Creating 240v from two 120v outlets

Now this may seem like a stupid question, and while I know a good amount about lasers I don't claim to be an electrician in any way. I have 240v service to my house for my dryer and stove, but they are very far away from my lasers which run on 240v power. In my room, however, I have two 120v outlets in close proximity which are on two separate breakers. My question is, can I combine two of these outlets (again, on separate breakers) to create 240v to plug a laser into? I realize this could cause some problems if one breaker blew and the other one didn't (although if one blew I think the other would instantly go as well due to the spike in current draw) so its probably not a good idea anyway, I just wanted to see if it is in the realm of possibility at all.

i would not try that . the 240v need's a bigger awg wire . plus it's not in the same spot in the pannle as the 240v for the washer and drier . that 12awg/14awg for the 120v is way to small for that and you will proly burn your house down . don't quote me but i think the 240v need's 10awg 3 wire for that kinda current .the way to do it would be to run a new wire from the pannle to the room and if you have the space on the 240v "rail" you can just add it to the pannle with the proper breaker .

I don't think it will work, since all the power comes in from the tap, it may short out and that isn't good

DTMF has the correct solution. You HAVE to wire in a new breaker into the bus bar for the 240 Volt line in your house. He's also correct about the heavier gauge wire. If you use the wire for 120 Volt current, you'll wind up with Cu. puddles amidst the charred remnants of what used to be your dwelling. ( I was a store supervisor for ACE Hardware once upon a time), & had to take tests to learn all that jazz [smiley=vrolijk_26.gif] rob

Depending on how much power you need, use a single outlet and a 120V to 240V step-up transformer. Your washer and dryer have special power connectors because they consume on the order of 7000W or more. If you don't need that kind of power you can probably just get away with the transformer.

Using 2 sockets for higher voltage isnt to be recommended, but it could be done as long as they are in anti-phase. I know in the US things are sometimes wired like that.

In europe triphase is more common, with different power groups each running on a 120 degree seperated phase. Two phases can be used to get 400V instead of the normal 230V, but tripase sockets are obviously installed for things that need them (mainly motors).

This will not work.  Remember that all power from all the outlets comes from a single source.  This is like asking "I have one 3V battery, is there any way I can make 6V?".
Things might be different if the two outlets are not coming from the same source (like separate transformers or weird things going on), but I doubt you have the equipment or knowledge to test and take advantage of it.

You can't just stick some wires in and double the voltage, you will need some circuitry and I would recommend against building it yourself.

here's a usefull link: http://homerepair.about.com/od/electricalrepair/ss/240v_breaker.htm

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AWG determines the current. Insulation thickness determines maximum voltage. Otherwise, my HeNe would need 00000 wire. See wikipedia for rated currents. Rated voltages are almost always one of:

30V: signal cable
300V: junior service, the "J" in SJT or SJTOW. Almost all household wiring has this rating. insulation thickness is .013" min. for SVT and .027" for SJT and SPT
600V: industrial. minimum insulation is .04"

An exclusively 240V household requires SMALLER AWG. a 100W light bulb on 120V service will use .8 A. on 240V, .4A

They are NOT all the same phase. Some outlets are from the opposite phase, but they can be difficult to find. Using a multimeter and an extension cord test from one outlet's "hot" to the other outlet's "hot" with AC voltage selection (be sure the setting is in excess of 250V). The reading will either be 0V or 240V. Once you find a pair of outlets that are out of phase: simply wire a new outlet utilizing one outlet's hot line and the other outlet's hot line as either line of the new outlet and ground it preferably in an enclosure. The rated current will be whatever the lower rated of the two circuits is (likely 10A or 15A)

It's probably easier to just run an extension cord from the laundry room though.

This is entirely possible to do, but it would probably be safer and easier in the long run to just buy a big step up transformer from ebay.

I have a bank of neon sign transformers that draws something like 40 amps at 120v.  I couldn't run them all from the outlet in my room without tripping the 20A breaker so I had to bring in an extension cord from another room to get the needed power.  This was trickier than expected because I needed to find another outlet that was in phase with the one in my room.  When I tried the kitchen/bathroom and other areas I kept getting 240V or more from hot to hot.  I finally found a matching outlet in the basement and had to go buy a longer extension cord.

In theory if you want 240V all you need to do is combine two out-of-phase outlets. I wonder if there's a way to combine the wiring in your house to get three phase :-? Maybe if you brought an extension cord from a neighbors house or something ;D

I don't think I'd want to risk that expensive three-phase machinery with such a rig.

We really should find out what kind of wattage/current Gooey wants to drive.

Gooey the three phase inverter you have needs to be hooked up to good 240 30 amp outlet. Like the one for your dryer. If the two outlets in your room are on separate legs (separate breakers doesn't necessarily mean separate legs) of the main breaker panel then it is possible to have 240 available. But a normal household outlet is rated for 15 amps, some are 20 amp services, such as in the kitchen. If you decide you want to try that then, two 14awg extension cords (12awg would be better) into one 240 15 amp receptacle would be what you need, this depends upon the draw of the inverter. Both of the line sides of the cord(usually black wire) would be connected to the brass screws on the 240 receptacle, one on each side. The neutral wires(usually white) will have to be connected to the silver screw on the receptacle,two wires to one screw. The ground can be connected to the green screw. This will give you the two phases for your inverter, but as a electrician, I would not recommend it. It would be a whole lot better if you bought some 10/3 romex(10/2 ok. 10/3 better) and a 240 30 amp breaker and made a new run (if your service can handle the extra draw) to your room. It doesn't have to drop down thru the wall, you can mount the receptacle on the ceiling. Another thing to consider is chances are the 120 outlets in your room are not dedicated circuits (one outlet per breaker) so your inverter will be powered with a unbalanced load, your inverter won't like that. The ideal thing would be to buy the components needed and hire a electrician to do the labor.

Chuck

I think phase is a bad word for it. They're both on the same phase technically and more akin to two batteries in series. Your house is powered by a transformer with a grounded center-tap. Here's a diagram from paint

I believe the correct term is LEG. You have two 120VAC legs

It is not possible to go from single phase or anti-phase to threephase using transformers - those can only perform 0 or 180 degree signal rotation, not the required 120 degrees required to get threephasic power.

In europe, the situation is different because the urban distribution nets are set up as triphase, and the low voltage (ie 230V) system has to follow suit (it's common for one transformer to supply a rather large area here). Sometimes homes are connected only to one phase (and neutral), in which case it is common for the next house to be on another phase and so on - power draw from each phase must be equal on average.

As for powering lasers: The whole phase thing usually doesnt matter, as the current is rectified to DC anyways. Rectifying 3 phase can however be done with smaller buffer caps if you have a neutral connection (you get 3 instead of 2 maxima each mains cycle).

Benm said:

Using 2 sockets for higher voltage isnt to be recommended, but it could be done as long as they are in anti-phase. I know in the US things are sometimes wired like that.

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This could go very bad. A friend has talked about once, that he used sockets in an ICE train but his equipment drawed to much so they shut down. I suggested trying to combine two or more of them to get more Amps out, but he says, that then the Train would set fire caused by the pahse shift. At his Dad's work someone done this similar - conected two phase-different to a motor and the thing bursted like a bomb ;D