What kinda plug is this?

[Jim Riseborough]

I have this plug, I think its 20A 240 volt, but not 100% sure. I put a meter on it, and I get 120, but only when I go from the left or right socket with the top socket. going straight across I dont get any voltage. I suspect its 120 each side, and 240 total.
My panel has it with a double breaker, is 20A on the breaker. The previous owner had an air compressor here, and its labeled that way.

I want to use it for my Grizzy planer and tablesaw. Also a compressor too. I will have to unplug each one each time to use obviously.

I currently have those all wired for 3 prong twist lock, so I would also like to switch the plug out eventually to a twist lock. I am assuming they are wired the same.

Just want to get educated and see if I need an electrician, or if I can handle.

353769

[Jay Aubuchon]

I believe that is a 20-amp 220-volt receptacle. See, for example, http://www.homedepot.com/p/Leviton-ProGrade-20-Amp-Double-Pole-Single-Outlet-Ivory-R51-05821-0IS/100357020

Your test results seem odd. If it is wired for 220-volt, you should see 220-volts across the bottom two.

[Myk Rian]

I wonder if the PO had a 120v compressor, and jury-rigged the outlet. Pull it out of the wall and trace the wiring.

[Bill Orbine]

I'm with Myk here......... I do wonder if both left and right are from the same 120v feed and not two separate 120v feeds needed to make the 240 volts.

[Jim Becker]

240v 20a fixture, but clearly not wired correctly given the readings you mention. I agree with Myk and Bill...you need to trace things back and pulling the unit out is the first step.

[Mark W Pugh]

Seriously? I'll go check my 220 outlet tomorrow. Both bottom slots are 120v in. Without the meter on a neutral/ground, how would you get a reading by placing the probes in the bottom 2 slots, which should both be hot?

Where am I wrong here? I know how I wired mine, and they work..

I say, for this moment in time, this outlet is wired for 220.

See this https://www.do-it-yourself-help.com/circuit_breaker_wiring_diagrams.html go down to your receptacle.

Oh, the double breaker is how 220 is normally done. When you say double breakers. I assume they are connected, so when you throw the switch to off, both breakers open, no power to either bottom slot.

[Jim Riseborough]

I will pull it out of the wall and see how its wired, and also the breaker. I tend to agree with MArk Pugh. If i put a meter across two hots, how would i get a reading.

[Ken Combs]

I will pull it out of the wall and see how its wired, and also the breaker. I tend to agree with MArk Pugh. If i put a meter across two hots, how would i get a reading.

The transformers customer side winding is center tapped, that tap is your white wire. The ends of that winding are brought out at 120v each, but 180deg out of phase with each other. So measured from the two bottom pins you see the peak voltage between those two, .
windings, /that's a really poor description, but if you google center tapped transformer there are lots of pics and info online.
edit"
If you only have 120 to neutral or ground, and no 240 between those pins, both are connected to the same bus in the panel. they must be connected to different buses in order to get the 120s out of phase as described (badly) above. I've seen guys inadvertently use a half-size two pole breaker. Those contact the same bus. A 'normal' two pole breaker contacts both buses.

a picture of your panel would help.
at the tra

[Mike Cutler]

Jim

It's a 6-20R, 20 amp, 240vac receptacle.
It should definitely read 240vac across the receptacle.Not sure why you're getting the readings your getting, unless your meter is over ranged on the setting you have it set to.

[Dan Friedrichs]

I will pull it out of the wall and see how its wired, and also the breaker. I tend to agree with MArk Pugh. If i put a meter across two hots, how would i get a reading.

It's AC, so the polarities flip many times each second. At the instant that one side is positive, the other one is negative, so when you measure the voltage between them, the magnitudes add.

[Peter Kuhlman]

The panel holding the breaker has 2 buss bars that are both 120 volts referenced to ground but 240 volts referenced to each other. The only way you can get a reading of no voltage across the 2 hot legs of the receptacle is if they are both fed from the same buss bar as this would give you the 120 volt to ground reading but no potential difference across them.

Start turning off breakers one at a time and take readings on both sides of the receptacle each time. I wonder if they are feeding the receptacle with 2 single pole breakers but have both of them fed by the same buss bar. Have seen this done a couple times. Something is wrong with the wiring and you need to be careful sorting this out if you are not familiar and experienced with electrical troubleshooting. DONT trust the panel labeling as it can be incorrect!

[graham collins]

I agree with the suggestion the meter might be set wrong and possibly nothing amiss with the outlet. it would be possible to rig the outlet to provide only 110v but it wouldn't be possible to plug a 110v compressor cord into that outlet so I doubt that was the scenario. It's a 220 outlet connected (by at least one wire) to a 2-pole breaker, seems he most likely scenario is that it's a standard installation and either being metered wrong or possibly (though unlikely IMO) one wire is loose. Should be easy enough to swap to a twist lock outlet.

[Jim Becker]

I will pull it out of the wall and see how its wired, and also the breaker. I tend to agree with MArk Pugh. If i put a meter across two hots, how would i get a reading.
The two hot legs are at opposite wave phase, so as long as your meter is set to read AC voltage, it will register the ~240v properly on the meter.

[Malcolm McLeod]

The two hot legs are at opposite wave phase, so as long as your meter is set to read AC voltage, it will register the ~240v properly on the meter.

Mr. Becker is correct. The 2 hot legs of typical USA household 240VAC service are each at 120VAC potential (to ground), but their wave forms are 180 degrees out of phase (offset from each other), so the simplistic result is that at any particular moment you measure from the 'peak' of one to the 'valley' of the other - - and get 240V. This 240V is what a meter should 'see', as well as your 240V motor, etc.

If you measure 120V on L1<>G and L2<>G, but get (zero) 0V from L1<>L2, then the receptacle is incorrectly wired for use with anything. The only way anything will function on this is if it uses the Gnd lead as a conductor. Generally speaking, this would also imply there is a problem with the wiring in the 'motor' allowing current to flow to the ground, but this opens a whole new rabbit hole of speculation and conjecture.

Photos of meter on a 240V AC circuit, and what it should read on a properly wired 240VAC plug, like the OP's follow:

This from left leg to ground--
353811

This from right leg to ground--
353812

This from left to right leg--
353813

For some who have responded, please ask yourself why it's called "240V" if you don't measure 240V somewhere.

[Jim Riseborough]

Yea, my bad, I just didnt meter it correct. I rechecked, and I am getting 230ish V.

Glad I went through this, the plug ground was not connected. I am going to replace with a twist lock type anyway that will allow me to use my existing plugs on my saw and planer. I can rewire a compressor when I get one thats 240

Glad I have 240V though!!

353820353821353822

[CPeter James]

Just a suggestion. If the all 240V (nominal) circuits are wired using 12-2 wire I would wire all of them with L6-20 outlets and put L6-20 plugs on the cords and then build an extension cord with L6-20 fixtures. This gives you great flexibility and for that time when you need to move a tool to mill a very long board, you have the extension cord to allow it. Also, it you decide to rearrange your shop, you can do that.
CPeter

[Jim Riseborough]

I have all my tools and a cord with L6-20 already. I will switch the wall outlet to match.

[John K Jordan]

For some who have responded, please ask yourself why it's called "240V" if you don't measure 240V somewhere.

The actual voltage at any one outlet it may vary considerably over time, the exact voltage depending on factors such as the utility capacity, distance, wiring, and how many users are sucking how much power from the system at the time. I usually see between 220 and 245+. (At the moment, the UPS servicing my cable modem and router measures the line voltage at 123.) At times of peak use (hot summer evenings) power companies have been known to implement rolling brownouts (intentional voltage reduction) to prevent total blackouts.

I think it is tradition that allows 110/220, 115/230, or 120/240 to all be correct. The exact numbers used may matter to a purist, an "expert", or the electrical police. I think the important thing is that everyone understands that saying 220 or 230 or 240 means the same thing to normal humans.

JKJ

[Jim Becker]

"Today's" nominal supply voltage to homes, etc., is 240v, but John is correct that it absolutely varies for many reasons and the "nominal" has changed over time. I actually had an issue here a number of years ago where the line voltage was dropping far enough that my MiniMax slider was shutting down. (the electronics monitors voltage and when it drops below a minimum level, it cuts off the machine from starting) The power company wouldn't do anything about it, so I had to install a transformer on the machine to rectify things. Two years later, they actually did change out an old transformer at the pole and the line voltage magically returned to "normal".

[Dan Friedrichs]

I think Malcom's point is that if you measure "0V", it's not 220/230/240V :)

[mike wacker]

Mr. Becker is correct. The 2 hot legs of typical USA household 240VAC service are each at 120VAC potential (to ground), but their wave forms are 180 degrees out of phase (offset from each other), so the simplistic result is that at any particular moment you measure from the 'peak' of one to the 'valley' of the other - - and get 240V. This 240V is what a meter should 'see', as well as your 240V motor, etc.

If you measure 120V on L1<>G and L2<>G, but get (zero) 0V from L1<>L2, then the receptacle is incorrectly wired for use with anything. The only way anything will function on this is if it uses the Gnd lead as a conductor. Generally speaking, this would also imply there is a problem with the wiring in the 'motor' allowing current to flow to the ground, but this opens a whole new rabbit hole of speculation and conjecture.

Photos of meter on a 240V AC circuit, and what it should read on a properly wired 240VAC plug, like the OP's follow:

This from left leg to ground--
353811

This from right leg to ground--
353812

This from left to right leg--
353813

For some who have responded, please ask yourself why it's called "240V" if you don't measure 240V somewhere.

Malcolm,

Very fine post with GREAT pictures. Nice Job. Really boils the point down to what the receptical (sp) should be delivering if wired correctly.

[mike wacker]

The actual voltage at any one outlet it may vary considerably over time, the exact voltage depending on factors such as the utility capacity, distance, wiring, and how many users are sucking how much power from the system at the time. I usually see between 220 and 245+. (At the moment, the UPS servicing my cable modem and router measures the line voltage at 123.) At times of peak use (hot summer evenings) power companies have been known to implement rolling brownouts (intentional voltage reduction) to prevent total blackouts.

I think it is tradition that allows 110/220, 115/230, or 120/240 to all be correct. The exact numbers used may matter to a purist, an "expert", or the electrical police. I think the important thing is that everyone understands that saying 220 or 230 or 240 means the same thing to normal humans.

JKJ

Let me throw another wrinkle in the whole 110/220, 115/230, 120/240 volt numbers. If you're really close to the Utility's sub station you might even see 125/250. Not a big deal except for your old incandescent lamps that would be brighter but not last as long, lol. And to throw a real twist in, if you where in a heavy urban area, think big city, New York, Philly, Chicago, etc, you might be on what I've heard called 3-wire network. That would be two legs of 208 volt three phase so now you might be measuring 120/208. No worries, all your tools, electric stoves, dryer are all designed to go roundy round with these ranges of energy delivery. Being a nerd sucks sometimes.

[Eric Anderson]

I'm not an electrician, and there are many more folks more knowledgeable about electricity than me, but I thought when doing 240v wiring, where there was not both 240 and 120 together, (like a dryer or range) that you wire the two hots and the ground and not the neutral. In the picture above, it appears that the neutral is wired to the receptacle and I was thinking the ground should be wired and the neutral capped off. Is this wiring correct?

[Malcolm McLeod]

I'm not an electrician, and there are many more folks more knowledgeable about electricity than me, but I thought when doing 240v wiring, where there was not both 240 and 120 together, (like a dryer or range) that you wire the two hots and the ground and not the neutral. In the picture above, it appears that the neutral is wired to the receptacle and I was thinking the ground should be wired and the neutral capped off. Is this wiring correct?

Assuming the overall physical condition of the wire itself is sound (no broken conductors), then the bare ground wire should terminate on the back of the receptacle. The white (neutral) should be wire nutted (or at least taped). - - And I believe Jim R. has stated he intends to re-wire to conform to this.

It may have been wired as he shows in the pictures for any number of reasons: the ground is damaged/broken (and 'white' is OK); the original installer/previous owner didn't know any better; or, the ground wasn't landed in the panel; etc..

[Jim Riseborough]

Assuming the overall physical condition of the wire itself is sound (no broken conductors), then the bare ground wire should terminate on the back of the receptacle. The white (neutral) should be wire nutted (or at least taped). - - And I believe Jim R. has stated he intends to re-wire to conform to this.

It may have been wired as he shows in the pictures for any number of reasons: the ground is damaged/broken (and 'white' is OK); the original installer/previous owner didn't know any better; or, the ground wasn't landed in the panel; etc..

Im not sure. The new plug I bought shows being wired with 2 hots and a ground

I get 120 if red/black to ground, or to white. It seems both are ok, just the white is acting the ground, since I dont need a neutral really?

353903353904

[Malcolm McLeod]

Jim, I was trying to answer Eric's question and may have gone too far...:confused:. Eric was correct that the bare ground wire should properly swap positions with the white neutral, based on your original photos. You plan to do so was also correct. Sorry if I've muddied the water.

On your new receptacle, it gets wired the same way - red and black to the 2 hot lugs respectively, and bare copper ground to the green lug, white gets capped off.

Other's have done a better job that I can about why in other threads - - but bottom line is that the white wire and the ground both have the same voltage 'potential' (and could function one in place of the other, except this is against code).

White wires are there to carry current in normal situations; ground wires only carry current when something is wrong. If we all use the same standard, nobody gets a nasty surprise.