Property im looking at has a utility building that id like to add a 240v dryer outlet.

The breaker box has 2 rows, in each row, there are 2 unused 120v spots, so a total of 4 empty spots.

How do you combine (2) 120v to get 240v ?

I googled and got over complicated answers.

There are two legs (hot) and a neutral in the box.  One hot to neutral is 120v.  2 hots to each other is 240v.

Short answer is you put a 240v breaker in the breaker panel. Every other slot is a different hot leg.  So a 240 v breaker takes up two slots
right next to each other and thus 2 different hot legs. Together you get 240v.

Do yourself a BIG favor and have an electrician install a 240v sub panel in the utility building,  NOT simply a 240v outlet. Reason being it's not much more work and gives you a lot more flexibility in the future.

ETA:  i was confused by your question on second look - is there already a panel in the building?  If so it's simply a matter of putting a 240v breaker in the panel, using the correct gauge wire, and connecting things properly -  more or less.  There are some safety issues with how the wire is run and protected.

Yes, as long as they are not on the same leg.  Power comes in as two 120V lines on seperate "legs", when you go across both you get 220V.

Yes, already a small breaker box, has 16 spots, 8 in each row and 4 spots are unused.

My question was, how do you wire the outlet, i know ill need an actual 250v breaker.

More then likely, ill have electrician do it , just trying to educate myself incase i would need to troubleshoot or cant get someone to do it initially

Username might check out...

Keep it simple there’s 3 taps on the back of the outlet. 1 gets a hot from 1 120v breaker and the other gets the other 120v line and 1 is a ground. No neutral unless it’s a new dryer with a 4 prong outlet. Then it gets a neutral for the 120v circuits in the dryer

Its this simple....

Line, line, GROUND

My understanding is that if the panel in the utility building is a sub panel the ground bus and the neutral bus have to be separated by code, so they are not exactly interchangeable in this situation. So my question would be in a 3 prong 240v is the 3rd neutral or ground. I would've thought neutral, but I'm not a sparky.

And thats why i gave up looking on google, didnt see that 2 answers were ever the same.

Call an electrician.

Search for 'split phase' and you will see applicable drawings.

The typical service is 120/240V split phase.
The two 'legs' are 180 degrees apart.
When one is at max positive the other is at max negative.

Europe (and other parts of the world) use 240 V to a neutral line.
It is very dangerous, thus all the fancy plugs and protection.
Many times the plugs have small fuses in them.

By using two 'legs' of 120 V that are out of phase we keep the
voltage down while having 240 V available for larger loads.
Each line is 120 V to neutral (grounded) conductor.

What is the breaker feeding the box like?
If it is two pole it is probably feeding 120/240 V  into the box.

Sub-panels are not required to have a main cutoff, but many do anyway.
It makes working in the box a lot safer.
With the main off the only voltage is on the inputs to that main breaker.

If they are in a detached building by code they are required to have a main disconnect.

Good catch. I was half asleep when I was searching google for a pic to post. Yes 240 circuits do not use a Neutral. The third goes to Ground. If the house was built before 1996 you may get by with a combined neutral/ground. I usually dont pay much attension as most of my house still has 2 pole outlets and knob and tube wiring. LOL

Lol, i plan to, messing with 120v isnt a problem, not touching 240v. But this is interesting discussion none-the-less.

If you need to ask hire a pro

Those old 10-30 outlets typically are wired to a neutral. I think they are relics from back when no one bothered with grounds.

I plan to,  still doesnt hurt to learn, not everyone was born with the knowledge, some of us like to actually learn and see how things work. Even when pro shows up ill still be there to learn. Im sure its easy enough but just like google, just like this thread, there seems to various bits of info on how to do this.

Depends, you are assuming there is 220 to the outbuilding. Could be 110 run to both legs, or a single leg panel. People do stupid things with outbuildings.

Could also have three-phase, who knows.

As brickeye said above, 240 is just 2 legs of 120. If you're not comfortable messing with 240 then you shouldn't be comfortable messing with 120. Even with 240, the maximum you or your body would see by accidentally touching a conductor is 120 unless you touched 2 conductors (both line conductors).

Based on your inability to correctly ID and describe the basic parts of a distribution system, I'd say hire out.

The NEC still has the exception that allows three wire service to large 240 V appliances.

For the most part the connector type used is very resistant to working loose.
If you use aluminum make sure to clean the individual wires at install and load them with Anti-Ox paste.

Separate building requires a "service disconnect."
and two ground rods.

What are you trying to power with the 240? That’s the first question.. say it’s a dyer, and it requires 19 amps.. you will simply need double pull 30amp beaker (not 20 needs to be 125% covered for the max draw)... Run the right wire for the amperage, and install the outlet.. The 2 legs in you panel run in a zig zag pattern.. So if your looking at the left side of your breakers, every other one is getting power from the right hot leg.. Clear as mud I know.. but anyway when your slap in a double pull breaker you end up grabbing 120 from the left hot leg and 120 from the right hot leg..  I literally just had to teach my self all this so I could run a sub panel to my garage so I could power a table saw.. just make sure you use the right gauge wire.. if you have a 30 amp breaker and run 14-16 gauge wire the wire may fail prior to your breaker tripping

there is a tradeoff with higher voltage -- for a given delivered power, it results in lower current.
and lower current, in turn, results in less I^2R heating of conductors and surrounding insulation.
accordingly, this decreases the likelihood of fire due to overloaded conductors and devices etc.

example: instead of an extension cord carrying 13A to a 1500W load, it carries 6.5A, and so on.

summary: with 240Vac mains, the shock hazard increases but the fire hazard decreases.
(i'll leave the economics out of the discussion here, but 240Vac single phase is less expensive to deploy than 120Vac/240Vac split phase)

btw, to the complete amusement of the safety world, the modern situation means that we ended up completely backwards.

the USA, with a lot of newer wood stick frame residential housing, would benefit from higher voltage and lower current.  (= reducing the fire hazard)
and Europe, with a lot of older stone and concrete residential housing, would benefit from lower voltage and higher current  (= reducing the shock hazard)

but it didn't work out that way.

The Europeans tapped out the copper on the continent years ago.

The higher voltage and lower current allows the use of far smaller conductors,
at the expense of thicker insulation and moderately more danger from shock.

The power losses in conductors are NOT a significant issue at 120 V if you treat the cords correctly.

Electrical fires are often traced to defective equipment or improper
installation and modifications.

A since most of the time a lot of the evidence has been destroyed.
Educated guesses rule the day.

I do remember one fire investigation that an insurance company hired me to review.

We found multiple examples of cords that had been coiled up tightly.
The copper wire was all that remained, still in a compact bundle.
And then when we went into a less damaged area we saw even more
cords bundled up tight with tie-wraps on them to keep it 'neat.'

Someones OCD had taken over and he burned his house down.
Extension cords, and most appliance cords, are NOT designed to be used when bundled.
Spread them out so they can cool.

Even with a correctly designed cordage or wiring bundling can be a real problem.
I saw a guy that had 'organized' the wiring in his panel board with tie wraps.
You could see the heat discoloration on many of the neutral wires near the wraps.

Wiring in boxes is NOT designed to be bundled.
That is one way you can cause excess heat to be trapped and temperatures can climb.
It is not that the loss is excessive.
It is that the installation has been altered in a way that causes problems.
While a larger panel board can be hard to work in and follow circuits,
bundling up those wire is NOT a good idea.

AT least the temperature rating of common NM cable installtion has been increased of late.
The PVC in millions of installations is only rated for 70 C at best.
The newer insulation is similar to THHN and while thinner is rated 90 C.
The addition of Nylon to the insulation it what improves the temperature rating.
In some sizes you can see the outer nylon layer easily.

It acts to hold the bulk of the insulation together.

These minor changes spread over many many millions of
installations is what lower risk over the long run.

That’s a replacement only dryer recep, new circuits must be 4 wire and use a 4-prong 30A recep.

NM cable is rated at 60 degrees C.  THHN is rated at 90 but only when used in a raceway system.

https://www.encorewire.com/products/nm-b-copper.html

Thanks for replies, if i get property, ill get electrician to do work. Wont take a pro any time at all ( providing all is up to code / specs )

And to answer above, its for a clothes dryer



I have no problem with 120v , have replaced countless outlets, switches, added lights to barn, wired hot water tank, etc, never touched 240v tho.