# How to obtain a neutral point in delta connection?

If I want to connect a load from phase to neutral in delta, how do I achieve it? So far the closest thing I could think of is convert the delta to star. I may be wrong, please guide me to get a solution.

Just for info, I have a 3 phase 415 V PMG generator and would like to connect it to a single phase 240 V load.

• Delta doesn't rely on neutral therefore your opening sentence is an impossibility. Dec 4, 2014 at 9:56
• Is this on a mains installation, or generator, or what? A few more details would help. Dec 4, 2014 at 13:49
• Sarenya, I see you are in Malaysia. I don't know how the power system works there. It may be that one of the nodes on the delta configuration is connected to earth ground. If so, that node would be "neutral." A load connected from there to either of the other two nodes will have single phase 50 Hz power. If you are not concerned about getting electrocuted, you can try to determine if one of the delta nodes is grounded, and also measure the voltage from phase to phase (pick any two nodes) and report back what it is. Do be careful. Mains voltage can kill you. Dec 4, 2014 at 18:46
• I have a 3 phase 415V delta generator, I would like to connect it to single phase 240 V load. How do i do that? Dec 5, 2014 at 0:02
• Connecting one leg of the delta to ground is inadvisable. It means that all insulation must be rated for 415V to ground (instead of 230V to ground) and will make it impossible to see if there are any earth faults on the grounded phase. I see it as unsafe and I wouldn't do it. Dec 5, 2014 at 5:32

I think you need to re-evaluate what you are trying to do.

If you want to connect your three-phase generator to a single-phase load, there is no way you can do this without causing un-balanced loading of the generator. Three-phase generators really don't like unbalanced loads and you will likely cause damage to the generator.

Similarly, there is no arrangement of transformers that will allow you to direct all the output of a three-phase generator into one single phase load. You would be able to connect a bank of three separate single-phase loads using a delta-wye transformer bank, but not a single 240 VAC load.

What you want is closer to a rectifier-inverter, which accepts three phase, 415 VAC at the input, and produces single-phase 240 VAC at the output. This will accept all the power from the generator and use it to power a single 240 VAC load.

An easy way to get such an inverter-rectifier would be to buy an uninterruptible power supply (UPS) with 3-phase 415V input and 240 VAC output. This is expensive, but the only sane way of doing what you are asking.

At all times, ensure you follow the relevant electrical regulations and laws in your country.

Edit: Or, if you only want to power 240V light bulbs, presumably because you want to put some kind of load on your test generator - take pairs of light bulbs and connect them between phases. Then each bulb will see 208V (half of 415V.)

I would recommend using sets of six lightbulbs, i.e. pairs across each phase, so you present a balanced load to the generator.

Like so:

• @sarenya, What is the power rating of the load, and what is the power output of the generator? If the load is very small, maybe we don't have to worry about the unbalance. To all: what about using an isolation transformer on a single phase of the delta generator, then grounding one side of the isolation transformer? Is there any chance that would be OK, code wise? Dec 5, 2014 at 16:44
• @Li-aung Yip, I'm planning to power up few light bulbs. The rating of the bulbs would be 240-V, 50 Hz 18W per bulbs. my target is around 300 W of load Dec 8, 2014 at 0:14
• @Sarenya: You hadn't mentioned what kind of load you were going to put on this. I assume you just need some kind of load (any load!) so you can test your generator. See my edited answer. Dec 8, 2014 at 9:55
• @Li-aungYip sory for that,I'm planing to use on inductive and resistive load. To be exact florescent light bulbs. Dec 9, 2014 at 0:06

The only way to get a neutral point in a three-phase system is to use a star topology. The only (real) way to convert a delta into a star topology is to use a delta-to-star transformer (AKA Delta-Wye transformer).

You often find them at the top of wooden poles. I don't know off hand if there are consumer (industrial) units available, most google searches seem to take me to power distribution (sub-station) type transformers.

It may be possible (though I don't know how "recommended") to create one using three 1:1 isolation transformers wired in delta on one side and star on the other.

• Do you have a source for this assertion? Different people mean different things when they say "neutral." In electrician speak, I believe "neutral" is whatever is connected to earth ground. There is no reason why you cannot ground one node of a delta configuration. It may not be the usual arrangement, but it is possible. Also, some delta installations have a grounded center tap on one of the phases. Dec 4, 2014 at 18:54
• No, neutral is the 0V point at the centre of the star. It may be connected to earth (and often is at the substation). Electrical principals for technicians Vol 2, pp 68: "The common point is referred to as a neutral..." ISBN 0713134437 Dec 4, 2014 at 19:16
• Pedantic clarification: neutral is 0V, and zero current in a balanced system. In an unbalanced system the current is the sum of the three phase vectors of the three phase currents. Dec 4, 2014 at 19:41
• So grounded delta fails to be neutral because it is not balanced, I guess. I would still like to hear more from the OP about what she is trying to do. (Assuming "she" due to results of image search on name "Sarenya.") Dec 4, 2014 at 20:32
• For the record, and not to be contrary (not exactly) - corner grounding and center tap grounding absolutely does happen in delta systems, and on a 240/208/120 high-leg delta system, the grounded center tap line is absolutely called neutral.
– user39962
Feb 8, 2016 at 11:53