I bought a 240V single phase, space heater for heating up a warehouse space. The warehouse has 240V power in a delta configuration (no neutral). My understanding is that in a delta configuration, the line voltage between any two phases is the same as the phase voltage, in this case, 240V. So I should be able to wire the the heater between any two lines, right?
asked Dec 12, 2016 at 19:33
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Thanks for everyone that helped here. It definitely gave me a better understanding of the variety of electrical systems around as well as a confirmation of my understanding of the system currently installed in the warehouse provided by @Harper.– ScotBirminghamCommented Dec 14, 2016 at 0:17
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4 Answers
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.
answered Dec 13, 2016 at 4:59
Harper - Reinstate MonicaHarper - Reinstate Monica
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Funny, this is exactly the configuration that the machine from this older question of mine required. If you and @ScotBirmingham don't mind you could add an answer to my question, stating where this 240V delta configuration is used.– AndreKRCommented Dec 13, 2016 at 22:58
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2@EdBeal Fixed. I meant "hack" like "clever rearrangement". Commented Dec 13, 2016 at 23:45
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Thanks. This is what I understood to be true but wanted confirmation. @AndreKR This is the power system in a warehouse space. It's not residential. Commented Dec 14, 2016 at 0:09
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Yes, you are correct. You can wire the heater across any two of the three phases.
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1THIS IS A DELTA!!! Phase B should be a wild leg DO NOT USE LEG B or smoke will be present.– Ed BealCommented Dec 12, 2016 at 20:22
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14Ed, this is an unfair down vote and incorrect. In a delta system, the phase-to-phase voltage is the same. The B phase, or high leg only becomes a problem when you are wiring a 120V load to a panel box with a 120/240 three phase high leg delta service. The voltage across the neutral and the high-leg will be 208V. That is where the smoke begins and why the wire must be orange colored. A 240V single phase load will work just fine across any two of three phases. Commented Dec 12, 2016 at 20:48
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3Two down votes by people who clearly don't understand three phase systems. Very disappointing. I want someone to prove me wrong and explain why. Otherwise this is promoting false information. Commented Dec 12, 2016 at 21:32
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7THERE IS NO HIGH LEG. Not all Delta is high leg. High-leg is a compromise to get 120V out of delta, and it's funny stuff that needs special handling. Unless someone tells you it's high-leg or wild-leg, it is not. Commented Dec 12, 2016 at 22:32
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1@Harper Exactly. This is a 240V only service that most likely accompanies a separate 120/240 split phase lighting panel. Plus its a 240V load meaning that the high leg would never be an issue to begin with even if it were present. Commented Dec 12, 2016 at 22:49
My understanding is that in a delta configuration, the line voltage between any two phases is the same as the phase voltage, in this case, 240V.
'phase voltage' is not a great term. It would generally be interpreted as phase-to-neutral voltage, but you said you have no neutral.
3-phase delta works like this:
If you're sure you have no neutral, you can ignore the neutral in the diagram and the 120 and 208 that it can provide.
So I should be able to wire the the heater between any two lines, right?
You should be able to wire the heater between any two hots, Yes. Measure voltage first to make sure it's 240 like you expect.
answered Dec 12, 2016 at 21:29
Billy left SE for CodidactBilly left SE for Codidact
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1Phase voltage is the proper term if referring to the actual phase voltage. If you took a 240V delta transformer bank apart and treated each transformer as a single phase, you would measure a 240V phase voltage. Once wired up as a delta bank, the system is now a three phase system and has a phase-to-phase voltage of 240V, the same voltage as the phase voltage. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. Commented Dec 12, 2016 at 21:49
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2No. You're describing "high leg" or "wild leg" delta. Plain old 240V delta exists too. Normal deltas can only supply the named voltage. There is no way to tap it for fractional voltages. People often assume there MUST be a way to derive 120V; not necessarily. Often 120V is installed as a completely separate service. Commented Dec 12, 2016 at 22:29
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1Delta is common in older industrial areas or supplied where the customers three phase requirement is quite small, e.g. a farm or small business with a few motors. Utilities don't install new delta services unless they are maintaining an existing system or the customer explicitly requires it. Though, in rural areas it is common to find open delta banks fed from open wye primaries. Cheaper to install when a customer down the road from a set of primaries requires light three phase service. Two primary phases, and a neutral feed two cans creating a 120/240 delta. Commented Dec 12, 2016 at 22:46
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1We have delta all over the place. Five services and none of them are wye. Well wait, we have one wye in an office structure, mainly for lighting. Commented Dec 12, 2016 at 23:00
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1@Harper Why would you want Delta over Wye? Is there more to that than the cost of the forth conductor? Commented Dec 13, 2016 at 0:20
If this is a DELTA usually the B leg is colored Orange and will be 2x the standard voltage. WYE connected systems all 3 legs have the same voltage. Verify the voltages prior to making any connections!!! Added for all those that have not worked on deltas with single phase. By code the system has to be grounded and can create the wild leg. Use of a wild leg will double the voltage to ground when used with single phase. Code requires equipment like this to have the highest voltage rating not dual voltage because of the high leg. At least this is code in the U.S. that has not changed for years. So ether there is a wild leg or a corner grounded. A single phase load would need to be on one of the grounded legs.
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5There is no double voltage in a delta service. You are thinking of the the high leg voltage, also called bastard voltage. High leg voltage is 208V and only appears across the neutral and B phase. The neutral is derived by center tapping one of the three (or two if open delta) transformers. It also serves as the ground reference. That transformer is often physically larger and colloquially called the lighting can. It only becomes an issue when wiring up 120V loads in a panel box which is serviced by a 120/240 three phase high leg delta. Commented Dec 12, 2016 at 21:13
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3You're thinking of high leg or wild leg delta, as described in Billy C's post. Not all delta is high-leg. However if it is high-leg, the high leg must be orange. It's the only restriction on "hot" color I'm aware of. Commented Dec 12, 2016 at 22:30
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2Furthermore, connecting a 240V space heater B-to-neutral in a high leg setup won't kill it, it'll just run somewhat...wimpily off the 208V present there. Commented Dec 12, 2016 at 23:40
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4According to code the high leg must be orange. According to my eyesight, the last place I worked at that had a high leg it was black.– MazuraCommented Dec 13, 2016 at 1:40
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1Orange is the new black :) Sorry couldn't resist! Commented Dec 13, 2016 at 5:48