Thanks! I've been hung up on the terminology, and feeling frustrated and misunderstood a little on that front, but this was going to be my next question.

So, even though no single load in the machine is seeing more than 240V across it, since there's the potential for 415V between various points (if something were mis-wired, or if an accident or part failure occurred) the machine as a whole is now considered 415V, right?

That makes a lot of sense to me, and it was one of my concerns. When it's just random end users in the field doing these conversions, it's not a regulatory issue for us... but if we ever sold a machine in this configuration, we'd need to label it as 415V or more, and pass UL, CSA, CE, etc. at the higher voltage standards. Does that sound right?

Thanks again.

One common method of indicating equipment three phase voltage rating is thus:-

240/415V; 3 wire + N + PE

The first value is the line to neutral voltage, the second is the phase to phase voltage, followed by the number of phase wires – with this equipment having a neutral and protective earth connection.

The ‘PE’ is sometimes replaced with the circled earth symbol.

Although much of this thread has referenced 240V single phase, 415V three phase voltages found in many parts of the world; in the USA many industrial installations have a 277/480V equivalent system.

 

Hi,

We usually call the wire to wire voltage the "line to line" voltage, which means across two lines not using the neutral. We then call the single phase of a wye system the "line to neutral" voltage. So here we might have 120vac line to neutral, but 208vac line to line.

Once of the differences in 3 phase wye (which is three lines and a single neutral) as compared to three separate phases is the 3 phase system has 4 wires and three separate phases would have 6 wires.
Yes three of them are neutral, so the voltages are (almost) the same. But with only one neutral you have only imbalance current in the neutral wire. In the 3 separate single phase system you have current in all three neutrals, at least until they get back to the breaker box.

So do this:
Calculate the current in all three neutrals of the 3 single phase circuits which will have neutral wires that extend all the way back to the breaker box.
Now later connect the three neutrals together AT THE LOAD and recalculate the current in the (now) one wire that is now the neutral wire.
Compare results, current in three neutrals vs the current in the one neutral.
You may be surprised a little if you've never done this before.
BTW used a balanced 3 phase load to start, or just 3 resistive loads of the same value ofr each phase.
This little experiment will show the difference between a 3 phase system and 3 completely separate phases.

Well, I haven't actually done the calculations, but if I'm understanding you correctly, I'm familiar with the concept.

Because of the phase differences, current through a shared neutral cancels out when current is returning from more than one phase. In the case of perfectly balanced loads, there's zero current in the neutral.

The first time I heard about this, I was pretty sure it was some sort of witchcraft! Once I looked at the graphs of the phase relationships and thought about it though, it makes perfect sense. It only seems like magic.

 

Well, I haven't actually done the calculations, but if I'm understanding you correctly, I'm familiar with the concept.

Because of the phase differences, current through a shared neutral cancels out when current is returning from more than one phase. In the case of perfectly balanced loads, there's zero current in the neutral.

The first time I heard about this, I was pretty sure it was some sort of witchcraft! Once I looked at the graphs of the phase relationships and thought about it though, it makes perfect sense. It only seems like magic.

Hello again,

And the implications of that are for one a single neutral wire can be used and that eliminates two wires right there. Also, any current in the neutral means there is a load imbalance.
So a couple of useful things come out of this.

 

My post was to inspire thinking. To inspire it more, take a look a this https://www.asi-ez.com/member/x483-Multiple-Wire-Modules.asp website.

What's done a lot is to bus the main power into a control cabinet and then span out to smaller breakers.
The wire to the smaller breakers doesn't have to be the rated at the incoming wire rating. The loads are protected and even if the circuit breaker fails shorted, the wire would act as a fuse and a fire would be contained.

I once got the job of re-wiring a vapor dryer because the wire wasn't adequate.

What I've seen done is to make the incoming power a small NEMA enclosure. In the system I saw this done it also contained a relay to cut power and included a pressure switch and door interlocks which did a power cut.

 

Well, I haven't actually done the calculations, but if I'm understanding you correctly, I'm familiar with the concept.

Because of the phase differences, current through a shared neutral cancels out when current is returning from more than one phase. In the case of perfectly balanced loads, there's zero current in the neutral.

The first time I heard about this, I was pretty sure it was some sort of witchcraft! Once I looked at the graphs of the phase relationships and thought about it though, it makes perfect sense. It only seems like magic.

At college I never managed to get my head around trig identities – what might seem surprising is the voltage difference between two sine waves separated by 120 degrees is a sine wave whose rms value is the square root of 3 (1.73) x the fundamental sine wave value.

 

At college I never managed to get my head around trig identities – what might seem surprising is the voltage difference between two sine waves separated by 120 degrees is a sine wave whose rms value is the square root of 3 (1.73) x the fundamental sine wave value.

Hi,

Yes and that is probably because we dont see that kind of identity that much except in engineering.

For example:
C*sin(w*t+phc)=A*sin(w*t+pha)+B*sin(w*t+phb)

which has three different amplitudes A, B, C, and three different phase angles pha, phb, phc.
Knowing A, B, pha, and phb, we can calculate C and phc and thus go from two sin waves to one.

Also of course are:variations with K*cos(wt+phk) and the like.

That sqrt(3) amplitude is the result of at least one special case, and the phase changes also.

 

Thank you very much to everyone who's replied so far. I'd like to sum up and get some confirmation on a few key points I think I've gleaned from the responses. Please let me know if this sounds right:

• The conversion that our end users are doing is a legitimate way to wire things.
  • Using all three lines of a three-phase system, but only using them in conjunction with the neutral, so nothing inside the machine ever works with the higher line-to-line voltage, only the line-to-neutral voltage.
  • I had thought it was probably ok, but wasn't really sure.
• A machine wired as described, with all three lines of three phase power running into it, would be described as receiving three phase power, regardless of whether or not the higher line-to-line voltage is ever utilized.
  • In my head, this was more like three parallel single phase systems, but it seems like the responses here have indicated this is still considered a form of three phase.
• Regardless of what the configuration is called, as long as the three lines all enter the machine, the machine as a whole must be rated and labelled for the higher line-to-line voltage, even if that higher voltage is never used internally.
  • In our case the machine's internal components will all see 240V from line to neutral, and the line-to-line voltage will not be used anywhere.
  • However, the machine will have 415V line-to-line potential which could be a problem if there was an accident or something got wired improperly.

I'm pretty sure that all of the statements above were answered in previous posts, but I just wanted to double check. I feel like I understand the electrical concepts, the phase differences, the available voltages, etc. pretty well, but I'm still catching up on some of the terminology, and I know very little about international wiring standards, regulatory concerns, etc. It's the certifications and regulatory concerns that I'm most worried about at this point.

 

• A machine wired as described, with all three lines of three phase power running into it, would be described as receiving three phase power, regardless of whether or not the higher line-to-line voltage is ever utilized.
• Regardless of what the configuration is called, as long as the three lines all enter the machine, the machine as a whole must be rated and labelled for the higher line-to-line voltage, even if that higher voltage is never used internally.
  • In our case the machine's internal components will all see 240V from line to neutral, and the line-to-line voltage will not be used anywhere.
  • However, the machine will have 415V line-to-line potential which could be a problem if there was an accident or something got wired improperly.

I'm pretty sure that all of the statements above were answered in previous posts, but I just wanted to double check. I feel like I understand the electrical concepts, the phase differences, the available voltages, etc. pretty well, but I'm still catching up on some of the terminology, and I know very little about international wiring standards, regulatory concerns, etc. It's the certifications and regulatory concerns that I'm most worried about at this point.

As long as the machine requirements states the supply voltage required and 3ph and also the power (wattage) or current value.
Although it does not get into this area, a document that may help is NFPA79, Electrical Standards for Industrial Machinery. it is pretty much universal in most cases.
Max.

 

As long as the machine requirements states the supply voltage required and 3ph and also the power (wattage) or current value.
Although it does not get into this area, a document that may help is NFPA79, Electrical Standards for Industrial Machinery. it is pretty much universal in most cases.
Max.

Awesome, thanks!

As I said before, I'm hoping that we can just avoid offering this as a factory option, but if we do proceed down that path, I'll definitely check out NFPA79.

I really appreciate the help, and that reference. Sometimes the hardest part of these projects is knowing where to look for answers.