBREAKERSIZE.html

Have a look at that chart. A motor with 15 amps running, is recommended to have a 30 amp breaker.

Inrush!! Ah damnit I deal with this all day long at work but on multi-thousand HP machines, it never occured to me that I would have the same problem on this little guy

Now, something in my head tells me I can't just 'swap' that 20A for a 30A, that would be too easy, amirite?

 

[Jim Johnstone]

Do you happen to know the actual wire size that was used on that outlet?

 

[scoutkid]

Do you happen to know the actual wire size that was used on that outlet?

sorry for the delay, its 12.

 

[Jim Johnstone]

sorry for the delay, its 12.

12 is good for 20 amps, too bad it wasn't #10, then it'd be an easy swap to a 30 amp breaker.

The proper thing to do is rewire with #10 and a 30 amp breaker, I suppose you could do a 30 amp breaker on the #12, since the high load is only on startup for a few seconds, but I don't think I'd feel real good about that personally.

Maybe some electricians will chime in and give some more advice.

 

[Falcon67]

while thats a nice switch, its not UL listed (its a recognized component) and should not be installed in building wiring.

Nice catch - never noticed that. However, the pump relay guy wins my vote. Some twisted pair and a switch by the door would give me control over the big compressor from anywhere I wanted to run the bitty cable. We now own a well and the start relay control deal didn't click until just now. And I could use the fancy non-UL Listed switch as the low voltage switch.

 

[scoutkid]

12 is good for 20 amps, too bad it wasn't #10, then it'd be an easy swap to a 30 amp breaker.

The proper thing to do is rewire with #10 and a 30 amp breaker, I suppose you could do a 30 amp breaker on the #12, since the high load is only on startup for a few seconds, but I don't think I'd feel real good about that personally.

Maybe some electricians will chime in and give some more advice.

This might not be too hard. There is maybe 20' of wire between this dedicated breaker and the compressor shed on the other side of the wall. In fact, I could probably just tie the #10 to the #12 and pull it through in 2 shakes!

So other than that, my panel will be able to handle that 30A, (i have a 50A for my welder right next to it... )

 

[Charles (in GA)]

Using Table 430.248 of the code you find that a 3 hp motor at 230v is 17 amps. Your data plate says yours is 2.9 hp and is rated 15 amps at 240v so it real closely agrees with the table. You should size your conductor to the table amps, or FLC if known (that would be 15 amps in your case) and 430.22 says that for continuous duty you are to oversize conductors 125%. Whether this is continuous or not is a grey area but in any case, you are marginal on 12 gauge wire. You are allowed to size the dedicated motor circuit Over Current Protection up to 250% per 430.52 and with TD fuses it is 175%

You need to up the breaker to a 30 amp and see if that works without tripping.

Charles

 

[cdenton]

I suggest you purchase a 3/4" 120v solenoid valve to put on the pressure output of the compressor tank. Then wire it with a 120v switch and you have a simple solution. The benefit here is simplicity and the fact that when you power off the air will not drain out of the system. All of the other solutions will allow the system to leak down.

 

[TimGrz]

Why wouldn't this work?

Eaton Cutler-Hammer 30 amp 120/240-Volt 7,200-Watt Fused General-Duty Safety Switch



240V/30A, good for >9hp, UL Listed, and at $14.97 seems like a good deal.

I know this one is fused, but they do have non-fused as well. Hell, at 15 bucks plus the price of a fuse, may be worth the belt and suspenders approach anyway.

/tg

 

[sberry]

Some interesting responses here,,, but for the breaker tripping I would change it to a 30 and call it a day.

 

[scoutkid]

Using Table 430.248 of the code you find that a 3 hp motor at 230v is 17 amps. Your data plate says yours is 2.9 hp and is rated 15 amps at 240v so it real closely agrees with the table. You should size your conductor to the table amps, or FLC if known (that would be 15 amps in your case) and 430.22 says that for continuous duty you are to oversize conductors 125%. Whether this is continuous or not is a grey area but in any case, you are marginal on 12 gauge wire. You are allowed to size the dedicated motor circuit Over Current Protection up to 250% per 430.52 and with TD fuses it is 175%

You need to up the breaker to a 30 amp and see if that works without tripping.

Charles

Some interesting responses here,,, but for the breaker tripping I would change it to a 30 and call it a day.

UPDATE: I did, and it worked perfect!! I am by no means a pro, and even when I am in the shop working the unit has to kick back on maybe twice in a day?

 

[Iluke]

I may be wrong, but don't most compressors have a pressure-relief function built into their on-off switch that, as I understand it, dumps the pressure from the cylinder before starting the motor. The point of this is to avoid too-heavy start-up loads. Wouldn't this function be defeated if you add a seperate switch that interrupts the line power without releasing the cylinder pressure?

 

[Norcal]

I may be wrong, but don't most compressors have a pressure-relief function built into their on-off switch that, as I understand it, dumps the pressure from the cylinder before starting the motor. The point of this is to avoid too-heavy start-up loads. Wouldn't this function be defeated if you add a seperate switch that interrupts the line power without releasing the cylinder pressure?

The relief valve is not a electrical device.