Question for electricians - 240VAC

[MikeC]

OK, I know there's a at least a handful of electrically savvy people browsing SPCR. I need your help.

I want to add 240VAC testing for SPCR's PSU reviews. It so happens that part of the lab used to be a kitchen, and there is a 240VAC two-phase outlet in there which used to be for an electric stove/oven.



Here's the question: Is there a simple way to convert this into a standard 3-prong (2 live + ground) single phase 240VAC outlet?

Fire away, guys.

[Mar.]

Why would you want to run a PSU off of 240V?

[Rusty075]

Why would you want to run a PSU off of 240V?

To test for efficiency differences between PSU's running the North American voltage versus the EU voltage.


I don't have a good answer for your plug question Mike, (sorry) but I do have a question of my own: How are you planning on dealing with the 60Hz vs 50Hz issue?

[Mar.]

The frequencies will be different, it can be done but you're better off just buying a commercially-available transformer.

[MikeC]

All the auto-sensing PSUs work off 50~60Hz, not 50 / 60. The ones that are 50 / 60, well if they really don't work with the "wrong" HZ, too bad, for now.

[Rusty075]

The frequencies will be different, it can be done but you're better off just buying a commercially-available transformer.

No, a transformer is not what is needed. A transformer will adjust the voltage, not the frequency. Mike will need some sort of a rectifier/inverter setup to convert the 60Hz to 50. EDIT: Nevermind..Mike's right, I forgot that the PSU's are autosensing. Athough it would be an interesting experiment to see if the extra ripple from 50Hz has any effect.

Which is course is a later step...once we firgure out how to plug the thing in properly. I've never seen a plug like that Mike, it is a Canadian-only thing? Maybe pull it out from the wall so we can see what connects where one it?

[MikeC]

Uh, pull it from the wall? Until/unless I can figure out which breaker controls this, no way I am touching it.

Not sure if it is only a Canadian thing -- it's what feeds 240VAC into high current devices live stoves and dryers around here, and I am pretty sure it is 2-phase; ie, there are 2 120VAC lines in the 3 prongs, A, B, C. D is ground, for sure. I am guessing that tapping A & C might give me 240 on 2 conductors, but I want to be pretty sure before I even poke multimeter leads in there.

[sthayashi]

Mike, why so scared to put multimeter leads in there? I do this all the time. Just be damn sure you don't have any metal to cross the leads.

Typically the 240V coming in IS single phase. If you ever get a chance to have a look at the lines coming into your house, you'll see 3 wires (at least that's the case around here, and FYI, I'm not an electrician). The 3 wires are 2 for the 240V and a center tap that effectively turns 240V into 2 phases of 120V.

[MikeC]

OK steve. I gotcha.

Let's see if we get any confirmation from someone who IS an electrician... Or a reference at some authoritative web site.

[Mar.]

Power supplies aren't the most delicate piece of electronic equipment out there, they're pretty tolerant of a varying supply voltage/frequency, so long as it isn't too far off. A step-down transformer SHOULD work. I'm no electrician though, I mainly work with 5V....

[m0002a]

OK steve. I gotcha.

Let's see if we get any confirmation from someone who IS an electrician... Or a reference at some authoritative web site.

If I were you, I would not trust anyone's anawer unless they scanned and posted their electrician license.

[Mar.]

Man, just call an electrician and ASK them.

[gr8r-x]

OK, I know there's a at least a handful of electrically savvy people browsing SPCR. I need your help.

I want to add 240VAC testing for SPCR's PSU reviews. It so happens that part of the lab used to be a kitchen, and there is a 240VAC two-phase outlet in there which used to be for an electric stove/oven.



Here's the question: Is there a simple way to convert this into a standard 3-prong (2 live + ground) single phase 240VAC outlet?

Fire away, guys.

Well.. From what I just google'd, it's definately not a standard plug... Anywhere.

http://www.interpower.com/ic/guide.htm

I'd have to guess that maybe it was fitted as part of whatever appliance was installed. If it was a 240V oven/stove/etc, and you're up in 110V land, it very reasonable that it would have a proprietary connector.

And I'm with the others, just stick a multimeter lead in there... As long as your meter is rated ~240V (or >), you should be fine. Know I've done it before and I'm still around to talk about it.

Hell, as a kid, I wrapped a pipe cleaner around the 2 + terminals on my Atari power supply and plugged it in. Flicking the switch was the hardest part, or so I'm told.. Power outlet is still charred to this day.

[sthayashi]

Well.. From what I just google'd, it's definately not a standard plug... Anywhere.

I'd have to guess that maybe it was fitted as part of whatever appliance was installed. If it was a 240V oven/stove/etc, and you're up in 110V land, it very reasonable that it would have a proprietary connector.

And I'm with the others, just stick a multimeter lead in there... As long as your meter is rated ~240V (or >), you should be fine. Know I've done it before and I'm still around to talk about it.

It IS very much a standard plug, just not outside North America. Mike, the outlet you have is classified as a NEMA 14-50. I had to do some googling for it.

Here's a PDF on how it ought to be wired:
http://www.cooperwiringdevices.com/cata ... ERENCE.pdf

Most multimeters are rated for up to about 600V, even the cheap ones. The safety rating for it should be right on there. Just be sure to use the V~ setting (or VAC). You generally won't hurt anything, but you'll get funky readings at best.

This doesn't answer your question on is there a simple way of doing this conversion. I don't know if you can buy off-the-shelf 14-50 to IEC cables or not, but that would be the easiest solution.

[MikeC]

OK, I suppose I should check the voltages. I do think it has to be A & C = 240VAC.

[Mar.]

Seems like that particluar outlet gives 250VAC, rather than the 230V european standard. 250V is the upper limit the "safe" range of your power supply's IEC connector, so I'd say you're pushing it.

What I'm trying to say is, I have no doubt that it CAN be done safely, but you've managed all this time without it, so why bother?

[gr8r-x]

It IS very much a standard plug, just not outside North America. Mike, the outlet you have is classified as a NEMA 14-50. I had to do some googling for it.

That humble pie was delicious.. Thanks for the correction, and that documentation was VERY thorough. I never knew so many different variants of power plugs existed. I mean, I was aware of the varying ones between countries and amp ratings, but that's just a whole new level of .. well.. something.

[moritz]

Too bad I was late, because I just read a fair amount about the various HVAC power plugs on Wikipedia - sthayashi's PDF is a lot more detailed, though. Just for fun, here's the page on domestic power plugs.

[sthayashi]

That humble pie was delicious.. Thanks for the correction, and that documentation was VERY thorough. I never knew so many different variants of power plugs existed. I mean, I was aware of the varying ones between countries and amp ratings, but that's just a whole new level of .. well.. something.

No need for humble pie. If you're not familiar with North American byzantine outlets, then there's no reason you should have been able to identify that outlet. Hell, at work I have seen at least 3 different outlets for 240V.

MikeC, I think I can come up with a way to connect that outlet to an IEC plug, but the problem is that it involves $80 + some work

[MikeC]

sthayashi --

Not sure what that device you link is. If it is just a plug, it's one hell of an expensive plug! I know I can pick up one of those plugs a LOT cheaper than that & wire it to a standard AC outlet.

The key issues is still which of the two contacts give 240VAC. It's what I have to measure. Need a plug to do it though, have no safe contacts I can poke and hold into the outlet for the multimeter probes.

[sthayashi]

It's a plug that you can wire up things to. Glad you can find a plug for cheaper, because this isn't something I can find online for some reason.

Do your multimeter probes not reach the contacts within the plug directly?

You're most likely correct about A&C being 240VAC. In the PDF file that I linked earlier, it shows exactly that, with A&B and B&C being 120VAC, and D is Earth.

[Freelancer77]

Mike,

On the picture, B is neutral (that doesn't mean ground), A is 120VAC compared to B, C is 120VAC compared to B (but in the opposing phase). Therefore, A to C is 240VAC.

You needn't fear taking meter readings from a normal outlet. Don't be barefoot, standing in water, or on leather soles. If you're really worried, grab some kitchen rubber gloves. Take the AC voltage of A, B, and C each on the red lead using D as the common. Then you'll know. I suspect you'll find B doesn't show you an AC voltage. Then take the DC voltage at B. It might be only 37VDC, but it's a constant to serve as the center reference for A and C.

What I say next is conjecture, since I am clueless about Canadian wiring standards. You "should" be able to wire up for a 240VAC PSU by applying A to one blade, C to the other, and D to ground, ignoring B. The autosensing ability of the PSU "should" adjust for the difference between the DC center of the sine waves on A and C, and regardless there is an average 240VAC difference between the two.

Is there a circuit breaker or fuse on the circuit? If so, I'd recommend wiring a PSU's 12V output lines to a nice hefty transformer, and plug it in. A good PSU will go offline in an under- or over-current or an over-voltage, which I don't need to tell you. At the worst you pop the CB. Just stand back when you flip the switch.

Have you tried contacting a power department for your city/region? They may have free information on the wiring specifics and how to handle what you're doing. They like their customers alive, it makes collecting bills so much easier.

[postul8or]

Figuring out which breaker controls this plug shouldn't be that hard. Instead of being a 15 amp breaker it will probably be 30 or else there will be two 15 amp switches in tandem.

[perplex]

would the efficiency be less or more with 240V as opposed to 115V ?

[madman2003]

Efficiency should be better with 230/240 VAC than with 110/115 VAC. Adding (A)PFC which most psu's in europe have roughly negates that advantage. (not sure about the exact numbers)

[pdf27]

On the picture, B is neutral (that doesn't mean ground), A is 120VAC compared to B, C is 120VAC compared to B (but in the opposing phase). Therefore, A to C is 240VAC.

Hang on a sec, aren't most power systems three phase rather than two phase? If so then connecting across any two 120VAC wires will give 208VAC rather than 240VAC (208 = 120 * sqrt(3) ).

The way power systems (in the UK anyway) typically work is that there will be three phases with a 120 degree phase angle between them, and a neutral (ground) wire. Each phase is at 240v relative to ground, while the voltage between any two phases will be 415v (240 * sqrt(3) ).

So basically, you can't get 240v from a three phase supply where the phases are at 120v. If the supply (i.e. that leaving the power station) is in two phases you will though - and I don't know how many phases the power system has in the US/Canada.

Note: this is all from the three phase power lectures I did for my degree (aero/mechanical engineering) and I am in no way a qualified electrician!

[sthayashi]

Hang on a sec, aren't most power systems three phase rather than two phase? If so then connecting across any two 120VAC wires will give 208VAC rather than 240VAC (208 = 120 * sqrt(3) ).

The way power systems (in the UK anyway) typically work is that there will be three phases with a 120 degree phase angle between them, and a neutral (ground) wire. Each phase is at 240v relative to ground, while the voltage between any two phases will be 415v (240 * sqrt(3) ).

So basically, you can't get 240v from a three phase supply where the phases are at 120v. If the supply (i.e. that leaving the power station) is in two phases you will though - and I don't know how many phases the power system has in the US/Canada.

Note: this is all from the three phase power lectures I did for my degree (aero/mechanical engineering) and I am in no way a qualified electrician!

I'm a little surprised and disappointed there was no response to this. Domestic power in the US and I'm guessing in Canada is typically a single phase 240V coming in. This is very easily splittable into 2 phases of 120V. Technically speaking it IS 2 phases of 120V coming in, but usually it's from a single phase 240V.

Now when you get into power for complexes like apartments and condos, it's a different story and what you've described is pretty much how it goes. This is usually because complexes actually have a legitimate use for 3-phase power (for their HVAC systems, no doubt), and the same power gets split in different ways.

But since most homes in North America don't really have a need for 3-phase power, they don't receive it.

Note: Most of the above was written based on what I've learned since this topic started. I find it all very fascinating, but like the rest of you, I'm still a student and by no means a master. I could very easily be in error here and not realize it.