3 phase (delta) power to single phase space heater
Here's what 3-phase delta looks like.

This happens to be 240V and uses the common 3-phase colors of black, red, blue. 



It's that simple, folks.  3 phases, No Neutral.   

One error of belief is thinking every service must have a neutral.  It doesn't.   This was Tesla's genius.

Delta is used in industrial facilities where a few tools need a medium amount of power for a few larger tools.  It would be rare to see lighting or other minor loads run off it.  A motor which takes 240V 3-phase can typically be jumpered to also work on 480V 3-phase, and that is much more efficient to distribute. I would never install 240V today, I'd install 480V. 

Obviously there's only one voltage.  Pretty straightforward.  Now what's this?  

 

It's the exact same thing.  The only difference is using alternate colors. The point here is that any color may be used (except white, gray or green) including orange.  NEC doctrine is the electrician is expected to measure the circuit to determine voltages. Prince fan? Use Purple Pink Black. 

Hook your heater between any two hots.

They are all 240V. Done.

The only other issue is balancing.  If you have several loads, try to put them on alternate phases so you load the 3 phases evenly. 

We're done here.  





So what's this Other Thing then?

This thread is dominated by discussion of some other system which is not relevant to OP.  It's a red herring.  But since it keeps coming up, let's talk about it.  This is "high-leg" or "wild-leg" delta, which is a clever rearrangement of delta to get 120V single-phase loads also - to avoid the cost of a separate 240/120V single-phase service. See how a neutral has been added halfway down a phase.   



If you want to use 120V appliances, this only works on 240V delta.  

Notice two mandatory wire colors.  Of course, neutral must be white or gray.  The "wild leg" - with much higher voltage to neutral - must be orange. It's one of very few cases where a "hot" color is mandated. However in any other circuit, you can use orange for any hot, and that's exactly what happened in our second example. That means if you see black-red-orange-white, it could be anything including 600V wye.  You better test it.

So when someone says "Delta" they do not mean "wild-leg delta". They mean "delta".  Don't go buying something that needs 120V or 208V expecting it to be there in delta service.  It won't be unless they specify wild-leg/high-leg. 

All the 120V loads load up the A-C phase.  If there's a desire to run a significant number of 120V circuits, 208V "wye" 3-phase does a better job of it, while allowing loads to be balanced. If lighting is the primary load, 480V "wye" is a "swiss army" voltage, allowing 240V/480V motors to run in delta connection and lighting to work in wye, using a hot-neutral 277V connection.