Compressor wiring suggestions

[Jet_Mech]

For the umpteenth time I will ask a question about compressor wiring. I did a search and didn't find a solution.

Particulars; 28X36 shop, 100 amp sub panel, 30A and 40A 240v circuits. I had the shop wired back in '09 the 30A was for a future drill press and the 40A was for a welder. Neither is in the works now or maybe never. The compressor is getting delivered today. It's a Saylor-Beall VT-735-80.

The placement of the SB puts it right next to the 40A circuit outlet for the welder. Like 2 feet. The 30A outlet is 17 feet down the same wall with a workbench and window in between. I would like to avoid running new wire.

Thanks to this site I learned there is no NEMA receptacle/plug rated above 3hp. Not really wanting to buy the pin type.

Can I replace the receptacle with a A/C disconnect non-fusible 60a pullout style? Providing there is enough wire length.

And if I do the 30A that is 17 feet away; Can I run conduit on top of the drywall above the workbench to reach the compressor?

Thanks. Apologies for beating a dead horse.

 

[Norcal]

You planning on using the 30A circuit? You did not mention what HP the compressor is but assuming 5 HP, the NEC requires using the values in article 430 to size the circuit, and be 125% of those values which for a 5HP single phase motor rated for 230V is 35A, so if the circuit is in conduit with THHN conductors would be 10 AWG, and if NM cable "Romex®" would require 8 AWG, since NM is sized from the 60° C column, there are numerous threads on why & I am to lazy to write it all out.

 

[wyliesdiesels]

This subject has been covered ad-nauseum.

I looked up that compressor and it has a 5HP motor, so as said above, you need 35a wire.

So what size and type of wire do you have feeding that 30a circuit? NM-b or THWN? A 30a breaker may nuisance trip as well

 

[Jet_Mech]

After the info I've read here and visually identifying the wire at the 30 amp receptacle it is insufficient. The 30 amp circuit is fed with 10 AWG NM-b. So that's out.

The 40A circuit has a 14-50 receptacle intended for a welder and is located right next to the compressor. It's fed with 6 awg. Not sure if I can tell the difference between thhn vs nm-b. But I believe it to be NM-b.

The wires in the junction box in the wall next to the compressor (welder outlet) are just long enough to connect to the receptacle. So feeding a non-fused disco would require adding wire.

If I thought spending $300 on a pin type plug and receptacle was going to be money well spent, I'd do that. But that's nutz. I've already spent way above my pay grade for a compressor. But then again I've looked at the cost of wire right now and all I gotta say is, whoa that's a lot!

I could surmise how to connect those 6awg wires to my compressor, but I'll defer to you two guys as I've read a lot of your posts. Obviously the receptacle goes away and if I ever do get a welder I'll solve that problem another time.

How do I connect my compressor to the available wires?

My apologies for the ad-nauseum death beating. But in my opinion my situation didn't fit anything within the search function. Thanks!

 

[mike93lx]

Use the 40a circuit and a disconnect as the junction. Liquidtite is a good,flexible method for connecting the compressor to that and just use #10thhn in it. Save the 6-50 for a future welder circuit.

The 30a circuit is still a great candidate for a welder in the future. The wire in a welder circuit can be undersized based on the duty cycle of the welder, so #10 will work fine with the 6-50 plug and a 50a breaker on many, many welders.

 

[Jet_Mech]

Use the 40a circuit and a disconnect as the junction.
.

Thanks! I don't believe I have enough wire length to connect to a disconnect. Can I add wire? (physically yes but code wise)

 

[mike93lx]

Thanks! I don't believe I have enough wire length to connect to a disconnect. Can I add wire? (physically yes but code wise)

In a junction box, sure. The connectors for large gauge wire are about $15 per wire

 

[Jet_Mech]

So I bought a Eaton 60 amp non-fusible ac disconnect box at Lowe's yesterday. Too bad I had to open it up to see the innards.

It does have a UL rating and a chart that is on the black plastic panel inside says its good to 10 hp. But it doesn't physically look robust enough for the work it needs to perform. The pullout disconnect is a lackluster, copper clad, aluminum wafer that loosely fits in rather small tension contacts. I'd feel better sticking pre 1982 pennies in there.

I find it hard to believe, comparing the physical characteristics of the box to a 14-50 receptacle and 50a plug that this ac disconnect box is superior. The inside of this box looks unimpressive.

I just looked inside the 30a Eaton disconnect for the H2O heater at work. The kind with the big on/off lever. In my opinion it's physical appearance is more suited to a heavy amp load from a air compressor than the ac disconnect box that has the appearance of a cheap chinese knock off with an illegal UL logo.


Is there a better option?

 

[mike93lx]

So why not get an industrial eaton disconnect?

 

[Jet_Mech]

So why not get an industrial eaton disconnect?

I have no knowledge of such things.

That sounds like a great idea. We do have a local store that is a few steps above the typical big box store. I'll check there. If not I'll check with my neighbor up the street who has an HVAC business as to where to get one.

Thanks Mike. (5.0 lx?)

 

[mike93lx]

I have no knowledge of such things.

That sounds like a great idea. We do have a local store that is a few steps above the typical big box store. I'll check there. If not I'll check with my neighbor up the street who has an HVAC business as to where to get one.

Thanks Mike. (5.0 lx?)

Personally, I would probably just get a properly rated disconnect from a trusted brand, like sqd, siemens, eaton. Aluminum buss bars are in millions of homes, including my own, without an issue.

That said, you can always buy heavier duty. I'd be ready for some sticker shock though.

I used to have a 93 notch back. Long gone, but this is the username I've had on forums for years, so it stays.

 

[pattenp]

Go back to lowes and get the Square-D 60A disconnect. It should have a breaker style disconnect switch.

 

[yatg]

Go back to lowes and get the Square-D 60A disconnect. It should have a breaker style disconnect switch.

My favorite. No fuzting with a loose part.

 

[Norcal]

The fusible pull out will be fine, if you were close would make you a deal on a safety switch which is what I prefer to use but they are expensive.

 

[Jet_Mech]

Thanks for the offer Norcal. I'll be returning the Eaton to Lowes. None of the box stores or the plumbing and electrical store have any disconnect boxes with knife switch in stock. I bought a new in the box GE TNG3322 off of ebay for 90 bucks shipped. Also the grounding kit (TGL1) for 10 bucks. Funny how the 2 pole disconnect boxes cost twice as much as a 3 pole. My local specialty electrical supply stores have prices far above online ordering. So I just researched the specs and looked to see if there were any available on ebay.

I expected something that was rated for 240V to be more heavy duty and the Eaton ac disco just didn't look like it.

Now to figure out what to do with the wire coming out of the wall and make it look decent. The junction box the 14-50 outlet was installed in is a 3.75"X4" plastic. No retailer sells a cover with knockout that fits the plastic box style junction box. I'll figure something out. There aren't knockouts on the back of the 3322.

 

[Norcal]

Thanks for the offer Norcal. I'll be returning the Eaton to Lowes. None of the box stores or the plumbing and electrical store have any disconnect boxes with knife switch in stock. I bought a new in the box GE TNG3322 off of ebay for 90 bucks shipped. Also the grounding kit (TGL1) for 10 bucks. Funny how the 2 pole disconnect boxes cost twice as much as a 3 pole. My local specialty electrical supply stores have prices far above online ordering. So I just researched the specs and looked to see if there were any available on ebay.

I expected something that was rated for 240V to be more heavy duty and the Eaton ac disco just didn't look like it.

Now to figure out what to do with the wire coming out of the wall and make it look decent. The junction box the 14-50 outlet was installed in is a 3.75"X4" plastic. No retailer sells a cover with knockout that fits the plastic box style junction box. I'll figure something out. There aren't knockouts on the back of the 3322.

Should have got the 3 pole & left the center pole unused. Since it is a GE, check all factory connections in the switch, even where the current carrying parts are fastened to the molded plastic, it's quick and easy & might save it from possibly melting, sadly now Siemens, & Eaton, use designs that are similar.

 

[mike93lx]

Thanks for the offer Norcal. I'll be returning the Eaton to Lowes. None of the box stores or the plumbing and electrical store have any disconnect boxes with knife switch in stock. I bought a new in the box GE TNG3322 off of ebay for 90 bucks shipped. Also the grounding kit (TGL1) for 10 bucks. Funny how the 2 pole disconnect boxes cost twice as much as a 3 pole. My local specialty electrical supply stores have prices far above online ordering. So I just researched the specs and looked to see if there were any available on ebay.

I expected something that was rated for 240V to be more heavy duty and the Eaton ac disco just didn't look like it.

Now to figure out what to do with the wire coming out of the wall and make it look decent. The junction box the 14-50 outlet was installed in is a 3.75"X4" plastic. No retailer sells a cover with knockout that fits the plastic box style junction box. I'll figure something out. There aren't knockouts on the back of the 3322.

There is no practical difference from a design standpoint between 120v and 240v. They are both low voltage

 

[Jet_Mech]

There is no practical difference from a design standpoint between 120v and 240v. They are both low voltage

Very true. But I almost always over do my projects. Tend to make mountains out of mole hills. You shoulda seen my gable vent fan project in my attic several years ago.

 

[Jet_Mech]

Should have got the 3 pole & left the center pole unused. Since it is a GE, check all factory connections in the switch, even where the current carrying parts are fastened to the molded plastic, it's quick and easy & might save it from possibly melting, sadly now Siemens, & Eaton, use designs that are similar.

Oops. The GE T-G-N (not tng) 3322 is what I bought. It's a 3 pole. Thanks. Will double check connections.

 

[mike93lx]

Very true. But I almost always over do my projects. Tend to make mountains out of mole hills. You shoulda seen my gable vent fan project in my attic several years ago.

That's all well and good. I was just commenting on your expectation that something be designed heavier duty for 240v.

 

[Jet_Mech]

That's all well and good. I was just commenting on your expectation that something be designed heavier duty for 240v.

No worries. It's a struggle at times. After working on stuff that flies six miles in the sky for over 3 decades, I often expect stuff to be certifiable to fly when I'm done with it.....figuratively speaking.