Crash Course on Which Receptacle I Need and Why

[89MustangGX]

Hello,

I'm finally getting ready to do a little electrical work in my garage, and one of my big goals is to get my new compressor wired up and running.

I will be running 10/3+ground romex wire off a 30amp 220v circuit breaker I am installing. This is called out by the compressor.

What's not called out, is which receptacle I need.

I bought the compressor used, and it has a 20amp plug on it (which I know is wrong), and I will be changing -- so I really have nothing to start from.

This is the first time I have run a 220 circuit and I see lots and lots of different receptacles, and about the only thing I know is I need my plug and receptacle to match.

So -- school me on which one I need please. And maybe some "why" so I learn a little bit would be helpful as well. Oh, and throw in some other FAQ stuff like why I wouldn't want to use a dryer receptacle and some other common stuff for good measure.

Oh, and if anyone has any tips or tricks for a first-timer I would appreciate it. I searched but most of you guys are pretty advanced and I didn't pick up very much.

Adam

 

[Wow]

I would strongly recommend standard 30A twistlock plugs. I've got a lot of them in my shop for 30A stuff and I love them. Very secure connection that can't get pulled out but easy to unplug.

Technically you can use pretty much any style of 30A plug/outlet combo you want, though I think the twistlock is more "standard" for tools.

 

[mrb]

You said you are running a 10/3 + ground romex, the compressor needs the neutral? If so, you would need 14-30 plug and receptacle, or L14-30 for twistlocks. If the compressor is really only 3 wire (two hots and a ground) the connectors would be 6-30 or L6-30 for twistlock. I have both types of twistlock if you need them cheap.

 

[89MustangGX]

Thanks for the replies.

The compressor is only wired as a 3 wire right now. I thought I would run the extra wire because I was thinking the minimal extra cost would help future proof me. I don't fully understand why some machines use 3 and some 4, but I figured it couldn't hurt.

It sounds like I will go with the L6-30 then.

OR, should I consider converting the compressor to a 4-wire setup? Can it be done? Is there any advantage?

Adam

 

[mrb]

Thanks for the replies.

The compressor is only wired as a 3 wire right now. I thought I would run the extra wire because I was thinking the minimal extra cost would help future proof me. I don't fully understand why some machines use 3 and some 4, but I figured it couldn't hurt.

It sounds like I will go with the L6-30 then.

OR, should I consider converting the compressor to a 4-wire setup? Can it be done? Is there any advantage?

Adam

Run 4 wire to the junction box if you like. If the compressor doesnt need the neutral there is no 4 wire setup you can do on it, you would only be wasting money on 4 wire connectors. What L6-30 do you need, a receptacle and a plug? Im 99.5% sure ive got those, ill check tomorrow.

 

[Wow]

It's a great idea to run that extra wire now while you can. I can't remember how many times I've wanted more wires in a finished building but I've never wanted less wires...

The reason some things use the extra wire is because they use 120v and 240v at the same time. You can get twice as many amps @ 120v from the same wiring if you take advantage of the neutral wire. Most shop things won't need both, but you can always make an extra 120v outlet out of it later if you want to...

 

[sberry]

The 3rd conductor is useless but since you have it tape off both ends of the white and tuck it away.

 

[89MustangGX]

Thanks for the info guys -- really helped me out and I appreciate it.

What L6-30 do you need, a receptacle and a plug? Im 99.5% sure ive got those, ill check tomorrow.

Yes -- sounds like I need an L6-30 receptacle and plug. I was hoping to get it done this week, but I could maybe put it off a little in this case.

I actually found that the existing cord has been repaired before (in addition to having the wrong plug on it), so I am going to make up a whole new cord for the compressor. That I think should be pretty straightforward though -- I'm just going to copy what's there already.

Adam

 

[Gary S]

You might want to read the manual. The manual for my compressor says "no plug". They want it hard wired directly to the box. Yours may prefer it the same way.

 

[sberry]

A plug can be a legal disconnect if its out of site from the panel. Ideally we would know what the fla motor rating is for this comp for sizing cord and plug.

 

[89MustangGX]

A plug can be a legal disconnect if its out of site from the panel. Ideally we would know what the fla motor rating is for this comp for sizing cord and plug.

Let's see if this works...

Adam

 

[sberry]

Yes, minimum of 10 wire, those ratings are fairly conservative. That machine will run fine from a 10/30, to 50-60 ft without issue especially if you have good incoming. Use a 30A rated plug.

 

[nate379]

WOW that sticker on that compressor is some serious CYA as far as I can tell!

A 200ft run on 10 gauge wire with a 22 amp load on it will drop 5 volts, or ~2%. Just barely enough to kick it up to 8 gauge really.

Not more than 5% drop was the older allowance per NEC I believe and now it's 2%. A pro sparky can chime in here, I'm just going off the info I read.


Anyhow, for the question, why not just run a standard 30 amp dryer plug? NEMA 10-30?

 

[Charles (in GA)]

Starting loads on a compressor can be three or four times the running loads, hence the conservative recommendations of the compressor manufacturer. They want it to start without struggling or having large drops at startup.

Charles

 

[sberry]

A dryer plug is not recommended, it is not a grounding type recept. I am guilty of using them for equipment but bond them. A welder recept would be better choice.

 

[dugger10]

Wire it without a plug, in a junction box with a cover. Thats how I do all mine, cheaper

 

[nate379]

I'm not sure what you mean. A dryer plug has 2 hots and a ground, how would that not be grounded?

A dryer plug is not recommended, it is not a grounding type recept. I am guilty of using them for equipment but bond them. A welder recept would be better choice.

 

[Wow]

Wire it without a plug, in a junction box with a cover. Thats how I do all mine, cheaper

Cheaper by 20 bux. I much prefer the convenience of being able to unplug anything anytime for any reason. How much did the compressor cost?

 

[sberry]

A dryer uses 2 hots and a neutral, the N terminal is isolated from the yoke. A grounding type is bonded, grounds any metal enclosure it is bolted in to. It is designed for tools that require a single voltage (240) like the comp.

 

[sberry]

We are talking about 3 wire recepts, a dryer or range isn't listed for common 240 equipment. Using romex and a plastic box or common surface mount recept would likely negate concerns but dryers run the 3rd back to a neutral. All this wouldn't be a huge issue coming from a main service entrance but for garages with 4 wire fed service panels it is, the ground needs to go to ground bar.

 

[mrb]

yeah ive got a hubbell L6-30 male, and a L6-30 receptacle you can have for a few bucks. I wont be able to get around to shipping until probably thursday. Send me a PM if you want them.

 

[89MustangGX]

yeah ive got a hubbell L6-30 male, and a L6-30 receptacle you can have for a few bucks. I wont be able to get around to shipping until probably thursday. Send me a PM if you want them.

I missed this offer somehow...damn.

Adam

 

[89MustangGX]

Receptacles installed and working!

Thanks for the help everyone!

Only thing I still was wondering about -- my 3 conductor cable was white, black, bare. I know white is normally neutral on a 120v setup. Do I need to put red tape on the white conductor or color it red or identify it somehow ... or is it just known on a 240v setup that white is hot?

Adam

 

[Charles (in GA)]

You should re mark both ends of the white conductor if used as a "hot". I use a red magic marker to color the wire red where it protrudes out of the sheathing.

Charles

 

[89MustangGX]

You should re mark both ends of the white conductor if used as a "hot". I use a red magic marker to color the wire red where it protrudes out of the sheathing.

Charles

I will do that -- thanks!

Adam